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Explore adding the Boolean to filter to narrow out null/undefined in array#filter #50377

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a99026a
Explore adding the Boolean to filter to narrow out null/undefined
orta Aug 19, 2022
4ac0e1d
Use the right file
orta Aug 19, 2022
0c5dbac
Use a different example, and get it in the readonly filter
orta Aug 21, 2022
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12 changes: 12 additions & 0 deletions src/lib/es5.d.ts
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Expand Up @@ -1229,6 +1229,12 @@ interface ReadonlyArray<T> {
* @param thisArg An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.
*/
filter<S extends T>(predicate: (value: T, index: number, array: readonly T[]) => value is S, thisArg?: any): S[];
/**
* Filters out nullish values from the array. Used when `Boolean` is passed as the argument to filter.
* @param predicate the `Boolean` constructor, which validates the truthiness of the value being mapped over.
* @param thisArg An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.
*/
filter<S extends T>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[];
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This looks like a hack solution. Is it to improve how ts infer the return type of a function so it can infer a type predicate?

arr.filter(x => typeof x === 'number')
// T[].filter<(x: T) => x is number>

arr.filter(x => x instanceof Q)
// T[].filter<(x: T) => x is Q>

arr.filter(x => x.kind === 1)
// ({ kind: 1, data: T } | { kind: 2, data: Q })[].filter<(x: ...) => x is { kind: 1, data: T }>

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No, this has nothing to do with inferring type predicates from function expressions, it’s just so you can use .filter(Boolean). See #50387.

/**
* Returns the elements of an array that meet the condition specified in a callback function.
* @param predicate A function that accepts up to three arguments. The filter method calls the predicate function one time for each element in the array.
Expand Down Expand Up @@ -1426,6 +1432,12 @@ interface Array<T> {
* @param thisArg An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.
*/
filter(predicate: (value: T, index: number, array: T[]) => unknown, thisArg?: any): T[];
/**
* Filters out nullish values from the array. Used when `Boolean` is passed as the argument to filter.
* @param predicate the `Boolean` constructor, which validates the truthiness of the value being mapped over.
* @param thisArg An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.
*/
filter<S extends T>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[];
/**
* Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.
* @param callbackfn A function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.
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4 changes: 2 additions & 2 deletions tests/baselines/reference/arrayFilter.symbols
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Expand Up @@ -14,9 +14,9 @@ var foo = [
]

foo.filter(x => x.name); //should accepted all possible types not only boolean!
>foo.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>foo.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>foo : Symbol(foo, Decl(arrayFilter.ts, 0, 3))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>x : Symbol(x, Decl(arrayFilter.ts, 6, 11))
>x.name : Symbol(name, Decl(arrayFilter.ts, 1, 5))
>x : Symbol(x, Decl(arrayFilter.ts, 6, 11))
Expand Down
4 changes: 2 additions & 2 deletions tests/baselines/reference/arrayFilter.types
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Expand Up @@ -22,9 +22,9 @@ var foo = [

foo.filter(x => x.name); //should accepted all possible types not only boolean!
>foo.filter(x => x.name) : { name: string; }[]
>foo.filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; }
>foo.filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; <S extends { name: string; }>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>foo : { name: string; }[]
>filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; }
>filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; <S extends { name: string; }>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>x => x.name : (x: { name: string; }) => string
>x : { name: string; }
>x.name : string
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14 changes: 14 additions & 0 deletions tests/baselines/reference/arrayFilterBoolean.js
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@@ -0,0 +1,14 @@
//// [arrayFilterBoolean.ts]
const mixed = [undefined, "string", null]
const mixedReadonly: Readonly<typeof mixed> = [undefined, "string", null]

const shouldBeJustStringForMutableArray = mixed.filter(Boolean)

const shouldBeJustStringForReadonlyArray = mixedReadonly.filter(Boolean)

//// [arrayFilterBoolean.js]
"use strict";
var mixed = [undefined, "string", null];
var mixedReadonly = [undefined, "string", null];
var shouldBeJustStringForMutableArray = mixed.filter(Boolean);
var shouldBeJustStringForReadonlyArray = mixedReadonly.filter(Boolean);
25 changes: 25 additions & 0 deletions tests/baselines/reference/arrayFilterBoolean.symbols
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@@ -0,0 +1,25 @@
=== tests/cases/compiler/arrayFilterBoolean.ts ===
const mixed = [undefined, "string", null]
>mixed : Symbol(mixed, Decl(arrayFilterBoolean.ts, 0, 5))
>undefined : Symbol(undefined)

const mixedReadonly: Readonly<typeof mixed> = [undefined, "string", null]
>mixedReadonly : Symbol(mixedReadonly, Decl(arrayFilterBoolean.ts, 1, 5))
>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
>mixed : Symbol(mixed, Decl(arrayFilterBoolean.ts, 0, 5))
>undefined : Symbol(undefined)

