Emit arrow function es6

src/compiler/checker.ts

@@ -4836,6 +4836,16 @@ module ts {
         function checkIdentifier(node: Identifier): Type {
             var symbol = getResolvedSymbol(node);
 
+            // As noted in ECMAScript 6 language spec, arrow functions never have an arguments objects.
+            // Although in down-level emit of arrow function, we emit it using function expression which means that
+            // arguments objects will be bound to the inner object; emitting arrow function natively in ES6, arguments objects
+            // will be bound to non-arrow function that contain this arrow function. This results in inconsistent behaviour.
+            // To avoid that we will give an error to users if they use arguments objects in arrow function so that they
+            // can explicitly bound arguments objects
+            if (symbol === argumentsSymbol && getContainingFunction(node).kind === SyntaxKind.ArrowFunction) {
+              error(node, Diagnostics.An_argument_object_has_different_behaviour_across_Javascript_versions_Use_function_expression_or_rest_parameters_instead);
+            }
+
             if (symbol.flags & SymbolFlags.Import) {
                 var symbolLinks = getSymbolLinks(symbol);
                 if (!symbolLinks.referenced) {
@@ -4890,7 +4900,14 @@ module ts {
             // Now skip arrow functions to get the "real" owner of 'this'.
             if (container.kind === SyntaxKind.ArrowFunction) {
                 container = getThisContainer(container, /* includeArrowFunctions */ false);
-                needToCaptureLexicalThis = true;
+
+                // When targeting es6, arrow function lexically bind "this" so we do not need to do the work of binding "this" in emitted code
+                if (compilerOptions.target >= ScriptTarget.ES6) {
+                    needToCaptureLexicalThis = false;
+                }
+                else {
+                    needToCaptureLexicalThis = true;
+                }
             }
 
             switch (container.kind) {

src/compiler/diagnosticInformationMap.generated.ts

@@ -452,5 +452,6 @@ module ts {
         You_cannot_rename_this_element: { code: 8000, category: DiagnosticCategory.Error, key: "You cannot rename this element." },
         yield_expressions_are_not_currently_supported: { code: 9000, category: DiagnosticCategory.Error, key: "'yield' expressions are not currently supported.", isEarly: true },
         Generators_are_not_currently_supported: { code: 9001, category: DiagnosticCategory.Error, key: "Generators are not currently supported.", isEarly: true },
+        An_argument_object_has_different_behaviour_across_Javascript_versions_Use_function_expression_or_rest_parameters_instead: { code: 9002, category: DiagnosticCategory.Error, key: "An argument object has different behaviour across Javascript versions. Use function expression or rest parameters instead" },
     };
 }