Bug 806056 - Add a frame bit that says if a frame is allowed to have abs/fixed pos. children when the style so indicates (position/transform usually). Copy the bit to next-in-flows. Don't call MarkAsAbsoluteContainingBlock for style changes on an existing frame unless that bit is set (style changes that recreates the frame resets it of course). Assert in MarkAs[Not]AbsoluteContainingBlock() that the bit is set. r=bz

layout/base/nsCSSFrameConstructor.cpp

@@ -1942,6 +1942,7 @@ nsCSSFrameConstructor::ConstructTable(nsFrameConstructorState& aState,
   const nsStyleDisplay* display = outerStyleContext->GetStyleDisplay();
 
   // Mark the table frame as an absolute container if needed
+  newFrame->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   if (display->IsPositioned(aParentFrame)) {
     aState.PushAbsoluteContainingBlock(newFrame, absoluteSaveState);
   }
@@ -2387,6 +2388,7 @@ nsCSSFrameConstructor::ConstructDocElementFrame(Element*                 aDocEle
   if (mHasRootAbsPosContainingBlock) {
     // Push the absolute containing block now so we can absolutely position
     // the root element
+    mDocElementContainingBlock->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
     state.PushAbsoluteContainingBlock(mDocElementContainingBlock,
                                       absoluteSaveState);
   }
@@ -2575,6 +2577,7 @@ nsCSSFrameConstructor::ConstructRootFrame(nsIFrame** aNewFrame)
   // The viewport is the containing block for 'fixed' elements
   mFixedContainingBlock = viewportFrame;
   // Make it an absolute container for fixed-pos elements
+  mFixedContainingBlock->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   mFixedContainingBlock->MarkAsAbsoluteContainingBlock();
 
   *aNewFrame = viewportFrame;
@@ -2844,6 +2847,7 @@ nsCSSFrameConstructor::ConstructPageFrame(nsIPresShell*  aPresShell,
   SetInitialSingleChild(aPageFrame, pageContentFrame);
   mFixedContainingBlock = pageContentFrame;
   // Make it an absolute container for fixed-pos elements
+  mFixedContainingBlock->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   mFixedContainingBlock->MarkAsAbsoluteContainingBlock();
 
   nsRefPtr<nsStyleContext> canvasPseudoStyle;
@@ -3150,6 +3154,7 @@ nsCSSFrameConstructor::ConstructFieldSetFrame(nsFrameConstructorState& aState,
   nsFrameConstructorSaveState absoluteSaveState;
   nsFrameItems                childItems;
 
+  newFrame->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   if (newFrame->IsPositioned()) {
     aState.PushAbsoluteContainingBlock(newFrame, absoluteSaveState);
   }
@@ -3726,11 +3731,12 @@ nsCSSFrameConstructor::ConstructFrameFromItemInternal(FrameConstructionItem& aIt
 
     if (bits & FCDATA_FORCE_NULL_ABSPOS_CONTAINER) {
       aState.PushAbsoluteContainingBlock(nullptr, absoluteSaveState);
-    } else if (!(bits & FCDATA_SKIP_ABSPOS_PUSH) &&
-               maybeAbsoluteContainingBlockDisplay->IsPositioned
-                   (maybeAbsoluteContainingBlock)) {
-      aState.PushAbsoluteContainingBlock(maybeAbsoluteContainingBlock,
-                                         absoluteSaveState);
+    } else if (!(bits & FCDATA_SKIP_ABSPOS_PUSH)) {
+      nsIFrame* cb = maybeAbsoluteContainingBlock;
+      cb->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
+      if (maybeAbsoluteContainingBlockDisplay->IsPositioned(cb)) {
+        aState.PushAbsoluteContainingBlock(cb, absoluteSaveState);
+      }
     }
 
