From 275dbc7537accc869da2e47d7f62c519ee223ad4 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Fri, 22 Jul 2016 14:01:59 -0700
Subject: [PATCH] Forbid `await await`

---
 src/compiler/parser.ts                        |  5 ++++-
 .../baselines/reference/awaitAwait.errors.txt | 10 +++++++++
 tests/baselines/reference/awaitAwait.js       | 21 +++++++++++++++++++
 tests/cases/compiler/awaitAwait.ts            |  4 ++++
 4 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/awaitAwait.errors.txt
 create mode 100644 tests/baselines/reference/awaitAwait.js
 create mode 100644 tests/cases/compiler/awaitAwait.ts

diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index 61c7698c59d..9c54de6ba13 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -3337,7 +3337,10 @@ namespace ts {
         function parseAwaitExpression() {
             const node = <AwaitExpression>createNode(SyntaxKind.AwaitExpression);
             nextToken();
-            node.expression = parseSimpleUnaryExpression();
+            node.expression = token === SyntaxKind.AwaitKeyword
+                // Forbid `await await`
+                ? <UnaryExpression>createMissingNode(SyntaxKind.Identifier, /*reportAtCurrentPosition*/ false, Diagnostics.Expression_expected)
+                : parseSimpleUnaryExpression();
             return finishNode(node);
         }
 
diff --git a/tests/baselines/reference/awaitAwait.errors.txt b/tests/baselines/reference/awaitAwait.errors.txt
new file mode 100644
index 00000000000..5a04051139c
--- /dev/null
+++ b/tests/baselines/reference/awaitAwait.errors.txt
@@ -0,0 +1,10 @@
+tests/cases/compiler/awaitAwait.ts(2,11): error TS1109: Expression expected.
+
+
+==== tests/cases/compiler/awaitAwait.ts (1 errors) ====
+    async function f() {
+        await await 0;
+              ~~~~~
+!!! error TS1109: Expression expected.
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/awaitAwait.js b/tests/baselines/reference/awaitAwait.js
new file mode 100644
index 00000000000..14fb3a11505
--- /dev/null
+++ b/tests/baselines/reference/awaitAwait.js
@@ -0,0 +1,21 @@
+//// [awaitAwait.ts]
+async function f() {
+    await await 0;
+}
+
+
+//// [awaitAwait.js]
+var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
+    return new (P || (P = Promise))(function (resolve, reject) {
+        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
+        function rejected(value) { try { step(generator.throw(value)); } catch (e) { reject(e); } }
+        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
+        step((generator = generator.apply(thisArg, _arguments)).next());
+    });
+};
+function f() {
+    return __awaiter(this, void 0, void 0, function* () {
+        yield ;
+        yield 0;
+    });
+}
diff --git a/tests/cases/compiler/awaitAwait.ts b/tests/cases/compiler/awaitAwait.ts
new file mode 100644
index 00000000000..5a405804b00
--- /dev/null
+++ b/tests/cases/compiler/awaitAwait.ts
@@ -0,0 +1,4 @@
+// @target: es6
+async function f() {
+    await await 0;
+}