Issue #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.

15 files changed, 68 insertions, 16 deletions

diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index fc458b5ebf..21068b6736 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -2618,7 +2618,8 @@ nsCSSFrameConstructor::ConstructDocElementFrame(Element*                 aDocEle
     newFrame = frameItems.FirstChild();
     NS_ASSERTION(frameItems.OnlyChild(), "multiple root element frames");
   } else {
-    MOZ_ASSERT(display->mDisplay == StyleDisplay::Block,
+    MOZ_ASSERT(display->mDisplay == StyleDisplay::Block ||
+               display->mDisplay == StyleDisplay::FlowRoot,
                "Unhandled display type for root element");
     contentFrame = NS_NewBlockFormattingContext(mPresShell, styleContext);
     nsFrameItems frameItems;
@@ -4741,6 +4742,7 @@ nsCSSFrameConstructor::FindDisplayData(const nsStyleDisplay* aDisplay,
   static const FrameConstructionDataByDisplay sDisplayData[] = {
     FCDATA_FOR_DISPLAY(StyleDisplay::None, UNREACHABLE_FCDATA()),
     FCDATA_FOR_DISPLAY(StyleDisplay::Block, UNREACHABLE_FCDATA()),
+    FCDATA_FOR_DISPLAY(StyleDisplay::FlowRoot, UNREACHABLE_FCDATA()),
     // To keep the hash table small don't add inline frames (they're
     // typically things like FONT and B), because we can quickly
     // find them if we need to.
@@ -4926,7 +4928,7 @@ nsCSSFrameConstructor::ConstructNonScrollableBlockWithConstructor(
        StyleDisplay::InlineBlock == aDisplay->mDisplay ||
        clipPaginatedOverflow) &&
       !aParentFrame->IsSVGText()) {
-    flags = NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT;
+    flags = NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS;
     if (clipPaginatedOverflow) {
       flags |= NS_BLOCK_CLIP_PAGINATED_OVERFLOW;
     }
@@ -5119,7 +5121,7 @@ nsCSSFrameConstructor::FlushAccumulatedBlock(nsFrameConstructorState& aState,
   // is not a suitable block.
   nsContainerFrame* blockFrame =
     NS_NewMathMLmathBlockFrame(mPresShell, blockContext);
-  blockFrame->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+  blockFrame->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
 
   InitAndRestoreFrame(aState, aContent, aParentFrame, blockFrame);
   ReparentFrames(this, blockFrame, aBlockItems);
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 74dbd63e67..c8455c1c9f 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -149,6 +149,7 @@ using namespace mozilla::gfx;
 #define GRID_ENABLED_PREF_NAME "layout.css.grid.enabled"
 #define GRID_TEMPLATE_SUBGRID_ENABLED_PREF_NAME "layout.css.grid-template-subgrid-value.enabled"
 #define WEBKIT_PREFIXES_ENABLED_PREF_NAME "layout.css.prefixes.webkit"
+#define DISPLAY_FLOW_ROOT_ENABLED_PREF_NAME "layout.css.display-flow-root.enabled"
 #define DISPLAY_CONTENTS_ENABLED_PREF_NAME "layout.css.display-contents.enabled"
 #define TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME "layout.css.text-align-unsafe-value.enabled"
 #define FLOAT_LOGICAL_VALUES_ENABLED_PREF_NAME "layout.css.float-logical-values.enabled"
@@ -314,6 +315,37 @@ WebkitPrefixEnabledPrefChangeCallback(const char* aPrefName, void* aClosure)
   }
 }
 
