literalTypeWidening.types

=== tests/cases/conformance/types/literal/literalTypeWidening.ts ===
// Widening vs. non-widening literal types

function f1() {
>f1 : () => void

    const c1 = "hello";  // Widening type "hello"
>c1 : "hello"
>"hello" : "hello"

    let v1 = c1;  // Type string
>v1 : string
>c1 : "hello"

    const c2 = c1;  // Widening type "hello"
>c2 : "hello"
>c1 : "hello"

    let v2 = c2;  // Type string
>v2 : string
>c2 : "hello"

    const c3: "hello" = "hello";  // Type "hello"
>c3 : "hello"
>"hello" : "hello"

    let v3 = c3;  // Type "hello"
>v3 : "hello"
>c3 : "hello"

    const c4: "hello" = c1;  // Type "hello"
>c4 : "hello"
>c1 : "hello"

    let v4 = c4;  // Type "hello"
>v4 : "hello"
>c4 : "hello"
}

function f2(cond: boolean) {
>f2 : (cond: boolean) => void
>cond : boolean

    const c1 = cond ? "foo" : "bar";  // widening "foo" | widening "bar"
>c1 : "foo" | "bar"
>cond ? "foo" : "bar" : "foo" | "bar"
>cond : boolean
>"foo" : "foo"
>"bar" : "bar"

    const c2: "foo" | "bar" = c1;  // "foo" | "bar"
>c2 : "foo" | "bar"
>c1 : "foo" | "bar"

    const c3 = cond ? c1 : c2;  // "foo" | "bar"
>c3 : "foo" | "bar"
>cond ? c1 : c2 : "foo" | "bar"
>cond : boolean
>c1 : "foo" | "bar"
>c2 : "foo" | "bar"

    const c4 = cond ? c3 : "baz";  // "foo" | "bar" | widening "baz"
>c4 : "foo" | "bar" | "baz"
>cond ? c3 : "baz" : "foo" | "bar" | "baz"
>cond : boolean
>c3 : "foo" | "bar"
>"baz" : "baz"

    const c5: "foo" | "bar" | "baz" = c4; // "foo" | "bar" | "baz"
>c5 : "foo" | "bar" | "baz"
>c4 : "foo" | "bar" | "baz"

    let v1 = c1;  // string
>v1 : string
>c1 : "foo" | "bar"

    let v2 = c2;  // "foo" | "bar"
>v2 : "foo" | "bar"
>c2 : "foo" | "bar"

    let v3 = c3;  // "foo" | "bar"
>v3 : "foo" | "bar"
>c3 : "foo" | "bar"

    let v4 = c4;  // string
>v4 : string
>c4 : "foo" | "bar" | "baz"

    let v5 = c5;  // "foo" | "bar" | "baz"
>v5 : "foo" | "bar" | "baz"
>c5 : "foo" | "bar" | "baz"
}

function f3() {
>f3 : () => void

    const c1 = 123;  // Widening type 123
>c1 : 123
>123 : 123

    let v1 = c1;  // Type number
>v1 : number
>c1 : 123

    const c2 = c1;  // Widening type 123
>c2 : 123
>c1 : 123

    let v2 = c2;  // Type number
>v2 : number
>c2 : 123

    const c3: 123 = 123;  // Type 123
>c3 : 123
>123 : 123

    let v3 = c3;  // Type 123
>v3 : 123
>c3 : 123

    const c4: 123 = c1;  // Type 123
>c4 : 123
>c1 : 123

    let v4 = c4;  // Type 123
>v4 : 123
>c4 : 123
}

function f4(cond: boolean) {
>f4 : (cond: boolean) => void
>cond : boolean

    const c1 = cond ? 123 : 456;  // widening 123 | widening 456
>c1 : 123 | 456
>cond ? 123 : 456 : 123 | 456
>cond : boolean
>123 : 123
>456 : 456

    const c2: 123 | 456 = c1;  // 123 | 456
>c2 : 123 | 456
>c1 : 123 | 456

    const c3 = cond ? c1 : c2;  // 123 | 456
>c3 : 123 | 456
>cond ? c1 : c2 : 123 | 456
>cond : boolean
>c1 : 123 | 456
>c2 : 123 | 456

    const c4 = cond ? c3 : 789;  // 123 | 456 | widening 789
>c4 : 123 | 456 | 789
>cond ? c3 : 789 : 123 | 456 | 789
>cond : boolean
>c3 : 123 | 456
>789 : 789

    const c5: 123 | 456 | 789 = c4; // 123 | 456 | 789
>c5 : 123 | 456 | 789
>c4 : 123 | 456 | 789

