Add unmeasurable variance kind for marking types whose variance resul…

…t is unreliable (#30416)

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

* Remove now-unneeded nongeneric checks

* Add rule allowing `Readonly<any>` to be `any` instead of `{readonly [index: string]: any}`

* All Unmeasurable variances to still shortcut structural comparisons in some cases

* Separate unmeasurable from unreliable to reduce the impact of this change, for now

* Fix lint

* Remove Readonly<any> -> any callout

* Add fix for circularity error triggered by deep signature return type comparisons with `this` types

src/compiler/types.ts

@@ -3735,7 +3735,7 @@ namespace ts {
         specifierCache?: Map<string>;     // For symbols corresponding to external modules, a cache of incoming path -> module specifier name mappings
         extendedContainers?: Symbol[];      // Containers (other than the parent) which this symbol is aliased in
         extendedContainersByFile?: Map<Symbol[]>;      // Containers (other than the parent) which this symbol is aliased in
-        variances?: Variance[];             // Alias symbol type argument variance cache
+        variances?: VarianceFlags[];             // Alias symbol type argument variance cache
     }
 
     /* @internal */
@@ -4131,20 +4131,24 @@ namespace ts {
     }
 
     /* @internal */
-    export const enum Variance {
-        Invariant     = 0,  // Neither covariant nor contravariant
-        Covariant     = 1,  // Covariant
-        Contravariant = 2,  // Contravariant
-        Bivariant     = 3,  // Both covariant and contravariant
-        Independent   = 4,  // Unwitnessed type parameter
+    export const enum VarianceFlags {
+        Invariant     =      0,  // Neither covariant nor contravariant
+        Covariant     = 1 << 0,  // Covariant
+        Contravariant = 1 << 1,  // Contravariant
+        Bivariant     = Covariant | Contravariant,  // Both covariant and contravariant
+        Independent   = 1 << 2,  // Unwitnessed type parameter
+        VarianceMask  = Invariant | Covariant | Contravariant | Independent, // Mask containing all measured variances without the unmeasurable flag
+        Unmeasurable  = 1 << 3,  // Variance result is unusable - relationship relies on structural comparisons which are not reflected in generic relationships
+        Unreliable    = 1 << 4,  // Variance result is unreliable - relationship relies on structural comparisons which are not reflected in generic relationships
+        AllowsStructuralFallback = Unmeasurable | Unreliable,
     }
 
     // Generic class and interface types
     export interface GenericType extends InterfaceType, TypeReference {
         /* @internal */
         instantiations: Map<TypeReference>;  // Generic instantiation cache
         /* @internal */
-        variances?: Variance[];  // Variance of each type parameter
+        variances?: VarianceFlags[];  // Variance of each type parameter
     }
 
