fix(stitching): observabeToAsyncIterator should preserve graphql errors

src/stitching/makeRemoteExecutableSchema.ts

@@ -29,6 +29,7 @@ import resolveParentFromTypename from './resolveFromParentTypename';
 import defaultMergedResolver from './defaultMergedResolver';
 import { checkResultAndHandleErrors } from './checkResultAndHandleErrors';
 import { observableToAsyncIterable } from './observableToAsyncIterable';
+import mapAsyncIterator from './mapAsyncIterator';
 import { Options as PrintSchemaOptions } from 'graphql/utilities/schemaPrinter';
 
 export type ResolverFn = (
@@ -181,7 +182,9 @@ function createSubscriptionResolver(name: string, link: ApolloLink): ResolverFn
     };
 
     const observable = execute(link, operation);
-
-    return observableToAsyncIterable(observable);
+    const originalAsyncIterator = observableToAsyncIterable(observable);
+    return mapAsyncIterator(originalAsyncIterator, result => ({
+      [info.fieldName]: checkResultAndHandleErrors(result, info),
+    }));
   };
 }

src/stitching/observableToAsyncIterable.ts

@@ -8,11 +8,11 @@ export function observableToAsyncIterable<T>(observable: Observable<T>): AsyncIt
 
   let listening = true;
 
-  const pushValue = ({ data }: any) => {
+  const pushValue = (value: any) => {
     if (pullQueue.length !== 0) {
-      pullQueue.shift()({ value: data, done: false });
+      pullQueue.shift()({ value, done: false });
     } else {
-      pushQueue.push({ value: data });
+      pushQueue.push({ value });
     }
   };