diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
index 7a0f12ce7ceaf..da9561b8eb413 100644
--- a/.github/pull_request_template.md
+++ b/.github/pull_request_template.md
@@ -1,8 +1,8 @@
 <!--
 Thank you for submitting a pull request!
 
-Here's a checklist you might find useful.
-* [ ] There is an associated issue that is labeled 'Bug' or 'help wanted'
+Please verify that:
+* [ ] There is an associated issue in the `Backlog` milestone (**required**)
 * [ ] Code is up-to-date with the `master` branch
 * [ ] You've successfully run `gulp runtests` locally
 * [ ] There are new or updated unit tests validating the change
@@ -12,4 +12,3 @@ Refer to CONTRIBUTING.MD for more details.
 -->
 
 Fixes #
-
diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index ad02d84a35bdd..96db98d337a73 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -1625,15 +1625,8 @@ namespace ts {
         }
 
         function hasExportDeclarations(node: ModuleDeclaration | SourceFile): boolean {
-            const body = node.kind === SyntaxKind.SourceFile ? node : node.body;
-            if (body && (body.kind === SyntaxKind.SourceFile || body.kind === SyntaxKind.ModuleBlock)) {
-                for (const stat of (<BlockLike>body).statements) {
-                    if (stat.kind === SyntaxKind.ExportDeclaration || stat.kind === SyntaxKind.ExportAssignment) {
-                        return true;
-                    }
-                }
-            }
-            return false;
+            const body = isSourceFile(node) ? node : tryCast(node.body, isModuleBlock);
+            return !!body && body.statements.some(s => isExportDeclaration(s) || isExportAssignment(s));
         }
 
         function setExportContextFlag(node: ModuleDeclaration | SourceFile) {
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ce56db4b962f4..33d2dd73876b8 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -94,8 +94,6 @@ namespace ts {
 
         const globalThisSymbol = createSymbol(SymbolFlags.Module, "globalThis" as __String, CheckFlags.Readonly);
         globalThisSymbol.exports = globals;
-        globalThisSymbol.valueDeclaration = createNode(SyntaxKind.Identifier) as Identifier;
-        (globalThisSymbol.valueDeclaration as Identifier).escapedText = "globalThis" as __String;
         globals.set(globalThisSymbol.escapedName, globalThisSymbol);
 
         const argumentsSymbol = createSymbol(SymbolFlags.Property, "arguments" as __String);
@@ -926,7 +924,12 @@ namespace ts {
                 recordMergedSymbol(target, source);
             }
             else if (target.flags & SymbolFlags.NamespaceModule) {
-                error(getNameOfDeclaration(source.declarations[0]), Diagnostics.Cannot_augment_module_0_with_value_exports_because_it_resolves_to_a_non_module_entity, symbolToString(target));
+                // Do not report an error when merging `var globalThis` with the built-in `globalThis`,
+                // as we will already report a "Declaration name conflicts..." error, and this error
+                // won't make much sense.
+                if (target !== globalThisSymbol) {
+                    error(getNameOfDeclaration(source.declarations[0]), Diagnostics.Cannot_augment_module_0_with_value_exports_because_it_resolves_to_a_non_module_entity, symbolToString(target));
+                }
             }
             else { // error
                 const isEitherEnum = !!(target.flags & SymbolFlags.Enum || source.flags & SymbolFlags.Enum);
@@ -1409,15 +1412,14 @@ namespace ts {
                         }
                         break;
                     case SyntaxKind.PropertyDeclaration:
-                    case SyntaxKind.PropertySignature:
                         // TypeScript 1.0 spec (April 2014): 8.4.1
                         // Initializer expressions for instance member variables are evaluated in the scope
                         // of the class constructor body but are not permitted to reference parameters or
                         // local variables of the constructor. This effectively means that entities from outer scopes
                         // by the same name as a constructor parameter or local variable are inaccessible
                         // in initializer expressions for instance member variables.
-                        if (isClassLike(location.parent) && !hasModifier(location, ModifierFlags.Static)) {
-                            const ctor = findConstructorDeclaration(location.parent);
+                        if (!hasModifier(location, ModifierFlags.Static)) {
+                            const ctor = findConstructorDeclaration(location.parent as ClassLikeDeclaration);
                             if (ctor && ctor.locals) {
                                 if (lookup(ctor.locals, name, meaning & SymbolFlags.Value)) {
                                     // Remember the property node, it will be used later to report appropriate error
@@ -9943,13 +9945,13 @@ namespace ts {
             return type.flags & TypeFlags.Union ? getIntersectionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly, noIndexSignatures))) :
                 type.flags & TypeFlags.Intersection ? getUnionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly, noIndexSignatures))) :
                 maybeTypeOfKind(type, TypeFlags.InstantiableNonPrimitive) ? getIndexTypeForGenericType(<InstantiableType | UnionOrIntersectionType>type, stringsOnly) :
-                getObjectFlags(type) & ObjectFlags.Mapped ? filterType(getConstraintTypeFromMappedType(<MappedType>type), t => !(noIndexSignatures && t.flags & (TypeFlags.Any | TypeFlags.String | TypeFlags.Number))) :
+                getObjectFlags(type) & ObjectFlags.Mapped ? filterType(getConstraintTypeFromMappedType(<MappedType>type), t => !(noIndexSignatures && t.flags & (TypeFlags.Any | TypeFlags.String))) :
                 type === wildcardType ? wildcardType :
                 type.flags & TypeFlags.Unknown ? neverType :
                 type.flags & (TypeFlags.Any | TypeFlags.Never) ? keyofConstraintType :
                 stringsOnly ? !noIndexSignatures && getIndexInfoOfType(type, IndexKind.String) ? stringType : getLiteralTypeFromProperties(type, TypeFlags.StringLiteral) :
                 !noIndexSignatures && getIndexInfoOfType(type, IndexKind.String) ? getUnionType([stringType, numberType, getLiteralTypeFromProperties(type, TypeFlags.UniqueESSymbol)]) :
-                !noIndexSignatures && getNonEnumNumberIndexInfo(type) ? getUnionType([numberType, getLiteralTypeFromProperties(type, TypeFlags.StringLiteral | TypeFlags.UniqueESSymbol)]) :
+                getNonEnumNumberIndexInfo(type) ? getUnionType([numberType, getLiteralTypeFromProperties(type, TypeFlags.StringLiteral | TypeFlags.UniqueESSymbol)]) :
                 getLiteralTypeFromProperties(type, TypeFlags.StringOrNumberLiteralOrUnique);
         }
 
@@ -10067,10 +10069,10 @@ namespace ts {
                 if (objectType.flags & (TypeFlags.Any | TypeFlags.Never)) {
                     return objectType;
                 }
-                const indexInfo = isTypeAssignableToKind(indexType, TypeFlags.NumberLike) && getIndexInfoOfType(objectType, IndexKind.Number) ||
-                    getIndexInfoOfType(objectType, IndexKind.String);
+                const stringIndexInfo = getIndexInfoOfType(objectType, IndexKind.String);
+                const indexInfo = isTypeAssignableToKind(indexType, TypeFlags.NumberLike) && getIndexInfoOfType(objectType, IndexKind.Number) || stringIndexInfo;
                 if (indexInfo) {
-                    if (accessFlags & AccessFlags.NoIndexSignatures) {
+                    if (accessFlags & AccessFlags.NoIndexSignatures && indexInfo === stringIndexInfo) {
                         if (accessExpression) {
                             error(accessExpression, Diagnostics.Type_0_cannot_be_used_to_index_type_1, typeToString(indexType), typeToString(originalObjectType));
                         }
@@ -14228,6 +14230,32 @@ namespace ts {
             return strictNullChecks ? getGlobalNonNullableTypeInstantiation(type) : type;
         }
 
+
+        /**
+         * Is source potentially coercible to target type under `==`.
+         * Assumes that `source` is a constituent of a union, hence
+         * the boolean literal flag on the LHS, but not on the RHS.
+         *
+         * This does not fully replicate the semantics of `==`. The
+         * intention is to catch cases that are clearly not right.
+         *
+         * Comparing (string | number) to number should not remove the
+         * string element.
+         *
+         * Comparing (string | number) to 1 will remove the string
+         * element, though this is not sound. This is a pragmatic
+         * choice.
+         *
+         * @see narrowTypeByEquality
+         *
+         * @param source
+         * @param target
+         */
+        function isCoercibleUnderDoubleEquals(source: Type, target: Type): boolean {
+            return ((source.flags & (TypeFlags.Number | TypeFlags.String | TypeFlags.BooleanLiteral)) !== 0)
+                && ((target.flags & (TypeFlags.Number | TypeFlags.String | TypeFlags.Boolean)) !== 0);
+        }
+
         /**
          * Return true if type was inferred from an object literal, written as an object type literal, or is the shape of a module
          * with no call or construct signatures.
@@ -16571,7 +16599,10 @@ namespace ts {
                     return type;
                 }
                 if (assumeTrue) {
-                    const narrowedType = filterType(type, t => areTypesComparable(t, valueType));
+                    const filterFn: (t: Type) => boolean = operator === SyntaxKind.EqualsEqualsToken ?
+                        (t => areTypesComparable(t, valueType) || isCoercibleUnderDoubleEquals(t, valueType)) :
+                        t => areTypesComparable(t, valueType);
+                    const narrowedType = filterType(type, filterFn);
                     return narrowedType.flags & TypeFlags.Never ? type : replacePrimitivesWithLiterals(narrowedType, valueType);
                 }
                 if (isUnitType(valueType)) {
@@ -21973,6 +22004,13 @@ namespace ts {
                     const arg = (<PrefixUnaryExpression>node).operand;
                     return op === SyntaxKind.MinusToken && (arg.kind === SyntaxKind.NumericLiteral || arg.kind === SyntaxKind.BigIntLiteral) ||
                         op === SyntaxKind.PlusToken && arg.kind === SyntaxKind.NumericLiteral;
+                case SyntaxKind.PropertyAccessExpression:
+                case SyntaxKind.ElementAccessExpression:
+                    const expr = (<PropertyAccessExpression | ElementAccessExpression>node).expression;
+                    if (isIdentifier(expr)) {
+                        const symbol = getSymbolAtLocation(expr);
+                        return !!(symbol && (symbol.flags & SymbolFlags.Enum) && getEnumKind(symbol) === EnumKind.Literal);
+                    }
             }
             return false;
         }
@@ -21981,7 +22019,7 @@ namespace ts {
             let exprType = checkExpression(expression, checkMode);
             if (isConstTypeReference(type)) {
                 if (!isValidConstAssertionArgument(expression)) {
-                    error(expression, Diagnostics.A_const_assertion_can_only_be_applied_to_a_string_number_boolean_array_or_object_literal);
+                    error(expression, Diagnostics.A_const_assertions_can_only_be_applied_to_references_to_enum_members_or_string_number_boolean_array_or_object_literals);
                 }
                 return getRegularTypeOfLiteralType(exprType);
             }
@@ -25629,7 +25667,7 @@ namespace ts {
             }
 
             if (!compilerOptions.experimentalDecorators) {
-                error(node, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_to_remove_this_warning);
+                error(node, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_in_your_tsconfig_or_jsconfig_to_remove_this_warning);
             }
 
             const firstDecorator = node.decorators[0];
@@ -26427,14 +26465,28 @@ namespace ts {
             }
             // For a binding pattern, validate the initializer and exit
             if (isBindingPattern(node.name)) {
-                // Don't validate for-in initializer as it is already an error
-                if (node.initializer && node.parent.parent.kind !== SyntaxKind.ForInStatement) {
-                    const initializerType = checkExpressionCached(node.initializer);
-                    if (strictNullChecks && node.name.elements.length === 0) {
-                        checkNonNullNonVoidType(initializerType, node);
+                const needCheckInitializer = node.initializer && node.parent.parent.kind !== SyntaxKind.ForInStatement;
+                const needCheckWidenedType = node.name.elements.length === 0;
+                if (needCheckInitializer || needCheckWidenedType) {
+                    // Don't validate for-in initializer as it is already an error
+                    const widenedType = getWidenedTypeForVariableLikeDeclaration(node);
+                    if (needCheckInitializer) {
+                        const initializerType = checkExpressionCached(node.initializer!);
+                        if (strictNullChecks && needCheckWidenedType) {
+                            checkNonNullNonVoidType(initializerType, node);
+                        }
+                        else {
+                            checkTypeAssignableToAndOptionallyElaborate(initializerType, getWidenedTypeForVariableLikeDeclaration(node), node, node.initializer);
+                        }
                     }
-                    else {
-                        checkTypeAssignableToAndOptionallyElaborate(initializerType, getWidenedTypeForVariableLikeDeclaration(node), node, node.initializer);
+                    // check the binding pattern with empty elements
+                    if (needCheckWidenedType) {
+                        if (isArrayBindingPattern(node.name)) {
+                            checkIteratedTypeOrElementType(widenedType, node, /* allowStringInput */ false, /* allowAsyncIterables */ false);
+                        }
+                        else if (strictNullChecks) {
+                            checkNonNullNonVoidType(widenedType, node);
+                        }
                     }
                 }
                 return;
@@ -30407,6 +30459,14 @@ namespace ts {
                     continue;
                 }
                 if (!isExternalOrCommonJsModule(file)) {
+                    // It is an error for a non-external-module (i.e. script) to declare its own `globalThis`.
+                    // We can't use `builtinGlobals` for this due to synthetic expando-namespace generation in JS files.
+                    const fileGlobalThisSymbol = file.locals!.get("globalThis" as __String);
+                    if (fileGlobalThisSymbol) {
+                        for (const declaration of fileGlobalThisSymbol.declarations) {
+                            diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0, "globalThis"));
+                        }
+                    }
                     mergeSymbolTable(globals, file.locals!);
                 }
                 if (file.jsGlobalAugmentations) {
@@ -30452,6 +30512,7 @@ namespace ts {
             getSymbolLinks(undefinedSymbol).type = undefinedWideningType;
             getSymbolLinks(argumentsSymbol).type = getGlobalType("IArguments" as __String, /*arity*/ 0, /*reportErrors*/ true);
             getSymbolLinks(unknownSymbol).type = errorType;
+            getSymbolLinks(globalThisSymbol).type = createObjectType(ObjectFlags.Anonymous, globalThisSymbol);
 
             // Initialize special types
             globalArrayType = getGlobalType("Array" as __String, /*arity*/ 1, /*reportErrors*/ true);
@@ -31179,6 +31240,13 @@ namespace ts {
 
             for (const prop of node.properties) {
                 if (prop.kind === SyntaxKind.SpreadAssignment) {
+                    if (inDestructuring) {
+                        // a rest property cannot be destructured any further
+                        const expression = skipParentheses(prop.expression);
+                        if (isArrayLiteralExpression(expression) || isObjectLiteralExpression(expression)) {
+                            return grammarErrorOnNode(prop.expression, Diagnostics.A_rest_element_cannot_contain_a_binding_pattern);
+                        }
+                    }
                     continue;
                 }
                 const name = prop.name;
@@ -31841,7 +31909,7 @@ namespace ts {
                     return false;
             }
 
-            return grammarErrorOnFirstToken(node, Diagnostics.A_declare_modifier_is_required_for_a_top_level_declaration_in_a_d_ts_file);
+            return grammarErrorOnFirstToken(node, Diagnostics.Top_level_declarations_in_d_ts_files_must_start_with_either_a_declare_or_export_modifier);
         }
 
         function checkGrammarTopLevelElementsForRequiredDeclareModifier(file: SourceFile): boolean {
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 4e37395f41e50..a2a1c8918a021 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -16,6 +16,7 @@ namespace ts {
         ["es2017", "lib.es2017.d.ts"],
         ["es2018", "lib.es2018.d.ts"],
         ["es2019", "lib.es2019.d.ts"],
+        ["es2020", "lib.es2020.d.ts"],
         ["esnext", "lib.esnext.d.ts"],
         // Host only
         ["dom", "lib.dom.d.ts"],
@@ -46,6 +47,8 @@ namespace ts {
         ["es2019.array", "lib.es2019.array.d.ts"],
         ["es2019.string", "lib.es2019.string.d.ts"],
         ["es2019.symbol", "lib.es2019.symbol.d.ts"],
+        ["es2020.string", "lib.es2020.string.d.ts"],
+        ["es2020.symbol.wellknown", "lib.es2020.symbol.wellknown.d.ts"],
         ["esnext.array", "lib.es2019.array.d.ts"],
         ["esnext.symbol", "lib.es2019.symbol.d.ts"],
         ["esnext.asynciterable", "lib.es2018.asynciterable.d.ts"],
@@ -210,6 +213,7 @@ namespace ts {
                 es2017: ScriptTarget.ES2017,
                 es2018: ScriptTarget.ES2018,
                 es2019: ScriptTarget.ES2019,
+                es2020: ScriptTarget.ES2020,
                 esnext: ScriptTarget.ESNext,
             }),
             affectsSourceFile: true,
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index b99304ddfedca..b3839842d3e60 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1639,39 +1639,6 @@ namespace ts {
         };
     }
 
-    /**
-     * High-order function, creates a function that executes a function composition.
-     * For example, `chain(a, b)` is the equivalent of `x => ((a', b') => y => b'(a'(y)))(a(x), b(x))`
-     *
-     * @param args The functions to chain.
-     */
-    export function chain<T, U>(...args: ((t: T) => (u: U) => U)[]): (t: T) => (u: U) => U;
-    export function chain<T, U>(a: (t: T) => (u: U) => U, b: (t: T) => (u: U) => U, c: (t: T) => (u: U) => U, d: (t: T) => (u: U) => U, e: (t: T) => (u: U) => U): (t: T) => (u: U) => U {
-        if (e) {
-            const args: ((t: T) => (u: U) => U)[] = [];
-            for (let i = 0; i < arguments.length; i++) {
-                args[i] = arguments[i];
-            }
-
-            return t => compose(...map(args, f => f(t)));
-        }
-        else if (d) {
-            return t => compose(a(t), b(t), c(t), d(t));
-        }
-        else if (c) {
-            return t => compose(a(t), b(t), c(t));
-        }
-        else if (b) {
-            return t => compose(a(t), b(t));
-        }
-        else if (a) {
-            return t => compose(a(t));
-        }
-        else {
-            return _ => u => u;
-        }
-    }
-
     /**
      * High-order function, composes functions. Note that functions are composed inside-out;
      * for example, `compose(a, b)` is the equivalent of `x => b(a(x))`.
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index a78e89f42beb3..45ec2a9ad427a 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -139,7 +139,7 @@
         "category": "Error",
         "code": 1045
     },
-    "A 'declare' modifier is required for a top level declaration in a .d.ts file.": {
+    "Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.": {
         "category": "Error",
         "code": 1046
     },
@@ -691,7 +691,7 @@
         "category": "Error",
         "code": 1218
     },
-    "Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.": {
+    "Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.": {
         "category": "Error",
         "code": 1219
     },
@@ -1031,7 +1031,7 @@
         "category": "Error",
         "code": 1354
     },
-    "A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.": {
+    "A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.": {
         "category": "Error",
         "code": 1355
     },
diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
index b8aa9fa2df465..8761cc0a08774 100644
--- a/src/compiler/moduleNameResolver.ts
+++ b/src/compiler/moduleNameResolver.ts
@@ -421,6 +421,7 @@ namespace ts {
      */
     export interface ModuleResolutionCache extends NonRelativeModuleNameResolutionCache {
         getOrCreateCacheForDirectory(directoryName: string, redirectedReference?: ResolvedProjectReference): Map<ResolvedModuleWithFailedLookupLocations>;
+        /*@internal*/ directoryToModuleNameMap: CacheWithRedirects<Map<ResolvedModuleWithFailedLookupLocations>>;
     }
 
     /**
@@ -429,6 +430,7 @@ namespace ts {
      */
     export interface NonRelativeModuleNameResolutionCache {
         getOrCreateCacheForModuleName(nonRelativeModuleName: string, redirectedReference?: ResolvedProjectReference): PerModuleNameCache;
+        /*@internal*/ moduleNameToDirectoryMap: CacheWithRedirects<PerModuleNameCache>;
     }
 
     export interface PerModuleNameCache {
@@ -436,34 +438,47 @@ namespace ts {
         set(directory: string, result: ResolvedModuleWithFailedLookupLocations): void;
     }
 
-    export function createModuleResolutionCache(currentDirectory: string, getCanonicalFileName: (s: string) => string): ModuleResolutionCache {
+    export function createModuleResolutionCache(currentDirectory: string, getCanonicalFileName: (s: string) => string, options?: CompilerOptions): ModuleResolutionCache {
         return createModuleResolutionCacheWithMaps(
-            createCacheWithRedirects(),
-            createCacheWithRedirects(),
+            createCacheWithRedirects(options),
+            createCacheWithRedirects(options),
             currentDirectory,
             getCanonicalFileName
         );
     }
 
+
     /*@internal*/
     export interface CacheWithRedirects<T> {
         ownMap: Map<T>;
         redirectsMap: Map<Map<T>>;
         getOrCreateMapOfCacheRedirects(redirectedReference: ResolvedProjectReference | undefined): Map<T>;
         clear(): void;
+        setOwnOptions(newOptions: CompilerOptions): void;
+        setOwnMap(newOwnMap: Map<T>): void;
     }
 
     /*@internal*/
-    export function createCacheWithRedirects<T>(): CacheWithRedirects<T> {
-        const ownMap: Map<T> = createMap();
+    export function createCacheWithRedirects<T>(options?: CompilerOptions): CacheWithRedirects<T> {
+        let ownMap: Map<T> = createMap();
         const redirectsMap: Map<Map<T>> = createMap();
         return {
             ownMap,
             redirectsMap,
             getOrCreateMapOfCacheRedirects,
-            clear
+            clear,
+            setOwnOptions,
+            setOwnMap
         };
 
