1 files changed, 94 insertions, 0 deletions
diff --git a/js/xpconnect/tests/browser/browser_weak_xpcwn.js b/js/xpconnect/tests/browser/browser_weak_xpcwn.js
new file mode 100644
index 0000000000..fc0fb502e0
--- /dev/null
+++ b/js/xpconnect/tests/browser/browser_weak_xpcwn.js
@@ -0,0 +1,94 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Check to see if a weak reference is dead.
+let weak_ref_dead = function (r) {
+  return !SpecialPowers.nondeterministicGetWeakMapKeys(r).length;
+};
+
+add_task(async function cc_xpcwn_dead() {
+  // This test demonstrates that a JS reflector for an XPCOM object
+  // (implemented via XPCWrappedNative) can be used as a weak map key, but it
+  // won't persist across a GC/CC if there are no other references to the key in
+  // JS. It would be nice if it did work, in which case we could delete this
+  // test, but it would be difficult to implement.
+
+  let wnMap = new WeakMap();
+
+  // Create a new C++ XPCOM container.
+  let container = Cc["@mozilla.org/array;1"].createInstance(Ci.nsIMutableArray);
+
+  {
+    // Create a new C++ XPCOM object, with a new JS reflector.
+    let str = Cc["@mozilla.org/supports-string;1"].createInstance(
+      Ci.nsISupportsString
+    );
+
+    // Set the string data so we can recognize it later.
+    str.data = "canary123";
+
+    // Store the C++ object in the C++ container.
+    container.appendElement(str);
+    is(container.Count(), 1, "The array should have one element");
+
+    // Use the JS reflector as a weak map key.
+    wnMap.set(str, {});
+    ok(!weak_ref_dead(wnMap), "weak map should have an entry");
+
+    // Make sure there are no references to the JS reflector.
+    str = null;
+  }
+
+  // Clean up the JS reflector.
+  SpecialPowers.forceGC();
+  SpecialPowers.forceCC();
+
+  ok(weak_ref_dead(wnMap), "The JS reflector has been freed.");
+
+  // Make a new JS reflector for the C++ XPCOM object.
+  let str2 = container.GetElementAt(0).QueryInterface(Ci.nsISupportsString);
+
+  is(str2.data, "canary123", "The C++ object we created still exists.");
+});
+
+add_task(async function cc_xpcwn_live() {
+  // This test is a slight variation of the previous one. It keeps a reference
+  // to the JS reflector for the C++ object, and shows that this keeps it from
+  // being removed from the weak map. This is mostly to show why it will work
+  // under some conditions.
+
+  let wnMap = new WeakMap();
+
+  // Create a new C++ XPCOM container.
+  let container = Cc["@mozilla.org/array;1"].createInstance(Ci.nsIMutableArray);
+
+  // Create a new C++ XPCOM object, with a new JS reflector, and hold alive
+  // the reflector.
+  let str = Cc["@mozilla.org/supports-string;1"].createInstance(
+    Ci.nsISupportsString
+  );
+
+  // Set the string data so we can recognize it later.
+  str.data = "canary345";
+
+  // Store the C++ object in the C++ container.
+  container.appendElement(str);
+  is(container.Count(), 1, "The array should have one element");
+
+  // Use the JS reflector as a weak map key.
+  wnMap.set(str, {});
+  ok(!weak_ref_dead(wnMap), "weak map should have an entry");
+
+  // Clean up the JS reflector.
+  SpecialPowers.forceGC();
+  SpecialPowers.forceCC();
+
+  ok(!weak_ref_dead(wnMap), "The JS reflector hasn't been freed.");
+
+  // Get a JS reflector from scratch for the C++ XPCOM object.
+  let str2 = container.GetElementAt(0).QueryInterface(Ci.nsISupportsString);
+  is(str, str2, "The JS reflector is the same");
+  is(str2.data, "canary345", "The C++ object hasn't changed");
+});