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.

2 files changed, 39 insertions, 3 deletions

diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index 6642a090d..d28e60740 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -2614,7 +2614,8 @@ 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;
@@ -4758,6 +4759,7 @@ 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.
@@ -4943,7 +4945,7 @@ 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;
     }
@@ -5112,7 +5114,7 @@ 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 5de6f2013..9b204d734 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.
@@ -7635,6 +7667,8 @@ 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,