Merge pull request microsoft#27021 from ajafff/fix-functiontype-emit

Fix FunctionType emit when only parameter has no type

Author: rbuckton

src/compiler/emitter.ts

@@ -2818,7 +2818,8 @@ namespace ts {
             const parameter = singleOrUndefined(parameters);
             return parameter
                 && parameter.pos === parentNode.pos // may not have parsed tokens between parent and parameter
-                && !(isArrowFunction(parentNode) && parentNode.type) // arrow function may not have return type annotation
+                && isArrowFunction(parentNode)      // only arrow functions may have simple arrow head
+                && !parentNode.type                 // arrow function may not have return type annotation
                 && !some(parentNode.decorators)     // parent may not have decorators
                 && !some(parentNode.modifiers)      // parent may not have modifiers
                 && !some(parentNode.typeParameters) // parent may not have type parameters

tests/baselines/reference/printerApi/printsNodeCorrectly.functionTypes.js

@@ -1 +1 @@
-[args => any, <T>(args) => any, (...args) => any, (args?) => any, (args: any) => any, ({}) => any]
+[(args) => any, <T>(args) => any, (...args) => any, (args?) => any, (args: any) => any, ({}) => any]