const shouldBeJustStringForMutableArray = mixed.filter(Boolean)
>shouldBeJustStringForMutableArray : Symbol(shouldBeJustStringForMutableArray, Decl(arrayFilterBoolean.ts, 3, 5))
>mixed.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>mixed : Symbol(mixed, Decl(arrayFilterBoolean.ts, 0, 5))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>Boolean : Symbol(Boolean, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))

const shouldBeJustStringForReadonlyArray = mixedReadonly.filter(Boolean)
>shouldBeJustStringForReadonlyArray : Symbol(shouldBeJustStringForReadonlyArray, Decl(arrayFilterBoolean.ts, 5, 5))
>mixedReadonly.filter : Symbol(ReadonlyArray.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>mixedReadonly : Symbol(mixedReadonly, Decl(arrayFilterBoolean.ts, 1, 5))
>filter : Symbol(ReadonlyArray.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>Boolean : Symbol(Boolean, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))

32 changes: 32 additions & 0 deletions tests/baselines/reference/arrayFilterBoolean.types
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@@ -0,0 +1,32 @@
=== tests/cases/compiler/arrayFilterBoolean.ts ===
const mixed = [undefined, "string", null]
>mixed : (string | null | undefined)[]
>[undefined, "string", null] : (string | null | undefined)[]
>undefined : undefined
>"string" : "string"
>null : null

const mixedReadonly: Readonly<typeof mixed> = [undefined, "string", null]
>mixedReadonly : readonly (string | null | undefined)[]
>mixed : (string | null | undefined)[]
>[undefined, "string", null] : (string | null | undefined)[]
>undefined : undefined
>"string" : "string"
>null : null

const shouldBeJustStringForMutableArray = mixed.filter(Boolean)
>shouldBeJustStringForMutableArray : (string | null | undefined)[]
>mixed.filter(Boolean) : (string | null | undefined)[]
>mixed.filter : { <S extends string | null | undefined>(predicate: (value: string | null | undefined, index: number, array: (string | null | undefined)[]) => value is S, thisArg?: any): S[]; (predicate: (value: string | null | undefined, index: number, array: (string | null | undefined)[]) => unknown, thisArg?: any): (string | null | undefined)[]; <S extends string | null | undefined>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>mixed : (string | null | undefined)[]
>filter : { <S extends string | null | undefined>(predicate: (value: string | null | undefined, index: number, array: (string | null | undefined)[]) => value is S, thisArg?: any): S[]; (predicate: (value: string | null | undefined, index: number, array: (string | null | undefined)[]) => unknown, thisArg?: any): (string | null | undefined)[]; <S extends string | null | undefined>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>Boolean : BooleanConstructor

const shouldBeJustStringForReadonlyArray = mixedReadonly.filter(Boolean)
>shouldBeJustStringForReadonlyArray : string[]
>mixedReadonly.filter(Boolean) : string[]
>mixedReadonly.filter : { <S extends string | null | undefined>(predicate: (value: string | null | undefined, index: number, array: readonly (string | null | undefined)[]) => value is S, thisArg?: any): S[]; <S extends string | null | undefined>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; (predicate: (value: string | null | undefined, index: number, array: readonly (string | null | undefined)[]) => unknown, thisArg?: any): (string | null | undefined)[]; }
>mixedReadonly : readonly (string | null | undefined)[]
>filter : { <S extends string | null | undefined>(predicate: (value: string | null | undefined, index: number, array: readonly (string | null | undefined)[]) => value is S, thisArg?: any): S[]; <S extends string | null | undefined>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; (predicate: (value: string | null | undefined, index: number, array: readonly (string | null | undefined)[]) => unknown, thisArg?: any): (string | null | undefined)[]; }
>Boolean : BooleanConstructor

12 changes: 6 additions & 6 deletions tests/baselines/reference/booleanFilterAnyArray.symbols
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Expand Up @@ -70,9 +70,9 @@ var ys: any[];

var ys = realanys.filter(Boolean)
>ys : Symbol(ys, Decl(booleanFilterAnyArray.ts, 16, 3), Decl(booleanFilterAnyArray.ts, 17, 3))
>realanys.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>realanys.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>realanys : Symbol(realanys, Decl(booleanFilterAnyArray.ts, 15, 11))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>Boolean : Symbol(Boolean, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))

var foo = [{ name: 'x' }]
Expand All @@ -86,9 +86,9 @@ var foor: Array<{name: string}>

