Add numeric constraint to type parameter of mapped types with name type and array constraints #55774

Andarist · 2023-09-18T16:53:09Z

closes #55762
expands on the logic introduced in #48837

At the moment K in the name type of a mapped type that iterates over keyof Arr refers to all properties of the array type, that includes length, toString, and more. #48837 changed K's constraint in such mapped types to include
number | `${number}` but the change only affected K in the template type part of the mapped type.

This change introduces a very similar change to the K's constraint - just within the name type part of the mapped type. This makes it easier to write types that transform tuples into objects. It's not impossible to write types like this today but I think that it's not intuitive and more cumbersome.

With the changes in this PR the types like this can be simplified as follows:

type StructDescriptor = ReadonlyArray<readonly [key: string, type: Decoder<any>]>;

type StructTypeFor<Descriptor extends StructDescriptor> = {
-    [K in keyof Descriptor & `${number}` as Descriptor[K][0]]: ValueTypeOf<Descriptor[K][1]>;
+    [K in keyof Descriptor as Descriptor[K][0]]: ValueTypeOf<Descriptor[K][1]>;
};

…pe and array constraints

RyanCavanaugh · 2023-09-18T18:52:49Z

An explanation of what's going on here would be really useful

Andarist · 2023-09-18T18:55:50Z

tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.errors.txt

@@ -0,0 +1,11 @@
+mappedTypeWithAsClauseAndLateBoundProperty2.ts(1,14): error TS4118: The type of this node cannot be serialized because its property '[iterator]' cannot be serialized.


This brings back the original expected result from #45190 , I later "fixed" it in #51650 .

However, this PR is changing what K refers to within the name type of a mapped type that iterates over keys of an array type. With this change, the mapped type in question was instantiated to { [x: number]: number; }. So I added & PropertyKey to the mapped type's constraint to make it non-homomorphic to fix the intention of this test case. And that brought back the original "expected" behavior.

Andarist · 2023-09-18T19:03:37Z

@RyanCavanaugh just added it, I hope this clarifies what this PR is about

gabritto · 2023-10-24T02:57:35Z

@typescript-bot pack this

typescript-bot · 2023-10-24T02:57:41Z

Heya @gabritto, I've started to run the tarball bundle task on this PR at 32ca0d3. You can monitor the build here.

typescript-bot · 2023-10-24T02:59:17Z

Hey @gabritto, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/158317/artifacts?artifactName=tgz&fileId=DA2622C7CF956675D7795F132648C7C9A55B95E8D7A0DDC948A9694CDA152D6202&fileName=/typescript-5.3.0-insiders.20231024.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@5.3.0-pr-55774-4".;

gabritto · 2023-10-24T19:39:56Z

src/compiler/checker.ts

@@ -13583,7 +13583,15 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
        const include = keyofStringsOnly ? TypeFlags.StringLiteral : TypeFlags.StringOrNumberLiteralOrUnique;
        if (isMappedTypeWithKeyofConstraintDeclaration(type)) {
            // We have a { [P in keyof T]: X }
-            forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(modifiersType, include, keyofStringsOnly, addMemberForKeyType);
+            if (nameType && isTupleType(modifiersType)) {


Why are we doing this only if there is a nameType?

good question - I'm not sure 😅 it feels like a leftover or something cause at the very least the array branch should be guarded in the same way (if at all). All tests pass without this so I'll push out a change with this removed in a moment

…pped-type-with-name-type

gabritto · 2023-10-24T22:27:30Z

src/compiler/checker.ts

+                addMemberForKeyType(numberType);
+            }
+            else {
+                forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(modifiersType, include, keyofStringsOnly, addMemberForKeyType);


Also, should this change be made inside forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType instead?
This function is called in getIndexTypeForMappedType, and also in checkTypeRelatedTo (to check if something is assignable to a target mapped type), so I think we want to keep the behavior consistent here, although I'm not 100% sure.

Those are good concerns and I need to take a deeper look at this. This requires more focus time from me so it will take some time before I get to it - but I will certainly circle back here and let you know once I have some conclusions for this.

