feat(PrivateComponentLoader): Explicit error message when loading a non-component

fixes #1062

modules/angular2/src/core/compiler/private_component_loader.js

@@ -2,8 +2,9 @@ import {Compiler} from './compiler';
 import {ShadowDomStrategy} from './shadow_dom_strategy';
 import {EventManager} from 'angular2/src/core/events/event_manager';
 import {DirectiveMetadataReader} from 'angular2/src/core/compiler/directive_metadata_reader';
+import {Component} from 'angular2/src/core/annotations/annotations';
 import {PrivateComponentLocation} from './private_component_location';
-import {Type} from 'angular2/src/facade/lang';
+import {Type, stringify, BaseException} from 'angular2/src/facade/lang';
 
 
 export class PrivateComponentLoader {
@@ -23,6 +24,11 @@ export class PrivateComponentLoader {
 
   load(type:Type, location:PrivateComponentLocation) {
     var annotation = this.directiveMetadataReader.read(type).annotation;
+
+    if (!(annotation instanceof Component)) {
+      throw new BaseException(`Could not load '${stringify(type)}' because it is not a component.`);
+    }
+
     return this.compiler.compile(type).then((componentProtoView) => {
       location.createComponent(
         type, annotation,

modules/angular2/test/core/compiler/private_component_loader_spec.js

@@ -0,0 +1,32 @@
+import {ddescribe, describe, it, iit, expect, beforeEach} from 'angular2/test_lib';
+import {DirectiveMetadataReader} from 'angular2/src/core/compiler/directive_metadata_reader';
+import {PrivateComponentLoader} from 'angular2/src/core/compiler/private_component_loader';
+import {Decorator, Viewport} from 'angular2/src/core/annotations/annotations';
+
+@Decorator({selector: 'someDecorator'})
+class SomeDecorator {}
+
+@Viewport({selector: 'someViewport'})
+class SomeViewport {}
+
+export function main() {
+  describe("PrivateComponentLoader", () => {
+    var loader;
+
+    beforeEach(() => {
+      loader = new PrivateComponentLoader(null, null, null,  new DirectiveMetadataReader());
+    });
+
+    describe('Load errors', () => {
+      it('should throw when trying to load a decorator', () => {
+        expect(() => loader.load(SomeDecorator, null))
+            .toThrowError("Could not load 'SomeDecorator' because it is not a component.");
+      });
+
+      it('should throw when trying to load a viewport', () => {
+        expect(() => loader.load(SomeViewport, null))
+            .toThrowError("Could not load 'SomeViewport' because it is not a component.");
+      });
+    });
+  });
+}