layout: Move BoxFragment's block-level info into a dedicated struct (#37938)

`BoxFragment` had 2 fields that are only relevant for block-level boxes:
`clearance` and a boxed `block_margins_collapsed_with_children`.

This moves both pieces of data into a new `BlockLevelLayoutInfo` struct,
which is boxed.

As a result, the size of `BoxFragment` is reduced from 272 to 264 bytes.

Testing: Unneeded (no behavior change)

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

components/layout/flow/mod.rs

@@ -32,7 +32,8 @@ use crate::formatting_contexts::{
     Baselines, IndependentFormattingContext, IndependentFormattingContextContents,
 };
 use crate::fragment_tree::{
-    BaseFragmentInfo, BoxFragment, CollapsedBlockMargins, CollapsedMargin, Fragment, FragmentFlags,
+    BaseFragmentInfo, BlockLevelLayoutInfo, BoxFragment, CollapsedBlockMargins, CollapsedMargin,
+    Fragment, FragmentFlags,
 };
 use crate::geom::{
     AuOrAuto, LazySize, LogicalRect, LogicalSides, LogicalSides1D, LogicalVec2, PhysicalPoint,
@@ -1175,8 +1176,7 @@ fn layout_in_flow_non_replaced_block_level_same_formatting_context(
         flow_layout.specific_layout_info,
     )
     .with_baselines(flow_layout.baselines)
-    .with_block_margins_collapsed_with_children(block_margins_collapsed_with_children)
+    .with_block_level_layout_info(block_margins_collapsed_with_children, clearance)
-    .with_clearance(clearance)
 }
 
 impl IndependentFormattingContext {
@@ -1288,7 +1288,7 @@ impl IndependentFormattingContext {
             layout.specific_layout_info,
         )
         .with_baselines(layout.baselines)
-        .with_block_margins_collapsed_with_children(block_margins_collapsed_with_children)
+        .with_block_level_layout_info(block_margins_collapsed_with_children, None)
     }
 
     /// Lay out a normal in flow non-replaced block that establishes an independent
@@ -1605,8 +1605,7 @@ impl IndependentFormattingContext {
             layout.specific_layout_info,
         )
         .with_baselines(layout.baselines)
-        .with_block_margins_collapsed_with_children(CollapsedBlockMargins::from_margin(&margin))
+        .with_block_level_layout_info(CollapsedBlockMargins::from_margin(&margin), clearance)
-        .with_clearance(clearance)
     }
 }
 
@@ -2076,7 +2075,13 @@ impl<'container> PlacementState<'container> {
                     return;
                 }
 
-                let fragment_block_margins = fragment.block_margins_collapsed_with_children();
+                let BlockLevelLayoutInfo {
+                    clearance,
+                    block_margins_collapsed_with_children: fragment_block_margins,
+                } = &**fragment
+                    .block_level_layout_info
+                    .as_ref()
+                    .expect("A block-level fragment should have a BlockLevelLayoutInfo.");
                 let mut fragment_block_size = fragment
                     .border_rect()
                     .size
@@ -2088,7 +2093,7 @@ impl<'container> PlacementState<'container> {
                 // > If the top and bottom margins of an element with clearance are adjoining,
                 // > its margins collapse with the adjoining margins of following siblings but that
                 // > resulting margin does not collapse with the bottom margin of the parent block.
-                if let Some(clearance) = fragment.clearance {
+                if let Some(clearance) = *clearance {
                     fragment_block_size += clearance;
                     // Margins can't be adjoining if they are separated by clearance.
                     // Setting `next_in_flow_margin_collapses_with_parent_start_margin` to false

components/layout/fragment_tree/box_fragment.rs

@@ -54,6 +54,19 @@ pub(crate) enum SpecificLayoutInfo {
     TableWrapper,
 }
 
+#[derive(MallocSizeOf)]
+pub(crate) struct BlockLevelLayoutInfo {
+    /// When the `clear` property is not set to `none`, it may introduce clearance.
+    /// Clearance is some extra spacing that is added above the top margin,
+    /// so that the element doesn't overlap earlier floats in the same BFC.
+    /// The presence of clearance prevents the top margin from collapsing with
+    /// earlier margins or with the bottom margin of the parent block.
+    /// <https://drafts.csswg.org/css2/#clearance>
+    pub clearance: Option<Au>,
+
+    pub block_margins_collapsed_with_children: CollapsedBlockMargins,
+}
+
 #[derive(MallocSizeOf)]
 pub(crate) struct BoxFragment {
     pub base: BaseFragment,
@@ -73,21 +86,11 @@ pub(crate) struct BoxFragment {
     pub border: PhysicalSides<Au>,
     pub margin: PhysicalSides<Au>,
 
