layout: Correct damage propagation and style repair for repaint-only layout (#37004)

When making last-minute changes to the repaint-only layout pass, damage
propagation was broken, meaning that full layout was always done. This
change fixes that, meaning that times in the `blaster.html` test case
now reflect those described in the original commit message from #36978.

In addition, some style repair is now fixed:
- `InlineFormattingContext`s now keep a `SharedInlineStyles` for the
root of the IFC
    which is updated during style repair.
 - `BlockFormattingContext`s now properly update their style.

These changes are verified by turning on repaint only layout for more
properties
in Stylo via servo/stylo#183.

Testing: Manual performance testing via `blaster.html`.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/layout/flow/inline/construct.rs

@@ -31,7 +31,7 @@ pub(crate) struct InlineFormattingContextBuilder {
     /// inline box stack, and importantly, one for every `display: contents` element that we are
     /// currently processing. Normally `display: contents` elements don't affect the structure of
     /// the [`InlineFormattingContext`], but the styles they provide do style their children.
-    shared_inline_styles_stack: Vec<SharedInlineStyles>,
+    pub shared_inline_styles_stack: Vec<SharedInlineStyles>,
 
     /// The collection of text strings that make up this [`InlineFormattingContext`] under
     /// construction.

components/layout/flow/inline/mod.rs

@@ -91,6 +91,7 @@ use line_breaker::LineBreaker;
 use malloc_size_of_derive::MallocSizeOf;
 use range::Range;
 use script::layout_dom::ServoLayoutNode;
+use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutNode};
 use servo_arc::Arc;
 use style::Zero;
 use style::computed_values::text_wrap_mode::T as TextWrapMode;
@@ -158,6 +159,10 @@ pub(crate) struct InlineFormattingContext {
     /// context in order to avoid duplicating this information.
     pub font_metrics: Vec<FontKeyAndMetrics>,
 
+    /// The [`SharedInlineStyles`] for the root of this [`InlineFormattingContext`] that are used to
+    /// share styles with all [`TextRun`] children.
+    pub(super) shared_inline_styles: SharedInlineStyles,
+
     pub(super) text_decoration_line: TextDecorationLine,
 
     /// Whether this IFC contains the 1st formatted line of an element:
@@ -237,12 +242,14 @@ impl InlineItem {
             InlineItem::OutOfFlowAbsolutelyPositionedBox(positioned_box, ..) => positioned_box
                 .borrow_mut()
                 .context
-                .repair_style(context, new_style),
+                .repair_style(context, node, new_style),
             InlineItem::OutOfFlowFloatBox(float_box) => float_box
                 .borrow_mut()
                 .contents
-                .repair_style(context, new_style),
-            InlineItem::Atomic(atomic, ..) => atomic.borrow_mut().repair_style(context, new_style),
+                .repair_style(context, node, new_style),
+            InlineItem::Atomic(atomic, ..) => {
+                atomic.borrow_mut().repair_style(context, node, new_style)
+            },
         }
     }
 
@@ -1699,6 +1706,11 @@ impl InlineFormattingContext {
             inline_items: builder.inline_items,
             inline_boxes: builder.inline_boxes,
             font_metrics,
+            shared_inline_styles: builder
+                .shared_inline_styles_stack
+                .last()
+                .expect("Should have at least one SharedInlineStyle for the root of an IFC")
+                .clone(),
             text_decoration_line: propagated_data.text_decoration,
             has_first_formatted_line,
             contains_floats: builder.contains_floats,
@@ -1707,6 +1719,11 @@ impl InlineFormattingContext {
         }
     }
 
+    pub(crate) fn repair_style(&self, node: &ServoLayoutNode, new_style: &Arc<ComputedValues>) {
+        *self.shared_inline_styles.style.borrow_mut() = new_style.clone();
+        *self.shared_inline_styles.selected.borrow_mut() = node.to_threadsafe().selected_style();
+    }
+
     pub(super) fn layout(
         &self,
         layout_context: &LayoutContext,

components/layout/flow/mod.rs

@@ -78,6 +78,15 @@ impl BlockContainer {
             BlockContainer::InlineFormattingContext(context) => context.contains_floats,
         }
     }
+
+    pub(crate) fn repair_style(&mut self, node: &ServoLayoutNode, new_style: &Arc<ComputedValues>) {
+        match self {
+            BlockContainer::BlockLevelBoxes(..) => {},
+            BlockContainer::InlineFormattingContext(inline_formatting_context) => {
+                inline_formatting_context.repair_style(node, new_style)
+            },
+        }
+    }
 }
 
 #[derive(Debug, MallocSizeOf)]
@@ -106,20 +115,21 @@ impl BlockLevelBox {
 
         match self {
             BlockLevelBox::Independent(independent_formatting_context) => {
-                independent_formatting_context.repair_style(context, new_style)
+                independent_formatting_context.repair_style(context, node, new_style)
             },
             BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(positioned_box) => positioned_box
                 .borrow_mut()
                 .context
-                .repair_style(context, new_style),
+                .repair_style(context, node, new_style),
             BlockLevelBox::OutOfFlowFloatBox(float_box) => {
-                float_box.contents.repair_style(context, new_style)
+                float_box.contents.repair_style(context, node, new_style)
             },
             BlockLevelBox::OutsideMarker(outside_marker) => {
                 outside_marker.repair_style(context, node, new_style)
             },
-            BlockLevelBox::SameFormattingContextBlock { base, .. } => {
+            BlockLevelBox::SameFormattingContextBlock { base, contents, .. } => {
                 base.repair_style(new_style);
+                contents.repair_style(node, new_style);
             },
         }
     }
@@ -477,6 +487,10 @@ impl BlockFormattingContext {
     pub(crate) fn layout_style<'a>(&self, base: &'a LayoutBoxBase) -> LayoutStyle<'a> {
         LayoutStyle::Default(&base.style)
     }
+
+    pub(crate) fn repair_style(&mut self, node: &ServoLayoutNode, new_style: &Arc<ComputedValues>) {
+        self.contents.repair_style(node, new_style);
+    }
 }
 
 /// Finds the min/max-content inline size of the block-level children of a block container.