Adds tests to ensure registered SO types aren't removed (elastic#207142)

fix elastic#207128

We have an integration test to check that saved objects aren't removed
and another that catches mappings changes.
This PR adds another assertion to ensure that the message is clear:
Removing a saved object type is not allowed after 8.8.

---------

Co-authored-by: Elastic Machine <[email protected]>

src/core/packages/saved-objects/migration-server-internal/src/core/unused_types.ts

@@ -11,6 +11,8 @@ import type { QueryDslQueryContainer } from '@elastic/elasticsearch/lib/api/type
 
 /**
  * Types that are no longer registered and need to be removed
+ * As of 8.8, no new types are allowed to be removed.
+ * Removing saved object types is not backward compatible
  */
 export const REMOVED_TYPES: string[] = [
   'apm-services-telemetry',

src/core/packages/saved-objects/server-internal/index.ts

@@ -11,6 +11,7 @@ export {
   MIGRATION_CLIENT_OPTIONS,
   SavedObjectsService,
   CoreSavedObjectsRouteHandlerContext,
+  SAVED_OBJECT_TYPES_COUNT,
 } from './src';
 export type {
   InternalSavedObjectsServiceStart,

src/core/packages/saved-objects/server-internal/src/index.ts

@@ -18,3 +18,4 @@ export type {
   InternalSavedObjectsRequestHandlerContext,
   InternalSavedObjectRouter,
 } from './internal_types';
+export { SAVED_OBJECT_TYPES_COUNT } from './object_types';

src/core/packages/saved-objects/server-internal/src/object_types/index.ts

@@ -8,3 +8,7 @@
  */
 
 export { registerCoreObjectTypes } from './registration';
+
+// set minimum number of registered saved objects to ensure no object types are removed after 8.8
+// declared in internal implementation exclicilty to prevent unintended changes.
+export const SAVED_OBJECT_TYPES_COUNT = 127 as const;

src/core/packages/saved-objects/server/src/type_registry.ts

@@ -8,7 +8,6 @@
  */
 
 import type { SavedObjectsType } from './saved_objects_type';
-
 /**
  * Registry holding information about all the registered {@link SavedObjectsType | saved object types}.
  */

src/core/server/integration_tests/ci_checks/saved_objects/check_registered_types.test.ts

@@ -15,6 +15,7 @@ import {
   createRootWithCorePlugins,
   type TestElasticsearchUtils,
 } from '@kbn/core-test-helpers-kbn-server';
+import { SAVED_OBJECT_TYPES_COUNT } from '@kbn/core-saved-objects-server-internal';
 
 describe('checking migration metadata changes on all registered SO types', () => {
   let esServer: TestElasticsearchUtils;
@@ -46,6 +47,8 @@ describe('checking migration metadata changes on all registered SO types', () =>
   // This test is meant to fail when any change is made in registered types that could potentially impact the SO migration.
   // Just update the snapshot by running this test file via jest_integration with `-u` and push the update.
   // The intent is to trigger a code review from the Core team to review the SO type changes.
+  // The number of types in the hashMap should never be reduced, it can only increase.
+  // Removing saved object types is forbidden after 8.8.
   it('detecting migration related changes in registered types', () => {
     const allTypes = typeRegistry.getAllTypes();
 
@@ -185,5 +188,6 @@ describe('checking migration metadata changes on all registered SO types', () =>
         "workplace_search_telemetry": "52b32b47ee576f554ac77cb1d5896dfbcfe9a1fb",
       }
     `);
+    expect(Object.keys(hashMap).length).toEqual(SAVED_OBJECT_TYPES_COUNT);
   });
 });

src/core/server/integration_tests/saved_objects/jest.integration.config.js

@@ -16,6 +16,7 @@ module.exports = {
   preset: '@kbn/test/jest_integration',
   rootDir: '../../../../..',
   roots: [
+    '<rootDir>/src/core/server/integration_tests/saved_objects/registration',
     '<rootDir>/src/core/server/integration_tests/saved_objects/routes',
     '<rootDir>/src/core/server/integration_tests/saved_objects/service',
     '<rootDir>/src/core/server/integration_tests/saved_objects/validation',