-    /// When the `clear` property is not set to `none`, it may introduce clearance.
-    /// Clearance is some extra spacing that is added above the top margin,
-    /// so that the element doesn't overlap earlier floats in the same BFC.
-    /// The presence of clearance prevents the top margin from collapsing with
-    /// earlier margins or with the bottom margin of the parent block.
-    /// <https://drafts.csswg.org/css2/#clearance>
-    pub clearance: Option<Au>,
-
     /// When this [`BoxFragment`] is for content that has a baseline, this tracks
     /// the first and last baselines of that content. This is used to propagate baselines
     /// to things such as tables and inline formatting contexts.
     baselines: Baselines,
 
-    block_margins_collapsed_with_children: Option<Box<CollapsedBlockMargins>>,
-
     /// The scrollable overflow of this box fragment in the same coordiante system as
     /// [`Self::content_rect`] ie a rectangle within the parent fragment's content
     /// rectangle. This does not take into account any transforms this fragment applies.
@@ -103,6 +106,9 @@ pub(crate) struct BoxFragment {
 
     /// Additional information of from layout that could be used by Javascripts and devtools.
     pub specific_layout_info: Option<SpecificLayoutInfo>,
+
+    /// Additional information for block-level boxes.
+    pub block_level_layout_info: Option<Box<BlockLevelLayoutInfo>>,
 }
 
 impl BoxFragment {
@@ -126,13 +132,12 @@ impl BoxFragment {
             padding,
             border,
             margin,
-            clearance: None,
             baselines: Baselines::default(),
-            block_margins_collapsed_with_children: None,
             scrollable_overflow: None,
             resolved_sticky_insets: AtomicRefCell::default(),
             background_mode: BackgroundMode::Normal,
             specific_layout_info,
+            block_level_layout_info: None,
         }
     }
 
@@ -185,16 +190,15 @@ impl BoxFragment {
         self.background_mode = BackgroundMode::None;
     }
 
-    pub fn with_block_margins_collapsed_with_children(
+    pub fn with_block_level_layout_info(
         mut self,
-        collapsed_margins: CollapsedBlockMargins,
+        block_margins_collapsed_with_children: CollapsedBlockMargins,
+        clearance: Option<Au>,
     ) -> Self {
-        self.block_margins_collapsed_with_children = Some(collapsed_margins.into());
+        self.block_level_layout_info = Some(Box::new(BlockLevelLayoutInfo {
-        self
+            block_margins_collapsed_with_children,
-    }
+            clearance,
-
+        }));
-    pub fn with_clearance(mut self, clearance: Option<Au>) -> Self {
-        self.clearance = clearance;
         self
     }
 
@@ -300,7 +304,6 @@ impl BoxFragment {
                 \npadding rect={:?}\
                 \nborder rect={:?}\
                 \nmargin={:?}\
-                \nclearance={:?}\
                 \nscrollable_overflow={:?}\
                 \nbaselines={:?}\
                 \noverflow={:?}",
@@ -309,7 +312,6 @@ impl BoxFragment {
             self.padding_rect(),
             self.border_rect(),
             self.margin,
-            self.clearance,
             self.scrollable_overflow(),
             self.baselines,
             self.style.effective_overflow(self.base.flags),
@@ -513,11 +515,4 @@ impl BoxFragment {
             _ => false,
         }
     }
-
-    pub(crate) fn block_margins_collapsed_with_children(&self) -> CollapsedBlockMargins {
-        match self.block_margins_collapsed_with_children.as_ref() {
-            Some(collapsed_block_margins) => *(collapsed_block_margins).clone(),
-            _ => CollapsedBlockMargins::zero(),
-        }
-    }
 }