layout: Move text decoration propagation to stacking context tree construction (#37069)

Text decorations have a special kind of propagation. Instead of
propating these during box tree construction, move propagation to
stacking context tree construction. This will allow for using a very
easy type of incremental layout when text decorations change. For
instance, when a link changes color during hovering over it, we can skip
all of box and fragment tree construction.

In addition, propagation works a bit better now and color and style
properly move down from their originating `Fragment`s.

This introduces three new failures, because now we are drawing the
text-decoration with the correct color in more places, which exposes an
issue we have with text-decorations not being drawn in relation to the
baseline (taking into account `vertical-align`).

Testing: There are tests for these changes.
Fixes #31736.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/layout/flow/construct.rs

@@ -199,7 +199,7 @@ impl<'dom, 'style> BlockContainerBuilder<'dom, 'style> {
             context,
             info,
             block_level_boxes: Vec::new(),
-            propagated_data: propagated_data.union(&info.style),
+            propagated_data,
             have_already_seen_first_line_for_text_indent: false,
             anonymous_box_info: None,
             anonymous_table_content: Vec::new(),
@@ -228,7 +228,6 @@ impl<'dom, 'style> BlockContainerBuilder<'dom, 'style> {
     fn finish_ongoing_inline_formatting_context(&mut self) -> Option<InlineFormattingContext> {
         self.inline_formatting_context_builder.take()?.finish(
             self.context,
-            self.propagated_data,
             !self.have_already_seen_first_line_for_text_indent,
             self.info.is_single_line_text_input(),
             self.info.style.writing_mode.to_bidi_level(),
@@ -280,16 +279,6 @@ impl<'dom, 'style> BlockContainerBuilder<'dom, 'style> {
         // creation of an inline table. It requires the parent to be an inline box.
         let inline_table = self.currently_processing_inline_box();
 
-        // Text decorations are not propagated to atomic inline-level descendants.
-        // From https://drafts.csswg.org/css2/#lining-striking-props:
-        // >  Note that text decorations are not propagated to floating and absolutely
-        // > positioned descendants, nor to the contents of atomic inline-level descendants
-        // > such as inline blocks and inline tables.
-        let propagated_data = match inline_table {
-            true => self.propagated_data.without_text_decorations(),
-            false => self.propagated_data,
-        };
-
         let contents: Vec<AnonymousTableContent<'dom>> =
             self.anonymous_table_content.drain(..).collect();
         let last_text = match contents.last() {
@@ -298,7 +287,7 @@ impl<'dom, 'style> BlockContainerBuilder<'dom, 'style> {
         };
 
         let (table_info, ifc) =
-            Table::construct_anonymous(self.context, self.info, contents, propagated_data);
+            Table::construct_anonymous(self.context, self.info, contents, self.propagated_data);
 
         if inline_table {
             self.ensure_inline_formatting_context_builder()
@@ -315,7 +304,7 @@ impl<'dom, 'style> BlockContainerBuilder<'dom, 'style> {
                 info: table_info,
                 box_slot: BoxSlot::dummy(),
                 kind: BlockLevelCreator::AnonymousTable { table_block },
-                propagated_data,
+                propagated_data: self.propagated_data,
             });
         }
 
@@ -464,7 +453,7 @@ impl<'dom> BlockContainerBuilder<'dom, '_> {
                 contents,
                 list_item_style,
             },
-            propagated_data: self.propagated_data.without_text_decorations(),
+            propagated_data: self.propagated_data,
         });
     }
 
@@ -480,15 +469,14 @@ impl<'dom> BlockContainerBuilder<'dom, '_> {
         else {
             // If this inline element is an atomic, handle it and return.
             let context = self.context;
-            let propagaged_data = self.propagated_data.without_text_decorations();
+            let propagated_data = self.propagated_data;
             let atomic = self.ensure_inline_formatting_context_builder().push_atomic(
                 IndependentFormattingContext::construct(
                     context,
                     info,
                     display_inside,
                     contents,
-                    // Text decorations are not propagated to atomic inline-level descendants.
-                    propagaged_data,
+                    propagated_data,
                 ),
             );
             box_slot.set(LayoutBox::InlineLevel(vec![atomic]));
@@ -550,7 +538,6 @@ impl<'dom> BlockContainerBuilder<'dom, '_> {
             .and_then(|builder| {
                 builder.split_around_block_and_finish(
                     self.context,
-                    self.propagated_data,
                     !self.have_already_seen_first_line_for_text_indent,
                     self.info.style.writing_mode.to_bidi_level(),
                 )
@@ -631,7 +618,7 @@ impl<'dom> BlockContainerBuilder<'dom, '_> {
             info: info.clone(),
             box_slot,
             kind,
-            propagated_data: self.propagated_data.without_text_decorations(),
+            propagated_data: self.propagated_data,
         });
     }
 