+// When the pref "layout.css.display-flow-root.enabled" changes, this function is
+// invoked to let us update kDisplayKTable, to selectively disable or restore
+// the entries for "flow-root" in that table.
+static void
+DisplayFlowRootEnabledPrefChangeCallback(const char* aPrefName, void* aClosure)
+{
+  NS_ASSERTION(strcmp(aPrefName, DISPLAY_FLOW_ROOT_ENABLED_PREF_NAME) == 0,
+               "Did you misspell " DISPLAY_FLOW_ROOT_ENABLED_PREF_NAME " ?");
+
+  static bool sIsDisplayFlowRootKeywordIndexInitialized;
+  static int32_t sIndexOfFlowRootInDisplayTable;
+  bool isDisplayFlowRootEnabled =
+    Preferences::GetBool(DISPLAY_FLOW_ROOT_ENABLED_PREF_NAME, false);
+
+  if (!sIsDisplayFlowRootKeywordIndexInitialized) {
+    // First run: find the position of "flow-root" in kDisplayKTable.
+    sIndexOfFlowRootInDisplayTable =
+      nsCSSProps::FindIndexOfKeyword(eCSSKeyword_flow_root,
+                                     nsCSSProps::kDisplayKTable);
+    sIsDisplayFlowRootKeywordIndexInitialized = true;
+  }
+
+  // OK -- now, stomp on or restore the "flow-root" entry in kDisplayKTable,
+  // depending on whether the pref is enabled vs. disabled.
+  if (sIndexOfFlowRootInDisplayTable >= 0) {
+    nsCSSProps::kDisplayKTable[sIndexOfFlowRootInDisplayTable].mKeyword =
+      isDisplayFlowRootEnabled ? eCSSKeyword_flow_root : eCSSKeyword_UNKNOWN;
+  }
+}
+
+
 // When the pref "layout.css.display-contents.enabled" changes, this function is
 // invoked to let us update kDisplayKTable, to selectively disable or restore
 // the entries for "contents" in that table.
@@ -7555,6 +7587,8 @@ static const PrefCallbacks kPrefCallbacks[] = {
     WebkitPrefixEnabledPrefChangeCallback },
   { TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME,
     TextAlignUnsafeEnabledPrefChangeCallback },
+  { DISPLAY_FLOW_ROOT_ENABLED_PREF_NAME,
+    DisplayFlowRootEnabledPrefChangeCallback },
   { DISPLAY_CONTENTS_ENABLED_PREF_NAME,
     DisplayContentsEnabledPrefChangeCallback },
   { FLOAT_LOGICAL_VALUES_ENABLED_PREF_NAME,
diff --git a/layout/forms/nsLegendFrame.cpp b/layout/forms/nsLegendFrame.cpp
index 95efc2c878..b985ed8fc3 100644
--- a/layout/forms/nsLegendFrame.cpp
+++ b/layout/forms/nsLegendFrame.cpp
@@ -24,9 +24,7 @@ NS_NewLegendFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 #endif
 
   nsIFrame* f = new (aPresShell) nsLegendFrame(aContext);
-  if (f) {
-    f->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
-  }
+  f->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   return f;
 }
 
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 | \
diff --git a/layout/style/nsCSSKeywordList.h b/layout/style/nsCSSKeywordList.h
index 34a46ffceb..9045da9ff1 100644
--- a/layout/style/nsCSSKeywordList.h
+++ b/layout/style/nsCSSKeywordList.h
@@ -285,6 +285,7 @@ CSS_KEY(flex, flex)
 CSS_KEY(flex-end, flex_end)
 CSS_KEY(flex-start, flex_start)
 CSS_KEY(flip, flip)
+CSS_KEY(flow-root, flow_root)
 CSS_KEY(forwards, forwards)
 CSS_KEY(fraktur, fraktur)
 CSS_KEY(from-image, from_image)
diff --git a/layout/style/nsCSSProps.cpp b/layout/style/nsCSSProps.cpp
index ac2978c277..24c97cf33e 100644
--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -1345,6 +1345,9 @@ KTableEntry nsCSSProps::kDisplayKTable[] = {
   // The next entry is controlled by the layout.css.display-contents.enabled
   // pref.
   { eCSSKeyword_contents,            StyleDisplay::Contents },
+  // The next entry is controlled by the layout.css.display-flow-root.enabled 
+  // pref.
+  { eCSSKeyword_flow_root,           StyleDisplay::FlowRoot },
   { eCSSKeyword_UNKNOWN,             -1 }
 };
 