+        function setOwnOptions(newOptions: CompilerOptions) {
+            options = newOptions;
+        }
+
+        function setOwnMap(newOwnMap: Map<T>) {
+            ownMap = newOwnMap;
+        }
+
         function getOrCreateMapOfCacheRedirects(redirectedReference: ResolvedProjectReference | undefined) {
             if (!redirectedReference) {
                 return ownMap;
@@ -471,7 +486,8 @@ namespace ts {
             const path = redirectedReference.sourceFile.path;
             let redirects = redirectsMap.get(path);
             if (!redirects) {
-                redirects = createMap();
+                // Reuse map if redirected reference map uses same resolution
+                redirects = !options || optionsHaveModuleResolutionChanges(options, redirectedReference.commandLine.options) ? createMap() : ownMap;
                 redirectsMap.set(path, redirects);
             }
             return redirects;
@@ -490,7 +506,7 @@ namespace ts {
         currentDirectory: string,
         getCanonicalFileName: GetCanonicalFileName): ModuleResolutionCache {
 
-        return { getOrCreateCacheForDirectory, getOrCreateCacheForModuleName };
+        return { getOrCreateCacheForDirectory, getOrCreateCacheForModuleName, directoryToModuleNameMap, moduleNameToDirectoryMap };
 
         function getOrCreateCacheForDirectory(directoryName: string, redirectedReference?: ResolvedProjectReference) {
             const path = toPath(directoryName, currentDirectory, getCanonicalFileName);
@@ -1106,7 +1122,7 @@ namespace ts {
         const packageInfo = considerPackageJson ? getPackageJsonInfo(candidate, "", onlyRecordFailures, state) : undefined;
         const packageId = packageInfo && packageInfo.packageId;
         const packageJsonContent = packageInfo && packageInfo.packageJsonContent;
-        const versionPaths = packageJsonContent && readPackageJsonTypesVersionPaths(packageJsonContent, state);
+        const versionPaths = packageInfo && packageInfo.versionPaths;
         return withPackageId(packageId, loadNodeModuleFromDirectoryWorker(extensions, candidate, onlyRecordFailures, state, packageJsonContent, versionPaths));
     }
 
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 61030ed39feaf..7e01e56f0693d 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -528,7 +528,8 @@ namespace ts {
         }
     }
 
-    function loadWithLocalCache<T>(names: string[], containingFile: string, redirectedReference: ResolvedProjectReference | undefined, loader: (name: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => T): T[] {
+    /* @internal */
+    export function loadWithLocalCache<T>(names: string[], containingFile: string, redirectedReference: ResolvedProjectReference | undefined, loader: (name: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => T): T[] {
         if (names.length === 0) {
             return [];
         }
@@ -773,7 +774,7 @@ namespace ts {
             });
         }
         else {
-            moduleResolutionCache = createModuleResolutionCache(currentDirectory, x => host.getCanonicalFileName(x));
+            moduleResolutionCache = createModuleResolutionCache(currentDirectory, x => host.getCanonicalFileName(x), options);
             const loader = (moduleName: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => resolveModuleName(moduleName, containingFile, options, host, moduleResolutionCache, redirectedReference).resolvedModule!; // TODO: GH#18217
             resolveModuleNamesWorker = (moduleNames, containingFile, _reusedNames, redirectedReference) => loadWithLocalCache<ResolvedModuleFull>(Debug.assertEachDefined(moduleNames), containingFile, redirectedReference, loader);
         }
@@ -1816,7 +1817,7 @@ namespace ts {
 
                 function walkArray(nodes: NodeArray<Node>) {
                     if (parent.decorators === nodes && !options.experimentalDecorators) {
-                        diagnostics.push(createDiagnosticForNode(parent, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_to_remove_this_warning));
+                        diagnostics.push(createDiagnosticForNode(parent, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_in_your_tsconfig_or_jsconfig_to_remove_this_warning));
                     }
 
                     switch (parent.kind) {
@@ -2721,10 +2722,6 @@ namespace ts {
                     createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_with_option_1, getEmitDeclarationOptionName(options), "isolatedModules");
                 }
 
-                if (options.noEmitOnError) {
-                    createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_with_option_1, "noEmitOnError", "isolatedModules");
-                }
-
                 if (options.out) {
                     createDiagnosticForOptionName(Diagnostics.Option_0_cannot_be_specified_with_option_1, "out", "isolatedModules");
                 }
diff --git a/src/compiler/transformer.ts b/src/compiler/transformer.ts
index 12d20d6c089eb..ba47d5b8106ff 100644
--- a/src/compiler/transformer.ts
+++ b/src/compiler/transformer.ts
@@ -151,7 +151,13 @@ namespace ts {
         performance.mark("beforeTransform");
 
         // Chain together and initialize each transformer.
-        const transformation = chain(...transformers)(context);
+        const transformersWithContext = transformers.map(t => t(context));
+        const transformation = (node: T): T => {
+            for (const transform of transformersWithContext) {
+                node = transform(node);
+            }
+            return node;
+        };
 
         // prevent modification of transformation hooks.
         state = TransformationState.Initialized;
diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index 63d621c665439..a70fb820e7950 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -2577,7 +2577,7 @@ namespace ts {
          */
         function visitEnumDeclaration(node: EnumDeclaration): VisitResult<Statement> {
             if (!shouldEmitEnumDeclaration(node)) {
-                return undefined;
+                return createNotEmittedStatement(node);
             }
 
             const statements: Statement[] = [];
diff --git a/src/compiler/tsbuild.ts b/src/compiler/tsbuild.ts
index c5d8c77a1bcd9..aed4ba48e94b0 100644
--- a/src/compiler/tsbuild.ts
+++ b/src/compiler/tsbuild.ts
@@ -401,6 +401,10 @@ namespace ts {
         setGetSourceFileAsHashVersioned(compilerHost, host);
         compilerHost.getParsedCommandLine = parseConfigFile;
 
+        compilerHost.resolveModuleNames = maybeBind(host, host.resolveModuleNames);
+        compilerHost.resolveTypeReferenceDirectives = maybeBind(host, host.resolveTypeReferenceDirectives);
+        let moduleResolutionCache = !compilerHost.resolveModuleNames ? createModuleResolutionCache(currentDirectory, getCanonicalFileName) : undefined;
+
         const buildInfoChecked = createFileMap<true>(toPath);
         let extendedConfigCache: Map<ExtendedConfigCacheEntry> | undefined;
 
@@ -1099,6 +1103,30 @@ namespace ts {
 
             // TODO: handle resolve module name to cache result in project reference redirect
             projectCompilerOptions = configFile.options;
+            // Update module resolution cache if needed
+            if (moduleResolutionCache) {
+                const projPath = toPath(proj);
+                if (moduleResolutionCache.directoryToModuleNameMap.redirectsMap.size === 0) {
+                    // The own map will be for projectCompilerOptions
+                    Debug.assert(moduleResolutionCache.moduleNameToDirectoryMap.redirectsMap.size === 0);
+                    moduleResolutionCache.directoryToModuleNameMap.redirectsMap.set(projPath, moduleResolutionCache.directoryToModuleNameMap.ownMap);
+                    moduleResolutionCache.moduleNameToDirectoryMap.redirectsMap.set(projPath, moduleResolutionCache.moduleNameToDirectoryMap.ownMap);
+                }
+                else {
+                    // Set correct own map
+                    Debug.assert(moduleResolutionCache.moduleNameToDirectoryMap.redirectsMap.size > 0);
+
+                    const ref: ResolvedProjectReference = {
+                        sourceFile: projectCompilerOptions.configFile!,
+                        commandLine: configFile
+                    };
+                    moduleResolutionCache.directoryToModuleNameMap.setOwnMap(moduleResolutionCache.directoryToModuleNameMap.getOrCreateMapOfCacheRedirects(ref));
+                    moduleResolutionCache.moduleNameToDirectoryMap.setOwnMap(moduleResolutionCache.moduleNameToDirectoryMap.getOrCreateMapOfCacheRedirects(ref));
+                }
+                moduleResolutionCache.directoryToModuleNameMap.setOwnOptions(projectCompilerOptions);
+                moduleResolutionCache.moduleNameToDirectoryMap.setOwnOptions(projectCompilerOptions);
+            }
+
             const program = host.createProgram(
                 configFile.fileNames,
                 configFile.options,
@@ -1371,6 +1399,13 @@ namespace ts {
             compilerHost.getSourceFile = getSourceFileWithCache!;
             extendedConfigCache = createMap();
 
+            const originalResolveModuleNames = compilerHost.resolveModuleNames;
+            if (!compilerHost.resolveModuleNames) {
+                const loader = (moduleName: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => resolveModuleName(moduleName, containingFile, projectCompilerOptions, compilerHost, moduleResolutionCache, redirectedReference).resolvedModule!;
+                compilerHost.resolveModuleNames = (moduleNames, containingFile, _reusedNames, redirectedReference) =>
+                    loadWithLocalCache<ResolvedModuleFull>(Debug.assertEachDefined(moduleNames), containingFile, redirectedReference, loader);
+            }
+
             const graph = getGlobalDependencyGraph();
             reportBuildQueue(graph);
             let anyFailed = false;
@@ -1432,6 +1467,8 @@ namespace ts {
             compilerHost.getSourceFile = savedGetSourceFile;
             readFileWithCache = savedReadFileWithCache;
             extendedConfigCache = undefined;
+            compilerHost.resolveModuleNames = originalResolveModuleNames;
+            moduleResolutionCache = undefined;
             return anyFailed ? ExitStatus.DiagnosticsPresent_OutputsSkipped : ExitStatus.Success;
         }
 
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index da5ab5a677263..e141e2b9daa82 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -4756,7 +4756,8 @@ namespace ts {
         ES2017 = 4,
         ES2018 = 5,
         ES2019 = 6,
-        ESNext = 7,
+        ES2020 = 7,
+        ESNext = 8,
         JSON = 100,
         Latest = ESNext,
     }
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 2e6c3ae4f866e..188f2f8630209 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -101,7 +101,12 @@ namespace ts {
     }
 
     export function changesAffectModuleResolution(oldOptions: CompilerOptions, newOptions: CompilerOptions): boolean {
-        return oldOptions.configFilePath !== newOptions.configFilePath || moduleResolutionOptionDeclarations.some(o =>
+        return oldOptions.configFilePath !== newOptions.configFilePath ||
+            optionsHaveModuleResolutionChanges(oldOptions, newOptions);
+    }
+
+    export function optionsHaveModuleResolutionChanges(oldOptions: CompilerOptions, newOptions: CompilerOptions) {
+        return moduleResolutionOptionDeclarations.some(o =>
             !isJsonEqual(getCompilerOptionValue(oldOptions, o), getCompilerOptionValue(newOptions, o)));
     }
 
@@ -2221,6 +2226,7 @@ namespace ts {
     function getNextJSDocCommentLocation(node: Node) {
         const parent = node.parent;
         if (parent.kind === SyntaxKind.PropertyAssignment ||
+            parent.kind === SyntaxKind.ExportAssignment ||
             parent.kind === SyntaxKind.PropertyDeclaration ||
             parent.kind === SyntaxKind.ExpressionStatement && node.kind === SyntaxKind.PropertyAccessExpression ||
             getNestedModuleDeclaration(parent) ||
@@ -4330,6 +4336,10 @@ namespace ts {
         return positionsAreOnSameLine(range1.end, getStartPositionOfRange(range2, sourceFile), sourceFile);
     }
 
+    export function isNodeArrayMultiLine(list: NodeArray<Node>, sourceFile: SourceFile): boolean {
+        return !positionsAreOnSameLine(list.pos, list.end, sourceFile);
+    }
+
     export function positionsAreOnSameLine(pos1: number, pos2: number, sourceFile: SourceFile) {
         return pos1 === pos2 ||
             getLineOfLocalPosition(sourceFile, pos1) === getLineOfLocalPosition(sourceFile, pos2);
@@ -4673,6 +4683,8 @@ namespace ts {
         switch (options.target) {
             case ScriptTarget.ESNext:
                 return "lib.esnext.full.d.ts";
+            case ScriptTarget.ES2020:
+                return "lib.es2020.full.d.ts";
             case ScriptTarget.ES2019:
                 return "lib.es2019.full.d.ts";
             case ScriptTarget.ES2018:
diff --git a/src/lib/es2020.d.ts b/src/lib/es2020.d.ts
new file mode 100644
index 0000000000000..fb55d987ebb5e
--- /dev/null
+++ b/src/lib/es2020.d.ts
@@ -0,0 +1,3 @@
+/// <reference lib="es2019" />
+/// <reference lib="es2020.string" />
+/// <reference lib="es2020.symbol.wellknown" />
diff --git a/src/lib/es2020.full.d.ts b/src/lib/es2020.full.d.ts
new file mode 100644
index 0000000000000..0d4b6d45d55ad
--- /dev/null
+++ b/src/lib/es2020.full.d.ts
@@ -0,0 +1,5 @@
+/// <reference lib="es2020" />
+/// <reference lib="dom" />
+/// <reference lib="webworker.importscripts" />
+/// <reference lib="scripthost" />
+/// <reference lib="dom.iterable" />
diff --git a/src/lib/es2020.string.d.ts b/src/lib/es2020.string.d.ts
new file mode 100644
index 0000000000000..335a0ac000577
--- /dev/null
+++ b/src/lib/es2020.string.d.ts
@@ -0,0 +1,10 @@
+/// <reference lib="es2015.iterable" />
+
+interface String {
+  /**
+    * Matches a string with a regular expression, and returns an iterable of matches
+    * containing the results of that search.
+    * @param regexp A variable name or string literal containing the regular expression pattern and flags.
+    */
+  matchAll(regexp: RegExp): IterableIterator<RegExpMatchArray>;
+}
diff --git a/src/lib/es2020.symbol.wellknown.d.ts b/src/lib/es2020.symbol.wellknown.d.ts
new file mode 100644
index 0000000000000..76e377e0be270
--- /dev/null
+++ b/src/lib/es2020.symbol.wellknown.d.ts
@@ -0,0 +1,19 @@
+/// <reference lib="es2015.iterable" />
+/// <reference lib="es2015.symbol" />
+
+interface SymbolConstructor {
+  /**
+   * A regular expression method that matches the regular expression against a string. Called
+   * by the String.prototype.matchAll method.
+   */
+  readonly matchAll: symbol;
+}
+
+interface RegExp {
+  /**
+   * Matches a string with this regular expression, and returns an iterable of matches
+   * containing the results of that search.
+   * @param string A string to search within.
+   */
+  [Symbol.matchAll](str: string): IterableIterator<RegExpMatchArray>;
+}
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index de4a612d3919f..d39613e515194 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -60,7 +60,7 @@ declare function encodeURI(uri: string): string;
   * Encodes a text string as a valid component of a Uniform Resource Identifier (URI).
   * @param uriComponent A value representing an encoded URI component.
   */
-declare function encodeURIComponent(uriComponent: string): string;
+declare function encodeURIComponent(uriComponent: string | number | boolean): string;
 
 /**
   * Computes a new string in which certain characters have been replaced by a hexadecimal escape sequence.
@@ -1446,7 +1446,9 @@ type Extract<T, U> = T extends U ? T : never;
 /**
  * Construct a type with the properties of T except for those in type K.
  */
-type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
+type Omit<T, K extends keyof any> = {
+    [P in Exclude<keyof T, K>]: T[P]
+};
 
 /**
  * Exclude null and undefined from T
diff --git a/src/lib/libs.json b/src/lib/libs.json
index fa5f4060acd6a..74611a938609c 100644
--- a/src/lib/libs.json
+++ b/src/lib/libs.json
@@ -7,6 +7,7 @@
         "es2017",
         "es2018",
         "es2019",
+        "es2020",
         "esnext",
         // Host only
         "dom.generated",
@@ -37,6 +38,8 @@
         "es2019.array",
         "es2019.string",
         "es2019.symbol",
+        "es2020.string",
+        "es2020.symbol.wellknown",
         "esnext.bigint",
         "esnext.intl",
         // Default libraries
@@ -46,6 +49,7 @@
         "es2017.full",
         "es2018.full",
         "es2019.full",
+        "es2020.full",
         "esnext.full"
     ],
     "paths": {
diff --git a/src/server/protocol.ts b/src/server/protocol.ts
index e5580874369e6..3da890a766ff7 100644
--- a/src/server/protocol.ts
+++ b/src/server/protocol.ts
@@ -3046,6 +3046,9 @@ namespace ts.server.protocol {
         ES2015 = "ES2015",
         ES2016 = "ES2016",
         ES2017 = "ES2017",
+        ES2018 = "ES2018",
+        ES2019 = "ES2019",
+        ES2020 = "ES2020",
         ESNext = "ESNext"
     }
 }
diff --git a/src/services/codefixes/fixEnableExperimentalDecorators.ts b/src/services/codefixes/fixEnableExperimentalDecorators.ts
index 8aeefe48a47b5..8ab1c2769104d 100644
--- a/src/services/codefixes/fixEnableExperimentalDecorators.ts
+++ b/src/services/codefixes/fixEnableExperimentalDecorators.ts
@@ -2,7 +2,7 @@
 namespace ts.codefix {
     const fixId = "enableExperimentalDecorators";
     const errorCodes = [
-        Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_to_remove_this_warning.code
+        Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_in_your_tsconfig_or_jsconfig_to_remove_this_warning.code
     ];
     registerCodeFix({
         errorCodes,
@@ -12,13 +12,20 @@ namespace ts.codefix {
                 return undefined;
             }
 
-            const changes = textChanges.ChangeTracker.with(context, changeTracker => makeChange(changeTracker, configFile));
+            const changes = textChanges.ChangeTracker.with(context, changeTracker => doChange(changeTracker, configFile));
             return [createCodeFixActionNoFixId(fixId, changes, Diagnostics.Enable_the_experimentalDecorators_option_in_your_configuration_file)];
         },
         fixIds: [fixId],
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes) => {
+            const { configFile } = context.program.getCompilerOptions();
+            if (configFile === undefined) {
+                return undefined;
+            }
+            doChange(changes, configFile);
+        }),
     });
 
-    function makeChange(changeTracker: textChanges.ChangeTracker, configFile: TsConfigSourceFile) {
+    function doChange(changeTracker: textChanges.ChangeTracker, configFile: TsConfigSourceFile) {
         setJsonCompilerOptionValue(changeTracker, configFile, "experimentalDecorators", createTrue());
     }
 }
diff --git a/src/services/outliningElementsCollector.ts b/src/services/outliningElementsCollector.ts
index 6f834512f0b48..650a107f4a5e7 100644
--- a/src/services/outliningElementsCollector.ts
+++ b/src/services/outliningElementsCollector.ts
@@ -153,8 +153,8 @@ namespace ts.OutliningElementsCollector {
     function getOutliningSpanForNode(n: Node, sourceFile: SourceFile): OutliningSpan | undefined {
         switch (n.kind) {
             case SyntaxKind.Block:
-                if (isFunctionBlock(n)) {
-                    return spanForNode(n.parent, /*autoCollapse*/ n.parent.kind !== SyntaxKind.ArrowFunction);
+                if (isFunctionLike(n.parent)) {
+                    return functionSpan(n.parent, n as Block, sourceFile);
                 }
                 // Check if the block is standalone, or 'attached' to some parent statement.
                 // If the latter, we want to collapse the block, but consider its hint span
@@ -225,18 +225,26 @@ namespace ts.OutliningElementsCollector {
             return spanForNode(node, /*autoCollapse*/ false, /*useFullStart*/ !isArrayLiteralExpression(node.parent) && !isCallExpression(node.parent), open);
         }
 
-        function spanForNode(hintSpanNode: Node, autoCollapse = false, useFullStart = true, open: SyntaxKind.OpenBraceToken | SyntaxKind.OpenBracketToken = SyntaxKind.OpenBraceToken): OutliningSpan | undefined {
+        function spanForNode(hintSpanNode: Node, autoCollapse = false, useFullStart = true, open: SyntaxKind.OpenBraceToken | SyntaxKind.OpenBracketToken = SyntaxKind.OpenBraceToken, close: SyntaxKind = open === SyntaxKind.OpenBraceToken ? SyntaxKind.CloseBraceToken : SyntaxKind.CloseBracketToken): OutliningSpan | undefined {
             const openToken = findChildOfKind(n, open, sourceFile);
-            const close = open === SyntaxKind.OpenBraceToken ? SyntaxKind.CloseBraceToken : SyntaxKind.CloseBracketToken;
             const closeToken = findChildOfKind(n, close, sourceFile);
-            if (!openToken || !closeToken) {
-                return undefined;
-            }
-            const textSpan = createTextSpanFromBounds(useFullStart ? openToken.getFullStart() : openToken.getStart(sourceFile), closeToken.getEnd());
-            return createOutliningSpan(textSpan, OutliningSpanKind.Code, createTextSpanFromNode(hintSpanNode, sourceFile), autoCollapse);
+            return openToken && closeToken && spanBetweenTokens(openToken, closeToken, hintSpanNode, sourceFile, autoCollapse, useFullStart);
         }
     }
 
