fix(effects): allow downleveled annotations (#98)

Applications using Google Closure Compiler with Angular's ngc can opt into downleveling specifically marked decorators into static properties. This change enables that usage.

Closes #93

modules/effects/spec/effects_metadata.spec.ts

@@ -23,6 +23,24 @@ describe('Effect Metadata', () => {
       ]);
     });
 
+    it('should get the effects metadata for a downleveled class instance', () => {
+      class Fixture {
+        static get propDecorators() {
+          return {
+            a: [{ type: Effect, args: [{ dispatch: false }] }],
+            b: [{ type: Effect, args: [] }],
+          };
+        }
+      }
+
+      const mock = new Fixture();
+
+      expect(getSourceMetadata(mock)).toEqual([
+        { propertyName: 'a', dispatch: false },
+        { propertyName: 'b', dispatch: true },
+      ]);
+    });
+
     it('should return an empty array if the class has not been decorated', () => {
       class Fixture {
         a: any;

modules/effects/src/effects_metadata.ts

@@ -11,7 +11,35 @@ export interface EffectMetadata {
   dispatch: boolean;
 }
 
+function hasStaticMetadata(sourceType: any): boolean {
+  return !!(sourceType as any).propDecorators;
+}
+
+function getStaticMetadata(sourceType: any): EffectMetadata[] {
+  const propDecorators = sourceType.propDecorators;
+  return Object.keys(propDecorators).reduce(
+    (all, key) => all.concat(getStaticMetadataEntry(propDecorators[key], key)),
+    []
+  );
+}
+
+function getStaticMetadataEntry(metadataEntry: any, propertyName: string) {
+  return metadataEntry
+    .filter((entry: any) => entry.type === Effect)
+    .map((entry: any) => {
+      let dispatch = true;
+      if (entry.args.length) {
+        dispatch = !!entry.args[0].dispatch;
+      }
+      return { propertyName, dispatch };
+    });
+}
+
 function getEffectMetadataEntries(sourceProto: any): EffectMetadata[] {
+  if (hasStaticMetadata(sourceProto.constructor)) {
+    return getStaticMetadata(sourceProto.constructor);
+  }
+
   if (r.hasOwnMetadata(METADATA_KEY, sourceProto)) {
     return r.getOwnMetadata(METADATA_KEY, sourceProto);
   }
@@ -23,6 +51,9 @@ function setEffectMetadataEntries(sourceProto: any, entries: EffectMetadata[]) {
   r.defineMetadata(METADATA_KEY, entries, sourceProto);
 }
 
+/**
+ * @Annotation
+ */
 export function Effect({ dispatch } = { dispatch: true }): PropertyDecorator {
   return function(target: any, propertyName: string) {
     const effects: EffectMetadata[] = getEffectMetadataEntries(target);