Unwrap substitution types early in getPropertyTypeForIndexType

src/compiler/checker.ts

@@ -18538,6 +18538,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function getPropertyTypeForIndexType(originalObjectType: Type, objectType: Type, indexType: Type, fullIndexType: Type, accessNode: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression | undefined, accessFlags: AccessFlags) {
+        if (indexType.flags & TypeFlags.Substitution) {
+            indexType = (indexType as SubstitutionType).baseType;
+        }
         const accessExpression = accessNode && accessNode.kind === SyntaxKind.ElementAccessExpression ? accessNode : undefined;
         const propName = accessNode && isPrivateIdentifier(accessNode) ? undefined : getPropertyNameFromIndex(indexType, accessNode);
 

tests/baselines/reference/nonGenericIndexedAccessInConditionalTrueBranch1.symbols

@@ -0,0 +1,39 @@
+//// [tests/cases/compiler/nonGenericIndexedAccessInConditionalTrueBranch1.ts] ////
+
+=== nonGenericIndexedAccessInConditionalTrueBranch1.ts ===
+// https://github.com/microsoft/TypeScript/issues/57109
+
+type A = {
+>A : Symbol(A, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 0, 0))
+
+  k: symbol;
+>k : Symbol(k, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 2, 10))
+
+};
+
+type B = "k" extends keyof A ? A["k"] : never;
+>B : Symbol(B, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 4, 2))
+>A : Symbol(A, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 0, 0))
+>A : Symbol(A, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 0, 0))
+
+type C = {
+>C : Symbol(C, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 6, 46))
+
+  k: symbol;
+>k : Symbol(k, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 8, 10))
+
+  other: boolean;
+>other : Symbol(other, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 9, 12))
+
+};
+
+type D = "k" extends keyof C ? C["k"] : never;
+>D : Symbol(D, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 11, 2))
+>C : Symbol(C, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 6, 46))
+>C : Symbol(C, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 6, 46))
+
+type E = "k" extends keyof C ? C["k" | "other"] : never;
+>E : Symbol(E, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 13, 46))
+>C : Symbol(C, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 6, 46))
+>C : Symbol(C, Decl(nonGenericIndexedAccessInConditionalTrueBranch1.ts, 6, 46))
+

tests/baselines/reference/nonGenericIndexedAccessInConditionalTrueBranch1.types

@@ -0,0 +1,41 @@
+//// [tests/cases/compiler/nonGenericIndexedAccessInConditionalTrueBranch1.ts] ////
+
+=== nonGenericIndexedAccessInConditionalTrueBranch1.ts ===
+// https://github.com/microsoft/TypeScript/issues/57109
+
+type A = {
+>A : A
+>  : ^
+
+  k: symbol;
+>k : symbol
+>  : ^^^^^^
+
+};
+
+type B = "k" extends keyof A ? A["k"] : never;
+>B : symbol
+>  : ^^^^^^
+
+type C = {
+>C : C
+>  : ^
+
+  k: symbol;
+>k : symbol
+>  : ^^^^^^
+
+  other: boolean;
+>other : boolean
+>      : ^^^^^^^
+
+};
+
+type D = "k" extends keyof C ? C["k"] : never;
+>D : symbol
+>  : ^^^^^^
+
+type E = "k" extends keyof C ? C["k" | "other"] : never;
+>E : boolean | symbol
+>  : ^^^^^^^^^^^^^^^^
+

tests/baselines/reference/substitutionTypeUsedAsIndex.symbols

@@ -0,0 +1,23 @@
+//// [tests/cases/compiler/substitutionTypeUsedAsIndex.ts] ////
+
+=== substitutionTypeUsedAsIndex.ts ===
+// repro from https://github.com/microsoft/TypeScript/issues/54886
+
+interface Dict_54886 {
+>Dict_54886 : Symbol(Dict_54886, Decl(substitutionTypeUsedAsIndex.ts, 0, 0))
+
+  foo: 1;
+>foo : Symbol(Dict_54886.foo, Decl(substitutionTypeUsedAsIndex.ts, 2, 22))
+
+  bar: 1;
+>bar : Symbol(Dict_54886.bar, Decl(substitutionTypeUsedAsIndex.ts, 3, 9))
+}
+
+type FF_54886 = "foo" extends "foo" | "bar" ? "foo" : never;
+>FF_54886 : Symbol(FF_54886, Decl(substitutionTypeUsedAsIndex.ts, 5, 1))
+
+type C_54886 = Dict_54886[FF_54886]; // ok
+>C_54886 : Symbol(C_54886, Decl(substitutionTypeUsedAsIndex.ts, 7, 60))
+>Dict_54886 : Symbol(Dict_54886, Decl(substitutionTypeUsedAsIndex.ts, 0, 0))
+>FF_54886 : Symbol(FF_54886, Decl(substitutionTypeUsedAsIndex.ts, 5, 1))
+

tests/baselines/reference/substitutionTypeUsedAsIndex.types

@@ -0,0 +1,23 @@
+//// [tests/cases/compiler/substitutionTypeUsedAsIndex.ts] ////
+
+=== substitutionTypeUsedAsIndex.ts ===
+// repro from https://github.com/microsoft/TypeScript/issues/54886
+
+interface Dict_54886 {
+  foo: 1;
+>foo : 1
+>    : ^
+
+  bar: 1;
+>bar : 1
+>    : ^
+}
+
+type FF_54886 = "foo" extends "foo" | "bar" ? "foo" : never;
+>FF_54886 : "foo"
+>         : ^^^^^
+
+type C_54886 = Dict_54886[FF_54886]; // ok
+>C_54886 : 1
+>        : ^
+

tests/cases/compiler/nonGenericIndexedAccessInConditionalTrueBranch1.ts

@@ -0,0 +1,18 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/57109
+
+type A = {
+  k: symbol;
+};
+
+type B = "k" extends keyof A ? A["k"] : never;
+
+type C = {
+  k: symbol;
+  other: boolean;
+};
+
+type D = "k" extends keyof C ? C["k"] : never;
+type E = "k" extends keyof C ? C["k" | "other"] : never;

tests/cases/compiler/substitutionTypeUsedAsIndex.ts

@@ -0,0 +1,12 @@
+// @strict: true
+// @noEmit: true
+
+// repro from https://github.com/microsoft/TypeScript/issues/54886
+
+interface Dict_54886 {
+  foo: 1;
+  bar: 1;
+}
+
+type FF_54886 = "foo" extends "foo" | "bar" ? "foo" : never;
+type C_54886 = Dict_54886[FF_54886]; // ok