+    function functionSpan(node: FunctionLike, body: Block, sourceFile: SourceFile): OutliningSpan | undefined {
+        const openToken = isNodeArrayMultiLine(node.parameters, sourceFile)
+            ? findChildOfKind(node, SyntaxKind.OpenParenToken, sourceFile)
+            : findChildOfKind(body, SyntaxKind.OpenBraceToken, sourceFile);
+        const closeToken = findChildOfKind(body, SyntaxKind.CloseBraceToken, sourceFile);
+        return openToken && closeToken && spanBetweenTokens(openToken, closeToken, node.parent, sourceFile, /*autoCollapse*/ node.parent.kind !== SyntaxKind.ArrowFunction);
+    }
+
+    function spanBetweenTokens(openToken: Node, closeToken: Node, hintSpanNode: Node, sourceFile: SourceFile, autoCollapse = false, useFullStart = true): OutliningSpan {
+        const textSpan = createTextSpanFromBounds(useFullStart ? openToken.getFullStart() : openToken.getStart(sourceFile), closeToken.getEnd());
+        return createOutliningSpan(textSpan, OutliningSpanKind.Code, createTextSpanFromNode(hintSpanNode, sourceFile), autoCollapse);
+    }
+
     function createOutliningSpan(textSpan: TextSpan, kind: OutliningSpanKind, hintSpan: TextSpan = textSpan, autoCollapse = false, bannerText = "..."): OutliningSpan {
         return { textSpan, kind, hintSpan, bannerText, autoCollapse };
     }
diff --git a/src/testRunner/compilerRunner.ts b/src/testRunner/compilerRunner.ts
index c55cd1aa5117a..76c7c728aa19a 100644
--- a/src/testRunner/compilerRunner.ts
+++ b/src/testRunner/compilerRunner.ts
@@ -5,7 +5,7 @@ const enum CompilerTestType {
 }
 
 interface CompilerFileBasedTest extends Harness.FileBasedTest {
-    payload?: Harness.TestCaseParser.TestCaseContent;
+    readonly content?: string;
 }
 
 class CompilerBaselineRunner extends RunnerBase {
@@ -74,7 +74,14 @@ class CompilerBaselineRunner extends RunnerBase {
         // Mocha holds onto the closure environment of the describe callback even after the test is done.
         // Everything declared here should be cleared out in the "after" callback.
         let compilerTest!: CompilerTest;
-        before(() => { compilerTest = new CompilerTest(fileName, test && test.payload, configuration); });
+        before(() => {
+            let payload;
+            if (test && test.content) {
+                const rootDir = test.file.indexOf("conformance") === -1 ? "tests/cases/compiler/" : ts.getDirectoryPath(test.file) + "/";
+                payload = Harness.TestCaseParser.makeUnitsFromTest(test.content, test.file, rootDir);
+            }
+            compilerTest = new CompilerTest(fileName, payload, configuration);
+        });
         it(`Correct errors for ${fileName}`, () => { compilerTest.verifyDiagnostics(); });
         it(`Correct module resolution tracing for ${fileName}`, () => { compilerTest.verifyModuleResolution(); });
         it(`Correct sourcemap content for ${fileName}`, () => { compilerTest.verifySourceMapRecord(); });
@@ -189,11 +196,9 @@ class CompilerTest {
     public static getConfigurations(file: string): CompilerFileBasedTest {
         // also see `parseCompilerTestConfigurations` in tests/webTestServer.ts
         const content = Harness.IO.readFile(file)!;
-        const rootDir = file.indexOf("conformance") === -1 ? "tests/cases/compiler/" : ts.getDirectoryPath(file) + "/";
-        const payload = Harness.TestCaseParser.makeUnitsFromTest(content, file, rootDir);
         const settings = Harness.TestCaseParser.extractCompilerSettings(content);
         const configurations = Harness.getFileBasedTestConfigurations(settings, /*varyBy*/ ["module", "target"]);
-        return { file, payload, configurations };
+        return { file, configurations, content };
     }
 
     public verifyDiagnostics() {
diff --git a/src/testRunner/unittests/config/commandLineParsing.ts b/src/testRunner/unittests/config/commandLineParsing.ts
index ccb2378c644a8..450b27e01ed4f 100644
--- a/src/testRunner/unittests/config/commandLineParsing.ts
+++ b/src/testRunner/unittests/config/commandLineParsing.ts
@@ -57,7 +57,7 @@ namespace ts {
             assertParseResult(["--lib", "es5,invalidOption", "0.ts"],
                 {
                     errors: [{
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'es2019', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'es2019.array', 'es2019.string', 'es2019.symbol', 'esnext.array', 'esnext.symbol', 'esnext.asynciterable', 'esnext.intl', 'esnext.bigint'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'es2019', 'es2020', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'es2019.array', 'es2019.string', 'es2019.symbol', 'es2020.string', 'es2020.symbol.wellknown', 'esnext.array', 'esnext.symbol', 'esnext.asynciterable', 'esnext.intl', 'esnext.bigint'.",
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category,
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         file: undefined,
@@ -161,7 +161,7 @@ namespace ts {
                         start: undefined,
                         length: undefined,
                     }, {
-                            messageText: "Argument for '--target' option must be: 'es3', 'es5', 'es6', 'es2015', 'es2016', 'es2017', 'es2018', 'es2019', 'esnext'.",
+                            messageText: "Argument for '--target' option must be: 'es3', 'es5', 'es6', 'es2015', 'es2016', 'es2017', 'es2018', 'es2019', 'es2020', 'esnext'.",
                             category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category,
                             code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
 
@@ -259,7 +259,7 @@ namespace ts {
             assertParseResult(["--lib", "es5,", "es7", "0.ts"],
                 {
                     errors: [{
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'es2019', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'es2019.array', 'es2019.string', 'es2019.symbol', 'esnext.array', 'esnext.symbol', 'esnext.asynciterable', 'esnext.intl', 'esnext.bigint'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'es2019', 'es2020', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'es2019.array', 'es2019.string', 'es2019.symbol', 'es2020.string', 'es2020.symbol.wellknown', 'esnext.array', 'esnext.symbol', 'esnext.asynciterable', 'esnext.intl', 'esnext.bigint'.",
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category,
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         file: undefined,
@@ -278,7 +278,7 @@ namespace ts {
             assertParseResult(["--lib", "es5, ", "es7", "0.ts"],
                 {
                     errors: [{
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'es2019', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'es2019.array', 'es2019.string', 'es2019.symbol', 'esnext.array', 'esnext.symbol', 'esnext.asynciterable', 'esnext.intl', 'esnext.bigint'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'es2019', 'es2020', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'es2019.array', 'es2019.string', 'es2019.symbol', 'es2020.string', 'es2020.symbol.wellknown', 'esnext.array', 'esnext.symbol', 'esnext.asynciterable', 'esnext.intl', 'esnext.bigint'.",
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category,
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         file: undefined,
diff --git a/tests/baselines/reference/1.0lib-noErrors.js b/tests/baselines/reference/1.0lib-noErrors.js
index ade0f4bf903b9..3dac98d9e5647 100644
--- a/tests/baselines/reference/1.0lib-noErrors.js
+++ b/tests/baselines/reference/1.0lib-noErrors.js
@@ -78,7 +78,7 @@ declare function encodeURI(uri: string): string;
   * Encodes a text string as a valid component of a Uniform Resource Identifier (URI).
   * @param uriComponent A value representing an encoded URI component.
   */
-declare function encodeURIComponent(uriComponent: string): string;
+declare function encodeURIComponent(uriComponent: string | number | boolean): string;
 
 interface PropertyDescriptor {
     configurable?: boolean;
@@ -1141,7 +1141,7 @@ declare var Array: {
     <T>(...items: T[]): T[];
     isArray(arg: any): boolean;
     prototype: Array<any>;
-}
+}

 
 //// [1.0lib-noErrors.js]
 /* *****************************************************************************
diff --git a/tests/baselines/reference/1.0lib-noErrors.symbols b/tests/baselines/reference/1.0lib-noErrors.symbols
index adedbdb9aa2dc..d67952e201c98 100644
--- a/tests/baselines/reference/1.0lib-noErrors.symbols
+++ b/tests/baselines/reference/1.0lib-noErrors.symbols
@@ -98,12 +98,12 @@ declare function encodeURI(uri: string): string;
   * Encodes a text string as a valid component of a Uniform Resource Identifier (URI).
   * @param uriComponent A value representing an encoded URI component.
   */
-declare function encodeURIComponent(uriComponent: string): string;
+declare function encodeURIComponent(uriComponent: string | number | boolean): string;
 >encodeURIComponent : Symbol(encodeURIComponent, Decl(1.0lib-noErrors.ts, 73, 48))
 >uriComponent : Symbol(uriComponent, Decl(1.0lib-noErrors.ts, 79, 36))
 
 interface PropertyDescriptor {
->PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 66))
+>PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 85))
 
     configurable?: boolean;
 >configurable : Symbol(PropertyDescriptor.configurable, Decl(1.0lib-noErrors.ts, 81, 30))
@@ -130,7 +130,7 @@ interface PropertyDescriptorMap {
 
     [s: string]: PropertyDescriptor;
 >s : Symbol(s, Decl(1.0lib-noErrors.ts, 91, 5))
->PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 66))
+>PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 85))
 }
 
 interface Object {
@@ -217,7 +217,7 @@ declare var Object: {
 >getOwnPropertyDescriptor : Symbol(getOwnPropertyDescriptor, Decl(1.0lib-noErrors.ts, 141, 32))
 >o : Symbol(o, Decl(1.0lib-noErrors.ts, 149, 29))
 >p : Symbol(p, Decl(1.0lib-noErrors.ts, 149, 36))
->PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 66))
+>PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 85))
 
     /** 
       * Returns the names of the own properties of an object. The own properties of an object are those that are defined directly 
@@ -250,7 +250,7 @@ declare var Object: {
 >o : Symbol(o, Decl(1.0lib-noErrors.ts, 171, 19))
 >p : Symbol(p, Decl(1.0lib-noErrors.ts, 171, 26))
 >attributes : Symbol(attributes, Decl(1.0lib-noErrors.ts, 171, 37))
->PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 66))
+>PropertyDescriptor : Symbol(PropertyDescriptor, Decl(1.0lib-noErrors.ts, 79, 85))
 
     /**
       * Adds one or more properties to an object, and/or modifies attributes of existing properties. 
@@ -2084,3 +2084,4 @@ declare var Array: {
 >prototype : Symbol(prototype, Decl(1.0lib-noErrors.ts, 1140, 31))
 >Array : Symbol(Array, Decl(1.0lib-noErrors.ts, 973, 23), Decl(1.0lib-noErrors.ts, 1133, 11))
 }
+
diff --git a/tests/baselines/reference/1.0lib-noErrors.types b/tests/baselines/reference/1.0lib-noErrors.types
index 1d9c67834e702..91e5fdc7b7356 100644
--- a/tests/baselines/reference/1.0lib-noErrors.types
+++ b/tests/baselines/reference/1.0lib-noErrors.types
@@ -98,9 +98,9 @@ declare function encodeURI(uri: string): string;
   * Encodes a text string as a valid component of a Uniform Resource Identifier (URI).
   * @param uriComponent A value representing an encoded URI component.
   */
-declare function encodeURIComponent(uriComponent: string): string;
->encodeURIComponent : (uriComponent: string) => string
->uriComponent : string
+declare function encodeURIComponent(uriComponent: string | number | boolean): string;
+>encodeURIComponent : (uriComponent: string | number | boolean) => string
+>uriComponent : string | number | boolean
 
 interface PropertyDescriptor {
     configurable?: boolean;
@@ -1911,3 +1911,4 @@ declare var Array: {
     prototype: Array<any>;
 >prototype : any[]
 }
+
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index c0cc90efdc770..d09582078be43 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -2625,9 +2625,10 @@ declare namespace ts {
         ES2017 = 4,
         ES2018 = 5,
         ES2019 = 6,
-        ESNext = 7,
+        ES2020 = 7,
+        ESNext = 8,
         JSON = 100,
-        Latest = 7
+        Latest = 8
     }
     enum LanguageVariant {
         Standard = 0,
@@ -3732,7 +3733,7 @@ declare namespace ts {
         get(directory: string): ResolvedModuleWithFailedLookupLocations | undefined;
         set(directory: string, result: ResolvedModuleWithFailedLookupLocations): void;
     }
-    function createModuleResolutionCache(currentDirectory: string, getCanonicalFileName: (s: string) => string): ModuleResolutionCache;
+    function createModuleResolutionCache(currentDirectory: string, getCanonicalFileName: (s: string) => string, options?: CompilerOptions): ModuleResolutionCache;
     function resolveModuleNameFromCache(moduleName: string, containingFile: string, cache: ModuleResolutionCache): ResolvedModuleWithFailedLookupLocations | undefined;
     function resolveModuleName(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations;
     function nodeModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations;
@@ -8141,6 +8142,9 @@ declare namespace ts.server.protocol {
         ES2015 = "ES2015",
         ES2016 = "ES2016",
         ES2017 = "ES2017",
+        ES2018 = "ES2018",
+        ES2019 = "ES2019",
+        ES2020 = "ES2020",
         ESNext = "ESNext"
     }
 }
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 61f5919396d74..817276dc5c5c6 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -2625,9 +2625,10 @@ declare namespace ts {
         ES2017 = 4,
         ES2018 = 5,
         ES2019 = 6,
-        ESNext = 7,
+        ES2020 = 7,
+        ESNext = 8,
         JSON = 100,
-        Latest = 7
+        Latest = 8
     }
     enum LanguageVariant {
         Standard = 0,
@@ -3732,7 +3733,7 @@ declare namespace ts {
         get(directory: string): ResolvedModuleWithFailedLookupLocations | undefined;
         set(directory: string, result: ResolvedModuleWithFailedLookupLocations): void;
     }
-    function createModuleResolutionCache(currentDirectory: string, getCanonicalFileName: (s: string) => string): ModuleResolutionCache;
+    function createModuleResolutionCache(currentDirectory: string, getCanonicalFileName: (s: string) => string, options?: CompilerOptions): ModuleResolutionCache;
     function resolveModuleNameFromCache(moduleName: string, containingFile: string, cache: ModuleResolutionCache): ResolvedModuleWithFailedLookupLocations | undefined;
     function resolveModuleName(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations;
     function nodeModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations;
diff --git a/tests/baselines/reference/constAssertions.errors.txt b/tests/baselines/reference/constAssertions.errors.txt
index 24fce1599012a..8ecce1377e344 100644
--- a/tests/baselines/reference/constAssertions.errors.txt
+++ b/tests/baselines/reference/constAssertions.errors.txt
@@ -1,7 +1,7 @@
 tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(44,32): error TS2540: Cannot assign to 'x' because it is a read-only property.
-tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(61,10): error TS1355: A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.
-tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(62,10): error TS1355: A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.
-tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(63,10): error TS1355: A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.
+tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(61,10): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
+tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(62,10): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
+tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(63,10): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
 
 
 ==== tests/cases/conformance/expressions/typeAssertions/constAssertions.ts (4 errors) ====
@@ -69,11 +69,11 @@ tests/cases/conformance/expressions/typeAssertions/constAssertions.ts(63,10): er
     
     let e1 = v1 as const;  // Error
              ~~
-!!! error TS1355: A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.
+!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
     let e2 = (true ? 1 : 0) as const;  // Error
              ~~~~~~~~~~~~~~
-!!! error TS1355: A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.
+!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
     let e3 = id(1) as const;  // Error
              ~~~~~
-!!! error TS1355: A 'const' assertion can only be applied to a string, number, boolean, array, or object literal.
+!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
     
