parser: Fix testing for missing list (microsoft#25411)

* parser: Fix testing for missing list

* Fix return type

Author: Andy

src/compiler/parser.ts

@@ -2090,8 +2090,18 @@ namespace ts {
             return result;
         }
 
-        function createMissingList<T extends Node>(): NodeArray<T> {
-            return createNodeArray<T>([], getNodePos());
+        interface MissingList<T extends Node> extends NodeArray<T> {
+            isMissingList: true;
+        }
+
+        function createMissingList<T extends Node>(): MissingList<T> {
+            const list = createNodeArray<T>([], getNodePos()) as MissingList<T>;
+            list.isMissingList = true;
+            return list;
+        }
+
+        function isMissingList(arr: NodeArray<Node>): boolean {
+            return !!(arr as MissingList<Node>).isMissingList;
         }
 
         function parseBracketedList<T extends Node>(kind: ParsingContext, parseElement: () => T, open: SyntaxKind, close: SyntaxKind): NodeArray<T> {
@@ -2260,8 +2270,7 @@ namespace ts {
                 case SyntaxKind.FunctionType:
                 case SyntaxKind.ConstructorType: {
                     const { parameters, type } = node as FunctionOrConstructorTypeNode;
-                    // parameters.pos === parameters.end only if we used parseMissingList, else should contain at least `()`
-                    return parameters.pos === parameters.end || typeHasArrowFunctionBlockingParseError(type);
+                    return isMissingList(parameters) || typeHasArrowFunctionBlockingParseError(type);
                 }
                 case SyntaxKind.ParenthesizedType:
                     return typeHasArrowFunctionBlockingParseError((node as ParenthesizedTypeNode).type);

tests/baselines/reference/parseArrowFunctionWithFunctionReturnType.js

@@ -0,0 +1,6 @@
+//// [parseArrowFunctionWithFunctionReturnType.ts]
+const fn = <T>(): (() => T) => null as any;
+
+
+//// [parseArrowFunctionWithFunctionReturnType.js]
+var fn = function () { return null; };

tests/baselines/reference/parseArrowFunctionWithFunctionReturnType.symbols

@@ -0,0 +1,6 @@
+=== tests/cases/compiler/parseArrowFunctionWithFunctionReturnType.ts ===
+const fn = <T>(): (() => T) => null as any;
+>fn : Symbol(fn, Decl(parseArrowFunctionWithFunctionReturnType.ts, 0, 5))
+>T : Symbol(T, Decl(parseArrowFunctionWithFunctionReturnType.ts, 0, 12))
+>T : Symbol(T, Decl(parseArrowFunctionWithFunctionReturnType.ts, 0, 12))
+

tests/baselines/reference/parseArrowFunctionWithFunctionReturnType.types

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/parseArrowFunctionWithFunctionReturnType.ts ===
+const fn = <T>(): (() => T) => null as any;
+>fn : <T>() => () => T
+><T>(): (() => T) => null as any : <T>() => () => T
+>T : T
+>T : T
+>null as any : any
+>null : null
+

tests/cases/compiler/parseArrowFunctionWithFunctionReturnType.ts

@@ -0,0 +1 @@
+const fn = <T>(): (() => T) => null as any;