We discussed the issue this PR addresses at design meeting today: #56233
I think the conclusion is: we definitely want the change that adds the number | `${number}` constraint to the type parameter K in the name type, but for now we don't want that change here where we limit K to range over the tuple indexes for a tuple type, or the number index signature for array types. The reason is, in short, we want to keep keyof as consistent as possible regarding its behavior on array and array-ish types, i.e. we don't want to add special behavior to keyof here.

This change here is needed. Usually, tuple types are immediately~ instantiated by instantiateMappedTupleType so they never go through resolveMappedTypeMembers. When mapping through a tuple we want a tuple back when the name type is not present - and tuple types are sufficiently different from regular object types that they require this special immediate instantiation (well, probably it could be deferred - just using a specialized mechanism or smth but that's beside the point here).

But with the introduction of this change, we introduce the ability to map a tuple type into an object type. So resolving of output's members stays deferred~ and, for the first time, we get a tuple modifiersType here. Implicitly, we know that this mapped type has the nameType based on the fact that we got that tuple modifiersType. So we need to limit the mapping accordingly.

I'm not sure I understand your comment, but here's where my understanding is at so far:

If we have a homomorphic mapped type (implying without a name type) that maps over a tuple type, we get a tuple type back and this special work is done in instantiateMappedTupleType (more specifically by calling instantiateMappedTupleType or instantiateMappedGenericTupleType). I think we can think of that as being a special behavior.

If we have a non-homomorphic mapped type, and more specifically it has a name type, that maps over a tuple type, we currently don't do any special behavior. If your type looks like { [P in keyof SomeTupleType as NameType ]: TemplateType }, then that one keyof is going to behave as it does in the most general case and get us all the properties of SomeTupleType, including array methods and the number index signature.

I think I don't understand why you said "we need to limit the mapping accordingly".
Why do we need to do this?
Is it because that's needed to fix/improve the example in the issue?
Is it because we have inconsistent behavior between the special case for homomorphic mapped types in instantiateMappedTypes vs the other behavior?

The consequences of not limiting the mapping are that, if you want your mapped type over a tuple type to behave nicely like in the issue's example, you may need to add a constraint to the constraint type, e.g. { [P in keyof SomeTupleType & `${number}` as NameType ]: TemplateType }, right?
I think what I understood from the design meeting is that we're ok with users needing this extra constraint, because we don't want to expand the special behavior of mapped types and keyof tuple types to apply to more cases.

Sorry if some of this is repeated from other comments, I'm trying to make sure I understand things.

If we have a homomorphic mapped type (implying without a name type) that maps over a tuple type, we get a tuple type back and this special work is done in instantiateMappedTupleType (more specifically by calling instantiateMappedTupleType or instantiateMappedGenericTupleType). I think we can think of that as being a special behavior.

This matches my understanding 👍

If we have a non-homomorphic mapped type, and more specifically it has a name type

If I understand correctly a mapped type can still be homomorphic - even if it has a name type. I confirmed that a type like this pass through getHomomorphicTypeVariable successfully

type Test<T> = { [K in keyof T as K & string]: T[K] }

It definitely dilutes the name though since it's not exactly that the output here will be of the same shape 🤷 But property symbols links, property modifiers, are nicely preserved when the name type is just filtering K and not remapping it.

If we have a non-homomorphic mapped type, and more specifically it has a name type, that maps over a tuple type, we currently don't do any special behavior. If your type looks like { [P in keyof SomeTupleType as NameType
]: TemplateType
}, then that one keyof is going to behave as it does in the most general case and get us all the properties of SomeTupleType, including array methods and the number index signature.

The rest here matches my understanding 👍

I think I don't understand why you said "we need to limit the mapping accordingly".
Why do we need to do this?
Is it because that's needed to fix/improve the example in the issue?