\ No newline at end of file
diff --git a/tests/baselines/reference/constEnum4.js b/tests/baselines/reference/constEnum4.js
new file mode 100644
index 0000000000000..dc7c4b0e593ec
--- /dev/null
+++ b/tests/baselines/reference/constEnum4.js
@@ -0,0 +1,13 @@
+//// [constEnum4.ts]
+if (1)
+    const enum A { }
+else if (2)
+    const enum B { }
+else
+    const enum C { }
+
+
+//// [constEnum4.js]
+if (1)
+else if (2)
+else
diff --git a/tests/baselines/reference/constEnum4.symbols b/tests/baselines/reference/constEnum4.symbols
new file mode 100644
index 0000000000000..0098e85c130ea
--- /dev/null
+++ b/tests/baselines/reference/constEnum4.symbols
@@ -0,0 +1,13 @@
+=== tests/cases/conformance/constEnums/constEnum4.ts ===
+if (1)
+    const enum A { }
+>A : Symbol(A, Decl(constEnum4.ts, 0, 6))
+
+else if (2)
+    const enum B { }
+>B : Symbol(B, Decl(constEnum4.ts, 2, 11))
+
+else
+    const enum C { }
+>C : Symbol(C, Decl(constEnum4.ts, 4, 4))
+
diff --git a/tests/baselines/reference/constEnum4.types b/tests/baselines/reference/constEnum4.types
new file mode 100644
index 0000000000000..a35e9f898bf8e
--- /dev/null
+++ b/tests/baselines/reference/constEnum4.types
@@ -0,0 +1,17 @@
+=== tests/cases/conformance/constEnums/constEnum4.ts ===
+if (1)
+>1 : 1
+
+    const enum A { }
+>A : A
+
+else if (2)
+>2 : 2
+
+    const enum B { }
+>B : B
+
+else
+    const enum C { }
+>C : C
+
diff --git a/tests/baselines/reference/constantEnumAssert.errors.txt b/tests/baselines/reference/constantEnumAssert.errors.txt
new file mode 100644
index 0000000000000..b384d3bd308e0
--- /dev/null
+++ b/tests/baselines/reference/constantEnumAssert.errors.txt
@@ -0,0 +1,59 @@
+tests/cases/compiler/constantEnumAssert.ts(45,20): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
+tests/cases/compiler/constantEnumAssert.ts(49,20): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
+
+
+==== tests/cases/compiler/constantEnumAssert.ts (2 errors) ====
+    enum E1 {
+        a,
+        b
+    }
+    
+    enum E2 {
+        a = 'a',
+        b = 'b'
+    }
+    
+    enum E3 {
+        a = 1,
+        b = a << 1,
+        c = a << 2,
+    }
+    
+    const enum E4 {
+        a,
+        b
+    }
+    
+    const E5 = {
+        a: 'a',
+        b: 'b'
+    }
+    
+    const foo1 = { a: E1.a }
+    
+    const foo2 = { a: E2.a }
+    
+    const foo3 = { a: E1.a } as const
+    
+    const foo4 = { a: E2.a } as const
+    
+    const foo5 = { a: E3.a } as const
+    
+    const foo6 = { a: E4.a } as const
+    
+    const foo7 = { a: E5.a } as const
+    
+    const foo8 = { a: E1.a as const }
+    
+    const foo9 = { a: E2.a as const }
+    
+    const foo10 = { a: E3.a as const }
+                       ~~~~
+!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
+    
+    const foo11 = { a: E4.a as const }
+    
+    const foo12 = { a: E5.a as const }
+                       ~~~~
+!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constantEnumAssert.js b/tests/baselines/reference/constantEnumAssert.js
new file mode 100644
index 0000000000000..85f3db9d93a77
--- /dev/null
+++ b/tests/baselines/reference/constantEnumAssert.js
@@ -0,0 +1,85 @@
+//// [constantEnumAssert.ts]
+enum E1 {
+    a,
+    b
+}
+
+enum E2 {
+    a = 'a',
+    b = 'b'
+}
+
+enum E3 {
+    a = 1,
+    b = a << 1,
+    c = a << 2,
+}
+
+const enum E4 {
+    a,
+    b
+}
+
+const E5 = {
+    a: 'a',
+    b: 'b'
+}
+
+const foo1 = { a: E1.a }
+
+const foo2 = { a: E2.a }
+
+const foo3 = { a: E1.a } as const
+
+const foo4 = { a: E2.a } as const
+
+const foo5 = { a: E3.a } as const
+
+const foo6 = { a: E4.a } as const
+
+const foo7 = { a: E5.a } as const
+
+const foo8 = { a: E1.a as const }
+
+const foo9 = { a: E2.a as const }
+
+const foo10 = { a: E3.a as const }
+
+const foo11 = { a: E4.a as const }
+
+const foo12 = { a: E5.a as const }
+
+
+//// [constantEnumAssert.js]
+var E1;
+(function (E1) {
+    E1[E1["a"] = 0] = "a";
+    E1[E1["b"] = 1] = "b";
+})(E1 || (E1 = {}));
+var E2;
+(function (E2) {
+    E2["a"] = "a";
+    E2["b"] = "b";
+})(E2 || (E2 = {}));
+var E3;
+(function (E3) {
+    E3[E3["a"] = 1] = "a";
+    E3[E3["b"] = 2] = "b";
+    E3[E3["c"] = 4] = "c";
+})(E3 || (E3 = {}));
+var E5 = {
+    a: 'a',
+    b: 'b'
+};
+var foo1 = { a: E1.a };
+var foo2 = { a: E2.a };
+var foo3 = { a: E1.a };
+var foo4 = { a: E2.a };
+var foo5 = { a: E3.a };
+var foo6 = { a: 0 /* a */ };
+var foo7 = { a: E5.a };
+var foo8 = { a: E1.a };
+var foo9 = { a: E2.a };
+var foo10 = { a: E3.a };
+var foo11 = { a: 0 /* a */ };
+var foo12 = { a: E5.a };
diff --git a/tests/baselines/reference/constantEnumAssert.symbols b/tests/baselines/reference/constantEnumAssert.symbols
new file mode 100644
index 0000000000000..3249dbe61ccaa
--- /dev/null
+++ b/tests/baselines/reference/constantEnumAssert.symbols
@@ -0,0 +1,140 @@
+=== tests/cases/compiler/constantEnumAssert.ts ===
+enum E1 {
+>E1 : Symbol(E1, Decl(constantEnumAssert.ts, 0, 0))
+
+    a,
+>a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+
+    b
+>b : Symbol(E1.b, Decl(constantEnumAssert.ts, 1, 6))
+}
+
+enum E2 {
+>E2 : Symbol(E2, Decl(constantEnumAssert.ts, 3, 1))
+
+    a = 'a',
+>a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+
+    b = 'b'
+>b : Symbol(E2.b, Decl(constantEnumAssert.ts, 6, 12))
+}
+
+enum E3 {
+>E3 : Symbol(E3, Decl(constantEnumAssert.ts, 8, 1))
+
+    a = 1,
+>a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+
+    b = a << 1,
+>b : Symbol(E3.b, Decl(constantEnumAssert.ts, 11, 10))
+>a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+
+    c = a << 2,
+>c : Symbol(E3.c, Decl(constantEnumAssert.ts, 12, 15))
+>a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+}
+
+const enum E4 {
+>E4 : Symbol(E4, Decl(constantEnumAssert.ts, 14, 1))
+
+    a,
+>a : Symbol(E4.a, Decl(constantEnumAssert.ts, 16, 15))
+
+    b
+>b : Symbol(E4.b, Decl(constantEnumAssert.ts, 17, 6))
+}
+
+const E5 = {
+>E5 : Symbol(E5, Decl(constantEnumAssert.ts, 21, 5))
+
+    a: 'a',
+>a : Symbol(a, Decl(constantEnumAssert.ts, 21, 12))
+
+    b: 'b'
+>b : Symbol(b, Decl(constantEnumAssert.ts, 22, 11))
+}
+
+const foo1 = { a: E1.a }
+>foo1 : Symbol(foo1, Decl(constantEnumAssert.ts, 26, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 26, 14))
+>E1.a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+>E1 : Symbol(E1, Decl(constantEnumAssert.ts, 0, 0))
+>a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+
+const foo2 = { a: E2.a }
+>foo2 : Symbol(foo2, Decl(constantEnumAssert.ts, 28, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 28, 14))
+>E2.a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+>E2 : Symbol(E2, Decl(constantEnumAssert.ts, 3, 1))
+>a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+
+const foo3 = { a: E1.a } as const
+>foo3 : Symbol(foo3, Decl(constantEnumAssert.ts, 30, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 30, 14))
+>E1.a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+>E1 : Symbol(E1, Decl(constantEnumAssert.ts, 0, 0))
+>a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+
+const foo4 = { a: E2.a } as const
+>foo4 : Symbol(foo4, Decl(constantEnumAssert.ts, 32, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 32, 14))
+>E2.a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+>E2 : Symbol(E2, Decl(constantEnumAssert.ts, 3, 1))
+>a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+
+const foo5 = { a: E3.a } as const
+>foo5 : Symbol(foo5, Decl(constantEnumAssert.ts, 34, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 34, 14))
+>E3.a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+>E3 : Symbol(E3, Decl(constantEnumAssert.ts, 8, 1))
+>a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+
+const foo6 = { a: E4.a } as const
+>foo6 : Symbol(foo6, Decl(constantEnumAssert.ts, 36, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 36, 14))
+>E4.a : Symbol(E4.a, Decl(constantEnumAssert.ts, 16, 15))
+>E4 : Symbol(E4, Decl(constantEnumAssert.ts, 14, 1))
+>a : Symbol(E4.a, Decl(constantEnumAssert.ts, 16, 15))
+
+const foo7 = { a: E5.a } as const
+>foo7 : Symbol(foo7, Decl(constantEnumAssert.ts, 38, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 38, 14))
+>E5.a : Symbol(a, Decl(constantEnumAssert.ts, 21, 12))
+>E5 : Symbol(E5, Decl(constantEnumAssert.ts, 21, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 21, 12))
+
+const foo8 = { a: E1.a as const }
+>foo8 : Symbol(foo8, Decl(constantEnumAssert.ts, 40, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 40, 14))
+>E1.a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+>E1 : Symbol(E1, Decl(constantEnumAssert.ts, 0, 0))
+>a : Symbol(E1.a, Decl(constantEnumAssert.ts, 0, 9))
+
+const foo9 = { a: E2.a as const }
+>foo9 : Symbol(foo9, Decl(constantEnumAssert.ts, 42, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 42, 14))
+>E2.a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+>E2 : Symbol(E2, Decl(constantEnumAssert.ts, 3, 1))
+>a : Symbol(E2.a, Decl(constantEnumAssert.ts, 5, 9))
+
+const foo10 = { a: E3.a as const }
+>foo10 : Symbol(foo10, Decl(constantEnumAssert.ts, 44, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 44, 15))
+>E3.a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+>E3 : Symbol(E3, Decl(constantEnumAssert.ts, 8, 1))
+>a : Symbol(E3.a, Decl(constantEnumAssert.ts, 10, 9))
+
+const foo11 = { a: E4.a as const }
+>foo11 : Symbol(foo11, Decl(constantEnumAssert.ts, 46, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 46, 15))
+>E4.a : Symbol(E4.a, Decl(constantEnumAssert.ts, 16, 15))
+>E4 : Symbol(E4, Decl(constantEnumAssert.ts, 14, 1))
+>a : Symbol(E4.a, Decl(constantEnumAssert.ts, 16, 15))
+
+const foo12 = { a: E5.a as const }
+>foo12 : Symbol(foo12, Decl(constantEnumAssert.ts, 48, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 48, 15))
+>E5.a : Symbol(a, Decl(constantEnumAssert.ts, 21, 12))
+>E5 : Symbol(E5, Decl(constantEnumAssert.ts, 21, 5))
+>a : Symbol(a, Decl(constantEnumAssert.ts, 21, 12))
+
diff --git a/tests/baselines/reference/constantEnumAssert.types b/tests/baselines/reference/constantEnumAssert.types
new file mode 100644
index 0000000000000..36d4f7f3abcd4
--- /dev/null
+++ b/tests/baselines/reference/constantEnumAssert.types
@@ -0,0 +1,172 @@
+=== tests/cases/compiler/constantEnumAssert.ts ===
+enum E1 {
+>E1 : E1
+
+    a,
+>a : E1.a
+
+    b
+>b : E1.b
+}
+
+enum E2 {
+>E2 : E2
+
+    a = 'a',
+>a : E2.a
+>'a' : "a"
+
+    b = 'b'
+>b : E2.b
+>'b' : "b"
+}
+
+enum E3 {
+>E3 : E3
+
+    a = 1,
+>a : E3
+>1 : 1
+
+    b = a << 1,
+>b : E3
+>a << 1 : number
+>a : E3
+>1 : 1
+
+    c = a << 2,
+>c : E3
+>a << 2 : number
+>a : E3
+>2 : 2
+}
+
+const enum E4 {
+>E4 : E4
+
+    a,
+>a : E4.a
+
+    b
+>b : E4.b
+}
+
+const E5 = {
+>E5 : { a: string; b: string; }
+>{    a: 'a',    b: 'b'} : { a: string; b: string; }
+
+    a: 'a',
+>a : string
+>'a' : "a"
+
+    b: 'b'
+>b : string
+>'b' : "b"
+}
+
+const foo1 = { a: E1.a }
+>foo1 : { a: E1; }
+>{ a: E1.a } : { a: E1; }
+>a : E1
+>E1.a : E1.a
+>E1 : typeof E1
+>a : E1.a
+
+const foo2 = { a: E2.a }
+>foo2 : { a: E2; }
+>{ a: E2.a } : { a: E2; }
+>a : E2
+>E2.a : E2.a
+>E2 : typeof E2
+>a : E2.a
+
+const foo3 = { a: E1.a } as const
+>foo3 : { readonly a: E1.a; }
+>{ a: E1.a } as const : { readonly a: E1.a; }
+>{ a: E1.a } : { readonly a: E1.a; }
+>a : E1.a
+>E1.a : E1.a
+>E1 : typeof E1
+>a : E1.a
+
+const foo4 = { a: E2.a } as const
+>foo4 : { readonly a: E2.a; }
+>{ a: E2.a } as const : { readonly a: E2.a; }
+>{ a: E2.a } : { readonly a: E2.a; }
+>a : E2.a
+>E2.a : E2.a
+>E2 : typeof E2
+>a : E2.a
+
+const foo5 = { a: E3.a } as const
+>foo5 : { readonly a: E3; }
+>{ a: E3.a } as const : { readonly a: E3; }
+>{ a: E3.a } : { readonly a: E3; }
+>a : E3
+>E3.a : E3
+>E3 : typeof E3
+>a : E3
+
+const foo6 = { a: E4.a } as const
+>foo6 : { readonly a: E4.a; }
+>{ a: E4.a } as const : { readonly a: E4.a; }
+>{ a: E4.a } : { readonly a: E4.a; }
+>a : E4.a
+>E4.a : E4.a
+>E4 : typeof E4
+>a : E4.a
+
+const foo7 = { a: E5.a } as const
+>foo7 : { readonly a: string; }
+>{ a: E5.a } as const : { readonly a: string; }
+>{ a: E5.a } : { readonly a: string; }
+>a : string
+>E5.a : string
+>E5 : { a: string; b: string; }
+>a : string
+
+const foo8 = { a: E1.a as const }
+>foo8 : { a: E1.a; }
+>{ a: E1.a as const } : { a: E1.a; }
+>a : E1.a
+>E1.a as const : E1.a
+>E1.a : E1.a
+>E1 : typeof E1
+>a : E1.a
+
+const foo9 = { a: E2.a as const }
+>foo9 : { a: E2.a; }
+>{ a: E2.a as const } : { a: E2.a; }
+>a : E2.a
+>E2.a as const : E2.a
+>E2.a : E2.a
+>E2 : typeof E2
+>a : E2.a
+
+const foo10 = { a: E3.a as const }
+>foo10 : { a: E3; }
+>{ a: E3.a as const } : { a: E3; }
+>a : E3
+>E3.a as const : E3
+>E3.a : E3
+>E3 : typeof E3
+>a : E3
+
+const foo11 = { a: E4.a as const }
+>foo11 : { a: E4.a; }
+>{ a: E4.a as const } : { a: E4.a; }
+>a : E4.a
+>E4.a as const : E4.a
+>E4.a : E4.a
+>E4 : typeof E4
+>a : E4.a
+
+const foo12 = { a: E5.a as const }
+>foo12 : { a: string; }
+>{ a: E5.a as const } : { a: string; }
+>a : string
+>E5.a as const : string
+>E5.a : string
+>E5 : { a: string; b: string; }
+>a : string
+
diff --git a/tests/baselines/reference/decoratorInJsFile1.errors.txt b/tests/baselines/reference/decoratorInJsFile1.errors.txt
index d660b6b28df1f..9cb55bd201692 100644
--- a/tests/baselines/reference/decoratorInJsFile1.errors.txt
+++ b/tests/baselines/reference/decoratorInJsFile1.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/compiler/a.js(2,7): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+tests/cases/compiler/a.js(2,7): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
 tests/cases/compiler/a.js(3,12): error TS8010: 'types' can only be used in a .ts file.
 