     if (bits & FCDATA_USE_CHILD_ITEMS) {
@@ -8160,7 +8166,8 @@ nsCSSFrameConstructor::ProcessRestyledFrames(nsStyleChangeList& aChangeList)
           // but we may be taking this path even if a transform has been
           // removed. It's OK to add the bit even if it's not needed.
           frame->AddStateBits(NS_FRAME_MAY_BE_TRANSFORMED);
-          if (!frame->IsAbsoluteContainer()) {
+          if (!frame->IsAbsoluteContainer() &&
+              (frame->GetStateBits() & NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN)) {
             frame->MarkAsAbsoluteContainingBlock();
           }
         } else {
@@ -11122,6 +11129,7 @@ nsCSSFrameConstructor::ConstructBlock(nsFrameConstructorState& aState,
   // children. So use the block and try to compensate with hacks
   // in nsBlockFrame::CalculateContainingBlockSizeForAbsolutes.
   nsFrameConstructorSaveState absoluteSaveState;
+  (*aNewFrame)->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   if (aAbsPosContainer) {
     //    NS_ASSERTION(aRelPos, "should have made area frame for this");
     aState.PushAbsoluteContainingBlock(*aNewFrame, absoluteSaveState);
@@ -11226,6 +11234,7 @@ nsCSSFrameConstructor::ConstructInline(nsFrameConstructorState& aState,
                                                   // because the object's destructor is significant
                                                   // this is part of the fix for bug 42372
 
+  newFrame->AddStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   if (positioned) {
     // Relatively positioned frames becomes a container for child
     // frames that are positioned
@@ -11339,8 +11348,8 @@ nsCSSFrameConstructor::CreateIBSiblings(nsFrameConstructorState& aState,
     InitAndRestoreFrame(aState, content, parentFrame, nullptr, inlineFrame,
                         false);
 
-    inlineFrame->AddStateBits(NS_FRAME_MAY_HAVE_GENERATED_CONTENT);
-
+    inlineFrame->AddStateBits(NS_FRAME_MAY_HAVE_GENERATED_CONTENT |
+                              NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
     if (aIsPositioned) {
       inlineFrame->MarkAsAbsoluteContainingBlock();
     }

layout/generic/nsFrame.cpp

@@ -251,6 +251,7 @@ nsIFrame::GetAbsoluteContainingBlock() const {
 void
 nsIFrame::MarkAsAbsoluteContainingBlock()
 {
+  MOZ_ASSERT(GetStateBits() & NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   NS_ASSERTION(!Properties().Get(AbsoluteContainingBlockProperty()),
                "Already has an abs-pos containing block property?");
   NS_ASSERTION(!HasAnyStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN),
@@ -267,6 +268,7 @@ nsIFrame::MarkAsNotAbsoluteContainingBlock()
                "Should have an abs-pos containing block property");
   NS_ASSERTION(HasAnyStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN),
                "Should have NS_FRAME_HAS_ABSPOS_CHILDREN state bit");
+  MOZ_ASSERT(HasAnyStateBits(NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN));
   RemoveStateBits(NS_FRAME_HAS_ABSPOS_CHILDREN);
   Properties().Delete(AbsoluteContainingBlockProperty());
 }
@@ -512,7 +514,8 @@ nsFrame::Init(nsIContent*      aContent,
     mState |= state & (NS_FRAME_INDEPENDENT_SELECTION |
                        NS_FRAME_IS_SPECIAL |
                        NS_FRAME_MAY_BE_TRANSFORMED |
-                       NS_FRAME_MAY_HAVE_GENERATED_CONTENT);
+                       NS_FRAME_MAY_HAVE_GENERATED_CONTENT |
+                       NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN);
   }
   if (mParent) {
     nsFrameState state = mParent->GetStateBits();

layout/generic/nsIFrame.h

@@ -164,8 +164,10 @@ typedef uint64_t nsFrameState;
 // e.g., it is absolutely positioned or floated
 #define NS_FRAME_OUT_OF_FLOW                        NS_FRAME_STATE_BIT(8)
 
-// This bit is available for re-use.
-//#define NS_FRAME_SELECTED_CONTENT                   NS_FRAME_STATE_BIT(9)
+// Frame can be an abs/fixed pos. container, if its style says so.
+// MarkAs[Not]AbsoluteContainingBlock will assert that this bit is set.
+// NS_FRAME_HAS_ABSPOS_CHILDREN must not be set when this bit is unset.
+#define NS_FRAME_CAN_HAVE_ABSPOS_CHILDREN           NS_FRAME_STATE_BIT(9)
 
 // If this bit is set, then the frame and _all_ of its descendant frames need
 // to be reflowed.