Make await x ** y fail to parse

Closes #984

Author: marijnh

acorn/src/expression.js

@@ -1029,6 +1029,6 @@ pp.parseAwait = function() {
 
   let node = this.startNode()
   this.next()
-  node.argument = this.parseMaybeUnary(null, false)
+  node.argument = this.parseMaybeUnary(null, true)
   return this.finishNode(node, "AwaitExpression")
 }

test/tests-asyncawait.js

@@ -3524,6 +3524,6 @@ test("({ async delete() {} })", {}, {ecmaVersion: 8})
 
 testFail("abc: async function a() {}", "Unexpected token (1:5)", {ecmaVersion: 8})
 
-test("(async() => { await 4 ** 2 })()", {}, {ecmaVersion: 8})
+testFail("(async() => { await 4 ** 2 })()", "Unexpected token (1:22)", {ecmaVersion: 8})
 
 testFail("4 + async() => 2", "Unexpected token (1:12)", {ecmaVersion: 8, loose: false})