 
@@ -6,7 +6,7 @@ tests/cases/compiler/a.js(3,12): error TS8010: 'types' can only be used in a .ts
     @SomeDecorator
     class SomeClass {
           ~~~~~~~~~
-!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
         foo(x: number) {
                ~~~~~~
 !!! error TS8010: 'types' can only be used in a .ts file.
diff --git a/tests/baselines/reference/destructuringAssignabilityCheck.errors.txt b/tests/baselines/reference/destructuringAssignabilityCheck.errors.txt
new file mode 100644
index 0000000000000..bbb4812cf00ed
--- /dev/null
+++ b/tests/baselines/reference/destructuringAssignabilityCheck.errors.txt
@@ -0,0 +1,43 @@
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(1,7): error TS2461: Type '{}' is not an array type.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(2,7): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(3,3): error TS2461: Type '{}' is not an array type.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(4,3): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(6,14): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(9,14): error TS2461: Type '{}' is not an array type.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(13,7): error TS2532: Object is possibly 'undefined'.
+tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts(15,7): error TS2461: Type '{}' is not an array type.
+
+
+==== tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts (8 errors) ====
+    const [] = {}; // should be error
+          ~~
+!!! error TS2461: Type '{}' is not an array type.
+    const {} = undefined; // error correctly
+          ~~
+!!! error TS2532: Object is possibly 'undefined'.
+    (([]) => 0)({}); // should be error
+      ~~
+!!! error TS2461: Type '{}' is not an array type.
+    (({}) => 0)(undefined); // should be error
+      ~~
+!!! error TS2532: Object is possibly 'undefined'.
+    
+    function foo({}: undefined) {
+                 ~~~~~~~~~~~~~
+!!! error TS2532: Object is possibly 'undefined'.
+        return 0
+    }
+    function bar([]: {}) {
+                 ~~~~~~
+!!! error TS2461: Type '{}' is not an array type.
+        return 0
+    }
+    
+    const { }: undefined = 1
+          ~~~
+!!! error TS2532: Object is possibly 'undefined'.
+    
+    const []: {} = {}
+          ~~
+!!! error TS2461: Type '{}' is not an array type.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/destructuringAssignabilityCheck.js b/tests/baselines/reference/destructuringAssignabilityCheck.js
new file mode 100644
index 0000000000000..2702d8b7f5c59
--- /dev/null
+++ b/tests/baselines/reference/destructuringAssignabilityCheck.js
@@ -0,0 +1,32 @@
+//// [destructuringAssignabilityCheck.ts]
+const [] = {}; // should be error
+const {} = undefined; // error correctly
+(([]) => 0)({}); // should be error
+(({}) => 0)(undefined); // should be error
+
+function foo({}: undefined) {
+    return 0
+}
+function bar([]: {}) {
+    return 0
+}
+
+const { }: undefined = 1
+
+const []: {} = {}
+
+
+//// [destructuringAssignabilityCheck.js]
+"use strict";
+var _a = {}; // should be error
+var _b = undefined; // error correctly
+(function (_a) { return 0; })({}); // should be error
+(function (_a) { return 0; })(undefined); // should be error
+function foo(_a) {
+    return 0;
+}
+function bar(_a) {
+    return 0;
+}
+var _c = 1;
+var _d = {};
diff --git a/tests/baselines/reference/destructuringAssignabilityCheck.symbols b/tests/baselines/reference/destructuringAssignabilityCheck.symbols
new file mode 100644
index 0000000000000..c9465f0e41aea
--- /dev/null
+++ b/tests/baselines/reference/destructuringAssignabilityCheck.symbols
@@ -0,0 +1,24 @@
+=== tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts ===
+const [] = {}; // should be error
+const {} = undefined; // error correctly
+>undefined : Symbol(undefined)
+
+(([]) => 0)({}); // should be error
+(({}) => 0)(undefined); // should be error
+>undefined : Symbol(undefined)
+
+function foo({}: undefined) {
+>foo : Symbol(foo, Decl(destructuringAssignabilityCheck.ts, 3, 23))
+
+    return 0
+}
+function bar([]: {}) {
+>bar : Symbol(bar, Decl(destructuringAssignabilityCheck.ts, 7, 1))
+
+    return 0
+}
+
+const { }: undefined = 1
+
+const []: {} = {}
+
diff --git a/tests/baselines/reference/destructuringAssignabilityCheck.types b/tests/baselines/reference/destructuringAssignabilityCheck.types
new file mode 100644
index 0000000000000..df4467cce6433
--- /dev/null
+++ b/tests/baselines/reference/destructuringAssignabilityCheck.types
@@ -0,0 +1,40 @@
+=== tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts ===
+const [] = {}; // should be error
+>{} : {}
+
+const {} = undefined; // error correctly
+>undefined : undefined
+
+(([]) => 0)({}); // should be error
+>(([]) => 0)({}) : number
+>(([]) => 0) : ([]: {}) => number
+>([]) => 0 : ([]: {}) => number
+>0 : 0
+>{} : {}
+
+(({}) => 0)(undefined); // should be error
+>(({}) => 0)(undefined) : number
+>(({}) => 0) : ({}: undefined) => number
+>({}) => 0 : ({}: undefined) => number
+>0 : 0
+>undefined : undefined
+
+function foo({}: undefined) {
+>foo : ({}: undefined) => number
+
+    return 0
+>0 : 0
+}
+function bar([]: {}) {
+>bar : ([]: {}) => number
+
+    return 0
+>0 : 0
+}
+
+const { }: undefined = 1
+>1 : 1
+
+const []: {} = {}
+>{} : {}
+
diff --git a/tests/baselines/reference/exportDefaultWithJSDoc1.symbols b/tests/baselines/reference/exportDefaultWithJSDoc1.symbols
new file mode 100644
index 0000000000000..bad38b845bb09
--- /dev/null
+++ b/tests/baselines/reference/exportDefaultWithJSDoc1.symbols
@@ -0,0 +1,15 @@
+=== tests/cases/compiler/a.js ===
+/**
+No type information for this code. * A number, or a string containing a number.
+No type information for this code. * @typedef {(number|string)} NumberLike
+No type information for this code. */
+No type information for this code.
+No type information for this code./** @type {NumberLike[]} */export default ([ ]);
+No type information for this code.
+No type information for this code.=== tests/cases/compiler/b.ts ===
+import A from './a'
+>A : Symbol(A, Decl(b.ts, 0, 6))
+
+A[0]
+>A : Symbol(A, Decl(b.ts, 0, 6))
+
diff --git a/tests/baselines/reference/exportDefaultWithJSDoc1.types b/tests/baselines/reference/exportDefaultWithJSDoc1.types
new file mode 100644
index 0000000000000..5e82e37b33b2a
--- /dev/null
+++ b/tests/baselines/reference/exportDefaultWithJSDoc1.types
@@ -0,0 +1,19 @@
+=== tests/cases/compiler/a.js ===
+/**
+ * A number, or a string containing a number.
+ * @typedef {(number|string)} NumberLike
+ */
+
+/** @type {NumberLike[]} */export default ([ ]);
+>([ ]) : (string | number)[]
+>[ ] : undefined[]
+
+=== tests/cases/compiler/b.ts ===
+import A from './a'
+>A : (string | number)[]
+
+A[0]
+>A[0] : string | number
+>A : (string | number)[]
+>0 : 0
+
diff --git a/tests/baselines/reference/exportDefaultWithJSDoc2.symbols b/tests/baselines/reference/exportDefaultWithJSDoc2.symbols
new file mode 100644
index 0000000000000..ff3e74a3fbe94
--- /dev/null
+++ b/tests/baselines/reference/exportDefaultWithJSDoc2.symbols
@@ -0,0 +1,15 @@
+=== tests/cases/compiler/a.js ===
+/**
+No type information for this code. * A number, or a string containing a number.
+No type information for this code. * @typedef {(number|string)} NumberLike
+No type information for this code. */
+No type information for this code.
+No type information for this code.export default /** @type {NumberLike[]} */([ ]);
+No type information for this code.
+No type information for this code.=== tests/cases/compiler/b.ts ===
+import A from './a'
+>A : Symbol(A, Decl(b.ts, 0, 6))
+
+A[0]
+>A : Symbol(A, Decl(b.ts, 0, 6))
+
diff --git a/tests/baselines/reference/exportDefaultWithJSDoc2.types b/tests/baselines/reference/exportDefaultWithJSDoc2.types
new file mode 100644
index 0000000000000..0fd9f022a7321
--- /dev/null
+++ b/tests/baselines/reference/exportDefaultWithJSDoc2.types
@@ -0,0 +1,19 @@
+=== tests/cases/compiler/a.js ===
+/**
+ * A number, or a string containing a number.
+ * @typedef {(number|string)} NumberLike
+ */
+
+export default /** @type {NumberLike[]} */([ ]);
+>([ ]) : (string | number)[]
+>[ ] : undefined[]
+
+=== tests/cases/compiler/b.ts ===
+import A from './a'
+>A : (string | number)[]
+
+A[0]
+>A[0] : string | number
+>A : (string | number)[]
+>0 : 0
+
diff --git a/tests/baselines/reference/generatorTypeCheck39.errors.txt b/tests/baselines/reference/generatorTypeCheck39.errors.txt
index aabb5a47a355d..fe0162233e09b 100644
--- a/tests/baselines/reference/generatorTypeCheck39.errors.txt
+++ b/tests/baselines/reference/generatorTypeCheck39.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck39.ts(5,16): error TS1163: A 'yield' expression is only allowed in a generator body.
-tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck39.ts(6,11): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck39.ts(6,11): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
 tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck39.ts(7,13): error TS1163: A 'yield' expression is only allowed in a generator body.
 
 
@@ -13,7 +13,7 @@ tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck39.ts(7,13): erro
 !!! error TS1163: A 'yield' expression is only allowed in a generator body.
         class C {
               ~
-!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
             x = yield 0;
                 ~~~~~
 !!! error TS1163: A 'yield' expression is only allowed in a generator body.
diff --git a/tests/baselines/reference/generatorTypeCheck59.errors.txt b/tests/baselines/reference/generatorTypeCheck59.errors.txt
index cba90154701af..5cec6ac1f2460 100644
--- a/tests/baselines/reference/generatorTypeCheck59.errors.txt
+++ b/tests/baselines/reference/generatorTypeCheck59.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck59.ts(3,11): error TS1163: A 'yield' expression is only allowed in a generator body.
-tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck59.ts(4,9): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck59.ts(4,9): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck59.ts (2 errors) ====
@@ -10,6 +10,6 @@ tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck59.ts(4,9): error
 !!! error TS1163: A 'yield' expression is only allowed in a generator body.
             m() { }
             ~
-!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
         };
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/generatorTypeCheck61.errors.txt b/tests/baselines/reference/generatorTypeCheck61.errors.txt
index ccc99f7ffbd34..a80949e8876af 100644
--- a/tests/baselines/reference/generatorTypeCheck61.errors.txt
+++ b/tests/baselines/reference/generatorTypeCheck61.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck61.ts(2,7): error TS1163: A 'yield' expression is only allowed in a generator body.
-tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck61.ts(3,11): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck61.ts(3,11): error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
 
 
 ==== tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck61.ts (2 errors) ====
@@ -9,5 +9,5 @@ tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck61.ts(3,11): erro
 !!! error TS1163: A 'yield' expression is only allowed in a generator body.
         class C {};
               ~
-!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option to remove this warning.
+!!! error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/globalThisCollision.errors.txt b/tests/baselines/reference/globalThisCollision.errors.txt
new file mode 100644
index 0000000000000..ea0fb9d9f434b
--- /dev/null
+++ b/tests/baselines/reference/globalThisCollision.errors.txt
@@ -0,0 +1,7 @@
+tests/cases/conformance/es2019/globalThisCollision.js(1,5): error TS2397: Declaration name conflicts with built-in global identifier 'globalThis'.
+
+
+==== tests/cases/conformance/es2019/globalThisCollision.js (1 errors) ====
+    var globalThis;
+        ~~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'globalThis'.
\ No newline at end of file
diff --git a/tests/baselines/reference/globalThisCollision.symbols b/tests/baselines/reference/globalThisCollision.symbols
new file mode 100644
index 0000000000000..088357fd537db
--- /dev/null
+++ b/tests/baselines/reference/globalThisCollision.symbols
@@ -0,0 +1,4 @@
+=== tests/cases/conformance/es2019/globalThisCollision.js ===
+var globalThis;
+>globalThis : Symbol(globalThis, Decl(globalThisCollision.js, 0, 3))
+
diff --git a/tests/baselines/reference/globalThisCollision.types b/tests/baselines/reference/globalThisCollision.types
new file mode 100644
index 0000000000000..476533be18cae
--- /dev/null
+++ b/tests/baselines/reference/globalThisCollision.types
@@ -0,0 +1,4 @@
+=== tests/cases/conformance/es2019/globalThisCollision.js ===
+var globalThis;
+>globalThis : any
+
diff --git a/tests/baselines/reference/isolatedModulesNoEmitOnError.errors.txt b/tests/baselines/reference/isolatedModulesNoEmitOnError.errors.txt
index 34ff251c16701..2ddfa178de239 100644
--- a/tests/baselines/reference/isolatedModulesNoEmitOnError.errors.txt
+++ b/tests/baselines/reference/isolatedModulesNoEmitOnError.errors.txt
@@ -1,6 +1,7 @@
-error TS5053: Option 'noEmitOnError' cannot be specified with option 'isolatedModules'.
+tests/cases/compiler/file1.ts(1,14): error TS2322: Type '3' is not assignable to type 'string'.
 
 
-!!! error TS5053: Option 'noEmitOnError' cannot be specified with option 'isolatedModules'.
-==== tests/cases/compiler/file1.ts (0 errors) ====
-    export var x;
\ No newline at end of file
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    export const x: string = 3;
+                 ~
+!!! error TS2322: Type '3' is not assignable to type 'string'.
\ No newline at end of file
diff --git a/tests/baselines/reference/isolatedModulesNoEmitOnError.symbols b/tests/baselines/reference/isolatedModulesNoEmitOnError.symbols
index 625dbfbe699b8..67306c205a7ea 100644
--- a/tests/baselines/reference/isolatedModulesNoEmitOnError.symbols
+++ b/tests/baselines/reference/isolatedModulesNoEmitOnError.symbols
@@ -1,4 +1,4 @@
 === tests/cases/compiler/file1.ts ===
-export var x;
->x : Symbol(x, Decl(file1.ts, 0, 10))
+export const x: string = 3;
+>x : Symbol(x, Decl(file1.ts, 0, 12))
 
diff --git a/tests/baselines/reference/isolatedModulesNoEmitOnError.types b/tests/baselines/reference/isolatedModulesNoEmitOnError.types
index 27dca700bb904..3a4f55b925cba 100644
--- a/tests/baselines/reference/isolatedModulesNoEmitOnError.types
+++ b/tests/baselines/reference/isolatedModulesNoEmitOnError.types
@@ -1,4 +1,5 @@
 === tests/cases/compiler/file1.ts ===
-export var x;
->x : any
+export const x: string = 3;
+>x : string
+>3 : 3
 
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt b/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
index aef57c129a33d..9a937066374ab 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
@@ -194,4 +194,14 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
     type StrictExclude<T, U> = T extends StrictExtract<T, U> ? never : T;
     type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
     type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;
+    
+    // Repros from #30938
+    
+    function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(param: T, cb: (element: T['elements'][number]) => void) {
+        cb(param.elements[0]);
+    }
+    
+    function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
+        cb(param[0]);
+    }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.js b/tests/baselines/reference/keyofAndIndexedAccess2.js
index 1788c40563c1b..906bcd0eab3de 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.js
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.js
@@ -115,6 +115,16 @@ type StrictExtract<T, U> = T extends U ? U extends T ? T : never : never;
 type StrictExclude<T, U> = T extends StrictExtract<T, U> ? never : T;
 type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
 type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;
+
+// Repros from #30938
+
+function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(param: T, cb: (element: T['elements'][number]) => void) {
+    cb(param.elements[0]);
+}
+
+function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
+    cb(param[0]);
+}
 
 
 //// [keyofAndIndexedAccess2.js]
@@ -190,3 +200,10 @@ export function getEntity(id, state) {
 function get123() {
     return 123; // Error
 }
+// Repros from #30938
+function fn(param, cb) {
+    cb(param.elements[0]);
+}
+function fn2(param, cb) {
+    cb(param[0]);
+}
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.symbols b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
index abbe38fd5c9c8..24e1a8b0674e7 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
@@ -434,3 +434,40 @@ type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;
 >Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 115, 20))
 >V : Symbol(V, Decl(keyofAndIndexedAccess2.ts, 115, 9))
 
+// Repros from #30938
+
+function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(param: T, cb: (element: T['elements'][number]) => void) {
+>fn : Symbol(fn, Decl(keyofAndIndexedAccess2.ts, 115, 69))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 119, 12))
+>elements : Symbol(elements, Decl(keyofAndIndexedAccess2.ts, 119, 23))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>elements : Symbol(elements, Decl(keyofAndIndexedAccess2.ts, 119, 51))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 119, 77))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 119, 12))
+>cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 119, 86))
+>element : Symbol(element, Decl(keyofAndIndexedAccess2.ts, 119, 92))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 119, 12))
+
+    cb(param.elements[0]);
+>cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 119, 86))
+>param.elements : Symbol(elements, Decl(keyofAndIndexedAccess2.ts, 119, 23), Decl(keyofAndIndexedAccess2.ts, 119, 51))
+>param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 119, 77))
+>elements : Symbol(elements, Decl(keyofAndIndexedAccess2.ts, 119, 23), Decl(keyofAndIndexedAccess2.ts, 119, 51))
+}
+
+function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
+>fn2 : Symbol(fn2, Decl(keyofAndIndexedAccess2.ts, 121, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 123, 13))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 123, 38))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 123, 13))
+>cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 123, 47))
+>element : Symbol(element, Decl(keyofAndIndexedAccess2.ts, 123, 53))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 123, 13))
+
+    cb(param[0]);
+>cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 123, 47))
+>param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 123, 38))
+}
+
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.types b/tests/baselines/reference/keyofAndIndexedAccess2.types
index 4eccf23a80430..6c0f3dff934d8 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.types
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.types
@@ -437,3 +437,37 @@ type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
 type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;
 >B : A<{ [Q in keyof T]: StrictExclude<A<{ [Q in keyof T[Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q][Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q][Q][Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q][Q][Q][Q][Q][Q]]: StrictExclude<A<{ [Q in keyof T[Q][Q][Q][Q][Q][Q][Q][Q][Q][Q]]: StrictExclude<A<any>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>, {}>; }>
 
+// Repros from #30938
+
+function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(param: T, cb: (element: T['elements'][number]) => void) {
+>fn : <T extends { elements: string[]; } | { elements: number[]; }>(param: T, cb: (element: T["elements"][number]) => void) => void
+>elements : string[]
+>elements : number[]
+>param : T
+>cb : (element: T["elements"][number]) => void
+>element : T["elements"][number]
+
+    cb(param.elements[0]);
+>cb(param.elements[0]) : void
+>cb : (element: T["elements"][number]) => void
+>param.elements[0] : string | number
+>param.elements : string[] | number[]
+>param : T
+>elements : string[] | number[]
+>0 : 0
+}
+
+function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
+>fn2 : <T extends string[]>(param: T, cb: (element: T[number]) => void) => void
+>param : T
+>cb : (element: T[number]) => void
+>element : T[number]
+
+    cb(param[0]);
+>cb(param[0]) : void
+>cb : (element: T[number]) => void
+>param[0] : string
+>param : T
+>0 : 0
+}
+
diff --git a/tests/baselines/reference/library-reference-10.trace.json b/tests/baselines/reference/library-reference-10.trace.json
index 3e6cf4432eaed..37f8ab543caee 100644
--- a/tests/baselines/reference/library-reference-10.trace.json
+++ b/tests/baselines/reference/library-reference-10.trace.json
@@ -4,7 +4,6 @@
     "'package.json' has 'typings' field 'jquery.d.ts' that references 'types/jquery/jquery.d.ts'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at './types/jquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'jquery.d.ts' that references 'types/jquery/jquery.d.ts'.",
     "File 'types/jquery/jquery.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for 'types/jquery/jquery.d.ts', result '/foo/types/jquery/jquery.d.ts'.",
@@ -14,7 +13,6 @@
     "'package.json' has 'typings' field 'jquery.d.ts' that references 'types/jquery/jquery.d.ts'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at './types/jquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'jquery.d.ts' that references 'types/jquery/jquery.d.ts'.",
     "File 'types/jquery/jquery.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for 'types/jquery/jquery.d.ts', result '/foo/types/jquery/jquery.d.ts'.",
diff --git a/tests/baselines/reference/library-reference-2.trace.json b/tests/baselines/reference/library-reference-2.trace.json
index 8a13d1e6f5455..b9b4cf08ca2ce 100644
--- a/tests/baselines/reference/library-reference-2.trace.json
+++ b/tests/baselines/reference/library-reference-2.trace.json
@@ -5,7 +5,6 @@
     "'package.json' has 'types' field 'jquery.d.ts' that references '/types/jquery/jquery.d.ts'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at '/types/jquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' does not have a 'typings' field.",
     "'package.json' has 'types' field 'jquery.d.ts' that references '/types/jquery/jquery.d.ts'.",
     "File '/types/jquery/jquery.d.ts' exist - use it as a name resolution result.",
@@ -17,7 +16,6 @@
     "'package.json' has 'types' field 'jquery.d.ts' that references '/types/jquery/jquery.d.ts'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at '/types/jquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' does not have a 'typings' field.",
     "'package.json' has 'types' field 'jquery.d.ts' that references '/types/jquery/jquery.d.ts'.",
     "File '/types/jquery/jquery.d.ts' exist - use it as a name resolution result.",
diff --git a/tests/baselines/reference/missingRequiredDeclare.d.errors.txt b/tests/baselines/reference/missingRequiredDeclare.d.errors.txt
index a673c948a4873..079de0b022260 100644
--- a/tests/baselines/reference/missingRequiredDeclare.d.errors.txt
+++ b/tests/baselines/reference/missingRequiredDeclare.d.errors.txt
@@ -1,10 +1,10 @@
-tests/cases/compiler/missingRequiredDeclare.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/compiler/missingRequiredDeclare.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 tests/cases/compiler/missingRequiredDeclare.d.ts(1,9): error TS1039: Initializers are not allowed in ambient contexts.
 
 
 ==== tests/cases/compiler/missingRequiredDeclare.d.ts (2 errors) ====
     var x = 1;
     ~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
             ~
 !!! error TS1039: Initializers are not allowed in ambient contexts.
\ No newline at end of file
diff --git a/tests/baselines/reference/narrowByEquality.errors.txt b/tests/baselines/reference/narrowByEquality.errors.txt
new file mode 100644
index 0000000000000..b391c4a07a1c4
--- /dev/null
+++ b/tests/baselines/reference/narrowByEquality.errors.txt
@@ -0,0 +1,71 @@
+tests/cases/compiler/narrowByEquality.ts(53,15): error TS2322: Type 'string | number' is not assignable to type 'number'.
+  Type 'string' is not assignable to type 'number'.
+tests/cases/compiler/narrowByEquality.ts(54,9): error TS2322: Type 'string | number' is not assignable to type 'number'.
+  Type 'string' is not assignable to type 'number'.
+
+
+==== tests/cases/compiler/narrowByEquality.ts (2 errors) ====
+    declare let x: number | string | boolean
+    declare let n: number;
+    declare let s: string;
+    declare let b: boolean;
+    
+    if (x == n) {
+        x;
+    }
+    
+    if (x == s) {
+        x;
+    }
+    
+    if (x == b) {
+        x;
+    }
+    
+    if (x == 1) {
+        x;
+    }
+    
+    if (x == "") {
+        x;
+    }
+    
+    if (x == "foo") {
+        x;
+    }
+    
+    if (x == true) {
+        x;
+    }
+    
+    if (x == false) {
+        x;
+    }
+    
+    declare let xAndObj: number | string | boolean | object
+    
+    if (xAndObj == {}) {
+        xAndObj;
+    }
+    
+    if (x == xAndObj) {
+        x;
+        xAndObj;
+    }
+    
+    // Repro from #24991
+    
+    function test(level: number | string):number {
+        if (level == +level) {
+            const q2: number = level; // error
+                  ~~
+!!! error TS2322: Type 'string | number' is not assignable to type 'number'.
+!!! error TS2322:   Type 'string' is not assignable to type 'number'.
+            return level;
+            ~~~~~~~~~~~~~
+!!! error TS2322: Type 'string | number' is not assignable to type 'number'.
+!!! error TS2322:   Type 'string' is not assignable to type 'number'.
+        }
+        return 0;
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/narrowByEquality.js b/tests/baselines/reference/narrowByEquality.js
new file mode 100644
index 0000000000000..a843040db7795
--- /dev/null
+++ b/tests/baselines/reference/narrowByEquality.js
@@ -0,0 +1,101 @@
+//// [narrowByEquality.ts]
+declare let x: number | string | boolean
+declare let n: number;
+declare let s: string;
+declare let b: boolean;
+
+if (x == n) {
+    x;
+}
+
+if (x == s) {
+    x;
+}
+
+if (x == b) {
+    x;
+}
+
+if (x == 1) {
+    x;
+}
+
+if (x == "") {
+    x;
+}
+
+if (x == "foo") {
+    x;
+}
+
+if (x == true) {
+    x;
+}
+
+if (x == false) {
+    x;
+}
+
+declare let xAndObj: number | string | boolean | object
+
+if (xAndObj == {}) {
+    xAndObj;
+}
+
+if (x == xAndObj) {
+    x;
+    xAndObj;
+}
+
+// Repro from #24991
+
+function test(level: number | string):number {
+    if (level == +level) {
+        const q2: number = level; // error
+        return level;
+    }
+    return 0;
+}
+
+
+//// [narrowByEquality.js]
+"use strict";
+if (x == n) {
+    x;
+}
+if (x == s) {
+    x;
+}
+if (x == b) {
+    x;
+}
+if (x == 1) {
+    x;
+}
+if (x == "") {
+    x;
+}
+if (x == "foo") {
+    x;
+}
+if (x == true) {
+    x;
+}
+if (x == false) {
+    x;
+}
+if (xAndObj == {}) {
+    xAndObj;
+}
+if (x == xAndObj) {
+    x;
+    xAndObj;
+}
+// Repro from #24991
+function test(level) {
+    if (level == +level) {
+        var q2 = level; // error
+        return level;
+    }
+    return 0;
+}
diff --git a/tests/baselines/reference/narrowByEquality.symbols b/tests/baselines/reference/narrowByEquality.symbols
new file mode 100644
index 0000000000000..02e2ae138d98e
--- /dev/null
+++ b/tests/baselines/reference/narrowByEquality.symbols
@@ -0,0 +1,113 @@
+=== tests/cases/compiler/narrowByEquality.ts ===
+declare let x: number | string | boolean
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+declare let n: number;
+>n : Symbol(n, Decl(narrowByEquality.ts, 1, 11))
+
+declare let s: string;
+>s : Symbol(s, Decl(narrowByEquality.ts, 2, 11))
+
+declare let b: boolean;
+>b : Symbol(b, Decl(narrowByEquality.ts, 3, 11))
+
+if (x == n) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+>n : Symbol(n, Decl(narrowByEquality.ts, 1, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == s) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+>s : Symbol(s, Decl(narrowByEquality.ts, 2, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == b) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+>b : Symbol(b, Decl(narrowByEquality.ts, 3, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == 1) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == "") {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == "foo") {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == true) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+if (x == false) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+}
+
+declare let xAndObj: number | string | boolean | object
+>xAndObj : Symbol(xAndObj, Decl(narrowByEquality.ts, 37, 11))
+
+if (xAndObj == {}) {
+>xAndObj : Symbol(xAndObj, Decl(narrowByEquality.ts, 37, 11))
+
+    xAndObj;
+>xAndObj : Symbol(xAndObj, Decl(narrowByEquality.ts, 37, 11))
+}
+
+if (x == xAndObj) {
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+>xAndObj : Symbol(xAndObj, Decl(narrowByEquality.ts, 37, 11))
+
+    x;
+>x : Symbol(x, Decl(narrowByEquality.ts, 0, 11))
+
+    xAndObj;
+>xAndObj : Symbol(xAndObj, Decl(narrowByEquality.ts, 37, 11))
+}
+
+// Repro from #24991
+
+function test(level: number | string):number {
+>test : Symbol(test, Decl(narrowByEquality.ts, 46, 1))
