Fixed a relationship check when apparent type of mapped type expands to a union

src/compiler/checker.ts

@@ -22447,7 +22447,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 }
                 const sourceIsPrimitive = !!(sourceFlags & TypeFlags.Primitive);
                 if (relation !== identityRelation) {
+                    const originalSource = source;
                     source = getApparentType(source);
+                    if (!(originalSource.flags & TypeFlags.Union) && source.flags & TypeFlags.Union && (result = unionOrIntersectionRelatedTo(source, target, reportErrors, intersectionState))) {
+                        return result;
+                    }
                     sourceFlags = source.flags;
                 }
                 else if (isGenericMappedType(source)) {

tests/baselines/reference/intersectionSatisfiesConstraint.types

@@ -29,9 +29,9 @@ const myFirstFunction = <T extends FirstInterface | SecondInterface>(param1: T)
 >3 : 3
 
     mySecondFunction(newParam)
->mySecondFunction(newParam) : { commonProperty: number; otherProperty: number; }
+>mySecondFunction(newParam) : T & { otherProperty: number; }
 >mySecondFunction : <T_1 extends { commonProperty: number; otherProperty: number; }>(newParam: T_1) => T_1
->newParam : (FirstInterface | SecondInterface) & { otherProperty: number; }
+>newParam : T & { otherProperty: number; }
 }
 
 const mySecondFunction = <T extends { commonProperty: number, otherProperty: number }>(newParam: T) => {

tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt

@@ -42,8 +42,10 @@ keyofAndIndexedAccessErrors.ts(103,9): error TS2322: Type 'Extract<keyof T, stri
   'Extract<keyof T, string>' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
     Type 'string & keyof T' is not assignable to type 'K'.
       'string & keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
-        Type 'string' is not assignable to type 'K'.
-          'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
+        Type 'String & string' is not assignable to type 'K'.
+          'String & string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
+            Type 'string' is not assignable to type 'K'.
+              'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
 keyofAndIndexedAccessErrors.ts(105,9): error TS2322: Type 'T[Extract<keyof T, string>]' is not assignable to type 'T[K]'.
   Type 'Extract<keyof T, string>' is not assignable to type 'K'.
     'Extract<keyof T, string>' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
@@ -249,8 +251,10 @@ keyofAndIndexedAccessErrors.ts(165,5): error TS2322: Type 'number' is not assign
 !!! error TS2322:   'Extract<keyof T, string>' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
 !!! error TS2322:     Type 'string & keyof T' is not assignable to type 'K'.
 !!! error TS2322:       'string & keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
-!!! error TS2322:         Type 'string' is not assignable to type 'K'.
-!!! error TS2322:           'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
+!!! error TS2322:         Type 'String & string' is not assignable to type 'K'.
+!!! error TS2322:           'String & string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
+!!! error TS2322:             Type 'string' is not assignable to type 'K'.
+!!! error TS2322:               'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string'.
             t[key] = tk; // ok, T[K] ==> T[keyof T]
             tk = t[key]; // error, T[keyof T] =/=> T[K]
             ~~

