arrayFlatMap.types

=== tests/cases/compiler/arrayFlatMap.ts ===
const array: number[] = [];
>array : number[]
>[] : number[]

const readonlyArray: ReadonlyArray<number> = [];
>readonlyArray : readonly number[]
>[] : 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 : number[]
>flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]
>(): ReadonlyArray<number> => [] : () => ReadonlyArray<number>
>[] : number[]

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 : readonly number[]
>flatMap : <U, This = undefined>(callback: (this: This, value: number, index: number, array: number[]) => U | readonly U[], thisArg?: This) => U[]
>(): ReadonlyArray<number> => [] : () => ReadonlyArray<number>
>[] : number[]