+>level : Symbol(level, Decl(narrowByEquality.ts, 50, 14))
+
+    if (level == +level) {
+>level : Symbol(level, Decl(narrowByEquality.ts, 50, 14))
+>level : Symbol(level, Decl(narrowByEquality.ts, 50, 14))
+
+        const q2: number = level; // error
+>q2 : Symbol(q2, Decl(narrowByEquality.ts, 52, 13))
+>level : Symbol(level, Decl(narrowByEquality.ts, 50, 14))
+
+        return level;
+>level : Symbol(level, Decl(narrowByEquality.ts, 50, 14))
+    }
+    return 0;
+}
+
diff --git a/tests/baselines/reference/narrowByEquality.types b/tests/baselines/reference/narrowByEquality.types
new file mode 100644
index 0000000000000..833e7537d68e8
--- /dev/null
+++ b/tests/baselines/reference/narrowByEquality.types
@@ -0,0 +1,132 @@
+=== tests/cases/compiler/narrowByEquality.ts ===
+declare let x: number | string | boolean
+>x : string | number | boolean
+
+declare let n: number;
+>n : number
+
+declare let s: string;
+>s : string
+
+declare let b: boolean;
+>b : boolean
+
+if (x == n) {
+>x == n : boolean
+>x : string | number | boolean
+>n : number
+
+    x;
+>x : string | number | boolean
+}
+
+if (x == s) {
+>x == s : boolean
+>x : string | number | boolean
+>s : string
+
+    x;
+>x : string | number | boolean
+}
+
+if (x == b) {
+>x == b : boolean
+>x : string | number | boolean
+>b : boolean
+
+    x;
+>x : string | number | boolean
+}
+
+if (x == 1) {
+>x == 1 : boolean
+>x : string | number | boolean
+>1 : 1
+
+    x;
+>x : 1
+}
+
+if (x == "") {
+>x == "" : boolean
+>x : string | number | boolean
+>"" : ""
+
+    x;
+>x : ""
+}
+
+if (x == "foo") {
+>x == "foo" : boolean
+>x : string | number | boolean
+>"foo" : "foo"
+
+    x;
+>x : "foo"
+}
+
+if (x == true) {
+>x == true : boolean
+>x : string | number | boolean
+>true : true
+
+    x;
+>x : true
+}
+
+if (x == false) {
+>x == false : boolean
+>x : string | number | boolean
+>false : false
+
+    x;
+>x : false
+}
+
+declare let xAndObj: number | string | boolean | object
+>xAndObj : string | number | boolean | object
+
+if (xAndObj == {}) {
+>xAndObj == {} : boolean
+>xAndObj : string | number | boolean | object
+>{} : {}
+
+    xAndObj;
+>xAndObj : object
+}
+
+if (x == xAndObj) {
+>x == xAndObj : boolean
+>x : string | number | boolean
+>xAndObj : string | number | boolean | object
+
+    x;
+>x : string | number | boolean
+
+    xAndObj;
+>xAndObj : string | number | boolean
+}
+
+// Repro from #24991
+
+function test(level: number | string):number {
+>test : (level: string | number) => number
+>level : string | number
+
+    if (level == +level) {
+>level == +level : boolean
+>level : string | number
+>+level : number
+>level : string | number
+
+        const q2: number = level; // error
+>q2 : number
+>level : string | number
+
+        return level;
+>level : string | number
+    }
+    return 0;
+>0 : 0
+}
+
diff --git a/tests/baselines/reference/omitTypeTestErrors01.errors.txt b/tests/baselines/reference/omitTypeTestErrors01.errors.txt
new file mode 100644
index 0000000000000..6b65e292b55f4
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTestErrors01.errors.txt
@@ -0,0 +1,27 @@
+tests/cases/compiler/omitTypeTestErrors01.ts(11,16): error TS2339: Property 'c' does not exist on type 'Omit<Foo, "c">'.
+tests/cases/compiler/omitTypeTestErrors01.ts(15,16): error TS2339: Property 'b' does not exist on type 'Omit<Foo, "c" | "b">'.
+
+
+==== tests/cases/compiler/omitTypeTestErrors01.ts (2 errors) ====
+    interface Foo {
+        a: string;
+        b: number;
+        c: boolean;
+    }
+    
+    export type Bar = Omit<Foo, "c">;
+    export type Baz = Omit<Foo, "b" | "c">;
+    
+    export function getBarC(bar: Bar) {
+        return bar.c;
+                   ~
+!!! error TS2339: Property 'c' does not exist on type 'Omit<Foo, "c">'.
+    }
+    
+    export function getBazB(baz: Baz) {
+        return baz.b;
+                   ~
+!!! error TS2339: Property 'b' does not exist on type 'Omit<Foo, "c" | "b">'.
+    }
+    
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/omitTypeTestErrors01.js b/tests/baselines/reference/omitTypeTestErrors01.js
new file mode 100644
index 0000000000000..03f1f5cc6b7b6
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTestErrors01.js
@@ -0,0 +1,44 @@
+//// [omitTypeTestErrors01.ts]
+interface Foo {
+    a: string;
+    b: number;
+    c: boolean;
+}
+
+export type Bar = Omit<Foo, "c">;
+export type Baz = Omit<Foo, "b" | "c">;
+
+export function getBarC(bar: Bar) {
+    return bar.c;
+}
+
+export function getBazB(baz: Baz) {
+    return baz.b;
+}
+
+
+
+//// [omitTypeTestErrors01.js]
+"use strict";
+exports.__esModule = true;
+function getBarC(bar) {
+    return bar.c;
+}
+exports.getBarC = getBarC;
+function getBazB(baz) {
+    return baz.b;
+}
+exports.getBazB = getBazB;
+
+
+//// [omitTypeTestErrors01.d.ts]
+interface Foo {
+    a: string;
+    b: number;
+    c: boolean;
+}
+export declare type Bar = Omit<Foo, "c">;
+export declare type Baz = Omit<Foo, "b" | "c">;
+export declare function getBarC(bar: Bar): any;
+export declare function getBazB(baz: Baz): any;
+export {};
diff --git a/tests/baselines/reference/omitTypeTestErrors01.symbols b/tests/baselines/reference/omitTypeTestErrors01.symbols
new file mode 100644
index 0000000000000..b913e20de4f93
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTestErrors01.symbols
@@ -0,0 +1,43 @@
+=== tests/cases/compiler/omitTypeTestErrors01.ts ===
+interface Foo {
+>Foo : Symbol(Foo, Decl(omitTypeTestErrors01.ts, 0, 0))
+
+    a: string;
+>a : Symbol(Foo.a, Decl(omitTypeTestErrors01.ts, 0, 15))
+
+    b: number;
+>b : Symbol(Foo.b, Decl(omitTypeTestErrors01.ts, 1, 14))
+
+    c: boolean;
+>c : Symbol(Foo.c, Decl(omitTypeTestErrors01.ts, 2, 14))
+}
+
+export type Bar = Omit<Foo, "c">;
+>Bar : Symbol(Bar, Decl(omitTypeTestErrors01.ts, 4, 1))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>Foo : Symbol(Foo, Decl(omitTypeTestErrors01.ts, 0, 0))
+
+export type Baz = Omit<Foo, "b" | "c">;
+>Baz : Symbol(Baz, Decl(omitTypeTestErrors01.ts, 6, 33))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>Foo : Symbol(Foo, Decl(omitTypeTestErrors01.ts, 0, 0))
+
+export function getBarC(bar: Bar) {
+>getBarC : Symbol(getBarC, Decl(omitTypeTestErrors01.ts, 7, 39))
+>bar : Symbol(bar, Decl(omitTypeTestErrors01.ts, 9, 24))
+>Bar : Symbol(Bar, Decl(omitTypeTestErrors01.ts, 4, 1))
+
+    return bar.c;
+>bar : Symbol(bar, Decl(omitTypeTestErrors01.ts, 9, 24))
+}
+
+export function getBazB(baz: Baz) {
+>getBazB : Symbol(getBazB, Decl(omitTypeTestErrors01.ts, 11, 1))
+>baz : Symbol(baz, Decl(omitTypeTestErrors01.ts, 13, 24))
+>Baz : Symbol(Baz, Decl(omitTypeTestErrors01.ts, 6, 33))
+
+    return baz.b;
+>baz : Symbol(baz, Decl(omitTypeTestErrors01.ts, 13, 24))
+}
+
+
diff --git a/tests/baselines/reference/omitTypeTestErrors01.types b/tests/baselines/reference/omitTypeTestErrors01.types
new file mode 100644
index 0000000000000..4b286c2c89cbf
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTestErrors01.types
@@ -0,0 +1,39 @@
+=== tests/cases/compiler/omitTypeTestErrors01.ts ===
+interface Foo {
+    a: string;
+>a : string
+
+    b: number;
+>b : number
+
+    c: boolean;
+>c : boolean
+}
+
+export type Bar = Omit<Foo, "c">;
+>Bar : Omit<Foo, "c">
+
+export type Baz = Omit<Foo, "b" | "c">;
+>Baz : Omit<Foo, "c" | "b">
+
+export function getBarC(bar: Bar) {
+>getBarC : (bar: Omit<Foo, "c">) => any
+>bar : Omit<Foo, "c">
+
+    return bar.c;
+>bar.c : any
+>bar : Omit<Foo, "c">
+>c : any
+}
+
+export function getBazB(baz: Baz) {
+>getBazB : (baz: Omit<Foo, "c" | "b">) => any
+>baz : Omit<Foo, "c" | "b">
+
+    return baz.b;
+>baz.b : any
+>baz : Omit<Foo, "c" | "b">
+>b : any
+}
+
+
diff --git a/tests/baselines/reference/omitTypeTests01.js b/tests/baselines/reference/omitTypeTests01.js
new file mode 100644
index 0000000000000..af244b8b02b39
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTests01.js
@@ -0,0 +1,44 @@
+//// [omitTypeTests01.ts]
+interface Foo {
+    a: string;
+    b: number;
+    c: boolean;
+}
+
+export type Bar = Omit<Foo, "c">;
+export type Baz = Omit<Foo, "b" | "c">;
+
+export function getBarA(bar: Bar) {
+    return bar.a;
+}
+
+export function getBazA(baz: Baz) {
+    return baz.a;
+}
+
+
+
+//// [omitTypeTests01.js]
+"use strict";
+exports.__esModule = true;
+function getBarA(bar) {
+    return bar.a;
+}
+exports.getBarA = getBarA;
+function getBazA(baz) {
+    return baz.a;
+}
+exports.getBazA = getBazA;
+
+
+//// [omitTypeTests01.d.ts]
+interface Foo {
+    a: string;
+    b: number;
+    c: boolean;
+}
+export declare type Bar = Omit<Foo, "c">;
+export declare type Baz = Omit<Foo, "b" | "c">;
+export declare function getBarA(bar: Bar): string;
+export declare function getBazA(baz: Baz): string;
+export {};
diff --git a/tests/baselines/reference/omitTypeTests01.symbols b/tests/baselines/reference/omitTypeTests01.symbols
new file mode 100644
index 0000000000000..93b492917855a
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTests01.symbols
@@ -0,0 +1,47 @@
+=== tests/cases/compiler/omitTypeTests01.ts ===
+interface Foo {
+>Foo : Symbol(Foo, Decl(omitTypeTests01.ts, 0, 0))
+
+    a: string;
+>a : Symbol(Foo.a, Decl(omitTypeTests01.ts, 0, 15))
+
+    b: number;
+>b : Symbol(Foo.b, Decl(omitTypeTests01.ts, 1, 14))
+
+    c: boolean;
+>c : Symbol(Foo.c, Decl(omitTypeTests01.ts, 2, 14))
+}
+
+export type Bar = Omit<Foo, "c">;
+>Bar : Symbol(Bar, Decl(omitTypeTests01.ts, 4, 1))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>Foo : Symbol(Foo, Decl(omitTypeTests01.ts, 0, 0))
+
+export type Baz = Omit<Foo, "b" | "c">;
+>Baz : Symbol(Baz, Decl(omitTypeTests01.ts, 6, 33))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>Foo : Symbol(Foo, Decl(omitTypeTests01.ts, 0, 0))
+
+export function getBarA(bar: Bar) {
+>getBarA : Symbol(getBarA, Decl(omitTypeTests01.ts, 7, 39))
+>bar : Symbol(bar, Decl(omitTypeTests01.ts, 9, 24))
+>Bar : Symbol(Bar, Decl(omitTypeTests01.ts, 4, 1))
+
+    return bar.a;
+>bar.a : Symbol(a)
+>bar : Symbol(bar, Decl(omitTypeTests01.ts, 9, 24))
+>a : Symbol(a)
+}
+
+export function getBazA(baz: Baz) {
+>getBazA : Symbol(getBazA, Decl(omitTypeTests01.ts, 11, 1))
+>baz : Symbol(baz, Decl(omitTypeTests01.ts, 13, 24))
+>Baz : Symbol(Baz, Decl(omitTypeTests01.ts, 6, 33))
+
+    return baz.a;
+>baz.a : Symbol(a)
+>baz : Symbol(baz, Decl(omitTypeTests01.ts, 13, 24))
+>a : Symbol(a)
+}
+
+
diff --git a/tests/baselines/reference/omitTypeTests01.types b/tests/baselines/reference/omitTypeTests01.types
new file mode 100644
index 0000000000000..549fcccc0f2f8
--- /dev/null
+++ b/tests/baselines/reference/omitTypeTests01.types
@@ -0,0 +1,39 @@
+=== tests/cases/compiler/omitTypeTests01.ts ===
+interface Foo {
+    a: string;
+>a : string
+
+    b: number;
+>b : number
+
+    c: boolean;
+>c : boolean
+}
+
+export type Bar = Omit<Foo, "c">;
+>Bar : Omit<Foo, "c">
+
+export type Baz = Omit<Foo, "b" | "c">;
+>Baz : Omit<Foo, "c" | "b">
+
+export function getBarA(bar: Bar) {
+>getBarA : (bar: Omit<Foo, "c">) => string
+>bar : Omit<Foo, "c">
+
+    return bar.a;
+>bar.a : string
+>bar : Omit<Foo, "c">
+>a : string
+}
+
+export function getBazA(baz: Baz) {
+>getBazA : (baz: Omit<Foo, "c" | "b">) => string
+>baz : Omit<Foo, "c" | "b">
+
+    return baz.a;
+>baz.a : string
+>baz : Omit<Foo, "c" | "b">
+>a : string
+}
+
+
diff --git a/tests/baselines/reference/parserEnumDeclaration3.d.errors.txt b/tests/baselines/reference/parserEnumDeclaration3.d.errors.txt
index 03bba3492e77f..9be61012304b4 100644
--- a/tests/baselines/reference/parserEnumDeclaration3.d.errors.txt
+++ b/tests/baselines/reference/parserEnumDeclaration3.d.errors.txt
@@ -1,9 +1,9 @@
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnumDeclaration3.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnumDeclaration3.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnumDeclaration3.d.ts (1 errors) ====
     enum E {
     ~~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
        A = 1
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserFunctionDeclaration2.d.errors.txt b/tests/baselines/reference/parserFunctionDeclaration2.d.errors.txt
index 6f836544efc90..b682d1b1e3fe5 100644
--- a/tests/baselines/reference/parserFunctionDeclaration2.d.errors.txt
+++ b/tests/baselines/reference/parserFunctionDeclaration2.d.errors.txt
@@ -1,11 +1,11 @@
-tests/cases/conformance/parser/ecmascript5/FunctionDeclarations/parserFunctionDeclaration2.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/FunctionDeclarations/parserFunctionDeclaration2.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 tests/cases/conformance/parser/ecmascript5/FunctionDeclarations/parserFunctionDeclaration2.d.ts(1,14): error TS1183: An implementation cannot be declared in ambient contexts.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/FunctionDeclarations/parserFunctionDeclaration2.d.ts (2 errors) ====
     function F() {
     ~~~~~~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
                  ~
 !!! error TS1183: An implementation cannot be declared in ambient contexts.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserModuleDeclaration1.d.errors.txt b/tests/baselines/reference/parserModuleDeclaration1.d.errors.txt
index 4f5b3b581d18c..4c88d2a29946b 100644
--- a/tests/baselines/reference/parserModuleDeclaration1.d.errors.txt
+++ b/tests/baselines/reference/parserModuleDeclaration1.d.errors.txt
@@ -1,8 +1,8 @@
-tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration1.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration1.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration1.d.ts (1 errors) ====
     module "Foo" {
     ~~~~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserModuleDeclaration2.d.errors.txt b/tests/baselines/reference/parserModuleDeclaration2.d.errors.txt
index 00c2fbb82a0cb..6ff076949570c 100644
--- a/tests/baselines/reference/parserModuleDeclaration2.d.errors.txt
+++ b/tests/baselines/reference/parserModuleDeclaration2.d.errors.txt
@@ -1,8 +1,8 @@
-tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration2.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration2.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration2.d.ts (1 errors) ====
     module M {
     ~~~~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserModuleDeclaration4.d.errors.txt b/tests/baselines/reference/parserModuleDeclaration4.d.errors.txt
index 2e75c6cbc509a..107c44c453671 100644
--- a/tests/baselines/reference/parserModuleDeclaration4.d.errors.txt
+++ b/tests/baselines/reference/parserModuleDeclaration4.d.errors.txt
@@ -1,11 +1,11 @@
-tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration4.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration4.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration4.d.ts(2,3): error TS1038: A 'declare' modifier cannot be used in an already ambient context.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration4.d.ts (2 errors) ====
     module M {
     ~~~~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
       declare module M1 {
       ~~~~~~~
 !!! error TS1038: A 'declare' modifier cannot be used in an already ambient context.
diff --git a/tests/baselines/reference/parserRegularExpression4.types b/tests/baselines/reference/parserRegularExpression4.types
index 1a0db05a48e48..1af56c7a24fc6 100644
--- a/tests/baselines/reference/parserRegularExpression4.types
+++ b/tests/baselines/reference/parserRegularExpression4.types
@@ -61,7 +61,7 @@ if (Ca.test(c.href) || Ba.test(c.href) && /(\\?|&)adurl=/.test(c.href) && !/(\\?
 >"&q=" + encodeURIComponent(W("q") || W("as_q") || A) : string
 >"&q=" : "&q="
 >encodeURIComponent(W("q") || W("as_q") || A) : string
->encodeURIComponent : (uriComponent: string) => string
+>encodeURIComponent : (uriComponent: string | number | boolean) => string
 >W("q") || W("as_q") || A : any
 >W("q") || W("as_q") : any
 >W("q") : any
diff --git a/tests/baselines/reference/parserVariableStatement1.d.errors.txt b/tests/baselines/reference/parserVariableStatement1.d.errors.txt
index eb6f799df74ab..ade6a2ea338af 100644
--- a/tests/baselines/reference/parserVariableStatement1.d.errors.txt
+++ b/tests/baselines/reference/parserVariableStatement1.d.errors.txt
@@ -1,10 +1,10 @@
-tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement1.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement1.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement1.d.ts(1,9): error TS1039: Initializers are not allowed in ambient contexts.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement1.d.ts (2 errors) ====
     var v = 1;
     ~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
             ~
 !!! error TS1039: Initializers are not allowed in ambient contexts.
\ No newline at end of file
diff --git a/tests/baselines/reference/parserVariableStatement2.d.errors.txt b/tests/baselines/reference/parserVariableStatement2.d.errors.txt
index c0cdb0e2ac4e2..fafb31d399963 100644
--- a/tests/baselines/reference/parserVariableStatement2.d.errors.txt
+++ b/tests/baselines/reference/parserVariableStatement2.d.errors.txt
@@ -1,7 +1,7 @@
-tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement2.d.ts(1,1): error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
+tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement2.d.ts(1,1): error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/Statements/parserVariableStatement2.d.ts (1 errors) ====
     var v;
     ~~~
-!!! error TS1046: A 'declare' modifier is required for a top level declaration in a .d.ts file.
\ No newline at end of file
+!!! error TS1046: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.
\ No newline at end of file
diff --git a/tests/baselines/reference/regexMatchAll.js b/tests/baselines/reference/regexMatchAll.js
new file mode 100644
index 0000000000000..5b169725ae27e
--- /dev/null
+++ b/tests/baselines/reference/regexMatchAll.js
@@ -0,0 +1,10 @@
+//// [regexMatchAll.ts]
+const matches = /\w/g[Symbol.matchAll]("matchAll");
+const array = [...matches];
+const { index, input } = array[0];
+
+
+//// [regexMatchAll.js]
+const matches = /\w/g[Symbol.matchAll]("matchAll");
+const array = [...matches];
+const { index, input } = array[0];
diff --git a/tests/baselines/reference/regexMatchAll.symbols b/tests/baselines/reference/regexMatchAll.symbols
new file mode 100644
index 0000000000000..aa811a1f67614
--- /dev/null
+++ b/tests/baselines/reference/regexMatchAll.symbols
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/regexMatchAll.ts ===
+const matches = /\w/g[Symbol.matchAll]("matchAll");
+>matches : Symbol(matches, Decl(regexMatchAll.ts, 0, 5))
+>Symbol.matchAll : Symbol(SymbolConstructor.matchAll, Decl(lib.es2020.symbol.wellknown.d.ts, --, --))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
+>matchAll : Symbol(SymbolConstructor.matchAll, Decl(lib.es2020.symbol.wellknown.d.ts, --, --))
+
+const array = [...matches];
+>array : Symbol(array, Decl(regexMatchAll.ts, 1, 5))
+>matches : Symbol(matches, Decl(regexMatchAll.ts, 0, 5))
+
+const { index, input } = array[0];
+>index : Symbol(index, Decl(regexMatchAll.ts, 2, 7))
+>input : Symbol(input, Decl(regexMatchAll.ts, 2, 14))
+>array : Symbol(array, Decl(regexMatchAll.ts, 1, 5))
+
diff --git a/tests/baselines/reference/regexMatchAll.types b/tests/baselines/reference/regexMatchAll.types
new file mode 100644
index 0000000000000..a109cdc46116b
--- /dev/null
+++ b/tests/baselines/reference/regexMatchAll.types
@@ -0,0 +1,24 @@
+=== tests/cases/compiler/regexMatchAll.ts ===
+const matches = /\w/g[Symbol.matchAll]("matchAll");
+>matches : IterableIterator<RegExpMatchArray>
+>/\w/g[Symbol.matchAll]("matchAll") : IterableIterator<RegExpMatchArray>
+>/\w/g[Symbol.matchAll] : (str: string) => IterableIterator<RegExpMatchArray>
+>/\w/g : RegExp
+>Symbol.matchAll : symbol
+>Symbol : SymbolConstructor
+>matchAll : symbol
+>"matchAll" : "matchAll"
+
+const array = [...matches];
+>array : RegExpMatchArray[]
+>[...matches] : RegExpMatchArray[]
+>...matches : RegExpMatchArray
+>matches : IterableIterator<RegExpMatchArray>
+
+const { index, input } = array[0];
+>index : number
+>input : string
+>array[0] : RegExpMatchArray
+>array : RegExpMatchArray[]
+>0 : 0
+
diff --git a/tests/baselines/reference/restPropertyWithBindingPattern.errors.txt b/tests/baselines/reference/restPropertyWithBindingPattern.errors.txt
new file mode 100644
index 0000000000000..7ad0cac9ce3bc
--- /dev/null
+++ b/tests/baselines/reference/restPropertyWithBindingPattern.errors.txt
@@ -0,0 +1,28 @@
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(1,6): error TS2501: A rest element cannot contain a binding pattern.
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(2,6): error TS2501: A rest element cannot contain a binding pattern.
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(2,6): error TS2701: The target of an object rest assignment must be a variable or a property access.
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(3,6): error TS2461: Type '{}' is not an array type.
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(3,6): error TS2501: A rest element cannot contain a binding pattern.
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(4,6): error TS2501: A rest element cannot contain a binding pattern.
+tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts(4,6): error TS2701: The target of an object rest assignment must be a variable or a property access.
+
+
+==== tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts (7 errors) ====
+    ({...{}} = {});
+         ~~
+!!! error TS2501: A rest element cannot contain a binding pattern.
+    ({...({})} = {});
+         ~~~~
+!!! error TS2501: A rest element cannot contain a binding pattern.
+         ~~~~
+!!! error TS2701: The target of an object rest assignment must be a variable or a property access.
+    ({...[]} = {});
+         ~~
+!!! error TS2461: Type '{}' is not an array type.
+         ~~
+!!! error TS2501: A rest element cannot contain a binding pattern.
+    ({...([])} = {});
+         ~~~~
+!!! error TS2501: A rest element cannot contain a binding pattern.
+         ~~~~
+!!! error TS2701: The target of an object rest assignment must be a variable or a property access.
\ No newline at end of file
diff --git a/tests/baselines/reference/restPropertyWithBindingPattern.js b/tests/baselines/reference/restPropertyWithBindingPattern.js
new file mode 100644
index 0000000000000..c4a4795d6827b
--- /dev/null
+++ b/tests/baselines/reference/restPropertyWithBindingPattern.js
@@ -0,0 +1,21 @@
+//// [restPropertyWithBindingPattern.ts]
+({...{}} = {});
+({...({})} = {});
+({...[]} = {});
+({...([])} = {});
+
+//// [restPropertyWithBindingPattern.js]
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) if (e.indexOf(p[i]) < 0)
+            t[p[i]] = s[p[i]];
+    return t;
+};
+var _a, _b;
+(_a = __rest({}, []));
+(({}) = __rest({}, []));
+(_b = __rest({}, []));
+(([]) = __rest({}, []));
diff --git a/tests/baselines/reference/restPropertyWithBindingPattern.symbols b/tests/baselines/reference/restPropertyWithBindingPattern.symbols
new file mode 100644
index 0000000000000..79b4b6745e3b4
--- /dev/null
+++ b/tests/baselines/reference/restPropertyWithBindingPattern.symbols
@@ -0,0 +1,6 @@
+=== tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts ===
+({...{}} = {});
+No type information for this code.({...({})} = {});
+No type information for this code.({...[]} = {});
+No type information for this code.({...([])} = {});
+No type information for this code.
\ No newline at end of file
diff --git a/tests/baselines/reference/restPropertyWithBindingPattern.types b/tests/baselines/reference/restPropertyWithBindingPattern.types
new file mode 100644
index 0000000000000..0cf290c792a4e
--- /dev/null
+++ b/tests/baselines/reference/restPropertyWithBindingPattern.types
@@ -0,0 +1,31 @@
+=== tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts ===
+({...{}} = {});
+>({...{}} = {}) : {}
+>{...{}} = {} : {}
+>{...{}} : {}
+>{} : {}
+>{} : {}
+
+({...({})} = {});
+>({...({})} = {}) : {}
+>{...({})} = {} : {}
+>{...({})} : {}
+>({}) : {}
+>{} : {}
+>{} : {}
+
+({...[]} = {});
+>({...[]} = {}) : {}
+>{...[]} = {} : {}
+>{...[]} : { [n: number]: undefined; length: number; toString(): string; toLocaleString(): string; pop(): undefined; push(...items: undefined[]): number; concat(...items: ConcatArray<undefined>[]): undefined[]; concat(...items: ConcatArray<undefined>[]): undefined[]; join(separator?: string): string; reverse(): undefined[]; shift(): undefined; slice(start?: number, end?: number): undefined[]; sort(compareFn?: (a: undefined, b: undefined) => number): undefined[]; splice(start: number, deleteCount?: number): undefined[]; splice(start: number, deleteCount: number, ...items: undefined[]): undefined[]; unshift(...items: undefined[]): number; indexOf(searchElement: undefined, fromIndex?: number): number; lastIndexOf(searchElement: undefined, fromIndex?: number): number; every(callbackfn: (value: undefined, index: number, array: undefined[]) => boolean, thisArg?: any): boolean; some(callbackfn: (value: undefined, index: number, array: undefined[]) => boolean, thisArg?: any): boolean; forEach(callbackfn: (value: undefined, index: number, array: undefined[]) => void, thisArg?: any): void; map<U>(callbackfn: (value: undefined, index: number, array: undefined[]) => U, thisArg?: any): U[]; filter<S extends undefined>(callbackfn: (value: undefined, index: number, array: undefined[]) => value is S, thisArg?: any): S[]; filter(callbackfn: (value: undefined, index: number, array: undefined[]) => any, thisArg?: any): undefined[]; reduce(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined): undefined; reduce(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined, initialValue: undefined): undefined; reduce<U>(callbackfn: (previousValue: U, currentValue: undefined, currentIndex: number, array: undefined[]) => U, initialValue: U): U; reduceRight(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined): undefined; reduceRight(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined, initialValue: undefined): undefined; reduceRight<U>(callbackfn: (previousValue: U, currentValue: undefined, currentIndex: number, array: undefined[]) => U, initialValue: U): U; }
+>[] : undefined[]
+>{} : {}
+
+({...([])} = {});
+>({...([])} = {}) : {}
+>{...([])} = {} : {}
+>{...([])} : { [n: number]: undefined; length: number; toString(): string; toLocaleString(): string; pop(): undefined; push(...items: undefined[]): number; concat(...items: ConcatArray<undefined>[]): undefined[]; concat(...items: ConcatArray<undefined>[]): undefined[]; join(separator?: string): string; reverse(): undefined[]; shift(): undefined; slice(start?: number, end?: number): undefined[]; sort(compareFn?: (a: undefined, b: undefined) => number): undefined[]; splice(start: number, deleteCount?: number): undefined[]; splice(start: number, deleteCount: number, ...items: undefined[]): undefined[]; unshift(...items: undefined[]): number; indexOf(searchElement: undefined, fromIndex?: number): number; lastIndexOf(searchElement: undefined, fromIndex?: number): number; every(callbackfn: (value: undefined, index: number, array: undefined[]) => boolean, thisArg?: any): boolean; some(callbackfn: (value: undefined, index: number, array: undefined[]) => boolean, thisArg?: any): boolean; forEach(callbackfn: (value: undefined, index: number, array: undefined[]) => void, thisArg?: any): void; map<U>(callbackfn: (value: undefined, index: number, array: undefined[]) => U, thisArg?: any): U[]; filter<S extends undefined>(callbackfn: (value: undefined, index: number, array: undefined[]) => value is S, thisArg?: any): S[]; filter(callbackfn: (value: undefined, index: number, array: undefined[]) => any, thisArg?: any): undefined[]; reduce(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined): undefined; reduce(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined, initialValue: undefined): undefined; reduce<U>(callbackfn: (previousValue: U, currentValue: undefined, currentIndex: number, array: undefined[]) => U, initialValue: U): U; reduceRight(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined): undefined; reduceRight(callbackfn: (previousValue: undefined, currentValue: undefined, currentIndex: number, array: undefined[]) => undefined, initialValue: undefined): undefined; reduceRight<U>(callbackfn: (previousValue: U, currentValue: undefined, currentIndex: number, array: undefined[]) => U, initialValue: U): U; }
+>([]) : undefined[]
+>[] : undefined[]
+>{} : {}
+
diff --git a/tests/baselines/reference/strictNullEmptyDestructuring.errors.txt b/tests/baselines/reference/strictNullEmptyDestructuring.errors.txt
index 2406ac27d98a1..cb50303d3500d 100644
--- a/tests/baselines/reference/strictNullEmptyDestructuring.errors.txt
+++ b/tests/baselines/reference/strictNullEmptyDestructuring.errors.txt
@@ -1,3 +1,4 @@
+tests/cases/compiler/strictNullEmptyDestructuring.ts(3,5): error TS2461: Type 'null' is not an array type.
 tests/cases/compiler/strictNullEmptyDestructuring.ts(3,5): error TS2531: Object is possibly 'null'.
 tests/cases/compiler/strictNullEmptyDestructuring.ts(5,5): error TS2531: Object is possibly 'null'.
 tests/cases/compiler/strictNullEmptyDestructuring.ts(7,2): error TS2531: Object is possibly 'null'.
@@ -11,11 +12,13 @@ tests/cases/compiler/strictNullEmptyDestructuring.ts(21,5): error TS2533: Object
 tests/cases/compiler/strictNullEmptyDestructuring.ts(23,2): error TS2533: Object is possibly 'null' or 'undefined'.
 
