1 files changed, 46 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/debug/Promise-race-dependent-promises.js b/js/src/jit-test/tests/debug/Promise-race-dependent-promises.js
new file mode 100644
index 0000000000..196d29aeae
--- /dev/null
+++ b/js/src/jit-test/tests/debug/Promise-race-dependent-promises.js
@@ -0,0 +1,46 @@
+// Promise.race(...) may add a dummy PromiseReaction which is only used for the
+// debugger.
+//
+// See BlockOnPromise when called from PerformPromiseRace for when this dummy
+// reaction is created.
+
+var g = newGlobal({newCompartment: true});
+var dbg = new Debugger();
+var gw = dbg.addDebuggee(g);
+
+function test(withFastPath) {
+    g.eval(`
+        function newPromiseCapability() {
+            var resolve, reject, promise = new Promise(function(r1, r2) {
+                resolve = r1;
+                reject = r2;
+            });
+            return {promise, resolve, reject};
+        }
+
+        var {promise: alwaysPending} = newPromiseCapability();
+
+        if (!${withFastPath}) {
+            // Disable the BlockOnPromise fast path by giving |alwaysPending| a
+            // non-default "then" function property. This will ensure the dummy
+            // reaction is created.
+            alwaysPending.then = function() {};
+        }
+
+        var result = Promise.race([alwaysPending]);
+    `);
+
+    var alwaysPending = gw.makeDebuggeeValue(g.alwaysPending);
+    var result = gw.makeDebuggeeValue(g.result);
+
+    assertEq(alwaysPending.promiseDependentPromises.length, 1);
+    assertEq(alwaysPending.promiseDependentPromises[0], result);
+
+    assertEq(result.promiseDependentPromises.length, 0);
+}
+
+// No dummy reaction created when the fast path is taken.
+test(true);
+
+// Dummy reaction is created when we can't take the fast path.
+test(false);