[Feature Flags] Reevaluate on context change (#251268)

Author: afharo

src/core/packages/feature-flags/browser-internal/src/feature_flags_service.test.ts

@@ -295,6 +295,11 @@ describe('FeatureFlagsService Browser', () => {
       addHandlerSpy.mock.calls[0][1]({ flagsChanged: ['my-flag'] });
       await expect(firstValueFrom(flag$)).resolves.toEqual(value);
       expect(observedValues).toHaveLength(2);
+
+      // Reevaluates and emits when the context is changed
+      await startContract.appendContext({ kind: 'multi', kibana: { key: 'kibana-2' } });
+      await expect(firstValueFrom(flag$)).resolves.toEqual(value);
+      expect(observedValues).toHaveLength(3);
     });
 
     test('observe a string flag', async () => {
@@ -316,6 +321,11 @@ describe('FeatureFlagsService Browser', () => {
       addHandlerSpy.mock.calls[0][1]({ flagsChanged: ['my-flag'] });
       await expect(firstValueFrom(flag$)).resolves.toEqual(value);
       expect(observedValues).toHaveLength(2);
+
+      // Reevaluates and emits when the context is changed
+      await startContract.appendContext({ kind: 'multi', kibana: { key: 'kibana-2' } });
+      await expect(firstValueFrom(flag$)).resolves.toEqual(value);
+      expect(observedValues).toHaveLength(3);
     });
 
     test('observe a number flag', async () => {
@@ -337,6 +347,11 @@ describe('FeatureFlagsService Browser', () => {
       addHandlerSpy.mock.calls[0][1]({ flagsChanged: ['my-flag'] });
       await expect(firstValueFrom(flag$)).resolves.toEqual(value);
       expect(observedValues).toHaveLength(2);
+
+      // Reevaluates and emits when the context is changed
+      await startContract.appendContext({ kind: 'multi', kibana: { key: 'kibana-2' } });
+      await expect(firstValueFrom(flag$)).resolves.toEqual(value);
+      expect(observedValues).toHaveLength(3);
     });
 
     test('with overrides', async () => {

src/core/packages/feature-flags/browser-internal/src/feature_flags_service.ts

@@ -19,7 +19,7 @@ import type {
 import { apm } from '@elastic/apm-rum';
 import { type Client, ClientProviderEvents, OpenFeature } from '@openfeature/web-sdk';
 import deepMerge from 'deepmerge';
-import { filter, map, startWith, Subject } from 'rxjs';
+import { filter, map, merge, startWith, Subject } from 'rxjs';
 import { get } from 'lodash';
 
 /**
@@ -40,6 +40,7 @@ export interface FeatureFlagsSetupDeps {
 export class FeatureFlagsService {
   private readonly featureFlagsClient: Client;
   private readonly logger: Logger;
+  private readonly contextChanged$ = new Subject<void>();
   private isProviderReadyPromise?: Promise<void>;
   private context: MultiContextEvaluationContext = { kind: 'multi' };
   private overrides: Record<string, unknown> = {};
@@ -104,7 +105,12 @@ export class FeatureFlagsService {
       }
     });
     const observeFeatureFlag$ = (flagName: string) =>
-      featureFlagsChanged$.pipe(
+      merge(
+        // Flag changes
+        featureFlagsChanged$,
+        // Context changes (we need to reevaluate)
+        this.contextChanged$.pipe(map(() => [flagName]))
+      ).pipe(
         filter((flagNames) => flagNames.includes(flagName)),
         startWith([flagName]) // only to emit on the first call
       );
@@ -221,5 +227,6 @@ export class FeatureFlagsService {
     // Merge the formatted context to append to the global context, and set it in the OpenFeature client.
     this.context = deepMerge(this.context, formattedContextToAppend);
     await OpenFeature.setContext(this.context);
+    this.contextChanged$.next();
   }
 }

src/core/packages/feature-flags/server-internal/src/feature_flags_service.test.ts