Yes - this is needed to fix/improve the example in the issue.

git diff without those lines

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts index f87f4479fa..d174690ace 100644 --- a/src/compiler/checker.ts +++ b/src/compiler/checker.ts @@ -13703,15 +13703,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker { const include = keyofStringsOnly ? TypeFlags.StringLiteral : TypeFlags.StringOrNumberLiteralOrUnique; if (isMappedTypeWithKeyofConstraintDeclaration(type)) { // We have a { [P in keyof T]: X } - if (isTupleType(modifiersType)) { - forEachType(getUnionType(getElementTypes(modifiersType).map((_, i) => getStringLiteralType("" + i))), addMemberForKeyType); - } - else if (isArrayType(modifiersType)) { - addMemberForKeyType(numberType); - } - else { - forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(modifiersType, include, keyofStringsOnly, addMemberForKeyType); - } + forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(modifiersType, include, keyofStringsOnly, addMemberForKeyType); } else { forEachType(getLowerBoundOfKeyType(constraintType), addMemberForKeyType); diff --git a/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types b/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types index 8b80020c7c..c28c1811a7 100644 --- a/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types +++ b/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types @@ -80,15 +80,15 @@ const struct1 = structDecoder1.decode(new ArrayBuffer(100)); const v1_1: number = struct1.a; >v1_1 : number ->struct1.a : number +>struct1.a : number | bigint >struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]> ->a : number +>a : number | bigint const v1_2: bigint = struct1.b; >v1_2 : bigint ->struct1.b : bigint +>struct1.b : number | bigint >struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]> ->b : bigint +>b : number | bigint declare const descriptor2: [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]] >descriptor2 : [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]] @@ -111,19 +111,19 @@ const struct2 = structDecoder2.decode(new ArrayBuffer(100)); const v2_1: number = struct2.a; >v2_1 : number ->struct2.a : number +>struct2.a : string | number | bigint >struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]> ->a : number +>a : string | number | bigint const v2_2: string = struct2.b; >v2_2 : string ->struct2.b : string +>struct2.b : string | number | bigint >struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]> ->b : string +>b : string | number | bigint const v2_3: bigint = struct2.c; >v2_3 : bigint ->struct2.c : bigint +>struct2.c : string | number | bigint >struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]> ->c : bigint +>c : string | number | bigint diff --git a/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.errors.txt b/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.errors.txt index a2f7f389e9..50b1a88109 100644 --- a/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.errors.txt +++ b/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.errors.txt @@ -1,4 +1,4 @@ -mappedTypeWithAsClauseAndLateBoundProperty.ts(3,1): error TS2741: Property 'length' is missing in type '{ [x: number]: number; [iterator]: () => IterableIterator<number>; [unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; }' but required in type 'number[]'. +mappedTypeWithAsClauseAndLateBoundProperty.ts(3,1): error TS2741: Property 'length' is missing in type '{ [x: number]: number; [iterator]: () => IterableIterator<number>; [unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; }' but required in type 'number[]'. ==== mappedTypeWithAsClauseAndLateBoundProperty.ts (1 errors) ==== @@ -6,6 +6,6 @@ mappedTypeWithAsClauseAndLateBoundProperty.ts(3,1): error TS2741: Property 'leng declare let src2: { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] }; tgt2 = src2; // Should error ~~~~ -!!! error TS2741: Property 'length' is missing in type '{ [x: number]: number; [iterator]: () => IterableIterator<number>; [unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; }' but required in type 'number[]'. +!!! error TS2741: Property 'length' is missing in type '{ [x: number]: number; [iterator]: () => IterableIterator<number>; [unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; }' but required in type 'number[]'. !!! related TS2728 lib.es5.d.ts:--:--: 'length' is declared here. \ No newline at end of file diff --git a/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.types b/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.types index a6302b7a11..c8b6485d30 100644 --- a/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.types +++ b/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.types @@ -5,10 +5,10 @@ declare let tgt2: number[]; >tgt2 : number[] declare