Improved mapped type support for arrays and tuples

src/compiler/checker.ts

@@ -8432,6 +8432,10 @@ namespace ts {
             return createTypeFromGenericGlobalType(globalArrayType, [elementType]);
         }
 
+        function createReadonlyArrayType(elementType: Type): ObjectType {
+            return createTypeFromGenericGlobalType(globalReadonlyArrayType, [elementType]);
+        }
+
         function getTypeFromArrayTypeNode(node: ArrayTypeNode): Type {
             const links = getNodeLinks(node);
             if (!links.resolvedType) {
@@ -10087,11 +10091,16 @@ namespace ts {
         }
 
         function instantiateMappedType(type: MappedType, mapper: TypeMapper): Type {
-            // Check if we have a homomorphic mapped type, i.e. a type of the form { [P in keyof T]: X } for some
-            // type variable T. If so, the mapped type is distributive over a union type and when T is instantiated
-            // to a union type A | B, we produce { [P in keyof A]: X } | { [P in keyof B]: X }. Furthermore, for
-            // homomorphic mapped types we leave primitive types alone. For example, when T is instantiated to a
-            // union type A | undefined, we produce { [P in keyof A]: X } | undefined.
+            // For a momomorphic mapped type { [P in keyof T]: X }, where T is some type variable, the mapping
+            // operation depends on T as follows:
+            // * If T is a primitive type no mapping is performed and the result is simply T.
+            // * If T is a union type we distribute the mapped type over the union.
+            // * If T is an array we map to an array where the element type has been transformed.
+            // * If T is a tuple we map to a tuple where the element types have been transformed.
+            // * Otherwise we map to an object type where the type of each property has been transformed.
+            // For example, when T is instantiated to a union type A | B, we produce { [P in keyof A]: X } |
+            // { [P in keyof B]: X }, and when when T is instantiated to a union type A | undefined, we produce
+            // { [P in keyof A]: X } | undefined.
             const constraintType = getConstraintTypeFromMappedType(type);
             if (constraintType.flags & TypeFlags.Index) {
                 const typeVariable = (<IndexType>constraintType).type;
@@ -10100,7 +10109,11 @@ namespace ts {
                     if (typeVariable !== mappedTypeVariable) {
                         return mapType(mappedTypeVariable, t => {
                             if (isMappableType(t)) {
-                                return instantiateAnonymousType(type, createReplacementMapper(typeVariable, t, mapper));
+                                const replacementMapper = createReplacementMapper(typeVariable, t, mapper);
+                                return isArrayType(t) ? createArrayType(instantiateMappedTypeTemplate(type, numberType, /*isOptional*/ true, replacementMapper)) :
+                                    isReadonlyArrayType(t) ? createReadonlyArrayType(instantiateMappedTypeTemplate(type, numberType, /*isOptional*/ true, replacementMapper)) :
+                                    isTupleType(t) ? instantiateMappedTupleType(t, type, replacementMapper) :
+                                    instantiateAnonymousType(type, replacementMapper);
                             }
                             return t;
                         });
@@ -10114,6 +10127,26 @@ namespace ts {
             return type.flags & (TypeFlags.AnyOrUnknown | TypeFlags.InstantiableNonPrimitive | TypeFlags.Object | TypeFlags.Intersection);
         }
 
+        function instantiateMappedTupleType(tupleType: TupleTypeReference, mappedType: MappedType, mapper: TypeMapper) {
+            const minLength = tupleType.target.minLength;
+            const elementTypes = map(tupleType.typeArguments || emptyArray, (_, i) =>
+                instantiateMappedTypeTemplate(mappedType, getLiteralType("" + i), i >= minLength, mapper));
+            const modifiers = getMappedTypeModifiers(mappedType);
+            const newMinLength = modifiers & MappedTypeModifiers.IncludeOptional ? 0 :
+                modifiers & MappedTypeModifiers.ExcludeOptional ? getTypeReferenceArity(tupleType) - (tupleType.target.hasRestElement ? 1 : 0) :
+                minLength;
+            return createTupleType(elementTypes, newMinLength, tupleType.target.hasRestElement, tupleType.target.associatedNames);
+        }
+
+        function instantiateMappedTypeTemplate(type: MappedType, key: Type, isOptional: boolean, mapper: TypeMapper) {
+            const templateMapper = combineTypeMappers(mapper, createTypeMapper([getTypeParameterFromMappedType(type)], [key]));
+            const propType = instantiateType(getTemplateTypeFromMappedType(<MappedType>type.target || type), templateMapper);
+            const modifiers = getMappedTypeModifiers(type);
+            return strictNullChecks && modifiers & MappedTypeModifiers.IncludeOptional && !isTypeAssignableTo(undefinedType, propType) ? getOptionalType(propType) :
+                strictNullChecks && modifiers & MappedTypeModifiers.ExcludeOptional && isOptional ? getTypeWithFacts(propType, TypeFacts.NEUndefined) :
+                propType;
+        }
+
         function instantiateAnonymousType(type: AnonymousType, mapper: TypeMapper): AnonymousType {
             const result = <AnonymousType>createObjectType(type.objectFlags | ObjectFlags.Instantiated, type.symbol);
             if (type.objectFlags & ObjectFlags.Mapped) {
@@ -12441,6 +12474,10 @@ namespace ts {
             return !!(getObjectFlags(type) & ObjectFlags.Reference) && (<TypeReference>type).target === globalArrayType;
         }
 
