Issue mcp-graveyard/UXP#1641 - Implement CSS flow-root keyword

This is just a clean port of 1322191 and follow-up 1325970. It really seems to add create a new way to access existing code relating to block formatting and floating elements rather than implementing new functionality, and it is mercifully straightforwards.

4 files changed, 9 insertions, 5 deletions

diff --git a/layout/generic/ReflowInput.cpp b/layout/generic/ReflowInput.cpp
index 9f7b4368c3..077c68b5be 100644
--- a/layout/generic/ReflowInput.cpp
+++ b/layout/generic/ReflowInput.cpp
@@ -844,6 +844,7 @@ ReflowInput::InitFrameType(nsIAtom* aFrameType)
     case StyleDisplay::Flex:
     case StyleDisplay::WebkitBox:
     case StyleDisplay::Grid:
+    case StyleDisplay::FlowRoot:
     case StyleDisplay::RubyTextContainer:
       frameType = NS_CSS_FRAME_TYPE_BLOCK;
       break;
diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
index 4742db07e6..152b3d06ad 100644
--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -305,7 +305,7 @@ NS_NewBlockFormattingContext(nsIPresShell* aPresShell,
                              nsStyleContext* aStyleContext)
 {
   nsBlockFrame* blockFrame = NS_NewBlockFrame(aPresShell, aStyleContext);
-  blockFrame->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+  blockFrame->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   return blockFrame;
 }
 
@@ -6893,10 +6893,11 @@ nsBlockFrame::Init(nsIContent*       aContent,
   // (http://dev.w3.org/csswg/css-writing-modes/#block-flow)
   // If the box has contain: paint (or contain: strict), then it should also
   // establish a formatting context.
-  if ((GetParent() && StyleVisibility()->mWritingMode !=
+  if (StyleDisplay()->mDisplay == mozilla::StyleDisplay::FlowRoot ||
+      (GetParent() && StyleVisibility()->mWritingMode !=
                       GetParent()->StyleVisibility()->mWritingMode) ||
       StyleDisplay()->IsContainPaint()) {
-    AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+    AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   }
 
   if ((GetStateBits() &
diff --git a/layout/generic/nsFrameStateBits.h b/layout/generic/nsFrameStateBits.h
index f8b1e541c1..ba43e37d45 100644
--- a/layout/generic/nsFrameStateBits.h
+++ b/layout/generic/nsFrameStateBits.h
@@ -483,6 +483,9 @@ FRAME_STATE_BIT(Block, 22, NS_BLOCK_MARGIN_ROOT)
 // used to reserve space for the floated frames.
 FRAME_STATE_BIT(Block, 23, NS_BLOCK_FLOAT_MGR)
 
+// For setting the relevant bits on a block formatting context:
+#define NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS (NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT)
+
 FRAME_STATE_BIT(Block, 24, NS_BLOCK_HAS_LINE_CURSOR)
 
 FRAME_STATE_BIT(Block, 25, NS_BLOCK_HAS_OVERFLOW_LINES)
diff --git a/layout/generic/nsHTMLParts.h b/layout/generic/nsHTMLParts.h
index 243c432b2f..97edaf75c1 100644
--- a/layout/generic/nsHTMLParts.h
+++ b/layout/generic/nsHTMLParts.h
@@ -28,8 +28,7 @@ class nsTableColFrame;
 // These are all the block specific frame bits, they are copied from
 // the prev-in-flow to a newly created next-in-flow, except for the
 // NS_BLOCK_FLAGS_NON_INHERITED_MASK bits below.
-#define NS_BLOCK_FLAGS_MASK (NS_BLOCK_MARGIN_ROOT              | \
-                             NS_BLOCK_FLOAT_MGR                | \
+#define NS_BLOCK_FLAGS_MASK (NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS | \
                              NS_BLOCK_CLIP_PAGINATED_OVERFLOW  | \
                              NS_BLOCK_HAS_FIRST_LETTER_STYLE   | \
                              NS_BLOCK_FRAME_HAS_OUTSIDE_BULLET | \