Firestore: Fix "missing index" error message

packages/firestore/src/platform/browser_lite/fetch_connection.ts

@@ -69,9 +69,23 @@ export class FetchConnection extends RestConnection {
     }
 
     if (!response.ok) {
+      let errorMessage;
+      try {
+        // Try to get any error message text from server response.
+        //response.json returns an error object inside an array.
+        const [errorResponse] = (await response.json()) as [
+          {
+            error?: { message?: string };
+          }
+        ];
+        if (errorResponse.error?.message) {
+          errorMessage = errorResponse.error.message;
+        }
+      } catch (_ignored) {}
       throw new FirestoreError(
         mapCodeFromHttpStatus(response.status),
-        'Request failed with error: ' + response.statusText
+        //response body is an array with error object
+        'Request failed with error: ' + errorMessage ?? response.statusText
       );
     }
 

packages/firestore/test/integration/api/aggregation.test.ts

@@ -36,6 +36,7 @@ import {
   withTestCollection,
   withTestDb
 } from '../util/helpers';
+import { USE_EMULATOR } from '../util/settings';
 
 apiDescribe('Count quries', (persistence: boolean) => {
   it('can run count query getCountFromServer', () => {
@@ -118,4 +119,24 @@ apiDescribe('Count quries', (persistence: boolean) => {
       );
     });
   });
+
+  // Only verify the error message for missing indexes when running against
+  // production, since the Firestore Emulator does not require index creation
+  // and will, therefore, never fail in this situation.
+  // eslint-disable-next-line no-restricted-properties
+  (USE_EMULATOR ? it.skip : it)(
+    'getCountFromServer error message is good if missing index',
+    () => {
+      return withEmptyTestCollection(persistence, async coll => {
+        const query_ = query(
+          coll,
+          where('key1', '==', 42),
+          where('key2', '<', 42)
+        );
+        await expect(getCountFromServer(query_)).to.be.eventually.rejectedWith(
+          /index.*https:\/\/console\.firebase\.google\.com/
+        );
+      });
+    }
+  );
 });

packages/firestore/test/lite/integration.test.ts

@@ -83,7 +83,8 @@ import { runTransaction } from '../../src/lite-api/transaction';
 import { writeBatch } from '../../src/lite-api/write_batch';
 import {
   DEFAULT_PROJECT_ID,
-  DEFAULT_SETTINGS
+  DEFAULT_SETTINGS,
+  USE_EMULATOR
 } from '../integration/util/settings';
 
 import {
@@ -2380,4 +2381,24 @@ describe('Count quries', () => {
       expect(snapshot.data().count).to.equal(3);
     });
   });
+
+  // Only verify the error message for missing indexes when running against
+  // production, since the Firestore Emulator does not require index creation
+  // and will, therefore, never fail in this situation.
+  // eslint-disable-next-line no-restricted-properties
+  (USE_EMULATOR ? it.skip : it)(
+    'getCount error message is good if missing index',
+    () => {
+      return withTestCollection(async coll => {
+        const query_ = query(
+          coll,
+          where('key1', '==', 42),
+          where('key2', '<', 42)
+        );
+        await expect(getCount(query_)).to.be.eventually.rejectedWith(
+          /index.*https:\/\/console\.firebase\.google\.com/
+        );
+      });
+    }
+  );
 });