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Mark indexed access object type comparisons as unreliable (#52106)
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‎src/compiler/checker.ts

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@@ -21309,6 +21309,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
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// Relate components directly before falling back to constraint relationships
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// A type S[K] is related to a type T[J] if S is related to T and K is related to J.
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if (result = isRelatedTo((source as IndexedAccessType).objectType, (target as IndexedAccessType).objectType, RecursionFlags.Both, reportErrors)) {
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// This does _not_ generalize - specific instantiations of `S[K]` and `T[J]` may be related, even if the indexed accesses generally are not.
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// For example, `S = {x: string, a: string}`, `T = {x: string, b: string}`, `K = J = "x"`. `S` and `T` are unrelated, but the result of executing
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// `S["x"]` and `T["x"]` _are_. Given that, we have to flag the object type comparison here as "unreliable", since while the generic result can reliably
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// be used in the affirmative case, it failing is not an indicator that the structural result will not succeed.
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instantiateType((source as IndexedAccessType).objectType, reportUnreliableMapper);
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result &= isRelatedTo((source as IndexedAccessType).indexType, (target as IndexedAccessType).indexType, RecursionFlags.Both, reportErrors);
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}
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if (result) {

‎tests/baselines/reference/genericIndexedAccessVarianceComparisonResultCorrect.js

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//// [genericIndexedAccessVarianceComparisonResultCorrect.ts]
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class A {
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x: string = 'A';
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y: number = 0;
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}
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class B {
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x: string = 'B';
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z: boolean = true;
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}
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type T<X extends { x: any }> = Pick<X, 'x'>;
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type C = T<A>;
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type D = T<B>;
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type C_extends_D = C extends D ? true : false; // true
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type PickA_extends_PickB = Pick<A, 'x'> extends Pick<B, 'x'> ? true : false; // true
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type TA_extends_TB = T<A> extends T<B> ? true : false; // should be true
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declare let a: T<A>;
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declare let b: T<B>;
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declare let c: C;
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declare let d: D;
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b = a; // should be no error
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c = d;
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//// [genericIndexedAccessVarianceComparisonResultCorrect.js]
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var A = /** @class */ (function () {
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function A() {
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this.x = 'A';
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this.y = 0;
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}
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return A;
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}());
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var B = /** @class */ (function () {
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function B() {
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this.x = 'B';
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this.z = true;
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}
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return B;
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}());
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b = a; // should be no error
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c = d;

‎tests/baselines/reference/genericIndexedAccessVarianceComparisonResultCorrect.symbols

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=== tests/cases/compiler/genericIndexedAccessVarianceComparisonResultCorrect.ts ===
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class A {
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>A : Symbol(A, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 0, 0))
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x: string = 'A';
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>x : Symbol(A.x, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 0, 9))
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y: number = 0;
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>y : Symbol(A.y, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 1, 20))
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}
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class B {
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>B : Symbol(B, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 3, 1))
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x: string = 'B';
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>x : Symbol(B.x, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 5, 9))
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z: boolean = true;
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>z : Symbol(B.z, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 6, 20))
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}
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type T<X extends { x: any }> = Pick<X, 'x'>;
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>X : Symbol(X, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 10, 7))
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>x : Symbol(x, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 10, 18))
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>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
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>X : Symbol(X, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 10, 7))
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type C = T<A>;
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>C : Symbol(C, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 10, 44))
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>A : Symbol(A, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 0, 0))
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type D = T<B>;
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>D : Symbol(D, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 12, 14))
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>B : Symbol(B, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 3, 1))
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type C_extends_D = C extends D ? true : false; // true
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>C_extends_D : Symbol(C_extends_D, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 13, 14))
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>C : Symbol(C, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 10, 44))
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>D : Symbol(D, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 12, 14))
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type PickA_extends_PickB = Pick<A, 'x'> extends Pick<B, 'x'> ? true : false; // true
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>PickA_extends_PickB : Symbol(PickA_extends_PickB, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 15, 46))
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>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
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>A : Symbol(A, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 0, 0))
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>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
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>B : Symbol(B, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 3, 1))
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type TA_extends_TB = T<A> extends T<B> ? true : false; // should be true
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>TA_extends_TB : Symbol(TA_extends_TB, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 16, 76))
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>A : Symbol(A, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 0, 0))
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>B : Symbol(B, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 3, 1))
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declare let a: T<A>;
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>a : Symbol(a, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 19, 11))
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>A : Symbol(A, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 0, 0))
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declare let b: T<B>;
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>b : Symbol(b, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 20, 11))
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>T : Symbol(T, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 8, 1))
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>B : Symbol(B, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 3, 1))
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declare let c: C;
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>c : Symbol(c, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 21, 11))
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>C : Symbol(C, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 10, 44))
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declare let d: D;
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>d : Symbol(d, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 22, 11))
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>D : Symbol(D, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 12, 14))
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b = a; // should be no error
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>b : Symbol(b, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 20, 11))
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>a : Symbol(a, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 19, 11))
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c = d;
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>c : Symbol(c, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 21, 11))
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>d : Symbol(d, Decl(genericIndexedAccessVarianceComparisonResultCorrect.ts, 22, 11))
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‎tests/baselines/reference/genericIndexedAccessVarianceComparisonResultCorrect.types

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=== tests/cases/compiler/genericIndexedAccessVarianceComparisonResultCorrect.ts ===
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class A {
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>A : A
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x: string = 'A';
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>x : string
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>'A' : "A"
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y: number = 0;
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>y : number
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>0 : 0
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}
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class B {
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>B : B
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x: string = 'B';
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>x : string
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>'B' : "B"
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z: boolean = true;
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>z : boolean
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>true : true
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}
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type T<X extends { x: any }> = Pick<X, 'x'>;
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>T : T<X>
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>x : any
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type C = T<A>;
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>C : { x: string; }
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type D = T<B>;
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>D : { x: string; }
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type C_extends_D = C extends D ? true : false; // true
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>C_extends_D : true
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>true : true
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>false : false
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type PickA_extends_PickB = Pick<A, 'x'> extends Pick<B, 'x'> ? true : false; // true
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>PickA_extends_PickB : true
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>true : true
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>false : false
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type TA_extends_TB = T<A> extends T<B> ? true : false; // should be true
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>TA_extends_TB : true
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>true : true
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>false : false
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declare let a: T<A>;
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>a : T<A>
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declare let b: T<B>;
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>b : T<B>
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declare let c: C;
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>c : C
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declare let d: D;
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>d : D
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b = a; // should be no error
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>b = a : T<A>
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>b : T<B>
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>a : T<A>
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c = d;
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>c = d : D
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>c : C
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>d : D
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‎tests/cases/compiler/genericIndexedAccessVarianceComparisonResultCorrect.ts

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class A {
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x: string = 'A';
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y: number = 0;
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}
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class B {
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x: string = 'B';
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z: boolean = true;
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}
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type T<X extends { x: any }> = Pick<X, 'x'>;
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type C = T<A>;
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type D = T<B>;
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type C_extends_D = C extends D ? true : false; // true
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type PickA_extends_PickB = Pick<A, 'x'> extends Pick<B, 'x'> ? true : false; // true
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type TA_extends_TB = T<A> extends T<B> ? true : false; // should be true
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declare let a: T<A>;
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declare let b: T<B>;
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declare let c: C;
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declare let d: D;
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b = a; // should be no error
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c = d;

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