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Fix unsound Array.flatMap() typings #33630

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Fix unsound Array.flatMap() typings #33630

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262660d
Fix unsound Array.flatMap() typings
jablko Sep 26, 2019
3078223
Add tests
jablko Sep 26, 2019
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8 changes: 4 additions & 4 deletions src/lib/es2019.array.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,9 @@ interface ReadonlyArray<T> {
* thisArg is omitted, undefined is used as the this value.
*/
flatMap<U, This = undefined> (
callback: (this: This, value: T, index: number, array: T[]) => U | ReadonlyArray<U>,
callback: (this: This, value: T, index: number, array: T[]) => U,
thisArg?: This
): U[]
): (U extends readonly (infer V)[] ? V : U)[];


/**
Expand Down Expand Up @@ -125,9 +125,9 @@ interface Array<T> {
* thisArg is omitted, undefined is used as the this value.
*/
flatMap<U, This = undefined> (
callback: (this: This, value: T, index: number, array: T[]) => U | ReadonlyArray<U>,
callback: (this: This, value: T, index: number, array: T[]) => U,
thisArg?: This
): U[]
): (U extends readonly (infer V)[] ? V : U)[];

/**
* Returns a new array with all sub-array elements concatenated into it recursively up to the
Expand Down
8 changes: 8 additions & 0 deletions tests/baselines/reference/arrayFlatMap.js
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Expand Up @@ -3,10 +3,18 @@ const array: number[] = [];
const readonlyArray: ReadonlyArray<number> = [];
array.flatMap((): ReadonlyArray<number> => []); // ok
readonlyArray.flatMap((): ReadonlyArray<number> => []); // ok

// #19535

const [x] = [""].flatMap(undefined as () => string[] | string[][]);
x == "";


//// [arrayFlatMap.js]
var array = [];
var readonlyArray = [];
array.flatMap(function () { return []; }); // ok
readonlyArray.flatMap(function () { return []; }); // ok
// #19535
var x = [""].flatMap(undefined)[0];
x == "";
11 changes: 11 additions & 0 deletions tests/baselines/reference/arrayFlatMap.symbols
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Expand Up @@ -18,3 +18,14 @@ readonlyArray.flatMap((): ReadonlyArray<number> => []); // ok
>flatMap : Symbol(ReadonlyArray.flatMap, Decl(lib.es2019.array.d.ts, --, --))
>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --))

// #19535

const [x] = [""].flatMap(undefined as () => string[] | string[][]);
>x : Symbol(x, Decl(arrayFlatMap.ts, 7, 7))
>[""].flatMap : Symbol(Array.flatMap, Decl(lib.es2019.array.d.ts, --, --))
>flatMap : Symbol(Array.flatMap, Decl(lib.es2019.array.d.ts, --, --))
>undefined : Symbol(undefined)

x == "";
>x : Symbol(x, Decl(arrayFlatMap.ts, 7, 7))

25 changes: 21 additions & 4 deletions tests/baselines/reference/arrayFlatMap.types
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Expand Up @@ -9,17 +9,34 @@ const readonlyArray: ReadonlyArray<number> = [];

array.flatMap((): ReadonlyArray<number> => []); // ok
>array.flatMap((): ReadonlyArray<number> => []) : number[]
>array.flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]
>array.flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U, thisArg?: This) => (U extends readonly (infer V)[] ? V : U)[]
>array : number[]
>flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]
>flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U, thisArg?: This) => (U extends readonly (infer V)[] ? V : U)[]
>(): ReadonlyArray<number> => [] : () => readonly number[]
>[] : undefined[]

readonlyArray.flatMap((): ReadonlyArray<number> => []); // ok
>readonlyArray.flatMap((): ReadonlyArray<number> => []) : number[]
>readonlyArray.flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]
>readonlyArray.flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U, thisArg?: This) => (U extends readonly (infer V)[] ? V : U)[]
>readonlyArray : readonly number[]
>flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]
>flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U, thisArg?: This) => (U extends readonly (infer V)[] ? V : U)[]
>(): ReadonlyArray<number> => [] : () => readonly number[]
>[] : undefined[]

// #19535

const [x] = [""].flatMap(undefined as () => string[] | string[][]);
>x : string | string[]
>[""].flatMap(undefined as () => string[] | string[][]) : (string | string[])[]
>[""].flatMap : <U, This = undefined>(callback: (this: This, value: string, index: number, array: string[]) => U, thisArg?: This) => (U extends readonly (infer V)[] ? V : U)[]
>[""] : string[]
>"" : ""
>flatMap : <U, This = undefined>(callback: (this: This, value: string, index: number, array: string[]) => U, thisArg?: This) => (U extends readonly (infer V)[] ? V : U)[]
>undefined as () => string[] | string[][] : () => string[] | string[][]
>undefined : undefined

x == "";
>x == "" : boolean
>x : string | string[]
>"" : ""

5 changes: 5 additions & 0 deletions tests/cases/compiler/arrayFlatMap.ts
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Expand Up @@ -4,3 +4,8 @@ const array: number[] = [];
const readonlyArray: ReadonlyArray<number> = [];
array.flatMap((): ReadonlyArray<number> => []); // ok
readonlyArray.flatMap((): ReadonlyArray<number> => []); // ok

// #19535

const [x] = [""].flatMap(undefined as () => string[] | string[][]);
x == "";