tests/baselines/reference/mappedTypeUnionArrayTupleConstraint.symbols

@@ -0,0 +1,44 @@
+//// [tests/cases/compiler/mappedTypeUnionArrayTupleConstraint.ts] ////
+
+=== mappedTypeUnionArrayTupleConstraint.ts ===
+// https://github.com/microsoft/TypeScript/issues/56018
+
+type Renamed = readonly ({ [k: PropertyKey]: string } | undefined)[];
+>Renamed : Symbol(Renamed, Decl(mappedTypeUnionArrayTupleConstraint.ts, 0, 0))
+>k : Symbol(k, Decl(mappedTypeUnionArrayTupleConstraint.ts, 2, 28))
+>PropertyKey : Symbol(PropertyKey, Decl(lib.es5.d.ts, --, --))
+
+type Foo<T extends readonly (PropertyKey | undefined)[] | Renamed> =
+>Foo : Symbol(Foo, Decl(mappedTypeUnionArrayTupleConstraint.ts, 2, 69))
+>T : Symbol(T, Decl(mappedTypeUnionArrayTupleConstraint.ts, 4, 9))
+>PropertyKey : Symbol(PropertyKey, Decl(lib.es5.d.ts, --, --))
+>Renamed : Symbol(Renamed, Decl(mappedTypeUnionArrayTupleConstraint.ts, 0, 0))
+
+  T extends Renamed ? GetKeys<Required<T>> : Required<T>;
+>T : Symbol(T, Decl(mappedTypeUnionArrayTupleConstraint.ts, 4, 9))
+>Renamed : Symbol(Renamed, Decl(mappedTypeUnionArrayTupleConstraint.ts, 0, 0))
+>GetKeys : Symbol(GetKeys, Decl(mappedTypeUnionArrayTupleConstraint.ts, 5, 57))
+>Required : Symbol(Required, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeUnionArrayTupleConstraint.ts, 4, 9))
+>Required : Symbol(Required, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeUnionArrayTupleConstraint.ts, 4, 9))
+
+type GetKeys<R extends Renamed> = { [K in keyof R]: keyof R[K] };
+>GetKeys : Symbol(GetKeys, Decl(mappedTypeUnionArrayTupleConstraint.ts, 5, 57))
+>R : Symbol(R, Decl(mappedTypeUnionArrayTupleConstraint.ts, 7, 13))
+>Renamed : Symbol(Renamed, Decl(mappedTypeUnionArrayTupleConstraint.ts, 0, 0))
+>K : Symbol(K, Decl(mappedTypeUnionArrayTupleConstraint.ts, 7, 37))
+>R : Symbol(R, Decl(mappedTypeUnionArrayTupleConstraint.ts, 7, 13))
+>R : Symbol(R, Decl(mappedTypeUnionArrayTupleConstraint.ts, 7, 13))
+>K : Symbol(K, Decl(mappedTypeUnionArrayTupleConstraint.ts, 7, 37))
+
+// usage
+type A = Foo<["a"?]>;
+>A : Symbol(A, Decl(mappedTypeUnionArrayTupleConstraint.ts, 7, 65))
+>Foo : Symbol(Foo, Decl(mappedTypeUnionArrayTupleConstraint.ts, 2, 69))
+
+type B = Foo<[{ a?: "b" }]>;
+>B : Symbol(B, Decl(mappedTypeUnionArrayTupleConstraint.ts, 10, 21))
+>Foo : Symbol(Foo, Decl(mappedTypeUnionArrayTupleConstraint.ts, 2, 69))
+>a : Symbol(a, Decl(mappedTypeUnionArrayTupleConstraint.ts, 11, 15))
+

tests/baselines/reference/mappedTypeUnionArrayTupleConstraint.types

@@ -0,0 +1,25 @@
+//// [tests/cases/compiler/mappedTypeUnionArrayTupleConstraint.ts] ////
+
+=== mappedTypeUnionArrayTupleConstraint.ts ===
+// https://github.com/microsoft/TypeScript/issues/56018
+
+type Renamed = readonly ({ [k: PropertyKey]: string } | undefined)[];
+>Renamed : readonly ({ [k: string]: string; [k: number]: string; [k: symbol]: string; } | undefined)[]
+>k : PropertyKey
+
+type Foo<T extends readonly (PropertyKey | undefined)[] | Renamed> =
+>Foo : Foo<T>
+
+  T extends Renamed ? GetKeys<Required<T>> : Required<T>;
+
+type GetKeys<R extends Renamed> = { [K in keyof R]: keyof R[K] };
+>GetKeys : GetKeys<R>
+
+// usage
+type A = Foo<["a"?]>;
+>A : ["a"]
+
+type B = Foo<[{ a?: "b" }]>;
+>B : ["a"]
+>a : "b" | undefined
+

tests/baselines/reference/mappedTypeUnionConstrainTupleTreatedAsArrayLike.errors.txt

@@ -1,4 +1,5 @@
 mappedTypeUnionConstrainTupleTreatedAsArrayLike.ts(9,9): error TS2322: Type 'HomomorphicMappedType<T>' is not assignable to type 'any[]'.
+  The type 'readonly [boolean]' is 'readonly' and cannot be assigned to the mutable type 'any[]'.
 
 
 ==== mappedTypeUnionConstrainTupleTreatedAsArrayLike.ts (1 errors) ====
@@ -13,6 +14,7 @@ mappedTypeUnionConstrainTupleTreatedAsArrayLike.ts(9,9): error TS2322: Type 'Hom
       const arr: any[] = [] as HomomorphicMappedType<T> // error
             ~~~
 !!! error TS2322: Type 'HomomorphicMappedType<T>' is not assignable to type 'any[]'.
+!!! error TS2322:   The type 'readonly [boolean]' is 'readonly' and cannot be assigned to the mutable type 'any[]'.
       const arr2: readonly any[] = [] as HomomorphicMappedType<T>
     }
 

tests/cases/compiler/mappedTypeUnionArrayTupleConstraint.ts

@@ -0,0 +1,15 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/56018
+
+type Renamed = readonly ({ [k: PropertyKey]: string } | undefined)[];
+
+type Foo<T extends readonly (PropertyKey | undefined)[] | Renamed> =
+  T extends Renamed ? GetKeys<Required<T>> : Required<T>;
+
+type GetKeys<R extends Renamed> = { [K in keyof R]: keyof R[K] };
+
+// usage
+type A = Foo<["a"?]>;
+type B = Foo<[{ a?: "b" }]>;