Bug 1575306 - Suppress reporting of uncaught testing sentinel, r=bzbarsky.

Differential Revision: https://phabricator.services.mozilla.com/D45964

--HG--
extra : moz-landing-system : lando

dom/chrome-webidl/PromiseDebugging.webidl

@@ -32,13 +32,14 @@ enum PromiseDebuggingState { "pending", "fulfilled", "rejected" };
 callback interface UncaughtRejectionObserver {
   /**
    * A Promise has been left in `rejected` state and is the
-   * last in its chain.
+   * last in its chain. If this callback returns true, the rejection
+   * will not be reported.
    *
    * @param p A currently uncaught Promise. If `p` is is eventually
    * caught, i.e. if its `then` callback is called, `onConsumed` will
    * be called.
    */
-  void onLeftUncaught(object p);
+  boolean onLeftUncaught(object p);
 
   /**
    * A Promise previously left uncaught is not the last in its

dom/promise/PromiseDebugging.cpp

@@ -265,14 +265,20 @@ void PromiseDebugging::FlushUncaughtRejectionsInternal() {
       continue;
     }
 
+    bool suppressReporting = false;
     for (size_t j = 0; j < observers.Length(); ++j) {
       RefPtr<UncaughtRejectionObserver> obs =
           static_cast<UncaughtRejectionObserver*>(observers[j].get());
 
-      obs->OnLeftUncaught(promise, IgnoreErrors());
+      if (obs->OnLeftUncaught(promise, IgnoreErrors())) {
+        suppressReporting = true;
+      }
+    }
+
+    if (!suppressReporting) {
+      JSAutoRealm ar(cx, promise);
+      Promise::ReportRejectedPromise(cx, promise);
     }
-    JSAutoRealm ar(cx, promise);
-    Promise::ReportRejectedPromise(cx, promise);
   }
   storage->mUncaughtRejections.clear();
 

toolkit/modules/tests/modules/PromiseTestUtils.jsm

@@ -102,7 +102,9 @@ var PromiseTestUtils = {
           this._ensureDOMPromiseRejectionsProcessedReason
         ) {
           observed = true;
+          return true;
         }
+        return false;
       },
       onConsumed() {},
     };