+        function isReadonlyArrayType(type: Type): boolean {
+            return !!(getObjectFlags(type) & ObjectFlags.Reference) && (<TypeReference>type).target === globalReadonlyArrayType;
+        }
+
         function isArrayLikeType(type: Type): boolean {
             // A type is array-like if it is a reference to the global Array or global ReadonlyArray type,
             // or if it is not the undefined or null type and if it is assignable to ReadonlyArray<any>
@@ -12996,6 +13033,22 @@ namespace ts {
                     return undefined;
                 }
             }
+            // For arrays and tuples we infer new arrays and tuples where the reverse mapping has been
+            // applied to the element type(s).
+            if (isArrayType(source)) {
+                return createArrayType(inferReverseMappedType((<TypeReference>source).typeArguments![0], target));
+            }
+            if (isReadonlyArrayType(source)) {
+                return createReadonlyArrayType(inferReverseMappedType((<TypeReference>source).typeArguments![0], target));
+            }
+            if (isTupleType(source)) {
+                const elementTypes = map(source.typeArguments || emptyArray, t => inferReverseMappedType(t, target));
+                const minLength = getMappedTypeModifiers(target) & MappedTypeModifiers.IncludeOptional ?
+                    getTypeReferenceArity(source) - (source.target.hasRestElement ? 1 : 0) : source.target.minLength;
+                return createTupleType(elementTypes, minLength, source.target.hasRestElement, source.target.associatedNames);
+            }
+            // For all other object types we infer a new object type where the reverse mapping has been
+            // applied to the type of each property.
             const reversed = createObjectType(ObjectFlags.ReverseMapped | ObjectFlags.Anonymous, /*symbol*/ undefined) as ReverseMappedType;
             reversed.source = source;
             reversed.mappedType = target;

tests/baselines/reference/mappedTypes4.types

@@ -103,7 +103,7 @@ type T01 = Readonly<A | B | C | null | undefined>;
 >null : null
 
 type T02 = Boxified<A | B[] | C | string>
->T02 : string | Boxified<A> | Boxified<C> | Boxified<B[]>
+>T02 : string | Boxified<A> | Boxified<C> | Box<B>[]
 >Boxified : Boxified<T>
 >A : A
 >B : B

