fix(incrementalDelivery) fixes null bubbling for async iterables

when a null bubbles up, no further payloads should be sent.

Author: yaacovCR

src/execution/__tests__/stream-test.ts

@@ -1056,8 +1056,8 @@ describe('Execute: stream directive', () => {
       nestedObject: {
         nonNullScalarField: () => Promise.resolve(null),
         async *nestedFriendList() {
-          yield await Promise.resolve(friends[0]);
-        },
+          yield await Promise.resolve(friends[0]); /* c8 ignore start */
+        } /* c8 ignore stop */,
       },
     });
     expectJSON(result).toDeepEqual({
@@ -1156,9 +1156,6 @@ describe('Execute: stream directive', () => {
             path: ['nestedObject', 'nestedFriendList', 0],
           },
         ],
-        hasNext: true,
-      },
-      {
         hasNext: false,
       },
     ]);
@@ -1183,8 +1180,8 @@ describe('Execute: stream directive', () => {
         deeperNestedObject: {
           nonNullScalarField: () => Promise.resolve(null),
           async *deeperNestedFriendList() {
-            yield await Promise.resolve(friends[0]);
-          },
+            yield await Promise.resolve(friends[0]); /* c8 ignore start */
+          } /* c8 ignore stop */,
         },
       },
     });
@@ -1271,14 +1268,17 @@ describe('Execute: stream directive', () => {
 
   it('Returns iterator and ignores errors when stream payloads are filtered', async () => {
     let returned = false;
-    let index = 0;
+    let requested = false;
     const iterable = {
       [Symbol.asyncIterator]: () => ({
         next: () => {
-          const friend = friends[index++];
-          if (!friend) {
-            return Promise.resolve({ done: true, value: undefined });
+          if (requested) {
+            /* c8 ignore next 3 */
+            // Not reached, iterator should end immediately.
+            expect.fail('Not reached');
           }
+          requested = true;
+          const friend = friends[0];
           return Promise.resolve({
             done: false,
             value: {
@@ -1356,17 +1356,12 @@ describe('Execute: stream directive', () => {
             ],
           },
         ],
-        hasNext: true,
+        hasNext: false,
       },
     });
-    const result3 = await iterator.next();
-    expectJSON(result3).toDeepEqual({
-      done: false,
-      value: { hasNext: false },
-    });
 
-    const result4 = await iterator.next();
-    expectJSON(result4).toDeepEqual({ done: true, value: undefined });
+    const result3 = await iterator.next();
+    expectJSON(result3).toDeepEqual({ done: true, value: undefined });
 
     assert(returned);
   });

src/execution/execute.ts

@@ -2026,43 +2026,52 @@ async function executeStreamIterator(
       exeContext,
     });
 
-    const dataPromise = executeStreamIteratorItem(
-      iterator,
-      exeContext,
-      fieldNodes,
-      info,
-      itemType,
-      asyncPayloadRecord,
-      itemPath,
-    );
-
-    asyncPayloadRecord.addItems(
-      dataPromise
-        .then(({ value }) => value)
-        .then(
-          (value) => [value],
-          (err) => {
-            asyncPayloadRecord.errors.push(err);
-            return null;
-          },
-        ),
-    );
+    let iteration;
     try {
       // eslint-disable-next-line no-await-in-loop
-      const { done } = await dataPromise;
-      if (done) {
-        break;
-      }
-    } catch (err) {
-      // entire stream has errored and bubbled upwards
+      iteration = await executeStreamIteratorItem(
+        iterator,
+        exeContext,
+        fieldNodes,
+        info,
+        itemType,
+        asyncPayloadRecord,
+        itemPath,
+      );
+    } catch (error) {
+      asyncPayloadRecord.errors.push(error);
       filterSubsequentPayloads(exeContext, path, asyncPayloadRecord);
+      asyncPayloadRecord.addItems(null);
+      // entire stream has errored and bubbled upwards
       if (iterator?.return) {
         iterator.return().catch(() => {
           // ignore errors
         });
       }
       return;
     }
+
+    const { done, value: completedItem } = iteration;
+
+    let completedItems: PromiseOrValue<Array<unknown> | null>;
+    if (isPromise(completedItem)) {
+      completedItems = completedItem.then(
+        (value) => [value],
+        (error) => {
+          asyncPayloadRecord.errors.push(error);
+          filterSubsequentPayloads(exeContext, path, asyncPayloadRecord);
+          return null;
+        },
+      );
+    } else {
+      completedItems = [completedItem];
+    }
+
+    asyncPayloadRecord.addItems(completedItems);
+
+    if (done) {
+      break;
+    }
     previousAsyncPayloadRecord = asyncPayloadRecord;
     index++;
   }