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index 1a451a2ef4..036d97f867 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -250,6 +250,7 @@ nsRuleNode::EnsureBlockDisplay(StyleDisplay& display,
   case StyleDisplay::Flex:
   case StyleDisplay::WebkitBox:
   case StyleDisplay::Grid:
+  case StyleDisplay::FlowRoot:
     // do not muck with these at all - already blocks
     // This is equivalent to nsStyleDisplay::IsBlockOutside.  (XXX Maybe we
     // should just call that?)
@@ -293,6 +294,7 @@ nsRuleNode::EnsureInlineDisplay(StyleDisplay& display)
   // see if the display value is already inline
   switch (display) {
     case StyleDisplay::Block:
+    case StyleDisplay::FlowRoot:
       display = StyleDisplay::InlineBlock;
       break;
     case StyleDisplay::Table:
diff --git a/layout/style/nsStyleConsts.h b/layout/style/nsStyleConsts.h
index 6d207aec9b..f54387aa8a 100644
--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -524,6 +524,7 @@ enum class FillMode : uint32_t;
 enum class StyleDisplay : uint8_t {
   None = 0,
   Block,
+  FlowRoot,
   Inline,
   InlineBlock,
   ListItem,
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index 4bda817ddb..f49cdc43ef 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -2890,7 +2890,8 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleDisplay
     return mozilla::StyleDisplay::Block == mDisplay ||
            mozilla::StyleDisplay::ListItem == mDisplay ||
            mozilla::StyleDisplay::InlineBlock == mDisplay ||
-           mozilla::StyleDisplay::TableCaption == mDisplay;
+           mozilla::StyleDisplay::TableCaption == mDisplay ||
+           mozilla::StyleDisplay::FlowRoot == mDisplay;
     // Should TABLE_CELL be included here?  They have
     // block frames nested inside of them.
     // (But please audit all callers before changing.)
@@ -2902,7 +2903,8 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleDisplay
            mozilla::StyleDisplay::WebkitBox == mDisplay ||
            mozilla::StyleDisplay::Grid == mDisplay ||
            mozilla::StyleDisplay::ListItem == mDisplay ||
-           mozilla::StyleDisplay::Table == mDisplay;
+           mozilla::StyleDisplay::Table == mDisplay ||
+           mozilla::StyleDisplay::FlowRoot == mDisplay;
   }
 
   static bool IsDisplayTypeInlineOutside(mozilla::StyleDisplay aDisplay) {
diff --git a/layout/style/test/property_database.js b/layout/style/test/property_database.js
index c75f7b498f..2d6352148a 100644
--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -7892,6 +7892,10 @@ if (IsCSSPropertyPrefEnabled("layout.css.background-clip-text.enabled")) {
   );
 }
 
+if (IsCSSPropertyPrefEnabled("layout.css.display-flow-root.enabled")) {
+  gCSSProperties["display"].other_values.push("flow-root");
+}
+
 // Copy aliased properties' fields from their alias targets.
 for (var prop in gCSSProperties) {
   var entry = gCSSProperties[prop];
diff --git a/layout/xul/nsXULLabelFrame.cpp b/layout/xul/nsXULLabelFrame.cpp
index 22b8754617..41e7e4d765 100644
--- a/layout/xul/nsXULLabelFrame.cpp
+++ b/layout/xul/nsXULLabelFrame.cpp
@@ -16,9 +16,7 @@ nsIFrame*
 NS_NewXULLabelFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 {
   nsXULLabelFrame* it = new (aPresShell) nsXULLabelFrame(aContext);
-
-  it->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
-
+  it->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   return it;
 }
 
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 5eed08f865..f3c660c124 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2606,6 +2606,9 @@ pref("layout.css.grid-template-subgrid-value.enabled", false);
 // Is support for CSS contain enabled?
 pref("layout.css.contain.enabled", false);
 
+// Is support for CSS display:flow-root enabled?
+pref("layout.css.display-flow-root.enabled", true);
+
 // Is support for CSS display:contents enabled?
 pref("layout.css.display-contents.enabled", true);