From bbbb56b08cb2ed96d96510b22938877fcf53c57b Mon Sep 17 00:00:00 2001
From: Yui <yuit@users.noreply.github.com>
Date: Thu, 5 May 2016 15:33:29 -0700
Subject: [PATCH] Allow async as parameter in arrowfunction (#8488)

* Allow async as a parameter name in simple arrow function

* Add tests
---
 src/compiler/parser.ts                                    | 7 ++++++-
 .../reference/arrowFunctionWithParameterNameAsync.js      | 6 ++++++
 .../reference/arrowFunctionWithParameterNameAsync.symbols | 7 +++++++
 .../reference/arrowFunctionWithParameterNameAsync.types   | 8 ++++++++
 .../arrowFunctionWithParameterNameAsync.ts                | 4 ++++
 5 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/arrowFunctionWithParameterNameAsync.js
 create mode 100644 tests/baselines/reference/arrowFunctionWithParameterNameAsync.symbols
 create mode 100644 tests/baselines/reference/arrowFunctionWithParameterNameAsync.types
 create mode 100644 tests/cases/conformance/async/es6/asyncArrowFunction/arrowFunctionWithParameterNameAsync.ts

diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index b4995a103f4..daebf8a930b 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -3002,9 +3002,14 @@ namespace ts {
         }
 
         function isUnParenthesizedAsyncArrowFunctionWorker(): Tristate {
+            // AsyncArrowFunctionExpression:
+            //      1) async[no LineTerminator here]AsyncArrowBindingIdentifier[?Yield][no LineTerminator here]=>AsyncConciseBody[?In]
+            //      2) CoverCallExpressionAndAsyncArrowHead[?Yield, ?Await][no LineTerminator here]=>AsyncConciseBody[?In]
             if (token === SyntaxKind.AsyncKeyword) {
                 nextToken();
-                if (scanner.hasPrecedingLineBreak()) {
+                // If the "async" is followed by "=>" token then it is not a begining of an async arrow-function
+                // but instead a simple arrow-function which will be parsed inside "parseAssignmentExpressionOrHigher"
+                if (scanner.hasPrecedingLineBreak() || token === SyntaxKind.EqualsGreaterThanToken) {
                     return Tristate.False;
                 }
                 // Check for un-parenthesized AsyncArrowFunction
diff --git a/tests/baselines/reference/arrowFunctionWithParameterNameAsync.js b/tests/baselines/reference/arrowFunctionWithParameterNameAsync.js
new file mode 100644
index 00000000000..0baea798c03
--- /dev/null
+++ b/tests/baselines/reference/arrowFunctionWithParameterNameAsync.js
@@ -0,0 +1,6 @@
+//// [arrowFunctionWithParameterNameAsync.ts]
+
+const x = async => async;
+
+//// [arrowFunctionWithParameterNameAsync.js]
+var x = function (async) { return async; };
diff --git a/tests/baselines/reference/arrowFunctionWithParameterNameAsync.symbols b/tests/baselines/reference/arrowFunctionWithParameterNameAsync.symbols
new file mode 100644
index 00000000000..26f36f48df7
--- /dev/null
+++ b/tests/baselines/reference/arrowFunctionWithParameterNameAsync.symbols
@@ -0,0 +1,7 @@
+=== tests/cases/conformance/async/es6/asyncArrowFunction/arrowFunctionWithParameterNameAsync.ts ===
+
+const x = async => async;
+>x : Symbol(x, Decl(arrowFunctionWithParameterNameAsync.ts, 1, 5))
+>async : Symbol(async, Decl(arrowFunctionWithParameterNameAsync.ts, 1, 9))
+>async : Symbol(async, Decl(arrowFunctionWithParameterNameAsync.ts, 1, 9))
+
diff --git a/tests/baselines/reference/arrowFunctionWithParameterNameAsync.types b/tests/baselines/reference/arrowFunctionWithParameterNameAsync.types
new file mode 100644
index 00000000000..4bdc60935ea
--- /dev/null
+++ b/tests/baselines/reference/arrowFunctionWithParameterNameAsync.types
@@ -0,0 +1,8 @@
+=== tests/cases/conformance/async/es6/asyncArrowFunction/arrowFunctionWithParameterNameAsync.ts ===
+
+const x = async => async;
+>x : (async: any) => any
+>async => async : (async: any) => any
+>async : any
+>async : any
+
diff --git a/tests/cases/conformance/async/es6/asyncArrowFunction/arrowFunctionWithParameterNameAsync.ts b/tests/cases/conformance/async/es6/asyncArrowFunction/arrowFunctionWithParameterNameAsync.ts
new file mode 100644
index 00000000000..1ade02c09d2
--- /dev/null
+++ b/tests/cases/conformance/async/es6/asyncArrowFunction/arrowFunctionWithParameterNameAsync.ts
@@ -0,0 +1,4 @@
+// @target: ES5
+// @noEmitHelpers: true
+
+const x = async => async;
\ No newline at end of file