Parenthesize `new F(await a)` and `x[await a]` correctly (#1513)

src/fast-path.js

@@ -395,10 +395,12 @@ FPp.needsParens = function() {
         case "LogicalExpression":
         case "SpreadElement":
         case "SpreadProperty":
-        case "NewExpression":
-        case "MemberExpression":
           return true;
 
+        case "MemberExpression":
+          return parent.object === node;
+
+        case "NewExpression":
         case "CallExpression":
           return parent.callee === node;
 

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

@@ -13,6 +13,10 @@ function *f(){
 async function f() {
   a = !(await f());
 }
+async () => {
+  new A(await x);
+  obj[await x];
+}
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 async function f() {
   (await f()).length;
@@ -26,6 +30,10 @@ function* f() {
 async function f() {
   a = !await f();
 }
+async () => {
+  new A(await x);
+  obj[await x];
+};
 
 `;
 

tests/async/await_parse.js

@@ -10,3 +10,7 @@ function *f(){
 async function f() {
   a = !(await f());
 }
+async () => {
+  new A(await x);
+  obj[await x];
+}