 
-==== tests/cases/compiler/strictNullEmptyDestructuring.ts (11 errors) ====
+==== tests/cases/compiler/strictNullEmptyDestructuring.ts (12 errors) ====
     // Repro from #20873
     
     let [] = null;
         ~~
+!!! error TS2461: Type 'null' is not an array type.
+        ~~
 !!! error TS2531: Object is possibly 'null'.
     
     let { } = null;
diff --git a/tests/baselines/reference/stringMatchAll.js b/tests/baselines/reference/stringMatchAll.js
new file mode 100644
index 0000000000000..fbb3c1174b731
--- /dev/null
+++ b/tests/baselines/reference/stringMatchAll.js
@@ -0,0 +1,10 @@
+//// [stringMatchAll.ts]
+const matches = "matchAll".matchAll(/\w/g);
+const array = [...matches];
+const { index, input } = array[0];
+
+
+//// [stringMatchAll.js]
+const matches = "matchAll".matchAll(/\w/g);
+const array = [...matches];
+const { index, input } = array[0];
diff --git a/tests/baselines/reference/stringMatchAll.symbols b/tests/baselines/reference/stringMatchAll.symbols
new file mode 100644
index 0000000000000..91ad541338ad4
--- /dev/null
+++ b/tests/baselines/reference/stringMatchAll.symbols
@@ -0,0 +1,15 @@
+=== tests/cases/compiler/stringMatchAll.ts ===
+const matches = "matchAll".matchAll(/\w/g);
+>matches : Symbol(matches, Decl(stringMatchAll.ts, 0, 5))
+>"matchAll".matchAll : Symbol(String.matchAll, Decl(lib.es2020.string.d.ts, --, --))
+>matchAll : Symbol(String.matchAll, Decl(lib.es2020.string.d.ts, --, --))
+
+const array = [...matches];
+>array : Symbol(array, Decl(stringMatchAll.ts, 1, 5))
+>matches : Symbol(matches, Decl(stringMatchAll.ts, 0, 5))
+
+const { index, input } = array[0];
+>index : Symbol(index, Decl(stringMatchAll.ts, 2, 7))
+>input : Symbol(input, Decl(stringMatchAll.ts, 2, 14))
+>array : Symbol(array, Decl(stringMatchAll.ts, 1, 5))
+
diff --git a/tests/baselines/reference/stringMatchAll.types b/tests/baselines/reference/stringMatchAll.types
new file mode 100644
index 0000000000000..d63de9540b5f6
--- /dev/null
+++ b/tests/baselines/reference/stringMatchAll.types
@@ -0,0 +1,22 @@
+=== tests/cases/compiler/stringMatchAll.ts ===
+const matches = "matchAll".matchAll(/\w/g);
+>matches : IterableIterator<RegExpMatchArray>
+>"matchAll".matchAll(/\w/g) : IterableIterator<RegExpMatchArray>
+>"matchAll".matchAll : (regexp: RegExp) => IterableIterator<RegExpMatchArray>
+>"matchAll" : "matchAll"
+>matchAll : (regexp: RegExp) => IterableIterator<RegExpMatchArray>
+>/\w/g : RegExp
+
+const array = [...matches];
+>array : RegExpMatchArray[]
+>[...matches] : RegExpMatchArray[]
+>...matches : RegExpMatchArray
+>matches : IterableIterator<RegExpMatchArray>
+
+const { index, input } = array[0];
+>index : number
+>input : string
+>array[0] : RegExpMatchArray
+>array : RegExpMatchArray[]
+>0 : 0
+
diff --git a/tests/baselines/reference/typesVersions.justIndex.trace.json b/tests/baselines/reference/typesVersions.justIndex.trace.json
index d69aa51f72ded..28e4a5cb3bfaf 100644
--- a/tests/baselines/reference/typesVersions.justIndex.trace.json
+++ b/tests/baselines/reference/typesVersions.justIndex.trace.json
@@ -12,7 +12,6 @@
     "'package.json' does not have a 'main' field.",
     "'package.json' has a 'typesVersions' field with version-specific path mappings.",
     "Found 'package.json' at '/a/package.json'.",
-    "'package.json' has a 'typesVersions' field with version-specific path mappings.",
     "'package.json' does not have a 'typings' field.",
     "'package.json' does not have a 'types' field.",
     "'package.json' does not have a 'main' field.",
diff --git a/tests/baselines/reference/typesVersionsDeclarationEmit.multiFileBackReferenceToSelf.trace.json b/tests/baselines/reference/typesVersionsDeclarationEmit.multiFileBackReferenceToSelf.trace.json
index cf08a29478f1d..464da214bae2a 100644
--- a/tests/baselines/reference/typesVersionsDeclarationEmit.multiFileBackReferenceToSelf.trace.json
+++ b/tests/baselines/reference/typesVersionsDeclarationEmit.multiFileBackReferenceToSelf.trace.json
@@ -6,7 +6,6 @@
     "'package.json' has 'types' field 'index' that references 'tests/cases/conformance/declarationEmit/node_modules/ext/index'.",
     "'package.json' has a 'typesVersions' field with version-specific path mappings.",
     "Found 'package.json' at 'tests/cases/conformance/declarationEmit/node_modules/ext/package.json'. Package ID is 'ext/ndex/index.d.ts@1.0.0'.",
-    "'package.json' has a 'typesVersions' field with version-specific path mappings.",
     "'package.json' does not have a 'typings' field.",
     "'package.json' has 'types' field 'index' that references 'tests/cases/conformance/declarationEmit/node_modules/ext/index'.",
     "'package.json' has a 'typesVersions' entry '>=3.1.0-0' that matches compiler version '3.1.0-dev', looking for a pattern to match module name 'index'.",
diff --git a/tests/baselines/reference/typingsLookup4.trace.json b/tests/baselines/reference/typingsLookup4.trace.json
index 86b386670d6a5..6409896ad1744 100644
--- a/tests/baselines/reference/typingsLookup4.trace.json
+++ b/tests/baselines/reference/typingsLookup4.trace.json
@@ -72,7 +72,6 @@
     "'package.json' has 'typings' field 'jquery.d.ts' that references '/node_modules/@types/jquery/jquery.d.ts'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at '/node_modules/@types/jquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'jquery.d.ts' that references '/node_modules/@types/jquery/jquery.d.ts'.",
     "File '/node_modules/@types/jquery/jquery.d.ts' exist - use it as a name resolution result.",
     "Resolving real path for '/node_modules/@types/jquery/jquery.d.ts', result '/node_modules/@types/jquery/jquery.d.ts'.",
@@ -82,7 +81,6 @@
     "'package.json' has 'typings' field 'kquery' that references '/node_modules/@types/kquery/kquery'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at '/node_modules/@types/kquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'kquery' that references '/node_modules/@types/kquery/kquery'.",
     "File '/node_modules/@types/kquery/kquery' does not exist.",
     "Loading module as file / folder, candidate module location '/node_modules/@types/kquery/kquery', target file type 'TypeScript'.",
@@ -96,7 +94,6 @@
     "'package.json' has 'typings' field 'lquery' that references '/node_modules/@types/lquery/lquery'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at '/node_modules/@types/lquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'lquery' that references '/node_modules/@types/lquery/lquery'.",
     "File '/node_modules/@types/lquery/lquery' does not exist.",
     "Loading module as file / folder, candidate module location '/node_modules/@types/lquery/lquery', target file type 'TypeScript'.",
@@ -108,7 +105,6 @@
     "'package.json' has 'typings' field 'mquery' that references '/node_modules/@types/mquery/mquery'.",
     "'package.json' does not have a 'typesVersions' field.",
     "Found 'package.json' at '/node_modules/@types/mquery/package.json'.",
-    "'package.json' does not have a 'typesVersions' field.",
     "'package.json' has 'typings' field 'mquery' that references '/node_modules/@types/mquery/mquery'.",
     "File '/node_modules/@types/mquery/mquery' does not exist.",
     "Loading module as file / folder, candidate module location '/node_modules/@types/mquery/mquery', target file type 'TypeScript'.",
diff --git a/tests/baselines/reference/user/assert.log b/tests/baselines/reference/user/assert.log
index 672c147428dee..60e693ae6f3ca 100644
--- a/tests/baselines/reference/user/assert.log
+++ b/tests/baselines/reference/user/assert.log
@@ -9,7 +9,7 @@ node_modules/assert/assert.js(130,10): error TS2339: Property 'generatedMessage'
 node_modules/assert/assert.js(132,10): error TS2339: Property 'message' does not exist on type 'typeof ok'.
 node_modules/assert/assert.js(133,10): error TS2339: Property 'generatedMessage' does not exist on type 'typeof ok'.
 node_modules/assert/assert.js(154,12): error TS2339: Property 'stack' does not exist on type 'typeof ok'.
-node_modules/assert/test.js(25,5): error TS2367: This condition will always return 'false' since the types 'string | undefined' and 'boolean' have no overlap.
+node_modules/assert/test.js(25,5): error TS2367: This condition will always return 'false' since the types 'string | undefined' and 'true' have no overlap.
 node_modules/assert/test.js(39,5): error TS2552: Cannot find name 'test'. Did you mean 'tests'?
 node_modules/assert/test.js(55,5): error TS2552: Cannot find name 'test'. Did you mean 'tests'?
 node_modules/assert/test.js(74,5): error TS2552: Cannot find name 'test'. Did you mean 'tests'?
diff --git a/tests/baselines/reference/user/chrome-devtools-frontend.log b/tests/baselines/reference/user/chrome-devtools-frontend.log
index 45afc61657ed1..45ba3fc971a56 100644
--- a/tests/baselines/reference/user/chrome-devtools-frontend.log
+++ b/tests/baselines/reference/user/chrome-devtools-frontend.log
@@ -869,16 +869,6 @@ node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighth
 node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(24079,1): error TS2323: Cannot redeclare exported variable 'Buf16'.
 node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(24080,1): error TS2323: Cannot redeclare exported variable 'Buf32'.
 node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(26059,1): error TS2323: Cannot redeclare exported variable 'deflate'.
-node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(27915,27): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'string'.
-  Type 'number' is not assignable to type 'string'.
-node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(27918,30): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'string'.
-  Type 'number' is not assignable to type 'string'.
-node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(27921,30): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'string'.
-  Type 'number' is not assignable to type 'string'.
-node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(27928,27): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'string'.
-  Type 'number' is not assignable to type 'string'.
-node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(27929,20): error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'string'.
-  Type 'number' is not assignable to type 'string'.
 node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(27956,16): error TS2323: Cannot redeclare exported variable 'parse'.
 node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(28222,51): error TS2300: Duplicate identifier '_read'.
 node_modules/chrome-devtools-frontend/front_end/audits2_worker/lighthouse/lighthouse-background.js(28457,20): error TS2339: Property 'emit' does not exist on type 'Readable'.
@@ -5027,9 +5017,9 @@ node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(42,20):
 node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(42,125): error TS2339: Property 'length1' does not exist on type 'number'.
 node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(42,138): error TS2339: Property 'length2' does not exist on type 'number'.
 node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(43,411): error TS2403: Subsequent variable declarations must have the same type.  Variable 'g' must be of type 'string', but here has type 'any'.
-node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(43,443): error TS2367: This condition will always return 'false' since the types 'number' and 'string' have no overlap.
-node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(44,7): error TS2367: This condition will always return 'false' since the types 'number' and 'string' have no overlap.
-node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(44,220): error TS2367: This condition will always return 'false' since the types 'number' and 'string' have no overlap.
+node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(43,443): error TS2367: This condition will always return 'false' since the types '1' and 'string' have no overlap.
+node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(44,7): error TS2367: This condition will always return 'false' since the types '-1' and 'string' have no overlap.
+node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(44,220): error TS2367: This condition will always return 'false' since the types '0' and 'string' have no overlap.
 node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(47,403): error TS2339: Property 'diffs' does not exist on type 'typeof diff_match_patch'.
 node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(47,417): error TS2339: Property 'start2' does not exist on type 'typeof diff_match_patch'.
 node_modules/chrome-devtools-frontend/front_end/diff/diff_match_patch.js(47,429): error TS2339: Property 'start1' does not exist on type 'typeof diff_match_patch'.
@@ -10912,7 +10902,7 @@ node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.j
 node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(822,79): error TS2339: Property 'charAt' does not exist on type 'void'.
 node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(823,41): error TS2339: Property 'length' does not exist on type 'void'.
 node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(823,88): error TS2339: Property 'charAt' does not exist on type 'void'.
-node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(839,9): error TS2367: This condition will always return 'false' since the types 'void' and 'number' have no overlap.
+node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(839,9): error TS2367: This condition will always return 'false' since the types 'void' and '0' have no overlap.
 node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(854,9): error TS1345: An expression of type 'void' cannot be tested for truthiness
 node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(862,12): error TS1345: An expression of type 'void' cannot be tested for truthiness
 node_modules/chrome-devtools-frontend/front_end/source_frame/SourcesTextEditor.js(862,13): error TS1345: An expression of type 'void' cannot be tested for truthiness
diff --git a/tests/baselines/reference/user/prettier.log b/tests/baselines/reference/user/prettier.log
index 22c00d2bd46bb..6ee6e91cb6bc2 100644
--- a/tests/baselines/reference/user/prettier.log
+++ b/tests/baselines/reference/user/prettier.log
@@ -1,6 +1,6 @@
 Exit Code: 1
 Standard output:
-node_modules/@typescript-eslint/typescript-estree/dist/parser.d.ts(1,8): error TS1192: Module '"/prettier/prettier/node_modules/typescript/lib/typescript"' has no default export.
+node_modules/@typescript-eslint/typescript-estree/dist/parser.d.ts(1,8): error TS1259: Module '"/prettier/prettier/node_modules/typescript/lib/typescript"' can only be default-imported using the 'esModuleInterop' flag
 src/cli/util.js(60,44): error TS2345: Argument of type 'null' is not assignable to parameter of type 'number | undefined'.
 src/cli/util.js(119,38): error TS2339: Property 'sync' does not exist on type '(...args: any[]) => any'.
 src/cli/util.js(372,29): error TS2532: Object is possibly 'undefined'.
diff --git a/tests/baselines/reference/user/uglify-js.log b/tests/baselines/reference/user/uglify-js.log
index 8f4b868d5527a..c5feff00abc0d 100644
--- a/tests/baselines/reference/user/uglify-js.log
+++ b/tests/baselines/reference/user/uglify-js.log
@@ -10,58 +10,58 @@ node_modules/uglify-js/lib/ast.js(932,25): error TS2339: Property 'self' does no
 node_modules/uglify-js/lib/ast.js(933,37): error TS2339: Property 'parent' does not exist on type 'TreeWalker'.
 node_modules/uglify-js/lib/compress.js(175,42): error TS2554: Expected 0 arguments, but got 1.
 node_modules/uglify-js/lib/compress.js(532,41): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(855,33): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(1110,38): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
-node_modules/uglify-js/lib/compress.js(1124,51): error TS2349: Cannot invoke an expression whose type lacks a call signature. Type 'true | ((node: any) => any)' has no compatible call signatures.
-node_modules/uglify-js/lib/compress.js(1188,53): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
-node_modules/uglify-js/lib/compress.js(1229,112): error TS2454: Variable 'args' is used before being assigned.
-node_modules/uglify-js/lib/compress.js(1230,29): error TS2532: Object is possibly 'undefined'.
-node_modules/uglify-js/lib/compress.js(1239,87): error TS2322: Type 'false' is not assignable to type 'number'.
-node_modules/uglify-js/lib/compress.js(1247,29): error TS2322: Type 'false' is not assignable to type 'never'.
-node_modules/uglify-js/lib/compress.js(1353,53): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(1454,38): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
-node_modules/uglify-js/lib/compress.js(1564,42): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(1596,41): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(1708,49): error TS2345: Argument of type 'number[]' is not assignable to parameter of type '[number, number, ...never[]]'.
+node_modules/uglify-js/lib/compress.js(858,33): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(1114,38): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
+node_modules/uglify-js/lib/compress.js(1128,51): error TS2349: Cannot invoke an expression whose type lacks a call signature. Type 'true | ((node: any) => any)' has no compatible call signatures.
+node_modules/uglify-js/lib/compress.js(1192,53): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
+node_modules/uglify-js/lib/compress.js(1233,112): error TS2454: Variable 'args' is used before being assigned.
+node_modules/uglify-js/lib/compress.js(1234,29): error TS2532: Object is possibly 'undefined'.
+node_modules/uglify-js/lib/compress.js(1243,87): error TS2322: Type 'false' is not assignable to type 'number'.
+node_modules/uglify-js/lib/compress.js(1251,29): error TS2322: Type 'false' is not assignable to type 'never'.
+node_modules/uglify-js/lib/compress.js(1359,53): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(1460,38): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
+node_modules/uglify-js/lib/compress.js(1570,42): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(1602,41): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(1714,49): error TS2345: Argument of type 'number[]' is not assignable to parameter of type '[number, number, ...never[]]'.
   Type 'number[]' is missing the following properties from type '[number, number, ...never[]]': 0, 1
-node_modules/uglify-js/lib/compress.js(2031,59): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(2069,53): error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[number, number, ...never[]]'.
+node_modules/uglify-js/lib/compress.js(2037,59): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(2075,53): error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[number, number, ...never[]]'.
   Type 'any[]' is missing the following properties from type '[number, number, ...never[]]': 0, 1
-node_modules/uglify-js/lib/compress.js(2217,34): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(2883,42): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3328,38): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3341,33): error TS2322: Type '"f"' is not assignable to type 'boolean'.
-node_modules/uglify-js/lib/compress.js(3475,33): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3528,29): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3545,29): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
-node_modules/uglify-js/lib/compress.js(3570,75): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3643,63): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3828,38): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(3849,24): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
-node_modules/uglify-js/lib/compress.js(3859,28): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
-node_modules/uglify-js/lib/compress.js(4018,21): error TS2403: Subsequent variable declarations must have the same type.  Variable 'defs' must be of type 'Dictionary & { set: (key: any, val: any) => Dictionary & { set: ...; add: (key: any, val: any) => Dictionary & { set: ...; add: ...; get: (key: any) => any; del: (key: any) => Dictionary & { set: ...; ... 8 more ...; toObject: () => any; }; ... 5 more ...; toObject: () => any; }; ... 7 more ...; toObject: () => any;...', but here has type 'any'.
-node_modules/uglify-js/lib/compress.js(4070,17): error TS2447: The '|=' operator is not allowed for boolean types. Consider using '||' instead.
-node_modules/uglify-js/lib/compress.js(4126,45): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(4238,33): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(4537,17): error TS2403: Subsequent variable declarations must have the same type.  Variable 'body' must be of type 'any[]', but here has type 'any'.
-node_modules/uglify-js/lib/compress.js(4621,37): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(4829,57): error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[RegExp, (string | undefined)?]'.
+node_modules/uglify-js/lib/compress.js(2223,34): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(2948,42): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3400,38): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3413,33): error TS2322: Type '"f"' is not assignable to type 'boolean'.
+node_modules/uglify-js/lib/compress.js(3547,33): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3600,29): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3617,29): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
+node_modules/uglify-js/lib/compress.js(3642,75): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3715,63): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3900,38): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(3921,24): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
+node_modules/uglify-js/lib/compress.js(3931,28): error TS2339: Property 'parent' does not exist on type 'TreeTransformer'.
+node_modules/uglify-js/lib/compress.js(4090,21): error TS2403: Subsequent variable declarations must have the same type.  Variable 'defs' must be of type 'Dictionary & { set: (key: any, val: any) => Dictionary & { set: ...; add: (key: any, val: any) => Dictionary & { set: ...; add: ...; get: (key: any) => any; del: (key: any) => Dictionary & { set: ...; ... 8 more ...; toObject: () => any; }; ... 5 more ...; toObject: () => any; }; ... 7 more ...; toObject: () => any;...', but here has type 'any'.
+node_modules/uglify-js/lib/compress.js(4142,17): error TS2447: The '|=' operator is not allowed for boolean types. Consider using '||' instead.
+node_modules/uglify-js/lib/compress.js(4203,45): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(4315,33): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(4614,17): error TS2403: Subsequent variable declarations must have the same type.  Variable 'body' must be of type 'any[]', but here has type 'any'.
+node_modules/uglify-js/lib/compress.js(4698,37): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(4906,57): error TS2345: Argument of type 'any[]' is not assignable to parameter of type '[RegExp, (string | undefined)?]'.
   Property '0' is missing in type 'any[]' but required in type '[RegExp, (string | undefined)?]'.
-node_modules/uglify-js/lib/compress.js(4987,45): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(4994,25): error TS2403: Subsequent variable declarations must have the same type.  Variable 'code' must be of type 'string', but here has type '{ get: () => string; toString: () => string; indent: () => void; indentation: () => number; current_width: () => number; should_break: () => boolean; has_parens: () => boolean; newline: () => void; print: (str: any) => void; ... 24 more ...; parent: (n: any) => any; }'.
-node_modules/uglify-js/lib/compress.js(4998,36): error TS2532: Object is possibly 'undefined'.
-node_modules/uglify-js/lib/compress.js(5003,41): error TS2339: Property 'get' does not exist on type 'string'.
-node_modules/uglify-js/lib/compress.js(5490,18): error TS2454: Variable 'is_strict_comparison' is used before being assigned.
-node_modules/uglify-js/lib/compress.js(5922,25): error TS2367: This condition will always return 'false' since the types 'boolean' and '"f"' have no overlap.
-node_modules/uglify-js/lib/compress.js(5949,47): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(6023,39): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(6095,39): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(6101,41): error TS2554: Expected 0 arguments, but got 1.
-node_modules/uglify-js/lib/compress.js(6534,43): error TS2454: Variable 'property' is used before being assigned.
-node_modules/uglify-js/lib/compress.js(6549,25): error TS2403: Subsequent variable declarations must have the same type.  Variable 'value' must be of type 'number', but here has type 'any'.
-node_modules/uglify-js/lib/compress.js(6552,46): error TS2339: Property 'has_side_effects' does not exist on type 'number'.
-node_modules/uglify-js/lib/compress.js(6558,25): error TS2403: Subsequent variable declarations must have the same type.  Variable 'value' must be of type 'number', but here has type 'any'.
-node_modules/uglify-js/lib/compress.js(6586,34): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(5070,45): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(5077,25): error TS2403: Subsequent variable declarations must have the same type.  Variable 'code' must be of type 'string', but here has type '{ get: () => string; toString: () => string; indent: () => void; indentation: () => number; current_width: () => number; should_break: () => boolean; has_parens: () => boolean; newline: () => void; print: (str: any) => void; ... 24 more ...; parent: (n: any) => any; }'.
+node_modules/uglify-js/lib/compress.js(5081,36): error TS2532: Object is possibly 'undefined'.
+node_modules/uglify-js/lib/compress.js(5086,41): error TS2339: Property 'get' does not exist on type 'string'.
+node_modules/uglify-js/lib/compress.js(5589,18): error TS2454: Variable 'is_strict_comparison' is used before being assigned.
+node_modules/uglify-js/lib/compress.js(6084,25): error TS2367: This condition will always return 'false' since the types 'boolean' and '"f"' have no overlap.
+node_modules/uglify-js/lib/compress.js(6111,47): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(6185,39): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(6257,39): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(6263,41): error TS2554: Expected 0 arguments, but got 1.
+node_modules/uglify-js/lib/compress.js(6696,43): error TS2454: Variable 'property' is used before being assigned.
+node_modules/uglify-js/lib/compress.js(6711,25): error TS2403: Subsequent variable declarations must have the same type.  Variable 'value' must be of type 'number', but here has type 'any'.
+node_modules/uglify-js/lib/compress.js(6714,46): error TS2339: Property 'has_side_effects' does not exist on type 'number'.
+node_modules/uglify-js/lib/compress.js(6720,25): error TS2403: Subsequent variable declarations must have the same type.  Variable 'value' must be of type 'number', but here has type 'any'.
+node_modules/uglify-js/lib/compress.js(6748,34): error TS2554: Expected 0 arguments, but got 1.
 node_modules/uglify-js/lib/minify.js(170,75): error TS2339: Property 'compress' does not exist on type 'Compressor'.
 node_modules/uglify-js/lib/mozilla-ast.js(566,33): error TS2554: Expected 0 arguments, but got 1.
 node_modules/uglify-js/lib/output.js(246,25): error TS2554: Expected 0 arguments, but got 2.
diff --git a/tests/cases/compiler/constantEnumAssert.ts b/tests/cases/compiler/constantEnumAssert.ts
new file mode 100644
index 0000000000000..d57845a7edfdd
--- /dev/null
+++ b/tests/cases/compiler/constantEnumAssert.ts
@@ -0,0 +1,49 @@
+enum E1 {
+    a,
+    b
+}
+
+enum E2 {
+    a = 'a',
+    b = 'b'
+}
+
+enum E3 {
+    a = 1,
+    b = a << 1,
+    c = a << 2,
+}
+
+const enum E4 {
+    a,
+    b
+}
+
+const E5 = {
+    a: 'a',
+    b: 'b'
+}
+
+const foo1 = { a: E1.a }
+
+const foo2 = { a: E2.a }
+
+const foo3 = { a: E1.a } as const
+
+const foo4 = { a: E2.a } as const
+
+const foo5 = { a: E3.a } as const
+
+const foo6 = { a: E4.a } as const
+
+const foo7 = { a: E5.a } as const
+
+const foo8 = { a: E1.a as const }
+
+const foo9 = { a: E2.a as const }
+
+const foo10 = { a: E3.a as const }
+
+const foo11 = { a: E4.a as const }
+
+const foo12 = { a: E5.a as const }
diff --git a/tests/cases/compiler/exportDefaultWithJSDoc1.ts b/tests/cases/compiler/exportDefaultWithJSDoc1.ts
new file mode 100644
index 0000000000000..2140ccc8aa164
--- /dev/null
+++ b/tests/cases/compiler/exportDefaultWithJSDoc1.ts
@@ -0,0 +1,16 @@
+
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+
+/**
+ * A number, or a string containing a number.
+ * @typedef {(number|string)} NumberLike
+ */
+
+// @Filename: a.js
+/** @type {NumberLike[]} */export default ([ ]);
+
+// @Filename: b.ts
+import A from './a'
+A[0]
\ No newline at end of file
diff --git a/tests/cases/compiler/exportDefaultWithJSDoc2.ts b/tests/cases/compiler/exportDefaultWithJSDoc2.ts
new file mode 100644
index 0000000000000..1b14248bfa668
--- /dev/null
+++ b/tests/cases/compiler/exportDefaultWithJSDoc2.ts
@@ -0,0 +1,16 @@
+
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+
+/**
+ * A number, or a string containing a number.
+ * @typedef {(number|string)} NumberLike
+ */
+
+// @Filename: a.js
+export default /** @type {NumberLike[]} */([ ]);
+
+// @Filename: b.ts
+import A from './a'
+A[0]
\ No newline at end of file
diff --git a/tests/cases/compiler/isolatedModulesNoEmitOnError.ts b/tests/cases/compiler/isolatedModulesNoEmitOnError.ts
index ce3085dbc3b9f..46ab4efcb089c 100644
--- a/tests/cases/compiler/isolatedModulesNoEmitOnError.ts
+++ b/tests/cases/compiler/isolatedModulesNoEmitOnError.ts
@@ -3,4 +3,4 @@
 // @target: es6
 