     export interface TupleType extends GenericType {

tests/baselines/reference/checkInfiniteExpansionTermination.errors.txt

@@ -0,0 +1,32 @@
+tests/cases/compiler/checkInfiniteExpansionTermination.ts(16,1): error TS2322: Type 'ISubject<Bar>' is not assignable to type 'IObservable<Foo>'.
+  Types of property 'n' are incompatible.
+    Type 'IObservable<Bar[]>' is not assignable to type 'IObservable<Foo[]>'.
+      Type 'Bar[]' is not assignable to type 'Foo[]'.
+        Property 'x' is missing in type 'Bar' but required in type 'Foo'.
+
+
+==== tests/cases/compiler/checkInfiniteExpansionTermination.ts (1 errors) ====
+    // Regression test for #1002
+    // Before fix this code would cause infinite loop
+
+    interface IObservable<T> {
+        n: IObservable<T[]>; // Needed, must be T[]
+    }
+
+    // Needed
+    interface ISubject<T> extends IObservable<T> { }
+
+    interface Foo { x }
+    interface Bar { y }
+
+    var values: IObservable<Foo>;
+    var values2: ISubject<Bar>;
+    values = values2;
+    ~~~~~~
+!!! error TS2322: Type 'ISubject<Bar>' is not assignable to type 'IObservable<Foo>'.
+!!! error TS2322:   Types of property 'n' are incompatible.
+!!! error TS2322:     Type 'IObservable<Bar[]>' is not assignable to type 'IObservable<Foo[]>'.
+!!! error TS2322:       Type 'Bar[]' is not assignable to type 'Foo[]'.
+!!! error TS2322:         Property 'x' is missing in type 'Bar' but required in type 'Foo'.
+!!! related TS2728 tests/cases/compiler/checkInfiniteExpansionTermination.ts:11:17: 'x' is declared here.
+

tests/baselines/reference/conditionalTypes1.errors.txt

@@ -19,12 +19,8 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(104,5): error TS2
   'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(106,5): error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>'.
   Type 'T[keyof T] extends Function ? keyof T : never' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
-    Type 'keyof T' is not assignable to type 'never'.
-      Type 'string | number | symbol' is not assignable to type 'never'.
-        Type 'string' is not assignable to type 'never'.
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(108,5): error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>'.
   Type 'T[keyof T] extends Function ? never : keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
-    Type 'keyof T' is not assignable to type 'never'.
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(114,5): error TS2322: Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
   Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
     Type 'string' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
@@ -195,15 +191,11 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(288,43): error TS
         ~
 !!! error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>'.
 !!! error TS2322:   Type 'T[keyof T] extends Function ? keyof T : never' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
-!!! error TS2322:     Type 'keyof T' is not assignable to type 'never'.
-!!! error TS2322:       Type 'string | number | symbol' is not assignable to type 'never'.
-!!! error TS2322:         Type 'string' is not assignable to type 'never'.
         z = x;
         z = y;  // Error
         ~
 !!! error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>'.
 !!! error TS2322:   Type 'T[keyof T] extends Function ? never : keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
-!!! error TS2322:     Type 'keyof T' is not assignable to type 'never'.
     }
 
     function f8<T>(x: keyof T, y: FunctionPropertyNames<T>, z: NonFunctionPropertyNames<T>) {

tests/baselines/reference/consistentAliasVsNonAliasRecordBehavior.errors.txt

@@ -0,0 +1,55 @@
+tests/cases/compiler/consistentAliasVsNonAliasRecordBehavior.ts(18,5): error TS2741: Property 'a' is missing in type 'Record<string, string>' but required in type 'Record2<"a", string>'.
+tests/cases/compiler/consistentAliasVsNonAliasRecordBehavior.ts(22,5): error TS2741: Property 'a' is missing in type 'Record2<string, string>' but required in type 'Record<"a", string>'.
+tests/cases/compiler/consistentAliasVsNonAliasRecordBehavior.ts(34,5): error TS2741: Property 'a' is missing in type 'Record<string, T>' but required in type 'Record2<"a", T>'.
+tests/cases/compiler/consistentAliasVsNonAliasRecordBehavior.ts(38,5): error TS2741: Property 'a' is missing in type 'Record2<string, T>' but required in type 'Record<"a", T>'.
+
+
+==== tests/cases/compiler/consistentAliasVsNonAliasRecordBehavior.ts (4 errors) ====
+    // TODO: FIXME: All the below cases labeled `no error` _should be an error_, and are only prevented from so being
+    // by incorrect variance-based relationships
+    // Ref: https://github.com/Microsoft/TypeScript/issues/29698
+
+    type Record2<K extends keyof any, T> = {
+        [P in K]: T;
+    };
+
+    function defaultRecord(x: Record<'a', string>, y: Record<string, string>) {
+        x = y; // no error, but error expected.
+    }
+
+    function customRecord(x: Record2<'a', string>, y: Record2<string, string>) {
+        x = y; // no error, but error expected.
+    }
+
+    function mixed1(x: Record2<'a', string>, y: Record<string, string>) {
+        x = y; // error
+        ~
+!!! error TS2741: Property 'a' is missing in type 'Record<string, string>' but required in type 'Record2<"a", string>'.
+    }
+
+    function mixed2(x: Record<'a', string>, y: Record2<string, string>) {
+        x = y; // error
+        ~
+!!! error TS2741: Property 'a' is missing in type 'Record2<string, string>' but required in type 'Record<"a", string>'.
+    }
+
+    function defaultRecord2<T>(x: Record<'a', T>, y: Record<string, T>) {
+        x = y; // no error, but error expected.
+    }
+
+    function customRecord2<T>(x: Record2<'a', T>, y: Record2<string, T>) {
+        x = y; // no error, but error expected.
+    }
+
+    function mixed3<T>(x: Record2<'a', T>, y: Record<string, T>) {
+        x = y; // error
+        ~
+!!! error TS2741: Property 'a' is missing in type 'Record<string, T>' but required in type 'Record2<"a", T>'.
+    }
+
+    function mixed4<T>(x: Record<'a', T>, y: Record2<string, T>) {
+        x = y; // error
+        ~
+!!! error TS2741: Property 'a' is missing in type 'Record2<string, T>' but required in type 'Record<"a", T>'.
+    }
+

tests/baselines/reference/consistentAliasVsNonAliasRecordBehavior.js

@@ -0,0 +1,70 @@
+//// [consistentAliasVsNonAliasRecordBehavior.ts]
+// TODO: FIXME: All the below cases labeled `no error` _should be an error_, and are only prevented from so being
+// by incorrect variance-based relationships
+// Ref: https://github.com/Microsoft/TypeScript/issues/29698
+
+type Record2<K extends keyof any, T> = {
+    [P in K]: T;
+};
+
+function defaultRecord(x: Record<'a', string>, y: Record<string, string>) {
+    x = y; // no error, but error expected.
+}
+
+function customRecord(x: Record2<'a', string>, y: Record2<string, string>) {