let src2: { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] }; ->src2 : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } +>src2 : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } tgt2 = src2; // Should error ->tgt2 = src2 : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } +>tgt2 = src2 : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } >tgt2 : number[] ->src2 : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } +>src2 : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } diff --git a/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.types b/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.types index 457a86874b..56eb6dec96 100644 --- a/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.types +++ b/tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.types @@ -2,8 +2,8 @@ === mappedTypeWithAsClauseAndLateBoundProperty2.ts === export const thing = (null as any as { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] }); ->thing : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } ->(null as any as { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] }) : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } ->null as any as { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] } : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } +>thing : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } +>(null as any as { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] }) : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } +>null as any as { [K in keyof number[] & PropertyKey as Exclude<K, "length">]: (number[])[K] } : { [x: number]: number; [Symbol.iterator]: () => IterableIterator<number>; [Symbol.unscopables]: { [x: number]: boolean; length?: boolean; toString?: boolean; toLocaleString?: boolean; pop?: boolean; push?: boolean; concat?: boolean; join?: boolean; reverse?: boolean; shift?: boolean; slice?: boolean; sort?: boolean; splice?: boolean; unshift?: boolean; indexOf?: boolean; lastIndexOf?: boolean; every?: boolean; some?: boolean; forEach?: boolean; map?: boolean; filter?: boolean; reduce?: boolean; reduceRight?: boolean; find?: boolean; findIndex?: boolean; fill?: boolean; copyWithin?: boolean; entries?: boolean; keys?: boolean; values?: boolean; includes?: boolean; flatMap?: boolean; flat?: boolean; [Symbol.iterator]?: boolean; readonly [Symbol.unscopables]?: boolean; }; toString: () => string; toLocaleString: () => string; pop: () => number; push: (...items: number[]) => number; concat: { (...items: ConcatArray<number>[]): number[]; (...items: (number | ConcatArray<number>)[]): number[]; }; join: (separator?: string) => string; reverse: () => number[]; shift: () => number; slice: (start?: number, end?: number) => number[]; sort: (compareFn?: (a: number, b: number) => number) => number[]; splice: { (start: number, deleteCount?: number): number[]; (start: number, deleteCount: number, ...items: number[]): number[]; }; unshift: (...items: number[]) => number; indexOf: (searchElement: number, fromIndex?: number) => number; lastIndexOf: (searchElement: number, fromIndex?: number) => number; every: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): boolean; }; some: (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => boolean; forEach: (callbackfn: (value: number, index: number, array: number[]) => void, thisArg?: any) => void; map: (callbackfn: (value: number, index: number, array: number[]) => U, thisArg?: any) => U[]; filter: { <S extends number>(predicate: (value: number, index: number, array: number[]) => value is S, thisArg?: any): S[]; (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any): number[]; }; reduce: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; reduceRight: { (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number): number; (callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: number[]) => number, initialValue: number): number; (callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: number[]) => U, initialValue: U): U; }; find: { <S extends number>(predicate: (value: number, index: number, obj: number[]) => value is S, thisArg?: any): S; (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any): number; }; findIndex: (predicate: (value: number, index: number, obj: number[]) => unknown, thisArg?: any) => number; fill: (value: number, start?: number, end?: number) => number[]; copyWithin: (target: number, start: number, end?: number) => number[]; entries: () => IterableIterator<[number, number]>; keys: () => IterableIterator<number>; values: () => IterableIterator<number>; includes: (searchElement: number, fromIndex?: number) => boolean; flatMap: <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]; flat: <A, D extends number = 1>(this: A, depth?: D) => FlatArray<A, D>[]; } >null as any : any

