Add tests

Author: jablko

tests/baselines/reference/arrayConcat2.js

@@ -6,6 +6,11 @@ a.concat('Hello');
 
 var b = new Array<string>();
 b.concat('hello');
+
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+x == "";
 
 
 //// [arrayConcat2.js]
@@ -14,3 +19,6 @@ a.concat("hello", 'world');
 a.concat('Hello');
 var b = new Array();
 b.concat('hello');
+// #19535
+var x = undefined.concat([""])[0];
+x == "";

tests/baselines/reference/arrayConcat2.symbols

@@ -21,3 +21,14 @@ 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, --, --))
 
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+>x : Symbol(x, Decl(arrayConcat2.ts, 10, 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, 10, 7))
+

tests/baselines/reference/arrayConcat2.types

@@ -30,3 +30,22 @@ b.concat('hello');
 >concat : { (...items: ConcatArray<string>[]): string[]; <U extends (string | ConcatArray<string>)[]>(...items: U): (string | Flatten<U[number]>)[]; }
 >'hello' : "hello"
 
+// #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 (string[] | ConcatArray<string[]>)[]>(...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 (string[] | ConcatArray<string[]>)[]>(...items: U): (string[] | Flatten<U[number]>)[]; }
+>[""] : string[]
+>"" : ""
+
+x == "";
+>x == "" : boolean
+>x : string | string[]
+>"" : ""
+

tests/cases/compiler/arrayConcat2.ts

@@ -5,3 +5,8 @@ a.concat('Hello');
 
 var b = new Array<string>();
 b.concat('hello');
+
+// #19535
+
+const [x] = (undefined as unknown as string[][]).concat([""]);
+x == "";