@@ -664,7 +651,7 @@ impl<'dom> BlockContainerBuilder<'dom, '_> {
             info: info.clone(),
             box_slot,
             kind,
-            propagated_data: self.propagated_data.without_text_decorations(),
+            propagated_data: self.propagated_data,
         });
     }
 
@@ -754,7 +741,7 @@ impl BlockLevelJob<'_> {
                     context,
                     info,
                     contents,
-                    self.propagated_data.without_text_decorations(),
+                    self.propagated_data,
                     false, /* is_list_item */
                 );
                 ArcRefCell::new(BlockLevelBox::OutsideMarker(OutsideMarker {

components/layout/flow/float.rs

@@ -897,8 +897,7 @@ impl FloatBox {
                 info,
                 display_inside,
                 contents,
-                // Text decorations are not propagated to any out-of-flow descendants
-                propagated_data.without_text_decorations(),
+                propagated_data,
             ),
         }
     }

components/layout/flow/inline/construct.rs

@@ -16,7 +16,6 @@ use super::{
     InlineBox, InlineBoxIdentifier, InlineBoxes, InlineFormattingContext, InlineItem,
     SharedInlineStyles,
 };
-use crate::PropagatedBoxTreeData;
 use crate::cell::ArcRefCell;
 use crate::context::LayoutContext;
 use crate::dom_traversal::NodeAndStyleInfo;
@@ -344,7 +343,6 @@ impl InlineFormattingContextBuilder {
     pub(crate) fn split_around_block_and_finish(
         &mut self,
         layout_context: &LayoutContext,
-        propagated_data: PropagatedBoxTreeData,
         has_first_formatted_line: bool,
         default_bidi_level: Level,
     ) -> Option<InlineFormattingContext> {
@@ -386,7 +384,6 @@ impl InlineFormattingContextBuilder {
 
         inline_builder_from_before_split.finish(
             layout_context,
-            propagated_data,
             has_first_formatted_line,
             /* is_single_line_text_input = */ false,
             default_bidi_level,
@@ -397,7 +394,6 @@ impl InlineFormattingContextBuilder {
     pub(crate) fn finish(
         self,
         layout_context: &LayoutContext,
-        propagated_data: PropagatedBoxTreeData,
         has_first_formatted_line: bool,
         is_single_line_text_input: bool,
         default_bidi_level: Level,
@@ -410,7 +406,6 @@ impl InlineFormattingContextBuilder {
         Some(InlineFormattingContext::new_with_builder(
             self,
             layout_context,
-            propagated_data,
             has_first_formatted_line,
             is_single_line_text_input,
             default_bidi_level,

components/layout/flow/inline/inline_box.rs

@@ -256,13 +256,7 @@ impl InlineBoxContainerState {
         }
 
         Self {
-            base: InlineContainerState::new(
-                style,
-                flags,
-                Some(parent_container),
-                parent_container.text_decoration_line,
-                font_metrics,
-            ),
+            base: InlineContainerState::new(style, flags, Some(parent_container), font_metrics),
             identifier: inline_box.identifier,
             base_fragment_info: inline_box.base.base_fragment_info,
             pbm,

components/layout/flow/inline/line.rs

@@ -15,7 +15,6 @@ use style::values::generics::box_::{GenericVerticalAlign, VerticalAlignKeyword};
 use style::values::generics::font::LineHeight;
 use style::values::specified::align::AlignFlags;
 use style::values::specified::box_::DisplayOutside;
-use style::values::specified::text::TextDecorationLine;
 use unicode_bidi::{BidiInfo, Level};
 use webrender_api::FontInstanceKey;
 
@@ -572,7 +571,6 @@ impl LineItemLayout<'_, '_> {
                 font_metrics: text_item.font_metrics,
                 font_key: text_item.font_key,
                 glyphs: text_item.text,
-                text_decoration_line: text_item.text_decoration_line,
                 justification_adjustment: self.justification_adjustment,
                 selection_range: text_item.selection_range,
             })),
@@ -765,7 +763,6 @@ pub(super) struct TextRunLineItem {
     pub text: Vec<std::sync::Arc<GlyphStore>>,
     pub font_metrics: FontMetrics,
     pub font_key: FontInstanceKey,
-    pub text_decoration_line: TextDecorationLine,
     /// The BiDi level of this [`TextRunLineItem`] to enable reordering.
     pub bidi_level: Level,
     pub selection_range: Option<Range<ByteIndex>>,

