fix: Better error for Collection Group Queries with documentId() curs…

…ors (#720)

dev/src/reference.ts

@@ -1418,6 +1418,25 @@ export class Query {
     let reference: DocumentReference;
 
     if (typeof val === 'string') {
+      const path = basePath.append(val);
+
+      if (this._queryOptions.allDescendants) {
+        if (!path.isDocument) {
+          throw new Error(
+            'When querying a collection group and ordering by ' +
+              'FieldPath.documentId(), the corresponding value must result in ' +
+              `a valid document path, but '${val}' is not because it ` +
+              'contains an odd number of segments.'
+          );
+        }
+      } else if (val.indexOf('/') !== -1) {
+        throw new Error(
+          'When querying a collection and ordering by FieldPath.documentId(), ' +
+            `the corresponding value must be a plain document ID, but '${val}' ` +
+            'contains a slash.'
+        );
+      }
+
       reference = new DocumentReference(this._firestore, basePath.append(val));
     } else if (val instanceof DocumentReference) {
       reference = val;

dev/test/query.ts

@@ -1356,7 +1356,9 @@ describe('startAt() interface', () => {
     expect(() => {
       query.orderBy(FieldPath.documentId()).startAt('doc/coll');
     }).to.throw(
-      'Only a direct child can be used as a query boundary. Found: "coll/doc/coll/doc/coll".'
+      'When querying a collection and ordering by FieldPath.documentId(), ' +
+        'the corresponding value must be a plain document ID, but ' +
+        "'doc/coll' contains a slash."
     );
   });
 
@@ -1867,4 +1869,19 @@ describe('collectionGroup queries', () => {
       );
     });
   });
+
+  it('rejects slashes', () => {
+    return createInstance().then(firestore => {
+      const query = firestore.collectionGroup('collectionId');
+
+      expect(() => {
+        query.orderBy(FieldPath.documentId()).startAt('coll');
+      }).to.throw(
+        'When querying a collection group and ordering by ' +
+          'FieldPath.documentId(), the corresponding value must result in a ' +
+          "valid document path, but 'coll' is not because it contains an odd " +
+          'number of segments.'
+      );
+    });
+  });
 });