block SO setup API calls after startup (#58718)

Author: pgayvallet

docs/development/core/server/kibana-plugin-server.savedobjectsservicesetup.md

@@ -16,6 +16,8 @@ export interface SavedObjectsServiceSetup
 
 When plugins access the Saved Objects client, a new client is created using the factory provided to `setClientFactory` and wrapped by all wrappers registered through `addClientWrapper`<!-- -->.
 
+All the setup APIs will throw if called after the service has started, and therefor cannot be used from legacy plugin code. Legacy plugins should use the legacy savedObject service until migrated.
+
 ## Example 1
 
 

src/core/MIGRATION_EXAMPLES.md

@@ -917,4 +917,10 @@ Would be converted to:
 
 ```typescript
 const migration: SavedObjectMigrationFn = (doc, { log }) => {...}
-```
+```
+
+### Remarks
+
+The `registerType` API will throw if called after the service has started, and therefor cannot be used from 
+legacy plugin code. Legacy plugins should use the legacy savedObjects service and the legacy way to register
+saved object types until migrated.

src/core/server/saved_objects/saved_objects_service.test.ts

@@ -232,6 +232,36 @@ describe('SavedObjectsService', () => {
       expect(migratorInstanceMock.runMigrations).toHaveBeenCalledTimes(1);
     });
 
+    it('throws when calling setup APIs once started', async () => {
+      const coreContext = createCoreContext({ skipMigration: false });
+      const soService = new SavedObjectsService(coreContext);
+      const setup = await soService.setup(createSetupDeps());
+      await soService.start({});
+
+      expect(() => {
+        setup.setClientFactoryProvider(jest.fn());
+      }).toThrowErrorMatchingInlineSnapshot(
+        `"cannot call \`setClientFactoryProvider\` after service startup."`
+      );
+
+      expect(() => {
+        setup.addClientWrapper(0, 'dummy', jest.fn());
+      }).toThrowErrorMatchingInlineSnapshot(
+        `"cannot call \`addClientWrapper\` after service startup."`
+      );
+
+      expect(() => {
+        setup.registerType({
+          name: 'someType',
+          hidden: false,
+          namespaceAgnostic: false,
+          mappings: { properties: {} },
+        });
+      }).toThrowErrorMatchingInlineSnapshot(
+        `"cannot call \`registerType\` after service startup."`
+      );
+    });
+
     describe('#getTypeRegistry', () => {
       it('returns the internal type registry of the service', async () => {
         const coreContext = createCoreContext({ skipMigration: false });

src/core/server/saved_objects/saved_objects_service.ts

@@ -61,6 +61,9 @@ import { registerRoutes } from './routes';
  * the factory provided to `setClientFactory` and wrapped by all wrappers
  * registered through `addClientWrapper`.
  *
+ * All the setup APIs will throw if called after the service has started, and therefor cannot be used
+ * from legacy plugin code. Legacy plugins should use the legacy savedObject service until migrated.
+ *
  * @example
  * ```ts
  * import { SavedObjectsClient, CoreSetup } from 'src/core/server';
@@ -275,6 +278,7 @@ export class SavedObjectsService
   private migrator$ = new Subject<KibanaMigrator>();
   private typeRegistry = new SavedObjectTypeRegistry();
   private validations: PropertyValidators = {};
+  private started = false;
 
   constructor(private readonly coreContext: CoreContext) {
     this.logger = coreContext.logger.get('savedobjects-service');
@@ -316,19 +320,28 @@ export class SavedObjectsService
 
     return {
       setClientFactoryProvider: provider => {
+        if (this.started) {
+          throw new Error('cannot call `setClientFactoryProvider` after service startup.');
+        }
         if (this.clientFactoryProvider) {
           throw new Error('custom client factory is already set, and can only be set once');
         }
         this.clientFactoryProvider = provider;
       },
       addClientWrapper: (priority, id, factory) => {
+        if (this.started) {
+          throw new Error('cannot call `addClientWrapper` after service startup.');
+        }
         this.clientFactoryWrappers.push({
           priority,
           id,
           factory,
         });
       },
       registerType: type => {
+        if (this.started) {
+          throw new Error('cannot call `registerType` after service startup.');
+        }
         this.typeRegistry.registerType(type);
       },
     };
@@ -415,6 +428,8 @@ export class SavedObjectsService
       clientProvider.addClientWrapperFactory(priority, id, factory);
     });
 
+    this.started = true;
+
     return {
       migrator,
       clientProvider,