fix(coreDirectives): Added an Error Message for invalid selectors on …

…component annotation

If the component selector is an empty string or not a string an error will be thrown.

Closes angular#3464

modules/angular2/src/core/metadata/directives.ts

@@ -1,4 +1,4 @@
-import {CONST, CONST_EXPR} from 'angular2/src/core/facade/lang';
+import {CONST, CONST_EXPR, isString, isBlank, makeTypeError} from 'angular2/src/core/facade/lang';
 import {InjectableMetadata} from 'angular2/src/core/di/metadata';
 import {ChangeDetectionStrategy} from 'angular2/change_detection';
 
@@ -831,6 +831,9 @@ export class ComponentMetadata extends DirectiveMetadata {
     viewBindings?: any[],
     changeDetection?: ChangeDetectionStrategy,
   } = {}) {
+    if (!isBlank(selector) && !(isString(selector) && selector.length > 0)) {
+      throw makeTypeError('The component annotation requires a string selector.');
+    }
     super({
       selector: selector,
       properties: properties,

modules/angular2/test/core/compiler/element_injector_spec.ts

@@ -479,7 +479,20 @@ export function main() {
           expect(pei.getBindingAtIndex(i).key.token).toBe(i);
         }
       });
-    });
+
+      it('should not error if selector is undefined', () => {
+        expect(function(){
+          new ComponentMetadata();
+        }).not.toThrow()
+      });
+
+      it('should throw an error if the selector is an empty string', () => {
+        expect(function(){
+          new ComponentMetadata({selector: ''});
+        }).toThrowError("The component annotation requires a string selector.")
+      });
+
+    );
   });
 
   describe("ElementInjector", () => {