TypeScript/tests/baselines/reference/keyRemappingKeyofResult(strict=false).js at 73d96e1768e7e564d1559cce96351a244575b4b4 · Andarist/TypeScript · GitHub

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

//// [keyRemappingKeyofResult.ts]
const sym = Symbol("")
type Orig = { [k: string]: any, str: any, [sym]: any }

type Okay = Exclude<keyof Orig, never>
// type Okay = string | number | typeof sym

type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
/* type Remapped = {
    str: any;
    [sym]: any;
} */
// no string index signature, right?

type Oops = Exclude<keyof Remapped, never>
declare let x: Oops;
x = sym;
x = "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>() {
    type Orig = { [k: string]: any, str: any, [sym]: any } & T;

    type Okay = keyof Orig;
    let a: Okay;
    a = "str";
    a = sym;
    a = "whatever";
    // type Okay = string | number | typeof sym

    type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
    /* type Remapped = {
        str: any;
        [sym]: any;
    } */
    // no string index signature, right?

    type Oops = keyof Remapped;
    let x: Oops;
    x = sym;
    x = "str";
}

// and another generic case with a _distributive_ mapping, to trigger a different branch in `getIndexType`
function g<T>() {
    type Orig = { [k: string]: any, str: any, [sym]: any } & T;

    type Okay = keyof Orig;
    let a: Okay;
    a = "str";
    a = sym;
    a = "whatever";
    // type Okay = string | number | typeof sym

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

    type Remapped = { [K in keyof Orig as DistributiveNonIndex<K>]: any }
    /* type Remapped = {
        str: any;
        [sym]: any;
    } */
    // no string index signature, right?

    type Oops = keyof Remapped;
    let x: Oops;
    x = sym;
    x = "str";
    x = "whatever"; // error
}

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

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

function test_57827<T>(z: StringKeys<T>) {
  const f: string = z;
  z = "foo"; // error
}

type StringKeys2<T> = keyof {
  [P in keyof T as T[P] extends string ? P : never]: any;
};

function h<T>(z: StringKeys2<T>) {
  z = "foo"; // error
  const f: string = z; // ok
}

export {};


//// [keyRemappingKeyofResult.js]
const sym = Symbol("");
x = sym;
x = "str";
// type Oops = typeof sym <-- what happened to "str"?
// equivalently, with an unresolved generic (no `exclude` shenanigans, since conditions won't execute):
function f() {
    let a;
    a = "str";
    a = sym;
    a = "whatever";
    let x;
    x = sym;
    x = "str";
}
// and another generic case with a _distributive_ mapping, to trigger a different branch in `getIndexType`
function g() {
    let a;
    a = "str";
    a = sym;
    a = "whatever";
    let x;
    x = sym;
    x = "str";
    x = "whatever"; // error
}
function test_57827(z) {
    const f = z;
    z = "foo"; // error
}
function h(z) {
    z = "foo"; // error
    const f = z; // ok
}
export {};