Defer index types on remapping mapped types

src/compiler/checker.ts

@@ -1304,6 +1304,12 @@ const enum MappedTypeModifiers {
     ExcludeOptional = 1 << 3,
 }
 
+const enum MappedTypeNameTypeKind {
+    None,
+    Filtering,
+    Remapping,
+}
+
 const enum ExpandingFlags {
     None = 0,
     Source = 1,
@@ -13731,7 +13737,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const constraintType = getConstraintTypeFromMappedType(type);
         const mappedType = (type.target as MappedType) || type;
         const nameType = getNameTypeFromMappedType(mappedType);
-        const shouldLinkPropDeclarations = !nameType || isFilteringMappedType(mappedType);
+        const shouldLinkPropDeclarations = getMappedTypeNameTypeKind(mappedType) !== MappedTypeNameTypeKind.Remapping;
         const templateType = getTemplateTypeFromMappedType(mappedType);
         const modifiersType = getApparentType(getModifiersTypeFromMappedType(type)); // The 'T' in 'keyof T'
         const templateModifiers = getMappedTypeModifiers(type);
@@ -13913,9 +13919,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return false;
     }
 
-    function isFilteringMappedType(type: MappedType): boolean {
+    function getMappedTypeNameTypeKind(type: MappedType): MappedTypeNameTypeKind {
         const nameType = getNameTypeFromMappedType(type);
-        return !!nameType && isTypeAssignableTo(nameType, getTypeParameterFromMappedType(type));
+        if (!nameType) {
+            return MappedTypeNameTypeKind.None;
+        }
+        return isTypeAssignableTo(nameType, getTypeParameterFromMappedType(type)) ? MappedTypeNameTypeKind.Filtering : MappedTypeNameTypeKind.Remapping;
     }
 
     function resolveStructuredTypeMembers(type: StructuredType): ResolvedType {
@@ -17612,7 +17621,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     function shouldDeferIndexType(type: Type, indexFlags = IndexFlags.None) {
         return !!(type.flags & TypeFlags.InstantiableNonPrimitive ||
             isGenericTupleType(type) ||
-            isGenericMappedType(type) && !hasDistributiveNameType(type) ||
+            isGenericMappedType(type) && (!hasDistributiveNameType(type) || getMappedTypeNameTypeKind(type) === MappedTypeNameTypeKind.Remapping) ||
             type.flags & TypeFlags.Union && !(indexFlags & IndexFlags.NoReducibleCheck) && isGenericReducibleType(type) ||
             type.flags & TypeFlags.Intersection && maybeTypeOfKind(type, TypeFlags.Instantiable) && some((type as IntersectionType).types, isEmptyAnonymousObjectType));
     }
@@ -18194,7 +18203,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // K is generic and N is assignable to P, instantiate E using a mapper that substitutes the index type for P.
         // For example, for an index access { [P in K]: Box<T[P]> }[X], we construct the type Box<T[X]>.
         if (isGenericMappedType(objectType)) {
-            if (!getNameTypeFromMappedType(objectType) || isFilteringMappedType(objectType)) {
+            if (getMappedTypeNameTypeKind(objectType) !== MappedTypeNameTypeKind.Remapping) {
                 return type[cache] = mapType(substituteIndexedMappedType(objectType, type.indexType), t => getSimplifiedType(t, writing));
             }
         }
@@ -40020,7 +40029,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // Check if the index type is assignable to 'keyof T' for the object type.
         const objectType = (type as IndexedAccessType).objectType;
         const indexType = (type as IndexedAccessType).indexType;
-        if (isTypeAssignableTo(indexType, getIndexType(objectType, IndexFlags.None))) {
+        // skip index type deferral on remapping mapped types
+        const objectIndexType = isGenericMappedType(objectType) && getMappedTypeNameTypeKind(objectType) === MappedTypeNameTypeKind.Remapping
+            ? getIndexTypeForMappedType(objectType, IndexFlags.None)
+            : getIndexType(objectType, IndexFlags.None);
+        if (isTypeAssignableTo(indexType, objectIndexType)) {
             if (
                 accessNode.kind === SyntaxKind.ElementAccessExpression && isAssignmentTarget(accessNode) &&
                 getObjectFlags(objectType) & ObjectFlags.Mapped && getMappedTypeModifiers(objectType as MappedType) & MappedTypeModifiers.IncludeReadonly

tests/baselines/reference/mappedTypeAsClauses.errors.txt

@@ -1,4 +1,4 @@
-mappedTypeAsClauses.ts(130,3): error TS2345: Argument of type '"a"' is not assignable to parameter of type '"b"'.
+mappedTypeAsClauses.ts(131,3): error TS2345: Argument of type '"a"' is not assignable to parameter of type '"b"'.
 