Let's recap what might happen for the simplest case with a fixed-size tuple like [["a", Decoder<number>], ["b", Decoder<string>]].

With the proposed change K is now constrained in the same way as the template type is. That means that its constraint is "0" | "1" (when instantiated with this tuple). It's not enough to just "suppress" this within the generic type, at the constraints level. We also need to account for this when instantiating those mapped types. If K is constrained "0" | "1" then why would we iterate here over all properties of tuples (including length, pop, etc)? That could even lead to some nasty errors since the constraints that allowed for the construction of this mapped type didn't account for those extra properties. We can instantiate nameType only with what has been allowed at the generic level: K & `${number}` .

It would get even more incorrect with variadic tuples as variadic positions (and positions after them) are not even properties. Their instantiated K is an index within the elements array.

The consequences of not limiting the mapping are that, if you want your mapped type over a tuple type to behave nicely like in the issue's example, you may need to add a constraint to the constraint type, e.g. { [P in keyof SomeTupleType & ${number} as NameType
]: TemplateType
}, right?

Right.

think what I understood from the design meeting is that we're ok with users needing this extra constraint, because we don't want to expand the special behavior of mapped types and keyof tuple types to apply to more cases.

Initially, I got the impression from those meeting notes that the ruling was in favor of this PR. It mentions:

But in homomorphic mapped types, the output is still presumably an array, so we don't need to mess with Array methods in that case

And I treat this case as a homomorphic mapped type (based on what I mentioned above).

But now... well, I'm not like super sure what was the ruling of that design meeting. Those notes are a little bit chaotic 😅 There is also a mention of this:

You'll still need something to avoid the numeric index signature

And ye, I guess I agree that this kinda makes sense to some extent but it's also not the case when it comes to the mentioned "special case":

type Test<T extends any[]> = { [K in keyof T]: K } type Result = Test<[boolean, '', ...number[]]> // ["0", "1", ..."2"[]]

The numeric signature doesn't come up in the output here. So I still think that the approach that I have used is good and that it fits the bigger picture nicely.

Sorry if some of this is repeated from other comments, I'm trying to make sure I understand things.

No worries. It's not like my understanding is perfect either. I appreciate the thoroughness of the review.

Do you have an example of what could go wrong if the K in the name type has the constraint but resolveMappedTypeMembers still has K iterating through the array methods?
If you don't, it's fine, but I think it would help.

K might get instantiated to things like (number | `${number}`) & "toString". That in turn reduces to never and indexing an object with never gets us the type of its index signature (not sure what the actual rule behind this is though). Arrays/tuples always include a number index signature and so we end up with all contained types instead of ones limited to their positions~ in tuples.

git diff

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts index f87f4479fa..fc6ee5694b 100644 --- a/src/compiler/checker.ts +++ b/src/compiler/checker.ts @@ -13702,16 +13702,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker { const templateModifiers = getMappedTypeModifiers(type); const include = keyofStringsOnly ? TypeFlags.StringLiteral : TypeFlags.StringOrNumberLiteralOrUnique; if (isMappedTypeWithKeyofConstraintDeclaration(type)) { // We have a { [P in keyof T]: X } - if (isTupleType(modifiersType)) { - forEachType(getUnionType(getElementTypes(modifiersType).map((_, i) => getStringLiteralType("" + i))), addMemberForKeyType); - } - else if (isArrayType(modifiersType)) { - addMemberForKeyType(numberType); - } - else { - forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(modifiersType, include, keyofStringsOnly, addMemberForKeyType); - } + forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(modifiersType, include, keyofStringsOnly, addMemberForKeyType); } else { forEachType(getLowerBoundOfKeyType(constraintType), addMemberForKeyType); diff --git a/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types b/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types index 8b80020c7c..c28c1811a7 100644 --- a/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types +++ b/tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types @@ -80,15 +80,15 @@ const struct1 = structDecoder1.decode(new ArrayBuffer(100)); const v1_1: number = struct1.a; >v1_1 : number ->struct1.a : number +>struct1.a : number | bigint >struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]> ->a : number +>a : number | bigint const v1_2: bigint = struct1.b; >v1_2 : bigint ->struct1.b : bigint +>struct1.b : number | bigint >struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]> ->b : bigint +>b : number | bigint declare const descriptor2: [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]] >descriptor2 : [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]] @@ -111,19 +111,19 @@ const struct2 = structDecoder2.decode(new ArrayBuffer(100)); const v2_1: number = struct2.a; >v2_1 : number ->struct2.a : number +>struct2.a : string | number | bigint >struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]> ->a : number +>a : string | number | bigint const v2_2: string = struct2.b; >v2_2 : string ->struct2.b : string +>struct2.b : string | number | bigint >struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]> ->b : string +>b : string | number | bigint const v2_3: bigint = struct2.c; >v2_3 : bigint ->struct2.c : bigint +>struct2.c : string | number | bigint >struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]> ->c : bigint +>c : string | number | bigint

Ok, so it seems like the design meeting discussion didn't cover all the facts.
It seems that we're already making the mapped type's type parameter K range over only the interesting tuple/array properties in:
-instantiateMappedType, for homomorphic mapped types without a name type.

getIndexTypeForMappedType, for non-homomorphic mapped types when the constraint type is a generic tuple type (see the call to getLowerBoundOfKeyType there).
So it seems the change in this PR wouldn't exactly be adding another special case to a mapped type's keyof, after all.

