Allow amp-experiment to prerender and bypass maximum build limit (#24745

)

* allow amp-experiment to prerender

* rename

build-system/tasks/presubmit-checks.js

@@ -707,6 +707,19 @@ const forbiddenTerms = {
       'src/inabox/amp-inabox.js',
     ],
   },
+  'isBuildRenderBlocking': {
+    message:
+      'This is a protected API. Please only override it the element is ' +
+      'render blocking',
+    whitelist: [
+      'src/service/resources-impl.js',
+      'src/service/resource.js',
+      'src/custom-element.js',
+      'src/base-element.js',
+      'extensions/amp-experiment/0.1/amp-experiment.js',
+      'extensions/amp-experiment/1.0/amp-experiment.js',
+    ],
+  },
   '^describe[\\.|\\(|$]': {
     message:
       'Top-level "describe" blocks in test files have been deprecated. ' +

extensions/amp-experiment/0.1/amp-experiment.js

@@ -29,6 +29,23 @@ export class AmpExperiment extends AMP.BaseElement {
     return layout == Layout.NODISPLAY || layout == Layout.CONTAINER;
   }
 
+  /** @override */
+  prerenderAllowed() {
+    /*
+     * Prerender is allowed because the client_id is only used to calculate
+     * the variant bucket.
+     * In the case where a client_id is first generated
+     * during prerender, the base cid will be stored in the AMP viewer domain.
+     */
+    return true;
+  }
+
+  /** @override */
+  isBuildRenderBlocking() {
+    // variantService is render blocking
+    return true;
+  }
+
   /** @override */
   buildCallback() {
     return getServicePromiseForDoc(this.getAmpDoc(), 'variant').then(

extensions/amp-experiment/1.0/amp-experiment.js

@@ -36,6 +36,23 @@ export class AmpExperiment extends AMP.BaseElement {
     return layout == Layout.NODISPLAY || layout == Layout.CONTAINER;
   }
 
+  /** @override */
+  prerenderAllowed() {
+    /*
+     * Prerender is allowed because the client_id is only used to calculate
+     * the variant bucket.
+     * In the case where a client_id is first generated
+     * during prerender, the base cid will be stored in the AMP viewer domain.
+     */
+    return true;
+  }
+
+  /** @override */
+  isBuildRenderBlocking() {
+    // variantService is render blocking
+    return true;
+  }
+
   /** @override */
   buildCallback() {
     const buildCallbackPromises = [

src/base-element.js

@@ -398,6 +398,18 @@ export class BaseElement {
     return false;
   }
 
+  /**
+   * Subclasses can override this method to indicate that it is has
+   * render-blocking service.
+   *
+   * The return value of this function is used to determine if the element
+   * built _and_ laid out will be prioritized.
+   * @return {boolean}
+   */
+  isBuildRenderBlocking() {
+    return false;
+  }
+
   /**
    * Subclasses can override this method to create a dynamic placeholder
    * element and return it to be appended to the element. This will only

src/custom-element.js

@@ -1013,6 +1013,15 @@ function createBaseCustomElementClass(win) {
       return this.implementation_.prerenderAllowed();
     }
 
+    /**
+     * Whether the element has render-blocking service.
+     * @return {boolean}
+     * @final
+     */
+    isBuildRenderBlocking() {
+      return this.implementation_.isBuildRenderBlocking();
+    }
+
     /**
      * Creates a placeholder for the element.
      * @return {?Element}

src/service/resource.js

@@ -652,6 +652,14 @@ export class Resource {
     return this.element.prerenderAllowed();
   }
 
+  /**
+   * Whether this element has render-blocking service.
+   * @return {boolean}
+   */
+  isBuildRenderBlocking() {
+    return this.element.isBuildRenderBlocking();
+  }
+
   /**
    * @param {number|boolean} viewport derived from renderOutsideViewport.
    * @return {!Promise} resolves when underlying element is built and within the

src/service/resources-impl.js

@@ -478,7 +478,11 @@ export class ResourcesImpl {
    * @private
    */
   buildResourceUnsafe_(resource, schedulePass, force = false) {
-    if (!this.isUnderBuildQuota_() && !force) {
+    if (
+      !this.isUnderBuildQuota_() &&
+      !force &&
+      !resource.isBuildRenderBlocking()
+    ) {
       return null;
     }
     const promise = resource.build();

test/unit/test-resources.js

@@ -1110,13 +1110,31 @@ describes.realWin('Resources discoverWork', {amp: true}, env => {
     resource1.element.isBuilt = () => false;
     resource1.element.idleRenderOutsideViewport = () => true;
     resource1.prerenderAllowed = () => true;
+    resource1.isBuildRenderBlocking = () => false;
     resource1.state_ = ResourceState.NOT_BUILT;
     resource1.build = sandbox.spy();
 
     resources.buildOrScheduleBuildForResource_(resource1);
     expect(resource1.build).to.not.be.called;
   });
 
+  it('should build render blocking resource even if quota is reached', () => {
+    sandbox.stub(resources.ampdoc, 'hasBeenVisible').callsFake(() => false);
+    sandbox.stub(resources, 'schedule_');
+    resources.documentReady_ = true;
+    resources.buildAttemptsCount_ = 21; // quota is 20
+
+    resource1.element.isBuilt = () => false;
+    resource1.element.idleRenderOutsideViewport = () => true;
+    resource1.prerenderAllowed = () => true;
+    resource1.isBuildRenderBlocking = () => true;
+    resource1.state_ = ResourceState.NOT_BUILT;
+    resource1.build = sandbox.spy();
+
+    resources.buildOrScheduleBuildForResource_(resource1);
+    expect(resource1.build).to.be.called;
+  });
+
   it('should layout resource if outside viewport but idle', () => {
     const schedulePassStub = sandbox.stub(resources, 'schedulePass');
     resources.documentReady_ = true;