Add assertions to EndReconstruct that all style contexts have been reresolved. (Bug 473871) r+sr=bzbarsky

layout/style/nsStyleContext.cpp

@@ -80,6 +80,14 @@ nsStyleContext::nsStyleContext(nsStyleContext* aParent,
   if (mParent) {
     mParent->AddRef();
     mParent->AddChild(this);
+#ifdef DEBUG
+    nsRuleNode *r1 = mParent->GetRuleNode(), *r2 = aRuleNode;
+    while (r1->GetParent())
+      r1 = r1->GetParent();
+    while (r2->GetParent())
+      r2 = r2->GetParent();
+    NS_ABORT_IF_FALSE(r1 == r2, "must be in the same rule tree as parent");
+#endif
   }
 
   ApplyStyleFixups(aPresContext);

layout/style/nsStyleContext.h

@@ -107,8 +107,6 @@ public:
 
   nsStyleContext* GetParent() const { return mParent; }
 
-  nsStyleContext* GetFirstChild() const { return mChild; }
-
   nsIAtom* GetPseudoType() const { return mPseudoTag; }
 
   NS_HIDDEN_(already_AddRefed<nsStyleContext>)
@@ -178,7 +176,7 @@ protected:
 
   NS_HIDDEN_(void) ApplyStyleFixups(nsPresContext* aPresContext);
 
-  nsStyleContext* mParent;
+  nsStyleContext* const mParent;
 
   // Children are kept in two circularly-linked lists.  The list anchor
   // is not part of the list (null for empty), and we point to the first

layout/style/nsStyleSet.cpp

@@ -144,8 +144,9 @@ nsStyleSet::BeginReconstruct()
   mOldRuleTree = mRuleTree;
   // Delete mRuleWalker because it holds a reference to the rule tree root
   delete mRuleWalker;
-  // Clear out the old style contexts; we don't need them anymore
-  mRoots.Clear();
+  // We don't need to clear out mRoots; NotifyStyleContextDestroyed
+  // will, and they're useful in EndReconstruct if they don't get
+  // completely cleared out.
 
   mRuleTree = newTree;
   mRuleWalker = ruleWalker;
@@ -156,6 +157,22 @@ nsStyleSet::BeginReconstruct()
 void
 nsStyleSet::EndReconstruct()
 {
+#ifdef DEBUG
+  for (PRInt32 i = mRoots.Length() - 1; i >= 0; --i) {
+    nsRuleNode *n = mRoots[i]->GetRuleNode();
+    while (n->GetParent()) {
+      n = n->GetParent();
+    }
+    // Since nsStyleContext's mParent and mRuleNode are immutable, and
+    // style contexts own their parents, and nsStyleContext asserts in
+    // its constructor that the style context and its parent are in the
+    // same rule tree, we don't need to check any of the children of
+    // mRoots; we only need to check the rule nodes of mRoots
+    // themselves.
+
+    NS_ABORT_IF_FALSE(n == mRuleTree, "style context has old rule node");
+  }
+#endif
   NS_ASSERTION(mOldRuleTree, "Unmatched begin/end?");
   // Reset the destroyed count; it's no longer valid
   mDestroyedCount = 0;