I think one thing left to potentially address in this PR is to add this change here to the implementation of forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType instead of to resolveMappedTypeMembers, that way the change also consistently applies to the other callers of this function (getIndexTypeForMappedType and structuredTypeRelatedTo). Let me know if you want to do this yourself or not, and thanks for clarifying things.

I'll take care of the requested changes in the coming days.

tests/cases/compiler/mappedTypeTupleConstraintTypeParameterInNameType.ts

gabritto

I left some implementation comments, but overall so far I think:

The added constraint to the name type is a good change, and I'm more confident about it. It is consistent with the added constraint we already have on the template type.
I am less sure of when it is we want to only map over the numerical index keys of a tuple/array type. It seems weird to only do it when there is a name type... But I don't know what the implications are of always being consistent and only mapping over the numerical index keys at all times. It certainly is sort of a lie, because tuples and array types do have the built-in methods present, but we're already leaning into it by saying K is constrained to number | ${number}.

gabritto · 2023-10-25T16:43:33Z

@typescript-bot run DT
@typescript-bot user test this
@typescript-bot test top100
@typescript-bot perf test this

typescript-bot · 2023-10-25T16:43:38Z

Heya @gabritto, I've started to run the regular perf test suite on this PR at 6876e98. You can monitor the build here.

Update: The results are in!

typescript-bot · 2023-10-25T16:43:38Z

Heya @gabritto, I've started to run the diff-based top-repos suite on this PR at 6876e98. You can monitor the build here.

Update: The results are in!

typescript-bot · 2023-10-25T16:43:38Z

Heya @gabritto, I've started to run the parallelized Definitely Typed test suite on this PR at 6876e98. You can monitor the build here.

Update: The results are in!

typescript-bot · 2023-10-25T16:43:38Z

Heya @gabritto, I've started to run the diff-based user code test suite on this PR at 6876e98. You can monitor the build here.

Update: The results are in!

typescript-bot · 2023-11-15T21:57:56Z

Heya @gabritto, I've started to run the tarball bundle task on this PR at b5c12ee. You can monitor the build here.

typescript-bot · 2023-11-15T21:59:31Z

Hey @gabritto, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/158614/artifacts?artifactName=tgz&fileId=B11099298AAC0B210571EDA213366902A5E8D58F8C425887FD7D070B2089AB2E02&fileName=/typescript-5.4.0-insiders.20231115.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@5.4.0-pr-55774-37".;

typescript-bot · 2023-11-15T22:13:12Z

Hey @gabritto, the results of running the DT tests are ready.
Everything looks the same!
You can check the log here.

typescript-bot · 2023-11-15T22:52:57Z

@gabritto Here are the results of running the top-repos suite comparing main and refs/pull/55774/merge:

Everything looks good!

gabritto · 2023-11-15T23:56:41Z

I came up with the following example to show that putting the change inside forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType does matter:

type Mapper<T> = {
    [K in keyof T as K]: T[K] extends NonNullable<T[K]> ? T[K] : never;
}

type Mapped = Mapper<[1, 2]>;
type Keys = keyof Mapper<[1, 2]>;

type SomeType = Mapped[Keys]; // Errors on early version of PR

…pped-type-with-name-type

Andarist · 2023-12-28T16:30:56Z

@gabritto great catch! I over-focused on mapped types with array/tuple constraints and I missed that this also impacts all homomorphic mapped types (even the unconstrained ones that might be instantiated with arrays/tuples). I pushed out the relevant test case, thanks ❤️

gabritto · 2024-01-10T18:42:25Z

@typescript-bot pack this

typescript-bot · 2024-01-10T18:42:29Z

Heya @gabritto, I've started to run the tarball bundle task on this PR at 0318886. You can monitor the build here.

