Bug 1773237 - Mark ignored promise as handled to avoid spurious unhandled rejection error r=evilpie

Differential Revision: https://phabricator.services.mozilla.com/D158589

dom/fetch/FetchStreamReader.cpp

@@ -146,10 +146,16 @@ void FetchStreamReader::CloseAndRelease(JSContext* aCx, nsresult aStatus) {
       // comments in ReadableStream::cancel() conveying the spec, step 2 of
       // 3.4.3 that specified ReadableStreamCancel is: If stream.[[state]] is
       // "closed", return a new promise resolved with undefined.
-      RefPtr<Promise> ignoredResultPromise =
+      RefPtr<Promise> cancelResultPromise =
           MOZ_KnownLive(mReader)->Cancel(aCx, errorValue, ignoredError);
       NS_WARNING_ASSERTION(!ignoredError.Failed(),
                            "Failed to cancel stream during close and release");
+      if (cancelResultPromise) {
+        bool setHandled = cancelResultPromise->SetAnyPromiseIsHandled();
+        NS_WARNING_ASSERTION(setHandled,
+                             "Failed to mark cancel promise as handled.");
+        (void)setHandled;
+      }
     }
 
     // We don't want to propagate exceptions during the cleanup.

dom/streams/test/xpcshell/bug-1773237.js

@@ -0,0 +1,11 @@
+// This test fails if there is an unhandled promise rejection
+var stream = new ReadableStream({
+  pull() {
+    return Promise.reject("foobar");
+  },
+});
+var response = new Response(stream);
+var text = response.text().then(
+  () => {},
+  e => {}
+);

dom/streams/test/xpcshell/xpcshell.ini

@@ -19,3 +19,4 @@ skip-if =
   tsan # Causes claim expired errors; see Bug 1770170.
 run-sequentially = very high failure rate in parallel
 [too-big-array-buffer.js]
+[bug-1773237.js]