TypeScript/tests/baselines/reference/keyRemappingKeyofResult(strict=false).types at 1a27fd94e27e1235e70ae8b7be763c599a8246ec · Andarist/TypeScript · GitHub

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//// [tests/cases/compiler/keyRemappingKeyofResult.ts] ////

=== keyRemappingKeyofResult.ts ===
const sym = Symbol("")
>sym : unique symbol
>Symbol("") : unique symbol
>Symbol : SymbolConstructor
>"" : ""

type Orig = { [k: string]: any, str: any, [sym]: any }
>Orig : { [k: string]: any; str: any; [sym]: any; }
>k : string
>str : any
>[sym] : any
>sym : unique symbol

type Okay = Exclude<keyof Orig, never>
>Okay : string | number | unique symbol

// type Okay = string | number | typeof sym

type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
>Remapped : { str: any; [sym]: any; }

/* type Remapped = {
    str: any;
    [sym]: any;
} */
// no string index signature, right?

type Oops = Exclude<keyof Remapped, never>
>Oops : unique symbol | "str"

declare let x: Oops;
>x : Oops

x = sym;
>x = sym : unique symbol
>x : Oops
>sym : unique symbol

x = "str";
>x = "str" : "str"
>x : Oops
>"str" : "str"

// type Oops = typeof sym <-- what happened to "str"?

// equivalently, with an unresolved generic (no `exclude` shenanigans, since conditions won't execute):
function f<T>() {
>f : <T>() => void

    type Orig = { [k: string]: any, str: any, [sym]: any } & T;
>Orig : { [k: string]: any; str: any; [sym]: any; } & T
>k : string
>str : any
>[sym] : any
>sym : unique symbol

    type Okay = keyof Orig;
>Okay : string | number | unique symbol | keyof T

    let a: Okay;
>a : string | number | unique symbol | keyof T

    a = "str";
>a = "str" : "str"
>a : string | number | unique symbol | keyof T
>"str" : "str"

    a = sym;
>a = sym : unique symbol
>a : string | number | unique symbol | keyof T
>sym : unique symbol

    a = "whatever";
>a = "whatever" : "whatever"
>a : string | number | unique symbol | keyof T
>"whatever" : "whatever"

    // type Okay = string | number | typeof sym

    type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
>Remapped : { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as {} extends Record<K, any> ? never : K]: any; }

    /* type Remapped = {
        str: any;
        [sym]: any;
    } */
    // no string index signature, right?

    type Oops = keyof Remapped;
>Oops : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as {} extends Record<K, any> ? never : K]: any; }

    let x: Oops;
>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as {} extends Record<K, any> ? never : K]: any; }

    x = sym;
>x = sym : unique symbol
>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as {} extends Record<K, any> ? never : K]: any; }
>sym : unique symbol

    x = "str";
>x = "str" : "str"
>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as {} extends Record<K, any> ? never : K]: any; }
>"str" : "str"
}

// and another generic case with a _distributive_ mapping, to trigger a different branch in `getIndexType`
function g<T>() {
>g : <T>() => void

    type Orig = { [k: string]: any, str: any, [sym]: any } & T;
>Orig : { [k: string]: any; str: any; [sym]: any; } & T
>k : string
>str : any
>[sym] : any
>sym : unique symbol

    type Okay = keyof Orig;
>Okay : string | number | unique symbol | keyof T

    let a: Okay;
>a : string | number | unique symbol | keyof T

    a = "str";
>a = "str" : "str"
>a : string | number | unique symbol | keyof T
>"str" : "str"

    a = sym;
>a = sym : unique symbol
>a : string | number | unique symbol | keyof T
>sym : unique symbol

    a = "whatever";
>a = "whatever" : "whatever"
>a : string | number | unique symbol | keyof T
>"whatever" : "whatever"

    // type Okay = string | number | typeof sym

    type NonIndex<T extends PropertyKey> = {} extends Record<T, any> ? never : T;
>NonIndex : {} extends Record<T, any> ? never : T

    type DistributiveNonIndex<T extends PropertyKey> = T extends unknown ? NonIndex<T> : never;
>DistributiveNonIndex : T extends unknown ? {} extends Record<T, any> ? never : T : never

    type Remapped = { [K in keyof Orig as DistributiveNonIndex<K>]: any }
>Remapped : { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as K extends unknown ? {} extends Record<K, any> ? never : K : never]: any; }

    /* type Remapped = {
        str: any;
        [sym]: any;
    } */
    // no string index signature, right?

    type Oops = keyof Remapped;
>Oops : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as K extends unknown ? {} extends Record<K, any> ? never : K : never]: any; }

    let x: Oops;
>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as K extends unknown ? {} extends Record<K, any> ? never : K : never]: any; }

    x = sym;
>x = sym : unique symbol
>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as K extends unknown ? {} extends Record<K, any> ? never : K : never]: any; }
>sym : unique symbol

    x = "str";
>x = "str" : "str"
>x : keyof { [K in keyof ({ [k: string]: any; str: any; [sym]: any; } & T) as K extends unknown ? {} extends Record<K, any> ? never : K : never]: any; }
>"str" : "str"
}

// https://github.com/microsoft/TypeScript/issues/57827

type StringKeys<T> = Extract<
>StringKeys : StringKeys<T>

  keyof {
    [P in keyof T as T[P] extends string ? P : never]: any;
  },
  string
>;

function test_57827<T>(z: StringKeys<T>) {
>test_57827 : <T>(z: StringKeys<T>) => void
>z : Extract<keyof { [P in keyof T as T[P] extends string ? P : never]: any; }, string>

  const f: string = z;
>f : string
>z : Extract<keyof { [P in keyof T as T[P] extends string ? P : never]: any; }, string>
}

export {};