core-plugin-api: Deprecate Plugin register and output

Co-authored-by: blam <ben@blam.sh>
Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: Johan Haals <johan.haals@gmail.com>

packages/core-app-api/src/app/AppManager.tsx

@@ -272,17 +272,26 @@ export class AppManager implements BackstageApp {
           const featureFlagsApi = this.getApiHolder().get(featureFlagsApiRef)!;
 
           for (const plugin of this.plugins.values()) {
-            for (const output of plugin.output()) {
-              switch (output.type) {
-                case 'feature-flag': {
-                  featureFlagsApi.registerFlag({
-                    name: output.name,
-                    pluginId: plugin.getId(),
-                  });
-                  break;
+            if ('getFeatureFlags' in plugin) {
+              for (const flag of plugin.getFeatureFlags()) {
+                featureFlagsApi.registerFlag({
+                  name: flag.name,
+                  pluginId: plugin.getId(),
+                });
+              }
+            } else {
+              for (const output of plugin.output()) {
+                switch (output.type) {
+                  case 'feature-flag': {
+                    featureFlagsApi.registerFlag({
+                      name: output.name,
+                      pluginId: plugin.getId(),
+                    });
+                    break;
+                  }
+                  default:
+                    break;
                 }
-                default:
-                  break;
               }
             }
           }

packages/core-plugin-api/src/plugin/Plugin.tsx

@@ -21,6 +21,7 @@ import {
   Extension,
   AnyRoutes,
   AnyExternalRoutes,
+  PluginFeatureFlagConfig,
 } from './types';
 import { AnyApiFactory } from '../apis';
 
@@ -44,6 +45,14 @@ export class PluginImpl<
     return this.config.apis ?? [];
   }
 
+  getFeatureFlags(): Iterable<PluginFeatureFlagConfig> {
+    const registeredFlags = this.output()
+      .filter(({ type }) => type === 'feature-flag')
+      .map(({ name }) => ({ name }));
+
+    return registeredFlags;
+  }
+
   get routes(): Routes {
     return this.config.routes ?? ({} as Routes);
   }
@@ -56,11 +65,18 @@ export class PluginImpl<
     if (this.storedOutput) {
       return this.storedOutput;
     }
-    if (!this.config.register) {
-      return [];
+    const outputs = new Array<PluginOutput>();
+    this.storedOutput = outputs;
+
+    if (this.config.featureFlags) {
+      for (const flag of this.config.featureFlags) {
+        outputs.push({ type: 'feature-flag', name: flag.name });
+      }
     }
 
-    const outputs = new Array<PluginOutput>();
+    if (!this.config.register) {
+      return outputs;
+    }
 
     this.config.register({
       featureFlags: {
@@ -70,7 +86,6 @@ export class PluginImpl<
       },
     });
 
-    this.storedOutput = outputs;
     return this.storedOutput;
   }
 

packages/core-plugin-api/src/plugin/types.ts

@@ -19,7 +19,7 @@ import { AnyApiFactory } from '../apis/system';
 
 /**
  * Replace with using {@link RouteRef}s.
- *
+ * @deprecated
  * @public
  */
 export type FeatureFlagOutput = {
@@ -31,6 +31,7 @@ export type FeatureFlagOutput = {
  * {@link FeatureFlagOutput} type.
  *
  * @public
+ * @deprecated Use {@link BackstagePlugin.getFeatureFlags} instead.
  */
 export type PluginOutput = FeatureFlagOutput;
 
@@ -71,13 +72,30 @@ export type BackstagePlugin<
   ExternalRoutes extends AnyExternalRoutes = {},
 > = {
   getId(): string;
+  /**
+   * @deprecated use getFeatureFlags instead.
+   * */
   output(): PluginOutput[];
   getApis(): Iterable<AnyApiFactory>;
+  /**
+   * Returns all registered feature flags for this plugin.
+   */
+  getFeatureFlags(): Iterable<PluginFeatureFlagConfig>;
   provide<T>(extension: Extension<T>): T;
   routes: Routes;
   externalRoutes: ExternalRoutes;
 };
 
+/**
+ * Plugin feature flag configuration.
+ *
+ * @public
+ */
+export type PluginFeatureFlagConfig = {
+  /** Feature flag name */
+  name: string;
+};
+
 /**
  * Plugin descriptor type.
  *
@@ -89,14 +107,17 @@ export type PluginConfig<
 > = {
   id: string;
   apis?: Iterable<AnyApiFactory>;
+  /** @deprecated use featureFlags property instead for defining feature flags */
   register?(hooks: PluginHooks): void;
   routes?: Routes;
   externalRoutes?: ExternalRoutes;
+  featureFlags?: PluginFeatureFlagConfig[];
 };
 
 /**
  * Holds hooks registered by the plugin.
  *
+ * @deprecated - feature flags are now registered in plugin config under featureFlags
  * @public
  */
 export type PluginHooks = {

plugins/cost-insights/src/plugin.ts

@@ -34,9 +34,7 @@ export const unlabeledDataflowAlertRef = createRouteRef({
 
 export const costInsightsPlugin = createPlugin({
   id: 'cost-insights',
-  register({ featureFlags }) {
-    featureFlags.register('cost-insights-currencies');
-  },
+  featureFlags: [{ name: 'cost-insights-currencies' }],
   routes: {
     root: rootRouteRef,
     growthAlerts: projectGrowthAlertRef,