Add tests

Author: jablko

Diff for: tests/baselines/reference/arrayConcat2.js

@@ -6,6 +6,21 @@ a.concat('Hello');
 
 var b = new Array<string>();
 b.concat('hello');
+
+const expected: undefined = undefined as Flatten<undefined>;
+
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+x == "";
+
+// #26378
+
+[""].concat([1]);
+
+// #26976
+
+[].concat([""]);
 
 
 //// [arrayConcat2.js]
@@ -14,3 +29,11 @@ a.concat("hello", 'world');
 a.concat('Hello');
 var b = new Array();
 b.concat('hello');
+var expected = undefined;
+// #19535
+var x = undefined.concat([""])[0];
+x == "";
+// #26378
+[""].concat([1]);
+// #26976
+[].concat([""]);

Diff for: tests/baselines/reference/arrayConcat2.symbols

@@ -21,3 +21,31 @@ b.concat('hello');
 >b : Symbol(b, Decl(arrayConcat2.ts, 5, 3))
 >concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 
+const expected: undefined = undefined as Flatten<undefined>;
+>expected : Symbol(expected, Decl(arrayConcat2.ts, 8, 5))
+>undefined : Symbol(undefined)
+>Flatten : Symbol(Flatten, Decl(lib.es5.d.ts, --, --))
+
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+>x : Symbol(x, Decl(arrayConcat2.ts, 12, 7))
+>(undefined as unknown as string[][]).concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>undefined : Symbol(undefined)
+>concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+x == "";
+>x : Symbol(x, Decl(arrayConcat2.ts, 12, 7))
+
+// #26378
+
+[""].concat([1]);
+>[""].concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+// #26976
+
+[].concat([""]);
+>[].concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+

Diff for: tests/baselines/reference/arrayConcat2.types

@@ -1,7 +1,7 @@
 === tests/cases/compiler/arrayConcat2.ts ===
 var a: string[] = [];
 >a : string[]
->[] : undefined[]
+>[] : never[]
 
 a.concat("hello", 'world');
 >a.concat("hello", 'world') : string[]
@@ -30,3 +30,48 @@ b.concat('hello');
 >concat : { (...items: ConcatArray<string>[]): string[]; <U extends any[]>(...items: U): (string | Flatten<U[number]>)[]; }
 >'hello' : "hello"
 
+const expected: undefined = undefined as Flatten<undefined>;
+>expected : undefined
+>undefined as Flatten<undefined> : undefined
+>undefined : undefined
+
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+>x : string | string[]
+>(undefined as unknown as string[][]).concat([""]) : (string | string[])[]
+>(undefined as unknown as string[][]).concat : { (...items: ConcatArray<string[]>[]): string[][]; <U extends any[]>(...items: U): (string[] | Flatten<U[number]>)[]; }
+>(undefined as unknown as string[][]) : string[][]
+>undefined as unknown as string[][] : string[][]
+>undefined as unknown : unknown
+>undefined : undefined
+>concat : { (...items: ConcatArray<string[]>[]): string[][]; <U extends any[]>(...items: U): (string[] | Flatten<U[number]>)[]; }
+>[""] : string[]
+>"" : ""
+
+x == "";
+>x == "" : boolean
+>x : string | string[]
+>"" : ""
+
+// #26378
+
+[""].concat([1]);
+>[""].concat([1]) : (string | number)[]
+>[""].concat : { (...items: ConcatArray<string>[]): string[]; <U extends any[]>(...items: U): (string | Flatten<U[number]>)[]; }
+>[""] : string[]
+>"" : ""
+>concat : { (...items: ConcatArray<string>[]): string[]; <U extends any[]>(...items: U): (string | Flatten<U[number]>)[]; }
+>[1] : number[]
+>1 : 1
+
+// #26976
+
+[].concat([""]);
+>[].concat([""]) : string[]
+>[].concat : { (...items: ConcatArray<never>[]): never[]; <U extends any[]>(...items: U): Flatten<U[number]>[]; }
+>[] : never[]
+>concat : { (...items: ConcatArray<never>[]): never[]; <U extends any[]>(...items: U): Flatten<U[number]>[]; }
+>[""] : string[]
+>"" : ""
+

