fix(injector): support arrow functions with no parenthesis

with arrow functions parenthesis are optional in case you have exactly
one argument to the function. the previous regexp assumed function
arguments are always inside parenthesis and so it didn't annotate
functions like `$http => $http.get(...)` correctly

Closes angular#12890

Author: Shahar Talmi

src/auto/injector.js

@@ -62,6 +62,7 @@
  * Implicit module which gets automatically added to each {@link auto.$injector $injector}.
  */
 
+var ARROW_ARG = /^([^\(]+?)=>/;
 var FN_ARGS = /^[^\(]*\(\s*([^\)]*)\)/m;
 var FN_ARG_SPLIT = /,/;
 var FN_ARG = /^\s*(_?)(\S+?)\1\s*$/;
@@ -70,7 +71,7 @@ var $injectorMinErr = minErr('$injector');
 
 function extractArgs(fn) {
   var fnText = fn.toString().replace(STRIP_COMMENTS, ''),
-      args = fnText.match(FN_ARGS);
+      args = fnText.match(ARROW_ARG) || fnText.match(FN_ARGS);
   return args;
 }
 

test/auto/injectorSpec.js

@@ -249,10 +249,27 @@ describe('injector', function() {
 
     // Only Chrome and Firefox support this syntax.
     if (/chrome|firefox/i.test(navigator.userAgent)) {
-      it('should be possible to annotate functions that are declared using ES6 syntax', function() {
+      describe('es6', function() {
         /*jshint -W061 */
-        // The function is generated using `eval` as just having the ES6 syntax can break some browsers.
-        expect(annotate(eval('({ fn(x) { return; } })').fn)).toEqual(['x']);
+        // The functions are generated using `eval` as just having the ES6 syntax can break some browsers.
+        it('should be possible to annotate functions that are declared using ES6 syntax', function() {
+          expect(annotate(eval('({ fn(x) { return; } })').fn)).toEqual(['x']);
+        });
+
+
+        it('should create $inject for arrow functions', function() {
+          expect(annotate(eval('(a, b) => a'))).toEqual(['a', 'b']);
+        });
+
+
+        it('should create $inject for arrow functions with no parenthesis', function() {
+          expect(annotate(eval('a => a'))).toEqual(['a']);
+        });
+
+
+        it('should take args before first arrow', function() {
+          expect(annotate(eval('a => b => b'))).toEqual(['a']);
+        });
         /*jshint +W061 */
       });
     }