From 49e1f7bbd70fc49397473e40ee2830f4e3cb4907 Mon Sep 17 00:00:00 2001
From: Olli Pettay <Olli.Pettay@helsinki.fi>
Date: Wed, 29 Jul 2015 13:28:45 +0300
Subject: [PATCH] Bug 1183604, add some more assertions to help implementing
 new cycle collectable classes, r=mccr8

--HG--
extra : rebase_source : e9f4bf6a9dce11e816b0f4f0cf1bfad61f831eeb
---
 dom/base/nsWrapperCache.h   |  2 ++
 dom/bindings/BindingUtils.h | 56 +++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/dom/base/nsWrapperCache.h b/dom/base/nsWrapperCache.h
index b6f37ca78b4c..af645a66a8b4 100644
--- a/dom/base/nsWrapperCache.h
+++ b/dom/base/nsWrapperCache.h
@@ -322,8 +322,10 @@ private:
                             nsScriptObjectTracer* aTracer);
 
 #ifdef DEBUG
+public:
   void CheckCCWrapperTraversal(void* aScriptObjectHolder,
                                nsScriptObjectTracer* aTracer);
+private:
 #endif // DEBUG
 
   /**
diff --git a/dom/bindings/BindingUtils.h b/dom/bindings/BindingUtils.h
index fc2e0ab85b8d..2e5d9b766470 100644
--- a/dom/bindings/BindingUtils.h
+++ b/dom/bindings/BindingUtils.h
@@ -879,6 +879,56 @@ struct TypeNeedsOuterization
     IsBaseOf<nsGlobalWindow, T>::value || IsSame<EventTarget, T>::value;
 };
 
+#ifdef DEBUG
+template<typename T, bool isISupports=IsBaseOf<nsISupports, T>::value>
+struct CheckWrapperCacheTracing
+{
+  static inline void Check(T* aObject)
+  {
+  }
+};
+
+template<typename T>
+struct CheckWrapperCacheTracing<T, true>
+{
+  static void Check(T* aObject)
+  {
+    // Rooting analysis thinks QueryInterface may GC, but we're dealing with
+    // a subset of QueryInterface, C++ only types here.
+    JS::AutoSuppressGCAnalysis nogc;
+
+    nsWrapperCache* wrapperCacheFromQI = nullptr;
+    aObject->QueryInterface(NS_GET_IID(nsWrapperCache),
+                            reinterpret_cast<void**>(&wrapperCacheFromQI));
+
+    MOZ_ASSERT(wrapperCacheFromQI,
+               "Missing nsWrapperCache from QueryInterface implementation?");
+
+    if (!wrapperCacheFromQI->GetWrapperPreserveColor()) {
+      // Can't assert that we trace the wrapper, since we don't have any
+      // wrapper to trace.
+      return;
+    }
+
+    nsISupports* ccISupports = nullptr;
+    aObject->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
+                            reinterpret_cast<void**>(&ccISupports));
+    MOZ_ASSERT(ccISupports,
+               "nsWrapperCache object which isn't cycle collectable?");
+
+    nsXPCOMCycleCollectionParticipant* participant = nullptr;
+    CallQueryInterface(ccISupports, &participant);
+    MOZ_ASSERT(participant, "Can't QI to CycleCollectionParticipant?");
+
+    bool wasPreservingWrapper = wrapperCacheFromQI->PreservingWrapper();
+    wrapperCacheFromQI->SetPreservingWrapper(true);
+    wrapperCacheFromQI->CheckCCWrapperTraversal(ccISupports, participant);
+    wrapperCacheFromQI->SetPreservingWrapper(wasPreservingWrapper);
+  }
+};
+
+#endif
+
 template <class T, GetOrCreateReflectorWrapBehavior wrapBehavior>
 MOZ_ALWAYS_INLINE bool
 DoGetOrCreateDOMReflector(JSContext* cx, T* value,
@@ -903,6 +953,12 @@ DoGetOrCreateDOMReflector(JSContext* cx, T* value,
       // figure out whether WrapObject() threw.
       return false;
     }
+
+#ifdef DEBUG
+    if (IsBaseOf<nsWrapperCache, T>::value) {
+      CheckWrapperCacheTracing<T>::Check(value);
+    }
+#endif
   }
 
 #ifdef DEBUG