Remove extra parenthesis around await inside of unary expression (#745)

Big props to @bakkot for mentioning that yield shouldn't be applied the same treatment.

Fixes #728

src/fast-path.js

@@ -354,12 +354,14 @@ FPp.needsParens = function(assumeExpressionContext) {
       }
 
     case "YieldExpression":
+      if (parent.type === "UnaryExpression") {
+        return true;
+      }
     case "AwaitExpression":
       switch (parent.type) {
         case "TaggedTemplateExpression":
         case "BinaryExpression":
         case "LogicalExpression":
-        case "UnaryExpression":
         case "SpreadElement":
         case "SpreadProperty":
         case "NewExpression":

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

@@ -4,13 +4,26 @@ async function g() {
   invariant(
     (await driver.navigator.getUrl()).substr(-7)
   );
-}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+}
+function *f(){
+  !(yield a);
+}
+async function f() {
+  a = !(await f());
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 async function f() {
   (await f()).length;
 }
 async function g() {
   invariant((await driver.navigator.getUrl()).substr(-7));
 }
+function* f() {
+  !(yield a);
+}
+async function f() {
+  a = !await f();
+}
 "
 `;
 

tests/async/await_parse.js

@@ -3,4 +3,10 @@ async function g() {
   invariant(
     (await driver.navigator.getUrl()).substr(-7)
   );
-}
+}
+function *f(){
+  !(yield a);
+}
+async function f() {
+  a = !(await f());
+}