typescript-bot · 2024-01-10T18:44:11Z

Hey @gabritto, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/159399/artifacts?artifactName=tgz&fileId=2E6AB43E4C51A0A1DE67DDDCCB43A0804BD9FCE66187EDF4B495D154A9A4BFDC02&fileName=/typescript-5.4.0-insiders.20240110.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@5.4.0-pr-55774-44".;

gabritto · 2024-01-10T20:01:57Z

So, what bothers me about this change is that now the following mapped types behave differently with regards to whether they produce some array-looking type or not:

type Mappy<T extends unknown[]> = { [K in keyof T as K]: T[K] };
type NotArray = Mappy<number[]>;

type HomMappy<T extends unknown[]> = { [K in keyof T]: T[K] };
type AnArray = HomMappy<number[]>;

The difference seems hard to explain...
(Although the example above contains a bug in current TS, in that NotArray is only almost an array because toString wrongly has type number 😬)

Update: there's already an issue and some duplicates about this: #40586

weswigham · 2024-01-10T20:26:35Z

The difference seems hard to explain

You could see the as clause as explicitly un-arraying the type. Which is basically how we see it internally.

gabritto · 2024-01-10T20:40:38Z

The difference seems hard to explain

You could see the as clause as explicitly un-arraying the type. Which is basically how we see it internally.

Yes, that's what's going on, but to some users that's not desired. Have we decided to say no to #40586 then?

Andarist · 2024-01-10T23:13:13Z

#40586 implies that sometimes you'd get an array and sometimes you wouldn't (it potentially could depend on the remapped keys, if they all stay numeric or not). That honestly feels more surprising to me than a consistent rule that if you use the name type then u get an object back.

… name type and array constraints (#55774)" This reverts commit 3f8707d.

Add numeric constraint to type parameter of mapped types with name ty…

c28fb9e

…pe and array constraints

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sandersn moved this from Not started to Waiting on reviewers in PR Backlog Sep 26, 2023

gabritto mentioned this pull request Oct 21, 2023

Can't remap tuple keys to object keys in mapped types #55762

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Merge remote-tracking branch 'origin/main' into numeric-constraint-ma…

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…pped-type-with-name-type

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Andarist added 2 commits October 25, 2023 09:17

Remove a redundant nameType check

c66fd92

add a test with a non-fixed sized tuple

6876e98

Andarist added 2 commits December 28, 2023 15:04

Merge remote-tracking branch 'origin/main' into numeric-constraint-ma…

b55610e

…pped-type-with-name-type

add an extra test case

0318886

weswigham approved these changes Jan 9, 2024

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Andarist requested a review from gabritto January 10, 2024 12:05

gabritto mentioned this pull request Jan 11, 2024

Mapped type applied to array type produces wrong toString, filter, etc type #57007

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gabritto merged commit 3f8707d into microsoft:main Jan 16, 2024
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PR Backlog automation moved this from Needs merge to Done Jan 16, 2024

Andarist mentioned this pull request Jan 16, 2024

Revise mapped tuple type instantiation logic #57031

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Revert "Add numeric constraint to type parameter of mapped types with…

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… name type and array constraints (#55774)" This reverts commit 3f8707d.

gabritto mentioned this pull request Jan 16, 2024

Revert "Add numeric constraint to type parameter of mapped types with… #57076

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rotu mentioned this pull request Feb 1, 2024

mapped type with remapped keys unexpectedly widens type #57265

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Andarist deleted the numeric-constraint-mapped-type-with-name-type branch April 17, 2024 22:08

Andarist mentioned this pull request Apr 18, 2024

Add numeric constraint to type parameter of mapped types with name type and array constraints (take 2) #58237

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		@@ -0,0 +1,11 @@
		mappedTypeWithAsClauseAndLateBoundProperty2.ts(1,14): error TS4118: The type of this node cannot be serialized because its property '[iterator]' cannot be serialized.

Add numeric constraint to type parameter of mapped types with name type and array constraints #55774

Add numeric constraint to type parameter of mapped types with name type and array constraints #55774

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