Handle both V1 and V2 of Cirrus' data structure

src/app/functions/server/getExperiments.ts

@@ -12,6 +12,14 @@ import {
 import { ExperimentationId } from "./getExperimentationId";
 import { getEnabledFeatureFlags } from "../../../db/tables/featureFlags";
 
+/**
+ * After we removing the `CirrusV2` flag, we can return the full `ExperimentData`/
+ * But until then, we can make the old experiment data object look like the new one,
+ * but we can't backfill the `Enrollments` property.
+ */
+export type ExperimentData_V2_Or_V2LikeV1 = Partial<ExperimentData> &
+  Required<Pick<ExperimentData, "Features">>;
+
 /**
  * Call the Cirrus sidecar, which returns a list of eligible experiments for the current user.
  *
@@ -28,7 +36,7 @@ export async function getExperiments(params: {
   locale: string;
   countryCode: string;
   previewMode: boolean;
-}): Promise<ExperimentData> {
+}): Promise<ExperimentData_V2_Or_V2LikeV1> {
   if (["local"].includes(process.env.APP_ENV ?? "local")) {
     return localExperimentData;
   }
@@ -78,16 +86,22 @@ export async function getExperiments(params: {
       throw new Error(`Cirrus request failed: ${response.statusText}`);
     }
 
-    const json = await response.json();
+    // With the `CirrusV2` flag enabled, the response is `ExperimentData`,
+    // otherwise, it's just `ExperimentData["Features"]`.
+    const json = (await response.json()) as
+      | ExperimentData
+      | ExperimentData["Features"];
 
-    let experimentData;
+    let experimentData: ExperimentData_V2_Or_V2LikeV1;
     if (flags.includes("CirrusV2")) {
-      experimentData = json["Features"];
+      experimentData = json as ExperimentData;
     } else {
-      experimentData = json;
+      experimentData = {
+        Features: json as ExperimentData["Features"],
+      };
     }
 
-    return (experimentData as ExperimentData) ?? defaultExperimentData;
+    return experimentData ?? defaultExperimentData;
   } catch (ex) {
     logger.error("Could not connect to Cirrus", {
       serverUrl,

src/app/hooks/useGlean.ts

@@ -44,7 +44,10 @@ export const useGlean = () => {
       // Record the `nimbus_*` keys on all events.
       // `nimbus_*` is set on every metric, but it's too much work for TypeScript
       // to infer that — hence the type assertion.
-      if (experimentData) {
+      if (
+        experimentData &&
+        typeof experimentData["Enrollments"] !== "undefined"
+      ) {
         (data as GleanMetricMap["button"]["click"]).nimbus_user_id =
           experimentData["Enrollments"]["nimbus_user_id"];
         (data as GleanMetricMap["button"]["click"]).nimbus_app_id =

src/app/layout.tsx

@@ -72,8 +72,11 @@ export default async function RootLayout({
     previewMode: nimbusPreviewMode === "true",
   });
 
-  const nimbus_user_id = experimentData["Enrollments"].nimbus_user_id;
-  if (nimbus_user_id !== experimentationId) {
+  const nimbus_user_id = experimentData["Enrollments"]?.nimbus_user_id;
+  if (
+    typeof nimbus_user_id !== "undefined" &&
+    nimbus_user_id !== experimentationId
+  ) {
     Sentry.captureMessage(
       `Nimbus user ID from Cirrus: [${nimbus_user_id}] did not match experimentationId: [${experimentationId}]`,
     );

src/contextProviders/experiments.tsx

@@ -5,14 +5,15 @@
 "use client";
 
 import { ReactNode, createContext, useContext } from "react";
-import { ExperimentData } from "../telemetry/generated/nimbus/experiments";
+import { ExperimentData_V2_Or_V2LikeV1 } from "../app/functions/server/getExperiments";
 
 interface ExperimentsProviderProps {
   children: ReactNode;
-  experimentData: ExperimentData;
+  experimentData: ExperimentData_V2_Or_V2LikeV1;
 }
 
-export const ExperimentsContext = createContext<ExperimentData | null>(null);
+export const ExperimentsContext =
+  createContext<ExperimentData_V2_Or_V2LikeV1 | null>(null);
 
 export const ExperimentsProvider = ({
   children,