var foor = foo.filter(x => x.name)
>foor : Symbol(foor, Decl(booleanFilterAnyArray.ts, 20, 3), Decl(booleanFilterAnyArray.ts, 21, 3))
>foo.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>foo.filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>foo : Symbol(foo, Decl(booleanFilterAnyArray.ts, 19, 3))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>x : Symbol(x, Decl(booleanFilterAnyArray.ts, 21, 22))
>x.name : Symbol(name, Decl(booleanFilterAnyArray.ts, 19, 12))
>x : Symbol(x, Decl(booleanFilterAnyArray.ts, 21, 22))
Expand All @@ -100,8 +100,8 @@ var foos: Array<boolean>

var foos = [true, true, false, null].filter((thing): thing is boolean => thing !== null)
>foos : Symbol(foos, Decl(booleanFilterAnyArray.ts, 22, 3), Decl(booleanFilterAnyArray.ts, 23, 3))
>[true, true, false, null].filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>[true, true, false, null].filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>filter : Symbol(Array.filter, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>thing : Symbol(thing, Decl(booleanFilterAnyArray.ts, 23, 45))
>thing : Symbol(thing, Decl(booleanFilterAnyArray.ts, 23, 45))
>thing : Symbol(thing, Decl(booleanFilterAnyArray.ts, 23, 45))
Expand Down
12 changes: 6 additions & 6 deletions tests/baselines/reference/booleanFilterAnyArray.types
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Expand Up @@ -45,9 +45,9 @@ var ys: any[];
var ys = realanys.filter(Boolean)
>ys : any[]
>realanys.filter(Boolean) : any[]
>realanys.filter : { <S extends any>(predicate: (value: any, index: number, array: any[]) => value is S, thisArg?: any): S[]; (predicate: (value: any, index: number, array: any[]) => unknown, thisArg?: any): any[]; }
>realanys.filter : { <S extends any>(predicate: (value: any, index: number, array: any[]) => value is S, thisArg?: any): S[]; (predicate: (value: any, index: number, array: any[]) => unknown, thisArg?: any): any[]; <S extends any>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>realanys : any[]
>filter : { <S extends any>(predicate: (value: any, index: number, array: any[]) => value is S, thisArg?: any): S[]; (predicate: (value: any, index: number, array: any[]) => unknown, thisArg?: any): any[]; }
>filter : { <S extends any>(predicate: (value: any, index: number, array: any[]) => value is S, thisArg?: any): S[]; (predicate: (value: any, index: number, array: any[]) => unknown, thisArg?: any): any[]; <S extends any>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>Boolean : BooleanConstructor

var foo = [{ name: 'x' }]
Expand All @@ -64,9 +64,9 @@ var foor: Array<{name: string}>
var foor = foo.filter(x => x.name)
>foor : { name: string; }[]
>foo.filter(x => x.name) : { name: string; }[]
>foo.filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; }
>foo.filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; <S extends { name: string; }>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>foo : { name: string; }[]
>filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; }
>filter : { <S extends { name: string; }>(predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => value is S, thisArg?: any): S[]; (predicate: (value: { name: string; }, index: number, array: { name: string; }[]) => unknown, thisArg?: any): { name: string; }[]; <S extends { name: string; }>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>x => x.name : (x: { name: string; }) => string
>x : { name: string; }
>x.name : string
Expand All @@ -79,13 +79,13 @@ var foos: Array<boolean>
var foos = [true, true, false, null].filter((thing): thing is boolean => thing !== null)
>foos : boolean[]
>[true, true, false, null].filter((thing): thing is boolean => thing !== null) : boolean[]
>[true, true, false, null].filter : { <S extends boolean>(predicate: (value: boolean, index: number, array: boolean[]) => value is S, thisArg?: any): S[]; (predicate: (value: boolean, index: number, array: boolean[]) => unknown, thisArg?: any): boolean[]; }
>[true, true, false, null].filter : { <S extends boolean>(predicate: (value: boolean, index: number, array: boolean[]) => value is S, thisArg?: any): S[]; (predicate: (value: boolean, index: number, array: boolean[]) => unknown, thisArg?: any): boolean[]; <S extends boolean>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>[true, true, false, null] : boolean[]
>true : true
>true : true
>false : false
>null : null
>filter : { <S extends boolean>(predicate: (value: boolean, index: number, array: boolean[]) => value is S, thisArg?: any): S[]; (predicate: (value: boolean, index: number, array: boolean[]) => unknown, thisArg?: any): boolean[]; }
>filter : { <S extends boolean>(predicate: (value: boolean, index: number, array: boolean[]) => value is S, thisArg?: any): S[]; (predicate: (value: boolean, index: number, array: boolean[]) => unknown, thisArg?: any): boolean[]; <S extends boolean>(predicate: BooleanConstructor, thisArg?: any): NonNullable<S>[]; }
>(thing): thing is boolean => thing !== null : (thing: boolean) => thing is boolean
>thing : boolean
>thing !== null : boolean
Expand Down
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