Fix object expression in arrow function expression (#897)

* Add new case for keeping parens around ObjectExpression in ArrowFunctionExpression.

* Add new test.

src/fast-path.js

@@ -246,6 +246,15 @@ FPp.needsParens = function(assumeExpressionContext) {
   }
 
   switch (node.type) {
+    case "CallExpression":
+      if (
+        node.callee.type === "ObjectExpression" &&
+        parent.type === "ArrowFunctionExpression"
+      ) {
+        return true;
+      }
+      return false;
+
     case "SpreadElement":
     case "SpreadProperty":
       return parent.type === "MemberExpression" &&

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

@@ -8,6 +8,7 @@ export default (() => {})();
 (() => {})\`\`;
 new (() => {});
 if ((() => {}) ? 1 : 0) {}
+let f = () => ({}())
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 (a => {}).length;
 typeof (() => {});
@@ -17,6 +18,7 @@ export default (() => {})();
 new (() => {})();
 if ((() => {}) ? 1 : 0) {
 }
+let f = () => ({}());
 "
 `;
 

tests/arrows/arrow_function_expression.js

@@ -5,3 +5,4 @@ export default (() => {})();
 (() => {})``;
 new (() => {});
 if ((() => {}) ? 1 : 0) {}
+let f = () => ({}())