Diff for: tests/baselines/reference/arrayFlat.js

@@ -0,0 +1,11 @@
+//// [arrayFlat.ts]
+// #24579 and #29604
+
+const [x] = [[""], [1]].flat();
+const assert: any extends typeof x ? true : false = false;
+
+
+//// [arrayFlat.js]
+// #24579 and #29604
+var x = [[""], [1]].flat()[0];
+var assert = false;

Diff for: tests/baselines/reference/arrayFlat.symbols

@@ -0,0 +1,12 @@
+=== tests/cases/compiler/arrayFlat.ts ===
+// #24579 and #29604
+
+const [x] = [[""], [1]].flat();
+>x : Symbol(x, Decl(arrayFlat.ts, 2, 7))
+>[[""], [1]].flat : Symbol(Array.flat, Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --) ... and 1 more)
+>flat : Symbol(Array.flat, Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --) ... and 1 more)
+
+const assert: any extends typeof x ? true : false = false;
+>assert : Symbol(assert, Decl(arrayFlat.ts, 3, 5))
+>x : Symbol(x, Decl(arrayFlat.ts, 2, 7))
+

Diff for: tests/baselines/reference/arrayFlat.types

@@ -0,0 +1,21 @@
+=== tests/cases/compiler/arrayFlat.ts ===
+// #24579 and #29604
+
+const [x] = [[""], [1]].flat();
+>x : string | number
+>[[""], [1]].flat() : (string | number)[]
+>[[""], [1]].flat : { (depth: 4): (string | number)[]; (depth: 3): (string | number)[]; (depth: 2): (string | number)[]; (depth?: 1): (string | number)[]; (depth: 0): (string[] | number[])[]; (depth: number): (string | number | string[] | number[])[]; }
+>[[""], [1]] : (string[] | number[])[]
+>[""] : string[]
+>"" : ""
+>[1] : number[]
+>1 : 1
+>flat : { (depth: 4): (string | number)[]; (depth: 3): (string | number)[]; (depth: 2): (string | number)[]; (depth?: 1): (string | number)[]; (depth: 0): (string[] | number[])[]; (depth: number): (string | number | string[] | number[])[]; }
+
+const assert: any extends typeof x ? true : false = false;
+>assert : boolean
+>x : string | number
+>true : true
+>false : false
+>false : false
+

Diff for: tests/baselines/reference/arrayFlatMap.js

@@ -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 == "";

Diff for: tests/baselines/reference/arrayFlatMap.symbols

@@ -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))
+

Diff for: tests/baselines/reference/arrayFlatMap.types

@@ -23,3 +23,20 @@ readonlyArray.flatMap((): ReadonlyArray<number> => []); // ok
 >(): 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>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => Flatten<U>[]
+>[""] : string[]
+>"" : ""
+>flatMap : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => Flatten<U>[]
+>undefined as () => string[] | string[][] : () => string[] | string[][]
+>undefined : undefined
+
+x == "";
+>x == "" : boolean
+>x : string | string[]
+>"" : ""
+

Diff for: tests/cases/compiler/arrayConcat2.ts

@@ -5,3 +5,19 @@ a.concat('Hello');
 
 var b = new Array<string>();
 b.concat('hello');
+
+const expected: undefined = undefined as Flatten<undefined>;
+
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+x == "";
+
+// #26378
+
+[""].concat([1]);
+
+// #26976
+
+// @strictNullChecks: true
+[].concat([""]);

Diff for: tests/cases/compiler/arrayFlat.ts

@@ -0,0 +1,6 @@
+// @lib: es2019
+
+// #24579 and #29604
+
+const [x] = [[""], [1]].flat();
+const assert: any extends typeof x ? true : false = false;

Diff for: tests/cases/compiler/arrayFlatMap.ts

@@ -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 == "";