Bug 1629588 - Ensure we don't setup a new provider if one already exists. r=gvn

Differential Revision: https://phabricator.services.mozilla.com/D70890

browser/components/newtab/lib/RecommendationProviderSwitcher.jsm

@@ -57,6 +57,15 @@ this.RecommendationProviderSwitcher = class RecommendationProviderSwitcher {
   setAffinityProvider(...args) {
     const { affinityProviderV2 } = this;
     if (affinityProviderV2 && affinityProviderV2.modelKeys) {
+      // A v2 provider is already set. This can happen when new stories come in
+      // and we need to update their scores.
+      // We can use the existing one, a fresh one is created after startup.
+      // Using the existing one might be a bit out of date,
+      // but it's fine for now. We can rely on restarts for updates.
+      // See bug 1629931 for improvements to this.
+      if (this.affinityProvider) {
+        return;
+      }
       // At this point we've determined we can successfully create a v2 personalization provider.
       this.affinityProvider = new PersonalityProvider(...args, {
         modelKeys: affinityProviderV2.modelKeys,

browser/components/newtab/test/unit/lib/RecommendationProviderSwitcher.test.js

@@ -31,6 +31,7 @@ describe("RecommendationProviderSwitcher", () => {
 
       assert.equal(feed.affinityProvider.modelKeys, undefined);
 
+      feed.affinityProvider = null;
       feed.affinityProviderV2 = {
         modelKeys: "1234",
       };
@@ -45,6 +46,31 @@ describe("RecommendationProviderSwitcher", () => {
 
       assert.equal(feed.affinityProvider.modelKeys, "1234");
     });
+    it("should use old provider", async () => {
+      feed.setAffinityProvider(
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        undefined
+      );
+
+      assert.equal(feed.affinityProvider.modelKeys, undefined);
+
+      feed.affinityProviderV2 = {
+        modelKeys: "1234",
+      };
+
+      feed.setAffinityProvider(
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        undefined
+      );
+
+      assert.equal(feed.affinityProvider.modelKeys, undefined);
+    });
   });
 
   describe("#init", () => {