components/layout/flow/inline/mod.rs

@@ -103,7 +103,7 @@ use style::properties::style_structs::InheritedText;
 use style::values::generics::box_::VerticalAlignKeyword;
 use style::values::generics::font::LineHeight;
 use style::values::specified::box_::BaselineSource;
-use style::values::specified::text::{TextAlignKeyword, TextDecorationLine};
+use style::values::specified::text::TextAlignKeyword;
 use style::values::specified::{TextAlignLast, TextJustify};
 use text_run::{
     TextRun, XI_LINE_BREAKING_CLASS_GL, XI_LINE_BREAKING_CLASS_WJ, XI_LINE_BREAKING_CLASS_ZWJ,
@@ -134,7 +134,7 @@ use crate::geom::{LogicalRect, LogicalVec2, ToLogical};
 use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
 use crate::sizing::{ComputeInlineContentSizes, ContentSizes, InlineContentSizesResult};
 use crate::style_ext::{ComputedValuesExt, PaddingBorderMargin};
-use crate::{ConstraintSpace, ContainingBlock, PropagatedBoxTreeData, SharedStyle};
+use crate::{ConstraintSpace, ContainingBlock, SharedStyle};
 
 // From gfxFontConstants.h in Firefox.
 static FONT_SUBSCRIPT_OFFSET_RATIO: f32 = 0.20;
@@ -163,8 +163,6 @@ pub(crate) struct InlineFormattingContext {
     /// 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:
     /// <https://www.w3.org/TR/css-pseudo-4/#first-formatted-line>.
     pub(super) has_first_formatted_line: bool,
@@ -628,12 +626,6 @@ pub(super) struct InlineContainerState {
     /// this inline box on the current line OR any previous line.
     has_content: RefCell<bool>,
 
-    /// Indicates whether this nesting level have text decorations in effect.
-    /// From <https://drafts.csswg.org/css-text-decor/#line-decoration>
-    // "When specified on or propagated to a block container that establishes
-    //  an IFC..."
-    text_decoration_line: TextDecorationLine,
-
     /// The block size contribution of this container's default font ie the size of the
     /// "strut." Whether this is integrated into the [`Self::nested_strut_block_sizes`]
     /// depends on the line-height quirk described in
@@ -1461,7 +1453,6 @@ impl InlineFormattingContextLayout<'_> {
                 inline_styles: text_run.inline_styles.clone(),
                 font_metrics,
                 font_key: ifc_font_info.key,
-                text_decoration_line: self.current_inline_container_state().text_decoration_line,
                 bidi_level,
                 selection_range,
             },
@@ -1655,7 +1646,6 @@ impl InlineFormattingContext {
     pub(super) fn new_with_builder(
         builder: InlineFormattingContextBuilder,
         layout_context: &LayoutContext,
-        propagated_data: PropagatedBoxTreeData,
         has_first_formatted_line: bool,
         is_single_line_text_input: bool,
         starting_bidi_level: Level,
@@ -1711,7 +1701,6 @@ impl InlineFormattingContext {
                 .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,
             is_single_line_text_input,
@@ -1781,7 +1770,6 @@ impl InlineFormattingContext {
                 style.to_arc(),
                 inline_container_state_flags,
                 None, /* parent_container */
-                self.text_decoration_line,
                 default_font_metrics.as_ref(),
             ),
             inline_box_state_stack: Vec::new(),
@@ -1879,10 +1867,8 @@ impl InlineContainerState {
         style: Arc<ComputedValues>,
         flags: InlineContainerStateFlags,
         parent_container: Option<&InlineContainerState>,
-        parent_text_decoration_line: TextDecorationLine,
         font_metrics: Option<&FontMetrics>,
     ) -> Self {
-        let text_decoration_line = parent_text_decoration_line | style.clone_text_decoration_line();
         let font_metrics = font_metrics.cloned().unwrap_or_else(FontMetrics::empty);
         let line_height = line_height(
             &style,
@@ -1919,7 +1905,6 @@ impl InlineContainerState {
             style,
             flags,
             has_content: RefCell::new(false),
-            text_decoration_line,
             nested_strut_block_sizes: nested_block_sizes,
             strut_block_sizes,
             baseline_offset,

components/layout/flow/root.rs

@@ -314,7 +314,7 @@ fn construct_for_root_element(
     let contents = ReplacedContents::for_element(root_element, context)
         .map_or_else(|| NonReplacedContents::OfElement.into(), Contents::Replaced);
 
-    let propagated_data = PropagatedBoxTreeData::default().union(&info.style);
+    let propagated_data = PropagatedBoxTreeData::default();
     let root_box = if box_style.position.is_absolutely_positioned() {
         BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(ArcRefCell::new(
             AbsolutelyPositionedBox::construct(context, &info, display_inside, contents),