[Discover] Render the sidebar even if documents fetching failed

src/plugins/discover/public/application/main/components/sidebar/discover_sidebar_responsive.tsx

@@ -168,6 +168,16 @@ export function DiscoverSidebarResponsive(props: DiscoverSidebarResponsiveProps)
             },
           });
           break;
+        case FetchStatus.ERROR:
+          dispatchSidebarStateAction({
+            type: DiscoverSidebarReducerActionType.DOCUMENTS_LOADED,
+            payload: {
+              dataView: selectedDataViewRef.current,
+              fieldCounts: {},
+              isPlainRecord: isPlainRecordType,
+            },
+          });
+          break;
         default:
           break;
       }

test/functional/apps/discover/group1/_sidebar.ts

@@ -510,6 +510,46 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         expect(allFields.includes('_bytes-runtimefield')).to.be(false);
       });
 
+      it('should render even when retrieving documents failed with an error', async () => {
+        await PageObjects.header.waitUntilLoadingHasFinished();
+
+        await testSubjects.missingOrFail('discoverNoResultsError');
+
+        expect(await PageObjects.discover.getSidebarAriaDescription()).to.be(
+          '53 available fields. 0 empty fields. 3 meta fields.'
+        );
+
+        await PageObjects.discover.addRuntimeField('_invalid-runtimefield', `emit(‘’);`);
+
+        await PageObjects.header.waitUntilLoadingHasFinished();
+
+        // error in fetching documents because of the invalid runtime field
+        await testSubjects.existOrFail('discoverNoResultsError');
+
+        await PageObjects.discover.waitUntilSidebarHasLoaded();
+
+        // check that the sidebar is rendered
+        expect(await PageObjects.discover.getSidebarAriaDescription()).to.be(
+          '54 available fields. 0 empty fields. 3 meta fields.'
+        );
+        let allFields = await PageObjects.discover.getAllFieldNames();
+        expect(allFields.includes('_invalid-runtimefield')).to.be(true);
+
+        await browser.refresh();
+        await PageObjects.header.waitUntilLoadingHasFinished();
+        await testSubjects.existOrFail('discoverNoResultsError'); // still has error
+
+        // check that the sidebar is rendered event after a refresh
+        allFields = await PageObjects.discover.getAllFieldNames();
+        expect(allFields.includes('_invalid-runtimefield')).to.be(true);
+
+        await PageObjects.discover.removeField('_invalid-runtimefield');
+        await PageObjects.header.waitUntilLoadingHasFinished();
+        await PageObjects.discover.waitUntilSidebarHasLoaded();
+
+        await testSubjects.missingOrFail('discoverNoResultsError');
+      });
+
       it('should work correctly when time range is updated', async function () {
         await esArchiver.loadIfNeeded(
           'test/functional/fixtures/es_archiver/index_pattern_without_timefield'