[8.x] [eem] _count guards against no valid sources (#204224) (#204310)

# Backport

This will backport the following commits from `main` to `8.x`:
- [[eem] _count guards against no valid sources
(#204224)](#204224)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Kevin
Lacabane","email":"kevin.lacabane@elastic.co"},"sourceCommit":{"committedDate":"2024-12-14T10:14:29Z","message":"[eem]
_count guards against no valid sources (#204224)\n\nThe query generation
expects at least 1 source to be
passed","sha":"9a8ed0d1359a3d5848ebcbe200dff44debf6736c","branchLabelMapping":{"^v9.0.0$":"main","^v8.18.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:fix","v9.0.0","backport:prev-minor","Team:obs-entities"],"title":"[eem]
_count guards against no valid sources
","number":204224,"url":"https://github.com/elastic/kibana/pull/204224","mergeCommit":{"message":"[eem]
_count guards against no valid sources (#204224)\n\nThe query generation
expects at least 1 source to be
passed","sha":"9a8ed0d1359a3d5848ebcbe200dff44debf6736c"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.0.0","branchLabelMappingKey":"^v9.0.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/204224","number":204224,"mergeCommit":{"message":"[eem]
_count guards against no valid sources (#204224)\n\nThe query generation
expects at least 1 source to be
passed","sha":"9a8ed0d1359a3d5848ebcbe200dff44debf6736c"}}]}]
BACKPORT-->

Co-authored-by: Kevin Lacabane <kevin.lacabane@elastic.co>

x-pack/platform/plugins/shared/entity_manager/server/lib/v2/entity_client.ts

@@ -144,6 +144,10 @@ export class EntityClient {
           errors: results.filter(isRejectedResult).map((result) => result.reason.message as string),
         }));
 
+        if (validSources.length === 0) {
+          return { type, value: 0, errors };
+        }
+
         const { query, filter } = getEntityCountQuery({
           sources: validSources,
           filters,

x-pack/test/api_integration/apis/entity_manager/count.ts

@@ -361,7 +361,7 @@ export default function ({ getService }: FtrProviderContext) {
       });
     });
 
-    it('is resilient to invalid sources', async () => {
+    it('is resilient to partially valid sources', async () => {
       await createEntityTypeDefinition(supertest, {
         type: { id: 'chumble', display_name: 'chumble' },
       });
@@ -417,5 +417,46 @@ export default function ({ getService }: FtrProviderContext) {
         ],
       });
     });
+
+    it('is resilient to no valid sources', async () => {
+      await createEntityTypeDefinition(supertest, {
+        type: { id: 'chumble', display_name: 'chumble' },
+      });
+      await Promise.all([
+        createEntitySourceDefinition(supertest, {
+          source: {
+            id: 'source1-with-chumbles',
+            type_id: 'chumble',
+            index_patterns: ['index-1-with-chumbles'],
+            identity_fields: ['service.name'],
+            metadata_fields: [],
+            filters: [],
+          },
+        }),
+        createEntitySourceDefinition(supertest, {
+          source: {
+            id: 'source2-with-chumbles',
+            type_id: 'chumble',
+            index_patterns: ['index-2-with-chumbles'],
+            identity_fields: ['service.name'],
+            metadata_fields: [],
+            filters: [],
+          },
+        }),
+      ]);
+
+      const result = await countEntities(supertest, {}, 200);
+
+      expect(result).toEqual({
+        total: 0,
+        types: {
+          chumble: 0,
+        },
+        errors: [
+          'No index found for source [source: source1-with-chumbles, type: chumble] with index patterns [index-1-with-chumbles]',
+          'No index found for source [source: source2-with-chumbles, type: chumble] with index patterns [index-2-with-chumbles]',
+        ],
+      });
+    });
   });
 }