+    x = y; // no error, but error expected.
+}
+
+function mixed1(x: Record2<'a', string>, y: Record<string, string>) {
+    x = y; // error
+}
+
+function mixed2(x: Record<'a', string>, y: Record2<string, string>) {
+    x = y; // error
+}
+
+function defaultRecord2<T>(x: Record<'a', T>, y: Record<string, T>) {
+    x = y; // no error, but error expected.
+}
+
+function customRecord2<T>(x: Record2<'a', T>, y: Record2<string, T>) {
+    x = y; // no error, but error expected.
+}
+
+function mixed3<T>(x: Record2<'a', T>, y: Record<string, T>) {
+    x = y; // error
+}
+
+function mixed4<T>(x: Record<'a', T>, y: Record2<string, T>) {
+    x = y; // error
+}
+
+
+//// [consistentAliasVsNonAliasRecordBehavior.js]
+// TODO: FIXME: All the below cases labeled `no error` _should be an error_, and are only prevented from so being
+// by incorrect variance-based relationships
+// Ref: https://github.com/Microsoft/TypeScript/issues/29698
+function defaultRecord(x, y) {
+    x = y; // no error, but error expected.
+}
+function customRecord(x, y) {
+    x = y; // no error, but error expected.
+}
+function mixed1(x, y) {
+    x = y; // error
+}
+function mixed2(x, y) {
+    x = y; // error
+}
+function defaultRecord2(x, y) {
+    x = y; // no error, but error expected.
+}
+function customRecord2(x, y) {
+    x = y; // no error, but error expected.
+}
+function mixed3(x, y) {
+    x = y; // error
+}
+function mixed4(x, y) {
+    x = y; // error
+}

tests/baselines/reference/consistentAliasVsNonAliasRecordBehavior.symbols

@@ -0,0 +1,125 @@
+=== tests/cases/compiler/consistentAliasVsNonAliasRecordBehavior.ts ===
+// TODO: FIXME: All the below cases labeled `no error` _should be an error_, and are only prevented from so being
+// by incorrect variance-based relationships
+// Ref: https://github.com/Microsoft/TypeScript/issues/29698
+
+type Record2<K extends keyof any, T> = {
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>K : Symbol(K, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 4, 13))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 4, 33))
+
+    [P in K]: T;
+>P : Symbol(P, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 5, 5))
+>K : Symbol(K, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 4, 13))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 4, 33))
+
+};
+
+function defaultRecord(x: Record<'a', string>, y: Record<string, string>) {
+>defaultRecord : Symbol(defaultRecord, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 6, 2))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 8, 23))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 8, 46))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+
+    x = y; // no error, but error expected.
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 8, 23))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 8, 46))
+}
+
+function customRecord(x: Record2<'a', string>, y: Record2<string, string>) {
+>customRecord : Symbol(customRecord, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 10, 1))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 12, 22))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 12, 46))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+
+    x = y; // no error, but error expected.
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 12, 22))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 12, 46))
+}
+
+function mixed1(x: Record2<'a', string>, y: Record<string, string>) {
+>mixed1 : Symbol(mixed1, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 14, 1))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 16, 16))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 16, 40))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+
+    x = y; // error
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 16, 16))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 16, 40))
+}
+
+function mixed2(x: Record<'a', string>, y: Record2<string, string>) {
+>mixed2 : Symbol(mixed2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 18, 1))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 20, 16))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 20, 39))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+
+    x = y; // error
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 20, 16))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 20, 39))
+}
+
+function defaultRecord2<T>(x: Record<'a', T>, y: Record<string, T>) {
+>defaultRecord2 : Symbol(defaultRecord2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 22, 1))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 24))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 27))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 24))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 45))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 24))
+
+    x = y; // no error, but error expected.
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 27))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 24, 45))
+}
+
+function customRecord2<T>(x: Record2<'a', T>, y: Record2<string, T>) {
+>customRecord2 : Symbol(customRecord2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 26, 1))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 23))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 26))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 23))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 45))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 23))
+
+    x = y; // no error, but error expected.
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 26))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 28, 45))
+}
+
+function mixed3<T>(x: Record2<'a', T>, y: Record<string, T>) {
+>mixed3 : Symbol(mixed3, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 30, 1))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 16))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 19))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 16))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 38))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 16))
+
+    x = y; // error
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 19))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 32, 38))
+}
+
+function mixed4<T>(x: Record<'a', T>, y: Record2<string, T>) {
+>mixed4 : Symbol(mixed4, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 34, 1))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 16))
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 19))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 16))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 37))
+>Record2 : Symbol(Record2, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 0, 0))
+>T : Symbol(T, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 16))
+
+    x = y; // error
+>x : Symbol(x, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 19))
+>y : Symbol(y, Decl(consistentAliasVsNonAliasRecordBehavior.ts, 36, 37))
+}
+