 
 ==== mappedTypeAsClauses.ts (1 errors) ====
@@ -30,7 +30,8 @@ mappedTypeAsClauses.ts(130,3): error TS2345: Argument of type '"a"' is not assig
     type DoubleProp<T> = { [P in keyof T & string as `${P}1` | `${P}2`]: T[P] }
     type TD1 = DoubleProp<{ a: string, b: number }>;  // { a1: string, a2: string, b1: number, b2: number }
     type TD2 = keyof TD1;  // 'a1' | 'a2' | 'b1' | 'b2'
-    type TD3<U> = keyof DoubleProp<U>;  // `${keyof U & string}1` | `${keyof U & string}2`
+    type TD3<U> = keyof DoubleProp<U>; // keyof DoubleProp<U>
+    type TD4 = TD3<{ a: string, b: number }>;  // 'a1' | 'a2' | 'b1' | 'b2'
 
     // Repro from #40619
 
@@ -155,4 +156,27 @@ mappedTypeAsClauses.ts(130,3): error TS2345: Argument of type '"a"' is not assig
     type TN3<T> = keyof { [P in keyof T as Exclude<Exclude<Exclude<P, 'c'>, 'b'>, 'a'>]: string };
     type TN4<T, U> = keyof { [K in keyof T as (K extends U ? T[K] : never) extends T[K] ? K : never]: string };
     type TN5<T, U> = keyof { [K in keyof T as keyof { [P in K as T[P] extends U ? K : never]: true }]: string };
+
+    // repro from https://github.com/microsoft/TypeScript/issues/55129
+    type Fruit =
+      | {
+          name: "apple";
+          color: "red";
+        }
+      | {
+          name: "banana";
+          color: "yellow";
+        }
+      | {
+          name: "orange";
+          color: "orange";
+        };
+    type Result1<T extends {name: string | number; color: string | number }> = {
+      [Key in T as `${Key['name']}:${Key['color']}`]: unknown
+    }; 
+    type Result2<T extends {name: string | number; color: string | number }> = keyof {
+      [Key in T as `${Key['name']}:${Key['color']}`]: unknown
+    }
+    type Test1 = keyof Result1<Fruit> // "apple:red" | "banana:yellow" | "orange:orange"
+    type Test2 = Result2<Fruit> // "apple:red" | "banana:yellow" | "orange:orange"
 

tests/baselines/reference/mappedTypeAsClauses.js

@@ -29,7 +29,8 @@ type TM1 = Methods<{ foo(): number, bar(x: string): boolean, baz: string | numbe
 type DoubleProp<T> = { [P in keyof T & string as `${P}1` | `${P}2`]: T[P] }
 type TD1 = DoubleProp<{ a: string, b: number }>;  // { a1: string, a2: string, b1: number, b2: number }
 type TD2 = keyof TD1;  // 'a1' | 'a2' | 'b1' | 'b2'
-type TD3<U> = keyof DoubleProp<U>;  // `${keyof U & string}1` | `${keyof U & string}2`
+type TD3<U> = keyof DoubleProp<U>; // keyof DoubleProp<U>
+type TD4 = TD3<{ a: string, b: number }>;  // 'a1' | 'a2' | 'b1' | 'b2'
 
 // Repro from #40619
 
@@ -152,6 +153,29 @@ type TN2<T> = keyof { [P in keyof T as 'a' extends P ? 'x' : 'y']: string };
 type TN3<T> = keyof { [P in keyof T as Exclude<Exclude<Exclude<P, 'c'>, 'b'>, 'a'>]: string };
 type TN4<T, U> = keyof { [K in keyof T as (K extends U ? T[K] : never) extends T[K] ? K : never]: string };
 type TN5<T, U> = keyof { [K in keyof T as keyof { [P in K as T[P] extends U ? K : never]: true }]: string };
+
+// repro from https://github.com/microsoft/TypeScript/issues/55129
+type Fruit =
+  | {
+      name: "apple";
+      color: "red";
+    }
+  | {
+      name: "banana";
+      color: "yellow";
+    }
+  | {
+      name: "orange";
+      color: "orange";
+    };
+type Result1<T extends {name: string | number; color: string | number }> = {
+  [Key in T as `${Key['name']}:${Key['color']}`]: unknown
+}; 
+type Result2<T extends {name: string | number; color: string | number }> = keyof {
+  [Key in T as `${Key['name']}:${Key['color']}`]: unknown
+}
+type Test1 = keyof Result1<Fruit> // "apple:red" | "banana:yellow" | "orange:orange"
+type Test2 = Result2<Fruit> // "apple:red" | "banana:yellow" | "orange:orange"
 
 
 //// [mappedTypeAsClauses.js]
@@ -217,6 +241,10 @@ type TD1 = DoubleProp<{
 }>;
 type TD2 = keyof TD1;
 type TD3<U> = keyof DoubleProp<U>;
+type TD4 = TD3<{
+    a: string;
+    b: number;
+}>;
 type Lazyify<T> = {
     [K in keyof T as `get${Capitalize<K & string>}`]: () => T[K];
 };
@@ -337,3 +365,27 @@ type TN5<T, U> = keyof {
         [P in K as T[P] extends U ? K : never]: true;
     }]: string;
 };
+type Fruit = {
+    name: "apple";
+    color: "red";
+} | {
+    name: "banana";
+    color: "yellow";
+} | {
+    name: "orange";
+    color: "orange";
+};
+type Result1<T extends {
+    name: string | number;
+    color: string | number;
+}> = {
+    [Key in T as `${Key['name']}:${Key['color']}`]: unknown;
+};
+type Result2<T extends {
+    name: string | number;
+    color: string | number;
+}> = keyof {
+    [Key in T as `${Key['name']}:${Key['color']}`]: unknown;
+};
+type Test1 = keyof Result1<Fruit>;
+type Test2 = Result2<Fruit>;