    let v1 = c1;  // number
>v1 : number
>c1 : 123 | 456

    let v2 = c2;  // 123 | 456
>v2 : 123 | 456
>c2 : 123 | 456

    let v3 = c3;  // 123 | 456
>v3 : 123 | 456
>c3 : 123 | 456

    let v4 = c4;  // number
>v4 : number
>c4 : 123 | 456 | 789

    let v5 = c5;  // 123 | 456 | 789
>v5 : 123 | 456 | 789
>c5 : 123 | 456 | 789
}

function f5() {
>f5 : () => void

    const c1 = "foo";
>c1 : "foo"
>"foo" : "foo"

    let v1 = c1;
>v1 : string
>c1 : "foo"

    const c2: "foo" = "foo";
>c2 : "foo"
>"foo" : "foo"

    let v2 = c2;
>v2 : "foo"
>c2 : "foo"

    const c3 = "foo" as "foo";
>c3 : "foo"
>"foo" as "foo" : "foo"
>"foo" : "foo"

    let v3 = c3;
>v3 : "foo"
>c3 : "foo"

    const c4 = <"foo">"foo";
>c4 : "foo"
><"foo">"foo" : "foo"
>"foo" : "foo"

    let v4 = c4;
>v4 : "foo"
>c4 : "foo"
}

declare function widening<T>(x: T): T;
>widening : <T>(x: T) => T
>x : T

declare function nonWidening<T extends string | number | symbol>(x: T): T;
>nonWidening : <T extends string | number | symbol>(x: T) => T
>x : T

function f6(cond: boolean) {
>f6 : (cond: boolean) => void
>cond : boolean

    let x1 = widening('a');
>x1 : string
>widening('a') : "a"
>widening : <T>(x: T) => T
>'a' : "a"

    let x2 = widening(10);
>x2 : number
>widening(10) : 10
>widening : <T>(x: T) => T
>10 : 10

    let x3 = widening(cond ? 'a' : 10);
>x3 : string | number
>widening(cond ? 'a' : 10) : "a" | 10
>widening : <T>(x: T) => T
>cond ? 'a' : 10 : "a" | 10
>cond : boolean
>'a' : "a"
>10 : 10

    let y1 = nonWidening('a');
>y1 : "a"
>nonWidening('a') : "a"
>nonWidening : <T extends string | number | symbol>(x: T) => T
>'a' : "a"

    let y2 = nonWidening(10);
>y2 : 10
>nonWidening(10) : 10
>nonWidening : <T extends string | number | symbol>(x: T) => T
>10 : 10

    let y3 = nonWidening(cond ? 'a' : 10);
>y3 : "a" | 10
>nonWidening(cond ? 'a' : 10) : "a" | 10
>nonWidening : <T extends string | number | symbol>(x: T) => T
>cond ? 'a' : 10 : "a" | 10
>cond : boolean
>'a' : "a"
>10 : 10
}

// Repro from #10898

type FAILURE = "FAILURE";
>FAILURE : "FAILURE"

const FAILURE = "FAILURE";
>FAILURE : "FAILURE"
>"FAILURE" : "FAILURE"

type Result<T> = T | FAILURE;
>Result : Result<T>

function doWork<T>(): Result<T> {
>doWork : <T>() => Result<T>

  return FAILURE;
>FAILURE : "FAILURE"
}

function isSuccess<T>(result: Result<T>): result is T {
>isSuccess : <T>(result: Result<T>) => result is T
>result : Result<T>

  return !isFailure(result);
>!isFailure(result) : boolean
>isFailure(result) : boolean
>isFailure : <T>(result: Result<T>) => result is "FAILURE"
>result : Result<T>
}

function isFailure<T>(result: Result<T>): result is FAILURE {
>isFailure : <T>(result: Result<T>) => result is "FAILURE"
>result : Result<T>

  return result === FAILURE;
>result === FAILURE : boolean
>result : Result<T>
>FAILURE : "FAILURE"
}

function increment(x: number): number {
>increment : (x: number) => number
>x : number

  return x + 1;
>x + 1 : number
>x : number
>1 : 1
}

let result = doWork<number>();
>result : Result<number>
>doWork<number>() : Result<number>
>doWork : <T>() => Result<T>

if (isSuccess(result)) {
>isSuccess(result) : boolean
>isSuccess : <T>(result: Result<T>) => result is T
>result : Result<number>

  increment(result);
>increment(result) : number
>increment : (x: number) => number
>result : number
}