tests/baselines/reference/mappedTypesArraysTuples.js

@@ -0,0 +1,144 @@
+//// [mappedTypesArraysTuples.ts]
+type Box<T> = { value: T };
+type Boxified<T> = { [P in keyof T]: Box<T[P]> };
+
+type T00 = Boxified<[number, string?, ...boolean[]]>;
+type T01 = Partial<[number, string?, ...boolean[]]>;
+type T02 = Required<[number, string?, ...boolean[]]>;
+
+type T10 = Boxified<string[]>;
+type T11 = Partial<string[]>;
+type T12 = Required<string[]>;
+type T13 = Boxified<ReadonlyArray<string>>;
+type T14 = Partial<ReadonlyArray<string>>;
+type T15 = Required<ReadonlyArray<string>>;
+
+type T20 = Boxified<(string | undefined)[]>;
+type T21 = Partial<(string | undefined)[]>;
+type T22 = Required<(string | undefined)[]>;
+type T23 = Boxified<ReadonlyArray<string | undefined>>;
+type T24 = Partial<ReadonlyArray<string | undefined>>;
+type T25 = Required<ReadonlyArray<string | undefined>>;
+
+type T30 = Boxified<Partial<string[]>>;
+type T31 = Partial<Boxified<string[]>>;
+
+type A = { a: string };
+type B = { b: string };
+
+type T40 = Boxified<A | A[] | ReadonlyArray<A> | [A, B] | string | string[]>;
+
+declare function unboxify<T>(x: Boxified<T>): T;
+
+declare let x10: [Box<number>, Box<string>, ...Box<boolean>[]];
+let y10 = unboxify(x10);
+
+declare let x11: Box<number>[];
+let y11 = unboxify(x11);
+
+declare let x12: { a: Box<number>, b: Box<string[]> };
+let y12 = unboxify(x12);
+
+declare function nonpartial<T>(x: Partial<T>): T;
+
+declare let x20: [number | undefined, string?, ...boolean[]];
+let y20 = nonpartial(x20);
+
+declare let x21: (number | undefined)[];
+let y21 = nonpartial(x21);
+
+declare let x22: { a: number | undefined, b?: string[] };
+let y22 = nonpartial(x22);
+
+type Awaited<T> = T extends PromiseLike<infer U> ? U : T;
+type Awaitified<T> = { [P in keyof T]: Awaited<T[P]> };
+
+declare function all<T extends any[]>(...values: T): Promise<Awaitified<T>>;
+
+function f1(a: number, b: Promise<number>, c: string[], d: Promise<string[]>) {
+    let x1 = all(a);
+    let x2 = all(a, b);
+    let x3 = all(a, b, c);
+    let x4 = all(a, b, c, d);
+}
+
+
+//// [mappedTypesArraysTuples.js]
+"use strict";
+var y10 = unboxify(x10);
+var y11 = unboxify(x11);
+var y12 = unboxify(x12);
+var y20 = nonpartial(x20);
+var y21 = nonpartial(x21);
+var y22 = nonpartial(x22);
+function f1(a, b, c, d) {
+    var x1 = all(a);
+    var x2 = all(a, b);
+    var x3 = all(a, b, c);
+    var x4 = all(a, b, c, d);
+}
+
+
+//// [mappedTypesArraysTuples.d.ts]
+declare type Box<T> = {
+    value: T;
+};
+declare type Boxified<T> = {
+    [P in keyof T]: Box<T[P]>;
+};
+declare type T00 = Boxified<[number, string?, ...boolean[]]>;
+declare type T01 = Partial<[number, string?, ...boolean[]]>;
+declare type T02 = Required<[number, string?, ...boolean[]]>;
+declare type T10 = Boxified<string[]>;
+declare type T11 = Partial<string[]>;
+declare type T12 = Required<string[]>;
+declare type T13 = Boxified<ReadonlyArray<string>>;
+declare type T14 = Partial<ReadonlyArray<string>>;
+declare type T15 = Required<ReadonlyArray<string>>;
+declare type T20 = Boxified<(string | undefined)[]>;
+declare type T21 = Partial<(string | undefined)[]>;
+declare type T22 = Required<(string | undefined)[]>;
+declare type T23 = Boxified<ReadonlyArray<string | undefined>>;
+declare type T24 = Partial<ReadonlyArray<string | undefined>>;
+declare type T25 = Required<ReadonlyArray<string | undefined>>;
+declare type T30 = Boxified<Partial<string[]>>;
+declare type T31 = Partial<Boxified<string[]>>;
+declare type A = {
+    a: string;
+};
+declare type B = {
+    b: string;
+};
+declare type T40 = Boxified<A | A[] | ReadonlyArray<A> | [A, B] | string | string[]>;
+declare function unboxify<T>(x: Boxified<T>): T;
+declare let x10: [Box<number>, Box<string>, ...Box<boolean>[]];
+declare let y10: [number, string, ...boolean[]];
+declare let x11: Box<number>[];
+declare let y11: number[];
+declare let x12: {
+    a: Box<number>;
+    b: Box<string[]>;
+};
+declare let y12: {
+    a: number;
+    b: string[];
+};
+declare function nonpartial<T>(x: Partial<T>): T;
+declare let x20: [number | undefined, string?, ...boolean[]];
+declare let y20: [number, string, ...boolean[]];
+declare let x21: (number | undefined)[];
+declare let y21: number[];
+declare let x22: {
+    a: number | undefined;
+    b?: string[];
+};
+declare let y22: {
+    a: number;
+    b: string[];
+};
+declare type Awaited<T> = T extends PromiseLike<infer U> ? U : T;
+declare type Awaitified<T> = {
+    [P in keyof T]: Awaited<T[P]>;
+};
+declare function all<T extends any[]>(...values: T): Promise<Awaitified<T>>;
+declare function f1(a: number, b: Promise<number>, c: string[], d: Promise<string[]>): void;