[discuss] Adopt common Service interface

src/core/server/plugins/types.ts

@@ -22,6 +22,7 @@ import { Type } from '@kbn/config-schema';
 
 import { ConfigPath, EnvironmentMode, PackageInfo } from '../config';
 import { LoggerFactory } from '../logging';
+import { Service } from '../../types';
 import { CoreSetup, CoreStart } from '..';
 
 export type PluginConfigSchema = Type<unknown> | null;
@@ -137,20 +138,19 @@ export interface DiscoveredPluginInternal extends DiscoveredPlugin {
 }
 
 /**
- * The interface that should be returned by a `PluginInitializer`.
+ * The type that should be returned by a `PluginInitializer`.
  *
  * @public
  */
-export interface Plugin<
+export type Plugin<
   TSetup = void,
   TStart = void,
   TPluginsSetup extends object = object,
   TPluginsStart extends object = object
-> {
-  setup(core: CoreSetup, plugins: TPluginsSetup): TSetup | Promise<TSetup>;
-  start(core: CoreStart, plugins: TPluginsStart): TStart | Promise<TStart>;
-  stop?(): void;
-}
+> = Service<
+  (core: CoreSetup, plugins: TPluginsSetup) => TSetup | Promise<TSetup>,
+  (core: CoreStart, plugins: TPluginsStart) => TStart | Promise<TStart>
+>;
 
 /**
  * Context that's available to plugins during initialization stage.

src/core/server/saved_objects/index.ts

@@ -35,6 +35,10 @@ export { SavedObjectsSerializer, RawDoc as SavedObjectsRawDoc } from './serializ
 
 export { SavedObjectsMigrationLogger } from './migrations/core/migration_logger';
 
-export { SavedObjectsService, SavedObjectsServiceStart } from './saved_objects_service';
+export {
+  ISavedObjectsService,
+  SavedObjectsService,
+  SavedObjectsServiceStart,
+} from './saved_objects_service';
 
 export { config } from './saved_objects_config';

src/core/server/saved_objects/saved_objects_service.ts

@@ -17,7 +17,7 @@
  * under the License.
  */
 
-import { CoreService } from 'src/core/types';
+import { Service, ServiceType } from 'src/core/types';
 import { first } from 'rxjs/operators';
 import {
   SavedObjectsClient,
@@ -63,8 +63,9 @@ export interface SavedObjectsSetupDeps {
 // eslint-disable-next-line @typescript-eslint/no-empty-interface
 export interface SavedObjectsStartDeps {}
 
-export class SavedObjectsService
-  implements CoreService<SavedObjectsServiceSetup, SavedObjectsServiceStart> {
+export type ISavedObjectsService = ServiceType<SavedObjectsService>;
+
+export class SavedObjectsService implements Service {
   private migrator: KibanaMigrator | undefined;
   private logger: Logger;
   private clientProvider: ISavedObjectsClientProvider<KibanaRequest> | undefined;

src/core/server/server.ts

@@ -27,7 +27,7 @@ import { LegacyService } from './legacy';
 import { Logger, LoggerFactory } from './logging';
 import { UiSettingsService } from './ui_settings';
 import { PluginsService, config as pluginsConfig } from './plugins';
-import { SavedObjectsService } from '../server/saved_objects';
+import { SavedObjectsService, ISavedObjectsService } from '../server/saved_objects';
 
 import { config as elasticsearchConfig } from './elasticsearch';
 import { config as httpConfig } from './http';
@@ -51,7 +51,7 @@ export class Server {
   private readonly legacy: LegacyService;
   private readonly log: Logger;
   private readonly plugins: PluginsService;
-  private readonly savedObjects: SavedObjectsService;
+  private readonly savedObjects: ISavedObjectsService;
   private readonly uiSettings: UiSettingsService;
 
   constructor(

src/core/types/core_service.ts

@@ -17,9 +17,41 @@
  * under the License.
  */
 
-/** @internal */
-export interface CoreService<TSetup = void, TStart = void> {
-  setup(...params: any[]): Promise<TSetup>;
-  start(...params: any[]): Promise<TStart>;
-  stop(): Promise<void>;
+/** @public */
+export type AnyFunction = (...args: any[]) => any;
+
+/** @public */
+export interface Service<
+  TSetup extends AnyFunction = AnyFunction,
+  TStart extends AnyFunction = AnyFunction
+> {
+  setup: TSetup;
+  start: TStart;
+  stop(): void;
 }
+
+/**
+ * Utility type for inferring the concrete type of a {@link Service}.
+ *
+ * @remarks
+ * TSDoc comments will be preserved and accessible in editors when using this utility type.
+ *
+ * @example
+ * ```ts
+ * // Implement the `Service` interface without having to specify the generics type arguments.
+ * export class MyService implements Service {
+ *  setup(x: number) { return 3 * x }
+ *  start() {}
+ *  stop() {}
+ * }
+ *
+ * // Use `ServiceType` to export an interface that automatically infers the generic type arguments.
+ * export type IMyService = ServiceType<MyService>;
+ * // ⇒ Service<(x: number) => number, () => void>
+ * ```
+ *
+ * @public
+ */
+export type ServiceType<T extends Service<any, any>> = T extends Service<infer TSetup, infer TStart>
+  ? Service<TSetup, TStart>
+  : never;