Add unmeasurable variance kind for marking types whose variance result is unreliable

src/compiler/checker.ts

@@ -670,6 +670,7 @@ namespace ts {
 
         let _jsxNamespace: __String;
         let _jsxFactoryEntity: EntityName | undefined;
+        let unmeasurableMarkerHandler: (() => void) | undefined;
 
         const subtypeRelation = createMap<RelationComparisonResult>();
         const assignableRelation = createMap<RelationComparisonResult>();
@@ -12973,6 +12974,9 @@ namespace ts {
                 }
 
                 function relateVariances(sourceTypeArguments: ReadonlyArray<Type> | undefined, targetTypeArguments: ReadonlyArray<Type> | undefined, variances: Variance[]) {
+                    if (some(variances, v => v === Variance.Unmeasurable)) {
+                        return undefined;
+                    }
                     if (result = typeArgumentsRelatedTo(sourceTypeArguments, targetTypeArguments, variances, reportErrors)) {
                         return result;
                     }
@@ -13006,6 +13010,13 @@ namespace ts {
                 }
             }
 
+            function reportUnmeasurableMarkers(p: TypeParameter) {
+                if (unmeasurableMarkerHandler && (p === markerSuperType || p === markerSubType || p === markerOtherType)) {
+                    unmeasurableMarkerHandler();
+                }
+                return p;
+            }
+
             // A type [P in S]: X is related to a type [Q in T]: Y if T is related to S and X' is
             // related to Y, where X' is an instantiation of X in which P is replaced with Q. Notice
             // that S and T are contra-variant whereas X and Y are co-variant.
@@ -13014,7 +13025,9 @@ namespace ts {
                         getCombinedMappedTypeOptionality(source) <= getCombinedMappedTypeOptionality(target));
                 if (modifiersRelated) {
                     let result: Ternary;
-                    if (result = isRelatedTo(getConstraintTypeFromMappedType(target), getConstraintTypeFromMappedType(source), reportErrors)) {
+                    const targetConstraint = getConstraintTypeFromMappedType(target);
+                    const sourceConstraint = instantiateType(getConstraintTypeFromMappedType(source), reportUnmeasurableMarkers);
+                    if (result = isRelatedTo(targetConstraint, sourceConstraint, reportErrors)) {
                         const mapper = createTypeMapper([getTypeParameterFromMappedType(source)], [getTypeParameterFromMappedType(target)]);
                         return result & isRelatedTo(instantiateType(getTemplateTypeFromMappedType(source), mapper), getTemplateTypeFromMappedType(target), reportErrors);
                     }
@@ -13489,6 +13502,9 @@ namespace ts {
                 cache.variances = emptyArray;
                 variances = [];
                 for (const tp of typeParameters) {
+                    let unmeasurable = false;
+                    const oldHandler = unmeasurableMarkerHandler;
+                    unmeasurableMarkerHandler = () => unmeasurable = true;
                     // We first compare instantiations where the type parameter is replaced with
                     // marker types that have a known subtype relationship. From this we can infer
                     // invariance, covariance, contravariance or bivariance.
@@ -13503,6 +13519,16 @@ namespace ts {
                     if (variance === Variance.Bivariant && isTypeAssignableTo(createMarkerType(cache, tp, markerOtherType), typeWithSuper)) {
                         variance = Variance.Independent;
                     }
+                    unmeasurableMarkerHandler = oldHandler;
+                    if (unmeasurable) {
+                        variance = Variance.Unmeasurable;
+                        const covariantID = getRelationKey(typeWithSub, typeWithSuper, assignableRelation);
+                        const contravariantID = getRelationKey(typeWithSuper, typeWithSub, assignableRelation);
+                        // We delete the results of these checks, as we want them to actually be run, see the `Unmeasurable` variance we cache,
+                        // And then fall back to a structural result.
+                        assignableRelation.delete(covariantID);
+                        assignableRelation.delete(contravariantID);
+                    }
                     variances.push(variance);
                 }
                 cache.variances = variances;

src/compiler/types.ts

@@ -4133,6 +4133,7 @@ namespace ts {
         Contravariant = 2,  // Contravariant
         Bivariant     = 3,  // Both covariant and contravariant
         Independent   = 4,  // Unwitnessed type parameter
+        Unmeasurable = 5,  // Variance result is unusable - relationship relies on structural comparisons which are not reflected in generic relationships
     }
 
     // Generic class and interface types

tests/baselines/reference/mappedTypes5.errors.txt

@@ -1,7 +1,6 @@
 tests/cases/conformance/types/mapped/mappedTypes5.ts(6,9): error TS2322: Type 'Partial<T>' is not assignable to type 'Readonly<T>'.
 tests/cases/conformance/types/mapped/mappedTypes5.ts(8,9): error TS2322: Type 'Partial<Readonly<T>>' is not assignable to type 'Readonly<T>'.
 tests/cases/conformance/types/mapped/mappedTypes5.ts(9,9): error TS2322: Type 'Readonly<Partial<T>>' is not assignable to type 'Readonly<T>'.
-  Type 'Partial<T>' is not assignable to type 'T'.
 
