Fix optional flow parenthesis (#1357)

In #1251, we now have a proper whitelist of all the types that should have parenthesis. Turns out, it included NullableTypeAnnotation which is `?a`. For `?a => void` this wasn't needed but for `(?(a => b)) => c` it was! It's better to always put it anyway if it's not just a simple literal.

I've added tests for all the combinations I could think of, so we'll catch regressions if they happen.

Fixes #1353

src/printer.js

@@ -2401,7 +2401,6 @@ function printFunctionParams(path, print, options, expandArg) {
   const flowTypeAnnotations = [
     "AnyTypeAnnotation",
     "NullLiteralTypeAnnotation",
-    "NullableTypeAnnotation",
     "GenericTypeAnnotation",
     "ThisTypeAnnotation",
     "NumberTypeAnnotation",
@@ -2411,14 +2410,17 @@ function printFunctionParams(path, print, options, expandArg) {
     "MixedTypeAnnotation",
     "BooleanTypeAnnotation",
     "BooleanLiteralTypeAnnotation",
-    "StringLiteralTypeAnnotation",
     "StringTypeAnnotation"
   ];
 
   const isFlowShorthandWithOneArg =
     (isObjectTypePropertyAFunction(parent) ||
       isTypeAnnotationAFunction(parent) ||
-      parent.type === "TypeAlias") &&
+      parent.type === "TypeAlias" ||
+      parent.type === "UnionTypeAnnotation" ||
+      parent.type === "IntersectionTypeAnnotation" ||
+      (parent.type === "FunctionTypeAnnotation" &&
+        parent.returnType === fun)) &&
     fun[paramsField].length === 1 &&
     fun[paramsField][0].name === null &&
     fun[paramsField][0].typeAnnotation &&

tests/flow_function_parentheses/__snapshots__/jsfmt.spec.js.snap

@@ -75,7 +75,7 @@ type f = /* comment */ arg => void;
 
 type f = arg /* comment */ => void;
 
-type f = ?arg => void;
+type f = (?arg) => void;
 
 class X {
   constructor(

tests/flow_return_arrow/__snapshots__/jsfmt.spec.js.snap

@@ -2,8 +2,48 @@
 
 exports[`issue-1249.js 1`] = `
 type Bar = ( number | string ) => number;
+type X = (?(number, number) => number) => void;
+type X = ?((number, number) => number) => void;
+type X = ?(number, number) => number => void;
+type X = 1234 => void;
+type X = 'abc' => void;
+type X = true => void;
+type X = false => void;
+type X = boolean => void;
+type X = number => void;
+type X = void => void;
+type X = null => void;
+type X = any => void;
+type X = empty => void;
+type X = mixed => void;
+type X = string => void;
+type X = abc => void;
+type X = a | b => void;
+type X = (a | b) => void;
+type X = a & b => void;
+type X = (a & b) => void;
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 type Bar = (number | string) => number;
+type X = (?(number, number) => number) => void;
+type X = ?((number, number) => number) => void;
+type X = ?(number, number) => number => void;
+type X = (1234) => void;
+type X = ("abc") => void;
+type X = true => void;
+type X = false => void;
+type X = boolean => void;
+type X = number => void;
+type X = void => void;
+type X = null => void;
+type X = any => void;
+type X = empty => void;
+type X = mixed => void;
+type X = string => void;
+type X = abc => void;
+type X = a | (b => void);
+type X = (a | b) => void;
+type X = a & (b => void);
+type X = (a & b) => void;
 
 `;
 
@@ -14,8 +54,8 @@ const f = (): (a & string => string) => {};
 function f(): string => string {}
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 const f = (): (string => string) => {};
-const f = (): a | ((string) => string) => {};
-const f = (): a & ((string) => string) => {};
+const f = (): a | (string => string) => {};
+const f = (): a & (string => string) => {};
 function f(): string => string {}
 
 `;

tests/flow_return_arrow/issue-1249.js

@@ -1 +1,21 @@
 type Bar = ( number | string ) => number;
+type X = (?(number, number) => number) => void;
+type X = ?((number, number) => number) => void;
+type X = ?(number, number) => number => void;
+type X = 1234 => void;
+type X = 'abc' => void;
+type X = true => void;
+type X = false => void;
+type X = boolean => void;
+type X = number => void;
+type X = void => void;
+type X = null => void;
+type X = any => void;
+type X = empty => void;
+type X = mixed => void;
+type X = string => void;
+type X = abc => void;
+type X = a | b => void;
+type X = (a | b) => void;
+type X = a & b => void;
+type X = (a & b) => void;