 // @filename: file1.ts
-export var x;
\ No newline at end of file
+export const x: string = 3;
\ No newline at end of file
diff --git a/tests/cases/compiler/narrowByEquality.ts b/tests/cases/compiler/narrowByEquality.ts
new file mode 100644
index 0000000000000..a0ebe09a9a9a7
--- /dev/null
+++ b/tests/cases/compiler/narrowByEquality.ts
@@ -0,0 +1,59 @@
+// @strict: true
+
+declare let x: number | string | boolean
+declare let n: number;
+declare let s: string;
+declare let b: boolean;
+
+if (x == n) {
+    x;
+}
+
+if (x == s) {
+    x;
+}
+
+if (x == b) {
+    x;
+}
+
+if (x == 1) {
+    x;
+}
+
+if (x == "") {
+    x;
+}
+
+if (x == "foo") {
+    x;
+}
+
+if (x == true) {
+    x;
+}
+
+if (x == false) {
+    x;
+}
+
+declare let xAndObj: number | string | boolean | object
+
+if (xAndObj == {}) {
+    xAndObj;
+}
+
+if (x == xAndObj) {
+    x;
+    xAndObj;
+}
+
+// Repro from #24991
+
+function test(level: number | string):number {
+    if (level == +level) {
+        const q2: number = level; // error
+        return level;
+    }
+    return 0;
+}
diff --git a/tests/cases/compiler/omitTypeTestErrors01.ts b/tests/cases/compiler/omitTypeTestErrors01.ts
new file mode 100644
index 0000000000000..fd3f5fc1e5d2a
--- /dev/null
+++ b/tests/cases/compiler/omitTypeTestErrors01.ts
@@ -0,0 +1,19 @@
+// @declaration: true
+
+interface Foo {
+    a: string;
+    b: number;
+    c: boolean;
+}
+
+export type Bar = Omit<Foo, "c">;
+export type Baz = Omit<Foo, "b" | "c">;
+
+export function getBarC(bar: Bar) {
+    return bar.c;
+}
+
+export function getBazB(baz: Baz) {
+    return baz.b;
+}
+
diff --git a/tests/cases/compiler/omitTypeTests01.ts b/tests/cases/compiler/omitTypeTests01.ts
new file mode 100644
index 0000000000000..d3b2ce26e1ec4
--- /dev/null
+++ b/tests/cases/compiler/omitTypeTests01.ts
@@ -0,0 +1,19 @@
+// @declaration: true
+
+interface Foo {
+    a: string;
+    b: number;
+    c: boolean;
+}
+
+export type Bar = Omit<Foo, "c">;
+export type Baz = Omit<Foo, "b" | "c">;
+
+export function getBarA(bar: Bar) {
+    return bar.a;
+}
+
+export function getBazA(baz: Baz) {
+    return baz.a;
+}
+
diff --git a/tests/cases/compiler/regexMatchAll.ts b/tests/cases/compiler/regexMatchAll.ts
new file mode 100644
index 0000000000000..b18ab9fd2968b
--- /dev/null
+++ b/tests/cases/compiler/regexMatchAll.ts
@@ -0,0 +1,5 @@
+// @target: es2020
+
+const matches = /\w/g[Symbol.matchAll]("matchAll");
+const array = [...matches];
+const { index, input } = array[0];
diff --git a/tests/cases/compiler/stringMatchAll.ts b/tests/cases/compiler/stringMatchAll.ts
new file mode 100644
index 0000000000000..9b2ae1a9d641f
--- /dev/null
+++ b/tests/cases/compiler/stringMatchAll.ts
@@ -0,0 +1,5 @@
+// @target: es2020
+
+const matches = "matchAll".matchAll(/\w/g);
+const array = [...matches];
+const { index, input } = array[0];
diff --git a/tests/cases/conformance/constEnums/constEnum4.ts b/tests/cases/conformance/constEnums/constEnum4.ts
new file mode 100644
index 0000000000000..c6dc5840c4682
--- /dev/null
+++ b/tests/cases/conformance/constEnums/constEnum4.ts
@@ -0,0 +1,6 @@
+if (1)
+    const enum A { }
+else if (2)
+    const enum B { }
+else
+    const enum C { }
diff --git a/tests/cases/conformance/decorators/1.0lib-noErrors.ts b/tests/cases/conformance/decorators/1.0lib-noErrors.ts
index 6966e3e70d07d..391c0926a82b7 100644
--- a/tests/cases/conformance/decorators/1.0lib-noErrors.ts
+++ b/tests/cases/conformance/decorators/1.0lib-noErrors.ts
@@ -78,7 +78,7 @@ declare function encodeURI(uri: string): string;
   * Encodes a text string as a valid component of a Uniform Resource Identifier (URI).
   * @param uriComponent A value representing an encoded URI component.
   */
-declare function encodeURIComponent(uriComponent: string): string;
+declare function encodeURIComponent(uriComponent: string | number | boolean): string;
 
 interface PropertyDescriptor {
     configurable?: boolean;
@@ -1141,4 +1141,4 @@ declare var Array: {
     <T>(...items: T[]): T[];
     isArray(arg: any): boolean;
     prototype: Array<any>;
-}
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/tests/cases/conformance/es2019/globalThisCollision.ts b/tests/cases/conformance/es2019/globalThisCollision.ts
new file mode 100644
index 0000000000000..d73a7b6217e64
--- /dev/null
+++ b/tests/cases/conformance/es2019/globalThisCollision.ts
@@ -0,0 +1,5 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @filename: globalThisCollision.js
+var globalThis;
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts b/tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts
new file mode 100644
index 0000000000000..af595c1621f96
--- /dev/null
+++ b/tests/cases/conformance/es6/destructuring/destructuringAssignabilityCheck.ts
@@ -0,0 +1,17 @@
+// @strict: true
+
+const [] = {}; // should be error
+const {} = undefined; // error correctly
+(([]) => 0)({}); // should be error
+(({}) => 0)(undefined); // should be error
+
+function foo({}: undefined) {
+    return 0
+}
+function bar([]: {}) {
+    return 0
+}
+
+const { }: undefined = 1
+
+const []: {} = {}
diff --git a/tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts b/tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts
new file mode 100644
index 0000000000000..fc7bd03561045
--- /dev/null
+++ b/tests/cases/conformance/es6/destructuring/restPropertyWithBindingPattern.ts
@@ -0,0 +1,4 @@
+({...{}} = {});
+({...({})} = {});
+({...[]} = {});
+({...([])} = {});
\ No newline at end of file
diff --git a/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts b/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts
index 26daf35ee50c4..356e0a42ae9b4 100644
--- a/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts
+++ b/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts
@@ -117,3 +117,13 @@ type StrictExtract<T, U> = T extends U ? U extends T ? T : never : never;
 type StrictExclude<T, U> = T extends StrictExtract<T, U> ? never : T;
 type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
 type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;
+
+// Repros from #30938
+
+function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(param: T, cb: (element: T['elements'][number]) => void) {
+    cb(param.elements[0]);
+}
+
+function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
+    cb(param[0]);
+}
diff --git a/tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptionsInJsconfig.ts b/tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptionsInJsconfig.ts
new file mode 100644
index 0000000000000..f8dcbf75e4824
--- /dev/null
+++ b/tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptionsInJsconfig.ts
@@ -0,0 +1,26 @@
+/// <reference path='fourslash.ts' />
+
+// @Filename: /dir/a.ts
+////declare const decorator: any;
+////class A {
+//// @decorator method() {};
+////};
+
+// @Filename: /dir/jsconfig.json
+////{
+////    "compilerOptions": {
+////    }
+////}
+
+goTo.file("/dir/a.ts");
+verify.codeFix({
+    description: "Enable the 'experimentalDecorators' option in your configuration file",
+    newFileContent: {
+        "/dir/jsconfig.json":
+`{
+    "compilerOptions": {
+        "experimentalDecorators": true,
+    }
+}`,
+    },
+});
diff --git a/tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptions.ts b/tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptionsInTsconfig.ts
similarity index 100%
rename from tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptions.ts
rename to tests/cases/fourslash/codefixEnableExperimentalDecorators_blankCompilerOptionsInTsconfig.ts
diff --git a/tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptionsInJsconfig.ts b/tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptionsInJsconfig.ts
new file mode 100644
index 0000000000000..2b0809fe8c8b5
--- /dev/null
+++ b/tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptionsInJsconfig.ts
@@ -0,0 +1,27 @@
+/// <reference path='fourslash.ts' />
+
+// @Filename: /dir/a.ts
+////declare const decorator: any;
+////class A {
+//// @decorator method() {};
+////};
+
+// @Filename: /dir/jsconfig.json
+////{
+////    "compilerOptions": {
+////        "experimentalDecorators": false,
+////    }
+////}
+
+goTo.file("/dir/a.ts");
+verify.codeFix({
+    description: "Enable the 'experimentalDecorators' option in your configuration file",
+    newFileContent: {
+        "/dir/jsconfig.json":
+`{
+    "compilerOptions": {
+        "experimentalDecorators": true,
+    }
+}`,
+    },
+});
diff --git a/tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptions.ts b/tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptionsInTsconfig.ts
similarity index 100%
rename from tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptions.ts
rename to tests/cases/fourslash/codefixEnableExperimentalDecorators_disabledInCompilerOptionsInTsconfig.ts
diff --git a/tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptionsInJsconfig.ts b/tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptionsInJsconfig.ts
new file mode 100644
index 0000000000000..644fce3a35f56
--- /dev/null
+++ b/tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptionsInJsconfig.ts
@@ -0,0 +1,22 @@
+/// <reference path='fourslash.ts' />
+
+// @Filename: /dir/a.ts
+////declare const decorator: any;
+////class A {
+//// @decorator method() {};
+////};
+
+// @Filename: /dir/jsconfig.json
+////{
+////}
+
+goTo.file("/dir/a.ts");
+verify.codeFix({
+    description: "Enable the 'experimentalDecorators' option in your configuration file",
+    newFileContent: {
+        "/dir/jsconfig.json":
+`{
+    "compilerOptions": { "experimentalDecorators": true },
+}`,
+    },
+});
diff --git a/tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptions.ts b/tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptionsInTsconfig.ts
similarity index 100%
rename from tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptions.ts
rename to tests/cases/fourslash/codefixEnableExperimentalDecorators_missingCompilerOptionsInTsconfig.ts
diff --git a/tests/cases/fourslash/outliningSpansForFunction.ts b/tests/cases/fourslash/outliningSpansForFunction.ts
new file mode 100644
index 0000000000000..acc00eedbee3a
--- /dev/null
+++ b/tests/cases/fourslash/outliningSpansForFunction.ts
@@ -0,0 +1,14 @@
+/// <reference path="fourslash.ts"/>
+
+////function f(x: number, y: number)[| {
+////    return x + y;
+////}|]
+////
+////function g[|(
+////    x: number,
+////    y: number,
+////): number {
+////    return x + y;
+////}|]
+
+verify.outliningSpansInCurrentFile(test.ranges());
diff --git a/tests/lib/lib.d.ts b/tests/lib/lib.d.ts
index ad17bec673e95..5f089bb3c82eb 100644
--- a/tests/lib/lib.d.ts
+++ b/tests/lib/lib.d.ts
@@ -77,7 +77,7 @@ declare function encodeURI(uri: string): string;
   * Encodes a text string as a valid component of a Uniform Resource Identifier (URI).
   * @param uriComponent A value representing an encoded URI component.
   */
-declare function encodeURIComponent(uriComponent: string): string;
+declare function encodeURIComponent(uriComponent: string | number | boolean): string;
 
 /**
   * Computes a new string in which certain characters have been replaced by a hexadecimal escape sequence.
diff --git a/tslint.json b/tslint.json
index 5952c770c5e7e..5b75ed1a55b74 100644
--- a/tslint.json
+++ b/tslint.json
@@ -1,6 +1,11 @@
 {
     "extends": "tslint:latest",
     "rulesDirectory": "built/local/tslint/rules",
+    "linterOptions": {
+        "exclude": [
+            "tests/**/*"
+        ]
+    },
     "rules": {
         "no-unnecessary-type-assertion": true,