 
 ==== tests/cases/conformance/types/mapped/mappedTypes5.ts (3 errors) ====
@@ -20,7 +19,6 @@ tests/cases/conformance/types/mapped/mappedTypes5.ts(9,9): error TS2322: Type 'R
         let b4: Readonly<T> = rp;  // Error
             ~~
 !!! error TS2322: Type 'Readonly<Partial<T>>' is not assignable to type 'Readonly<T>'.
-!!! error TS2322:   Type 'Partial<T>' is not assignable to type 'T'.
         let c1: Partial<Readonly<T>> = p;
         let c2: Partial<Readonly<T>> = r;
         let c3: Partial<Readonly<T>> = pr;

tests/baselines/reference/requiredMappedTypeModifierTrumpsVariance.errors.txt

@@ -0,0 +1,61 @@
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(5,1): error TS2741: Property 'a' is missing in type 'Required<{ b?: 1; x: 1; }>' but required in type 'Required<{ a?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(6,1): error TS2741: Property 'b' is missing in type 'Required<{ a?: 1; x: 1; }>' but required in type 'Required<{ b?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(8,3): error TS2339: Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(9,3): error TS2339: Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(18,1): error TS2322: Type 'Foo<{ b?: 1; x: 1; }>' is not assignable to type 'Foo<{ a?: 1; x: 1; }>'.
+  Types of property 'a' are incompatible.
+    Property 'a' is missing in type 'Required<{ b?: 1; x: 1; }>' but required in type 'Required<{ a?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(19,1): error TS2322: Type 'Foo<{ a?: 1; x: 1; }>' is not assignable to type 'Foo<{ b?: 1; x: 1; }>'.
+  Types of property 'a' are incompatible.
+    Property 'b' is missing in type 'Required<{ a?: 1; x: 1; }>' but required in type 'Required<{ b?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(21,6): error TS2339: Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts(22,6): error TS2339: Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+
+
+==== tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts (8 errors) ====
+    const a: Required<{ a?: 1; x: 1 }> = { a: 1, x: 1 };
+    const b: Required<{ b?: 1; x: 1 }> = { b: 1, x: 1 };
+    export let A = a;
+    export let B = b;
+    A = b; // Should Error
+    ~
+!!! error TS2741: Property 'a' is missing in type 'Required<{ b?: 1; x: 1; }>' but required in type 'Required<{ a?: 1; x: 1; }>'.
+!!! related TS2728 tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts:1:21: 'a' is declared here.
+    B = a; // Should Error
+    ~
+!!! error TS2741: Property 'b' is missing in type 'Required<{ a?: 1; x: 1; }>' but required in type 'Required<{ b?: 1; x: 1; }>'.
+!!! related TS2728 tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts:2:21: 'b' is declared here.
+
+    a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+      ~
+!!! error TS2339: Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+    b.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+      ~
+!!! error TS2339: Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+
+    interface Foo<T> {
+        a: Required<T>;
+    }
+    const aa: Foo<{ a?: 1; x: 1 }> = { a: { a: 1, x: 1 } };
+    const bb: Foo<{ b?: 1; x: 1 }> = { a: { b: 1, x: 1 } };
+    export let AA = aa;
+    export let BB = bb;
+    AA = bb; // Should Error
+    ~~
+!!! error TS2322: Type 'Foo<{ b?: 1; x: 1; }>' is not assignable to type 'Foo<{ a?: 1; x: 1; }>'.
+!!! error TS2322:   Types of property 'a' are incompatible.
+!!! error TS2322:     Property 'a' is missing in type 'Required<{ b?: 1; x: 1; }>' but required in type 'Required<{ a?: 1; x: 1; }>'.
+!!! related TS2728 tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts:14:17: 'a' is declared here.
+    BB = aa; // Should Error
+    ~~
+!!! error TS2322: Type 'Foo<{ a?: 1; x: 1; }>' is not assignable to type 'Foo<{ b?: 1; x: 1; }>'.
+!!! error TS2322:   Types of property 'a' are incompatible.
+!!! error TS2322:     Property 'b' is missing in type 'Required<{ a?: 1; x: 1; }>' but required in type 'Required<{ b?: 1; x: 1; }>'.
+!!! related TS2728 tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts:15:17: 'b' is declared here.
+
+    aa.a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+         ~
+!!! error TS2339: Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+    bb.a.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+         ~
+!!! error TS2339: Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.

