Layout: Continue support incremental box tree reconstruction for flex&taffy level box (#37854)

Layout: Continue support incremental box tree reconstruction for
flex&taffy level box

This change reuse the flex/taffy level box from old box slot if the box
slot is valid and there is no LayoutDamage to the element.

Testing: This should not change observable behavior and is thus covered
by existing WPT tests.

Signed-off-by: sharpshooter_pt <ibluegalaxy_taoj@163.com>

components/layout/construct_modern.rs

@@ -12,7 +12,7 @@ use style::selector_parser::PseudoElement;
 
 use crate::PropagatedBoxTreeData;
 use crate::context::LayoutContext;
-use crate::dom::BoxSlot;
+use crate::dom::{BoxSlot, LayoutBox};
 use crate::dom_traversal::{Contents, NodeAndStyleInfo, TraversalHandler};
 use crate::flow::inline::construct::InlineFormattingContextBuilder;
 use crate::flow::{BlockContainer, BlockFormattingContext};
@@ -78,10 +78,9 @@ impl<'dom> ModernContainerJob<'dom> {
                 };
 
                 Some(ModernItem {
-                    kind: ModernItemKind::InFlow,
+                    kind: ModernItemKind::InFlow(formatting_context),
                     order: 0,
                     box_slot: None,
-                    formatting_context,
                 })
             },
             ModernContainerJob::ElementOrPseudoElement {
@@ -91,6 +90,25 @@ impl<'dom> ModernContainerJob<'dom> {
                 box_slot,
             } => {
                 let is_abspos = info.style.get_box().position.is_absolutely_positioned();
+                let order = if is_abspos {
+                    0
+                } else {
+                    info.style.clone_order()
+                };
+
+                if let Some(layout_box) = box_slot
+                    .take_layout_box_if_undamaged(info.damage)
+                    .and_then(|layout_box| match &layout_box {
+                        LayoutBox::FlexLevel(_) | LayoutBox::TaffyItemBox(_) => Some(layout_box),
+                        _ => None,
+                    })
+                {
+                    return Some(ModernItem {
+                        kind: ModernItemKind::ReusedBox(layout_box),
+                        order,
+                        box_slot: Some(box_slot),
+                    });
+                }
 
                 // Text decorations are not propagated to any out-of-flow descendants. In addition,
                 // absolutes don't affect the size of ancestors so it is fine to allow descendent
@@ -108,21 +126,16 @@ impl<'dom> ModernContainerJob<'dom> {
                     propagated_data,
                 );
 
-                if is_abspos {
+                let kind = if is_abspos {
-                    Some(ModernItem {
+                    ModernItemKind::OutOfFlow(formatting_context)
-                        kind: ModernItemKind::OutOfFlow,
-                        order: 0,
-                        box_slot: Some(box_slot),
-                        formatting_context,
-                    })
                 } else {
+                    ModernItemKind::InFlow(formatting_context)
+                };
                 Some(ModernItem {
-                        kind: ModernItemKind::InFlow,
+                    kind,
-                        order: info.style.clone_order(),
+                    order,
                     box_slot: Some(box_slot),
-                        formatting_context,
                 })
-                }
             },
         }
     }
@@ -146,15 +159,15 @@ impl ModernContainerTextRun<'_> {
 }
 
 pub(crate) enum ModernItemKind {
-    InFlow,
+    InFlow(IndependentFormattingContext),
-    OutOfFlow,
+    OutOfFlow(IndependentFormattingContext),
+    ReusedBox(LayoutBox),
 }
 
 pub(crate) struct ModernItem<'dom> {
     pub kind: ModernItemKind,
     pub order: i32,
     pub box_slot: Option<BoxSlot<'dom>>,
-    pub formatting_context: IndependentFormattingContext,
 }
 
 impl<'dom> TraversalHandler<'dom> for ModernContainerBuilder<'_, 'dom> {

components/layout/flexbox/mod.rs

@@ -113,14 +113,21 @@ impl FlexContainer {
             .into_iter()
             .map(|item| {
                 let box_ = match item.kind {
-                    ModernItemKind::InFlow => ArcRefCell::new(FlexLevelBox::FlexItem(
+                    ModernItemKind::InFlow(independent_formatting_context) => ArcRefCell::new(
-                        FlexItemBox::new(item.formatting_context),
+                        FlexLevelBox::FlexItem(FlexItemBox::new(independent_formatting_context)),
-                    )),
+                    ),
-                    ModernItemKind::OutOfFlow => {
+                    ModernItemKind::OutOfFlow(independent_formatting_context) => {
-                        let abs_pos_box =
+                        let abs_pos_box = ArcRefCell::new(AbsolutelyPositionedBox::new(
-                            ArcRefCell::new(AbsolutelyPositionedBox::new(item.formatting_context));
+                            independent_formatting_context,
+                        ));
                         ArcRefCell::new(FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(abs_pos_box))
                     },
+                    ModernItemKind::ReusedBox(layout_box) => match layout_box {
+                        LayoutBox::FlexLevel(flex_level_box) => flex_level_box,
+                        _ => unreachable!(
+                            "Undamaged flex level element should be associated with flex level box"
+                        ),
+                    },
                 };
 
                 if let Some(box_slot) = item.box_slot {

components/layout/taffy/mod.rs

@@ -46,16 +46,23 @@ impl TaffyContainer {
             .into_iter()
             .map(|item| {
                 let box_ = match item.kind {
-                    ModernItemKind::InFlow => ArcRefCell::new(TaffyItemBox::new(
+                    ModernItemKind::InFlow(independent_formatting_context) => {
-                        TaffyItemBoxInner::InFlowBox(item.formatting_context),
+                        ArcRefCell::new(TaffyItemBox::new(TaffyItemBoxInner::InFlowBox(
-                    )),
+                            independent_formatting_context,
-                    ModernItemKind::OutOfFlow => {
+                        )))
-                        let abs_pos_box =
+                    },
-                            ArcRefCell::new(AbsolutelyPositionedBox::new(item.formatting_context));
+                    ModernItemKind::OutOfFlow(independent_formatting_context) => {
+                        let abs_pos_box = ArcRefCell::new(AbsolutelyPositionedBox::new(
+                            independent_formatting_context,
+                        ));
                         ArcRefCell::new(TaffyItemBox::new(
                             TaffyItemBoxInner::OutOfFlowAbsolutelyPositionedBox(abs_pos_box),
                         ))
                     },
+                    ModernItemKind::ReusedBox(layout_box) => match layout_box {
+                        LayoutBox::TaffyItemBox(taffy_item_box) => taffy_item_box,
+                        _ => unreachable!("Undamaged taffy level element should be associated with taffy level box"),
+                    },
                 };
 
                 if let Some(box_slot) = item.box_slot {