// Repro from #10898

type TestEvent = "onmouseover" | "onmouseout";
>TestEvent : TestEvent

function onMouseOver(): TestEvent { return "onmouseover"; }
>onMouseOver : () => TestEvent
>"onmouseover" : "onmouseover"

let x = onMouseOver();
>x : TestEvent
>onMouseOver() : TestEvent
>onMouseOver : () => TestEvent

// Repro from #23649

export function Set<K extends string>(...keys: K[]): Record<K, true | undefined> {
>Set : <K extends string>(...keys: K[]) => Record<K, true>
>keys : K[]
>true : true

  const result = {} as Record<K, true | undefined>
>result : Record<K, true>
>{} as Record<K, true | undefined> : Record<K, true>
>{} : {}
>true : true

  keys.forEach(key => result[key] = true)
>keys.forEach(key => result[key] = true) : void
>keys.forEach : (callbackfn: (value: K, index: number, array: K[]) => void, thisArg?: any) => void
>keys : K[]
>forEach : (callbackfn: (value: K, index: number, array: K[]) => void, thisArg?: any) => void
>key => result[key] = true : (key: K) => boolean
>key : K
>result[key] = true : true
>result[key] : Record<K, true>[K]
>result : Record<K, true>
>key : K
>true : true

  return result
>result : Record<K, true>
}

export function keys<K extends string, V>(obj: Record<K, V>): K[] {
>keys : <K extends string, V>(obj: Record<K, V>) => K[]
>obj : Record<K, V>

  return Object.keys(obj) as K[]
>Object.keys(obj) as K[] : K[]
>Object.keys(obj) : string[]
>Object.keys : (o: object) => string[]
>Object : ObjectConstructor
>keys : (o: object) => string[]
>obj : Record<K, V>
}

type Obj = { code: LangCode }
>Obj : Obj
>code : "fr" | "en" | "es" | "it" | "nl"

const langCodeSet = Set('fr', 'en', 'es', 'it', 'nl')
>langCodeSet : Record<"fr" | "en" | "es" | "it" | "nl", true>
>Set('fr', 'en', 'es', 'it', 'nl') : Record<"fr" | "en" | "es" | "it" | "nl", true>
>Set : <K extends string>(...keys: K[]) => Record<K, true>
>'fr' : "fr"
>'en' : "en"
>'es' : "es"
>'it' : "it"
>'nl' : "nl"

export type LangCode = keyof typeof langCodeSet
>LangCode : "fr" | "en" | "es" | "it" | "nl"
>langCodeSet : Record<"fr" | "en" | "es" | "it" | "nl", true>

export const langCodes = keys(langCodeSet)
>langCodes : ("fr" | "en" | "es" | "it" | "nl")[]
>keys(langCodeSet) : ("fr" | "en" | "es" | "it" | "nl")[]
>keys : <K extends string, V>(obj: Record<K, V>) => K[]
>langCodeSet : Record<"fr" | "en" | "es" | "it" | "nl", true>

const arr: Obj[] = langCodes.map(code => ({ code }))
>arr : Obj[]
>langCodes.map(code => ({ code })) : { code: "fr" | "en" | "es" | "it" | "nl"; }[]
>langCodes.map : <U>(callbackfn: (value: "fr" | "en" | "es" | "it" | "nl", index: number, array: ("fr" | "en" | "es" | "it" | "nl")[]) => U, thisArg?: any) => U[]
>langCodes : ("fr" | "en" | "es" | "it" | "nl")[]
>map : <U>(callbackfn: (value: "fr" | "en" | "es" | "it" | "nl", index: number, array: ("fr" | "en" | "es" | "it" | "nl")[]) => U, thisArg?: any) => U[]
>code => ({ code }) : (code: "fr" | "en" | "es" | "it" | "nl") => { code: "fr" | "en" | "es" | "it" | "nl"; }
>code : "fr" | "en" | "es" | "it" | "nl"
>({ code }) : { code: "fr" | "en" | "es" | "it" | "nl"; }
>{ code } : { code: "fr" | "en" | "es" | "it" | "nl"; }
>code : "fr" | "en" | "es" | "it" | "nl"

// Repro from #29081

function test<T extends { a: string, b: string }>(obj: T): T {
>test : <T extends { a: string; b: string; }>(obj: T) => T
>a : string
>b : string
>obj : T

    let { a, ...rest } = obj;
>a : string
>rest : Omit<T, "a">
>obj : T

    return { a: 'hello', ...rest } as T;
>{ a: 'hello', ...rest } as T : T
>{ a: 'hello', ...rest } : { a: string; } & Omit<T, "a">
>a : string
>'hello' : "hello"
>rest : Omit<T, "a">
}