Fix flow babel-generator function parantheses (#9523)

packages/babel-generator/src/node/parentheses.js

@@ -35,7 +35,16 @@ export function NullableTypeAnnotation(node: Object, parent: Object): boolean {
   return t.isArrayTypeAnnotation(parent);
 }
 
-export { NullableTypeAnnotation as FunctionTypeAnnotation };
+export function FunctionTypeAnnotation(node: Object, parent: Object): boolean {
+  return (
+    // (() => A) | (() => B)
+    t.isUnionTypeAnnotation(parent) ||
+    // (() => A) & (() => B)
+    t.isIntersectionTypeAnnotation(parent) ||
+    // (() => A)[]
+    t.isArrayTypeAnnotation(parent)
+  );
+}
 
 export function UpdateExpression(node: Object, parent: Object): boolean {
   return (

packages/babel-generator/test/fixtures/flow/opaque-type-alias/output.js

@@ -7,4 +7,4 @@ opaque type union = {
 } | {
   type: "B"
 };
-opaque type overloads = (x: string) => number & (x: number) => string;
+opaque type overloads = ((x: string) => number) & ((x: number) => string);

packages/babel-generator/test/fixtures/flow/parantheses/input.js

@@ -0,0 +1,3 @@
+type A = (<T>(T) => $Foo<T>) & (<T>(T) => $Foo<T>);
+type B = (<T>(T) => $Foo<T>) | (<T>(T) => $Foo<T>);
+type C = (<T>(T) => $Foo<T>)[];

packages/babel-generator/test/fixtures/flow/parantheses/output.js

@@ -0,0 +1,3 @@
+type A = (<T>(T) => $Foo<T>) & (<T>(T) => $Foo<T>);
+type B = (<T>(T) => $Foo<T>) | (<T>(T) => $Foo<T>);
+type C = (<T>(T) => $Foo<T>)[];

packages/babel-generator/test/fixtures/flow/type-alias/output.js

@@ -7,6 +7,6 @@ type union = {
 } | {
   type: "B"
 };
-type overloads = (x: string) => number & (x: number) => string;
+type overloads = ((x: string) => number) & ((x: number) => string);
 type func = (string) => string;
 type D = X.Y<Z>;

packages/babel-generator/test/fixtures/flow/type-annotations/output.js

@@ -180,7 +180,7 @@ class Array {
 
 }
 
-var x: () => number | () => string = fn;
+var x: () => number | (() => string) = fn;
 var x: typeof Y = Y;
 var x: typeof Y | number = Y;
 var {