tests/baselines/reference/requiredMappedTypeModifierTrumpsVariance.js

@@ -0,0 +1,43 @@
+//// [requiredMappedTypeModifierTrumpsVariance.ts]
+const a: Required<{ a?: 1; x: 1 }> = { a: 1, x: 1 };
+const b: Required<{ b?: 1; x: 1 }> = { b: 1, x: 1 };
+export let A = a;
+export let B = b;
+A = b; // Should Error
+B = a; // Should Error
+
+a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+b.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+
+interface Foo<T> {
+    a: Required<T>;
+}
+const aa: Foo<{ a?: 1; x: 1 }> = { a: { a: 1, x: 1 } };
+const bb: Foo<{ b?: 1; x: 1 }> = { a: { b: 1, x: 1 } };
+export let AA = aa;
+export let BB = bb;
+AA = bb; // Should Error
+BB = aa; // Should Error
+
+aa.a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+bb.a.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+
+//// [requiredMappedTypeModifierTrumpsVariance.js]
+"use strict";
+exports.__esModule = true;
+var a = { a: 1, x: 1 };
+var b = { b: 1, x: 1 };
+exports.A = a;
+exports.B = b;
+exports.A = b; // Should Error
+exports.B = a; // Should Error
+a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+b.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+var aa = { a: { a: 1, x: 1 } };
+var bb = { a: { b: 1, x: 1 } };
+exports.AA = aa;
+exports.BB = bb;
+exports.AA = bb; // Should Error
+exports.BB = aa; // Should Error
+aa.a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+bb.a.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.

tests/baselines/reference/requiredMappedTypeModifierTrumpsVariance.symbols

@@ -0,0 +1,92 @@
+=== tests/cases/compiler/requiredMappedTypeModifierTrumpsVariance.ts ===
+const a: Required<{ a?: 1; x: 1 }> = { a: 1, x: 1 };
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 5))
+>Required : Symbol(Required, Decl(lib.es5.d.ts, --, --))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 19))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 26))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 38))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 44))
+
+const b: Required<{ b?: 1; x: 1 }> = { b: 1, x: 1 };
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 5))
+>Required : Symbol(Required, Decl(lib.es5.d.ts, --, --))
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 19))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 26))
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 38))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 44))
+
+export let A = a;
+>A : Symbol(A, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 2, 10))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 5))
+
+export let B = b;
+>B : Symbol(B, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 3, 10))
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 5))
+
+A = b; // Should Error
+>A : Symbol(A, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 2, 10))
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 5))
+
+B = a; // Should Error
+>B : Symbol(B, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 3, 10))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 5))
+
+a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 0, 5))
+
+b.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 1, 5))
+
+interface Foo<T> {
+>Foo : Symbol(Foo, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 8, 4))
+>T : Symbol(T, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 14))
+
+    a: Required<T>;
+>a : Symbol(Foo.a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 18))
+>Required : Symbol(Required, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 14))
+}
+const aa: Foo<{ a?: 1; x: 1 }> = { a: { a: 1, x: 1 } };
+>aa : Symbol(aa, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 5))
+>Foo : Symbol(Foo, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 8, 4))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 15))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 22))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 34))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 39))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 45))
+
+const bb: Foo<{ b?: 1; x: 1 }> = { a: { b: 1, x: 1 } };
+>bb : Symbol(bb, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 5))
+>Foo : Symbol(Foo, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 8, 4))
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 15))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 22))
+>a : Symbol(a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 34))
+>b : Symbol(b, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 39))
+>x : Symbol(x, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 45))
+
+export let AA = aa;
+>AA : Symbol(AA, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 15, 10))
+>aa : Symbol(aa, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 5))
+
+export let BB = bb;
+>BB : Symbol(BB, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 16, 10))
+>bb : Symbol(bb, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 5))
+
+AA = bb; // Should Error
+>AA : Symbol(AA, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 15, 10))
+>bb : Symbol(bb, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 5))
+
+BB = aa; // Should Error
+>BB : Symbol(BB, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 16, 10))
+>aa : Symbol(aa, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 5))
+
+aa.a.b; // Property 'b' does not exist on type 'Required<{ a?: 1; x: 1; }>'.
+>aa.a : Symbol(Foo.a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 18))
+>aa : Symbol(aa, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 13, 5))
+>a : Symbol(Foo.a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 18))
+
+bb.a.a; // Property 'a' does not exist on type 'Required<{ b?: 1; x: 1; }>'.
+>bb.a : Symbol(Foo.a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 18))
+>bb : Symbol(bb, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 14, 5))
+>a : Symbol(Foo.a, Decl(requiredMappedTypeModifierTrumpsVariance.ts, 10, 18))
+