Allow embed to have services that its parent lacks

examples/a4a.amp.html

@@ -82,10 +82,18 @@ <h2>GMOSSP ad network</h2>
     <div fallback></div>
   </amp-ad>
 
-  <h2>Doubleclick</h2>
-  <amp-ad width="320" height="50"
-      type="doubleclick"
-      data-slot="/4119129/mobile_ad_banner">
+  <h2>Regular ad</h2>
+  <amp-ad data-slot="/30497360/a4a/non_a4a_native"
+    height="250"
+    type="doubleclick"
+    width="300">
+  </amp-ad>
+
+  <h2>A4A ad</h2>
+  <amp-ad data-slot="/30497360/a4a/a4a_native"
+    height="250"
+    type="doubleclick"
+    width="300">
   </amp-ad>
 </body>
 </html>

src/service.js

@@ -241,6 +241,7 @@ export function getServicePromiseOrNull(win, id) {
 
 /**
  * Returns a service for the given id and ampdoc (a per-ampdoc singleton).
+ * Expects service `id` to be registered.
  * @param {!Node|!./service/ampdoc-impl.AmpDoc} nodeOrDoc
  * @param {string} id of the service.
  * @return {T}
@@ -601,8 +602,8 @@ export function isEmbeddable(service) {
  */
 export function adoptServiceForEmbed(embedWin, serviceId) {
   const adopted = adoptServiceForEmbedIfEmbeddable(embedWin, serviceId);
-  dev().assert(adopted,
-      `${serviceId} required to implement EmbeddableService.`);
+  dev().assert(adopted, `Service ${serviceId} not found on parent ` +
+      'or doesn\'t implement EmbeddableService.');
 }
 
 
@@ -617,12 +618,17 @@ export function adoptServiceForEmbedIfEmbeddable(embedWin, serviceId) {
   const frameElement = /** @type {!Node} */ (dev().assert(
       embedWin.frameElement,
       'frameElement not found for embed'));
+  const ampdoc = getAmpdoc(frameElement);
+  const holder = getAmpdocServiceHolder(ampdoc);
+  if (!isServiceRegistered(holder, serviceId)) {
+    return false;
+  }
   const service = getServiceForDoc(frameElement, serviceId);
-  if (isEmbeddable(service)) {
-    service.adoptEmbedWindow(embedWin);
-    return true;
+  if (!isEmbeddable(service)) {
+    return false;
   }
-  return false;
+  service.adoptEmbedWindow(embedWin);
+  return true;
 }
 
 

test/functional/test-service.js

@@ -568,30 +568,42 @@ describe('service', () => {
         expect(isEmbeddable(nonEmbeddable)).to.be.false;
       });
 
-      it('should adopt embeddable', () => {
-        adoptServiceForEmbed(embedWin, 'embeddable');
-        expect(embeddable.adoptEmbedWindow).to.be.calledOnce;
-        expect(embeddable.adoptEmbedWindow.args[0][0]).to.equal(embedWin);
-      });
+      describe('adoptServiceForEmbed()', () => {
+        it('should adopt embeddable', () => {
+          adoptServiceForEmbed(embedWin, 'embeddable');
+          expect(embeddable.adoptEmbedWindow).to.be.calledOnce;
+          expect(embeddable.adoptEmbedWindow.args[0][0]).to.equal(embedWin);
+        });
+
+        it('should refuse adopt of non-embeddable', () => {
+          expect(() => {
+            adoptServiceForEmbed(embedWin, 'nonEmbeddable');
+          }).to.throw(/implement EmbeddableService/);
+        });
 
-      it('should refuse adopt of non-embeddable', () => {
-        expect(() => {
-          adoptServiceForEmbed(embedWin, 'nonEmbeddable');
-        }).to.throw(/required to implement EmbeddableService/);
+        it('should refuse adopt of unknown service', () => {
+          expect(() => {
+            adoptServiceForEmbed(embedWin, 'unknown');
+          }).to.throw(/unknown/);
+        });
       });
 
-      it('should adopt embeddable if embeddable', () => {
-        adoptServiceForEmbedIfEmbeddable(embedWin, 'embeddable');
-        expect(embeddable.adoptEmbedWindow).to.be.calledOnce;
-        expect(embeddable.adoptEmbedWindow.args[0][0]).to.equal(embedWin);
+      describe('adoptServiceForServiceIfEmbeddable()', () => {
+        it('should adopt embeddable if embeddable', () => {
+          adoptServiceForEmbedIfEmbeddable(embedWin, 'embeddable');
+          expect(embeddable.adoptEmbedWindow).to.be.calledOnce;
+          expect(embeddable.adoptEmbedWindow.args[0][0]).to.equal(embedWin);
 
-        adoptServiceForEmbedIfEmbeddable(embedWin, 'nonEmbeddable'); // No-op.
-      });
+          // Should not throw 'required to implement EmbeddableService' error.
+          adoptServiceForEmbedIfEmbeddable(embedWin, 'nonEmbeddable');
+        });
 
-      it('should refuse adopt of unknown service', () => {
-        expect(() => {
-          adoptServiceForEmbed(embedWin, 'unknown');
-        }).to.throw(/unknown/);
+        it('should soft fail adopt of unknown service', () => {
+          // If the embed has an extension service that the parent doesn't,
+          // e.g. AmpFormService if parent lacks amp-form extension.
+          const adopted = adoptServiceForEmbedIfEmbeddable(embedWin, 'unknown');
+          expect(adopted).to.be.false;
+        });
       });
     });
   });