@@ -201,6 +201,11 @@ describe('FeatureFlagsService Server', () => {
       addHandlerSpy.mock.calls[0][1]({ flagsChanged: ['my-flag'] });
       await expect(firstValueFrom(flag$)).resolves.toEqual(value);
       expect(observedValues).toHaveLength(2);
+
+      // Reevaluates and emits when the context is changed
+      startContract.appendContext({ kind: 'multi', kibana: { key: 'kibana-2' } });
+      await expect(firstValueFrom(flag$)).resolves.toEqual(value);
+      expect(observedValues).toHaveLength(3);
     });
 
     test('observe a string flag', async () => {
@@ -222,6 +227,11 @@ describe('FeatureFlagsService Server', () => {
       addHandlerSpy.mock.calls[0][1]({ flagsChanged: ['my-flag'] });
       await expect(firstValueFrom(flag$)).resolves.toEqual(value);
       expect(observedValues).toHaveLength(2);
+
+      // Reevaluates and emits when the context is changed
+      startContract.appendContext({ kind: 'multi', kibana: { key: 'kibana-2' } });
+      await expect(firstValueFrom(flag$)).resolves.toEqual(value);
+      expect(observedValues).toHaveLength(3);
     });
 
     test('observe a number flag', async () => {
@@ -243,6 +253,11 @@ describe('FeatureFlagsService Server', () => {
       addHandlerSpy.mock.calls[0][1]({ flagsChanged: ['my-flag'] });
       await expect(firstValueFrom(flag$)).resolves.toEqual(value);
       expect(observedValues).toHaveLength(2);
+
+      // Reevaluates and emits when the context is changed
+      startContract.appendContext({ kind: 'multi', kibana: { key: 'kibana-2' } });
+      await expect(firstValueFrom(flag$)).resolves.toEqual(value);
+      expect(observedValues).toHaveLength(3);
     });
 
     test('with overrides', async () => {

src/core/packages/feature-flags/server-internal/src/feature_flags_service.ts

@@ -24,7 +24,17 @@ import {
   NOOP_PROVIDER,
 } from '@openfeature/server-sdk';
 import deepMerge from 'deepmerge';
-import { filter, switchMap, startWith, Subject, BehaviorSubject, pairwise, takeUntil } from 'rxjs';
+import {
+  filter,
+  switchMap,
+  startWith,
+  Subject,
+  BehaviorSubject,
+  pairwise,
+  takeUntil,
+  merge,
+  map,
+} from 'rxjs';
 import { get } from 'lodash';
 import type { InitialFeatureFlagsGetter } from '@kbn/core-feature-flags-server/src/contracts';
 import { createOpenFeatureLogger } from './create_open_feature_logger';
@@ -56,6 +66,7 @@ export class FeatureFlagsService {
   private readonly logger: Logger;
   private readonly stop$ = new Subject<void>();
   private readonly overrides$ = new BehaviorSubject<Record<string, unknown>>({});
+  private readonly contextChanged$ = new Subject<void>();
   private context: MultiContextEvaluationContext = { kind: 'multi' };
   private initialFeatureFlagsGetter: InitialFeatureFlagsGetter = async () => ({});
 
@@ -117,7 +128,12 @@ export class FeatureFlagsService {
       featureFlagsChanged$.next(keys);
     });
     const observeFeatureFlag$ = (flagName: string) =>
-      featureFlagsChanged$.pipe(
+      merge(
+        // Flag changes
+        featureFlagsChanged$,
+        // Context changes (we need to reevaluate)
+        this.contextChanged$.pipe(map(() => [flagName]))
+      ).pipe(
         filter((flagNames) => flagNames.includes(flagName)),
         startWith([flagName]), // only to emit on the first call
         takeUntil(this.stop$) // stop the observable when the service stops
@@ -221,5 +237,6 @@ export class FeatureFlagsService {
     // Merge the formatted context to append to the global context, and set it in the OpenFeature client.
     this.context = deepMerge(this.context, formattedContextToAppend);
     OpenFeature.setContext(this.context);
+    this.contextChanged$.next();
   }
 }