Return the 'default' space even when spaces are disabled

This will allow users with spaces disabled to enable spaces without
losing data. The tradeoff is that they may be surprised when signals
don't exist within their configured xpack.siem.signalsIndex.

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/utils.test.ts

@@ -287,14 +287,7 @@ describe('utils', () => {
       });
     });
 
-    it('returns the configured index if spaces are disabled', () => {
-      const getSpaceId = jest.fn(() => undefined);
-      const index = getIndex(getSpaceId, mockConfig);
-
-      expect(index).toEqual('mockSignalsIndex');
-    });
-
-    it('appends the space id to the configured index if spaces are enabled', () => {
+    it('appends the space id to the configured index', () => {
       const getSpaceId = jest.fn(() => 'myspace');
       const index = getIndex(getSpaceId, mockConfig);
 

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/utils.ts

@@ -157,12 +157,9 @@ export const transformBulkError = (
   }
 };
 
-export const getIndex = (
-  getSpaceId: () => string | undefined,
-  config: LegacyServices['config']
-): string => {
-  const spaceId = getSpaceId();
+export const getIndex = (getSpaceId: () => string, config: LegacyServices['config']): string => {
   const signalsIndex = config().get<string>(`xpack.${APP_ID}.${SIGNALS_INDEX_KEY}`);
+  const spaceId = getSpaceId();
 
-  return spaceId ? `${signalsIndex}-${spaceId}` : signalsIndex;
+  return `${signalsIndex}-${spaceId}`;
 };

x-pack/legacy/plugins/siem/server/services/clients.ts

@@ -18,7 +18,7 @@ import { CoreStart, StartPlugins, SetupPlugins } from '../plugin';
 export interface Clients {
   actionsClient?: ActionsClient;
   clusterClient: IScopedClusterClient;
-  spacesClient: { getSpaceId: () => string | undefined };
+  spacesClient: { getSpaceId: () => string };
   savedObjectsClient: SavedObjectsClientContract;
 }
 interface LegacyClients {
@@ -58,7 +58,9 @@ export class ClientsService {
         actionsClient: await this.actions?.getActionsClientWithRequest?.(kibanaRequest),
         clusterClient: this.clusterClient!.asScoped(kibanaRequest),
         savedObjectsClient: this.savedObjects!.getScopedClient(kibanaRequest),
-        spacesClient: { getSpaceId: () => this.spacesService?.getSpaceId?.(kibanaRequest) },
+        spacesClient: {
+          getSpaceId: () => this.spacesService?.getSpaceId?.(kibanaRequest) ?? 'default',
+        },
       };
     };
   }