swc/crates/swc_ecma_parser/tests/tsc/intersectionReductionStrict.ts

// @strict: true

declare const sym1: unique symbol;
declare const sym2: unique symbol;

type T1 = string & 'a';  // 'a'
type T2 = 'a' & string & 'b';  // never
type T3 = number & 10;  // 10
type T4 = 10 & number & 20;  // never
type T5 = symbol & typeof sym1;  // typeof sym1
type T6 = typeof sym1 & symbol & typeof sym2;  // never
type T7 = string & 'a' & number & 10 & symbol & typeof sym1;  // never

type T10 = string & ('a' | 'b');  // 'a' | 'b'
type T11 = (string | number) & ('a' | 10);  // 'a' | 10

type N1 = 'a' & 'b';
type N2 = { a: string } & null;
type N3 = { a: string } & undefined;
type N4 = string & number;
type N5 = number & object;
type N6 = symbol & string;
type N7 = void & string;

type X = { x: string };

type X1 = X | 'a' & 'b';
type X2 = X | { a: string } & null;
type X3 = X | { a: string } & undefined;
type X4 = X | string & number;
type X5 = X | number & object;
type X6 = X | symbol & string;
type X7 = X | void & string;

type A = { kind: 'a', foo: string };
type B = { kind: 'b', foo: number };
type C = { kind: 'c', foo: number };

declare let ab: A & B;
ab.kind;  // Error

declare let x: A | (B & C);  // A
let a: A = x;

type AB = A & B;  // never
type BC = B & C;  // never

type U1 = Partial<A & B>;  // never
type U2 = Readonly<A & B>;  // never
type U3 = (A & B)['kind'];  // never
type U4 = A & B | B & C;  // never
type U5 = A | B & C;  // A

type K1 = keyof (A & B);  // string | number | symbol
type K2 = keyof A | keyof B;  // 'kind' | 'foo'

type Merge1<T, U> = { [P in keyof (T & U)]: P extends keyof T ? T[P] : U[P & keyof U] }
type Merge2<T, U> = { [P in keyof T | keyof U]: P extends keyof T ? T[P] : U[P & keyof U] }

type M1 = { a: 1, b: 2 } & { a: 2, c: 3 };  // never
type M2 = Merge1<{ a: 1, b: 2 }, { a: 2, c: 3 }>;  // {}
type M3 = Merge2<{ a: 1, b: 2 }, { a: 2, c: 3 }>;  // { a: 1, b: 2, c: 3 }

// Repro from #31663

const x1 = { a: 'foo', b: 42 };
const x2 = { a: 'foo', b: true };

declare let k: 'a' | 'b';

x1[k] = 'bar' as any;  // Error
x2[k] = 'bar' as any;  // Error

const enum Tag1 {}
const enum Tag2 {}

declare let s1: string & Tag1;
declare let s2: string & Tag2;

declare let t1: string & Tag1 | undefined;
declare let t2: string & Tag2 | undefined;

s1 = s2;
s2 = s1;

t1 = t2;
t2 = t1;

// Repro from #36736

const f1 = (t: "a" | ("b" & "c")): "a" => t;

type Container<Type extends string> = {
    type: Type;
}

const f2 = (t: Container<"a"> | (Container<"b"> & Container<"c">)): Container<"a"> => t;
const f3 = (t: Container<"a"> | (Container<"b"> & { dataB: boolean } & Container<"a">)): Container<"a"> => t;
const f4 = (t: number | (Container<"b"> & { dataB: boolean } & Container<"a">)): number => t;