fix: report error for mulitple union type (#2872)

Author: HerrCai0907

src/parser.ts

@@ -631,7 +631,7 @@ export class Parser extends DiagnosticEmitter {
     }
     // ... | type
     while (tn.skip(Token.Bar)) {
-      let nextType = this.parseType(tn, false, true);
+      let nextType = this.parseType(tn, true, false);
       if (!nextType) return null;
       let typeIsNull = type.kind == NodeKind.NamedType && (<NamedTypeNode>type).isNull;
       let nextTypeIsNull = nextType.kind == NodeKind.NamedType && (<NamedTypeNode>nextType).isNull;

tests/parser/union.ts

@@ -0,0 +1,9 @@
+export function foo(a: aaa | bbb | ccc): i32 {
+  return 1;
+}
+
+export function bar(a: i32 | u32 | f32): i32 {
+  return 1;
+}
+
+export let a: i32 | u32 | f32 | null = 1;

tests/parser/union.ts.fixture.ts

@@ -0,0 +1,4 @@
+export let a = 1;
+// ERROR 100: "Not implemented: union types" in union.ts(1,36+3)
+// ERROR 100: "Not implemented: union types" in union.ts(5,36+3)
+// ERROR 100: "Not implemented: union types" in union.ts(9,27+10)