Mutably borrow to do layout of independent formatting contexts

We want to compute content sizes on demand rather than eagerly so we will
need to mutate the independent formatting contexts that own the content sizes.

components/layout_2020/flexbox.rs

@@ -15,7 +15,6 @@ use crate::sizing::{BoxContentSizes, ContentSizes, ContentSizesRequest};
 use crate::style_ext::DisplayGeneratingBox;
 use crate::ContainingBlock;
 use rayon::iter::{IntoParallelIterator, ParallelIterator};
-use servo_arc::Arc;
 use std::borrow::Cow;
 use style::values::computed::Length;
 use style::values::specified::text::TextDecorationLine;
@@ -31,7 +30,7 @@ pub(crate) struct FlexContainer {
 #[derive(Debug, Serialize)]
 pub(crate) enum FlexLevelBox {
     FlexItem(IndependentFormattingContext),
-    OutOfFlowAbsolutelyPositionedBox(Arc<AbsolutelyPositionedBox>),
+    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
 }
 
 impl FlexContainer {
@@ -192,14 +191,14 @@ where
                     };
                     let box_ = if info.style.get_box().position.is_absolutely_positioned() {
                         // https://drafts.csswg.org/css-flexbox/#abspos-items
-                        ArcRefCell::new(FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(Arc::new(
-                            AbsolutelyPositionedBox::construct(
+                        ArcRefCell::new(FlexLevelBox::OutOfFlowAbsolutelyPositionedBox(
+                            ArcRefCell::new(AbsolutelyPositionedBox::construct(
                                 self.context,
                                 &info,
                                 display_inside,
                                 contents,
-                            ),
-                        )))
+                            )),
+                        ))
                     } else {
                         ArcRefCell::new(FlexLevelBox::FlexItem(
                             IndependentFormattingContext::construct(

components/layout_2020/flow/construct.rs

@@ -571,9 +571,14 @@ where
                 kind,
             });
         } else {
-            let box_ = ArcRefCell::new(InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(Arc::new(
-                AbsolutelyPositionedBox::construct(self.context, info, display_inside, contents),
-            )));
+            let box_ = ArcRefCell::new(InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(
+                ArcRefCell::new(AbsolutelyPositionedBox::construct(
+                    self.context,
+                    info,
+                    display_inside,
+                    contents,
+                )),
+            ));
             self.current_inline_level_boxes().push(box_.clone());
             box_slot.set(LayoutBox::InlineLevel(box_))
         }
@@ -722,10 +727,11 @@ where
                 display_inside,
                 contents,
             } => {
-                let block_level_box =
-                    ArcRefCell::new(BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(Arc::new(
+                let block_level_box = ArcRefCell::new(
+                    BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(ArcRefCell::new(
                         AbsolutelyPositionedBox::construct(context, info, display_inside, contents),
-                    )));
+                    )),
+                );
                 (block_level_box, ContainsFloats::No)
             },
             BlockLevelCreator::OutOfFlowFloatBox {

components/layout_2020/flow/inline.rs

@@ -20,6 +20,7 @@ use crate::sizing::ContentSizes;
 use crate::style_ext::{ComputedValuesExt, Display, DisplayGeneratingBox, DisplayOutside};
 use crate::ContainingBlock;
 use app_units::Au;
+use atomic_refcell::AtomicRef;
 use gfx::text::text_run::GlyphRun;
 use servo_arc::Arc;
 use style::properties::ComputedValues;
@@ -39,7 +40,7 @@ pub(crate) struct InlineFormattingContext {
 pub(crate) enum InlineLevelBox {
     InlineBox(InlineBox),
     TextRun(TextRun),
-    OutOfFlowAbsolutelyPositionedBox(Arc<AbsolutelyPositionedBox>),
+    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
     OutOfFlowFloatBox(FloatBox),
     Atomic(IndependentFormattingContext),
 }
@@ -275,7 +276,7 @@ impl InlineFormattingContext {
 
         loop {
             if let Some(child) = ifc.current_nesting_level.remaining_boxes.next() {
-                match &*child.borrow() {
+                match &mut *child.borrow_mut() {
                     InlineLevelBox::InlineBox(inline) => {
                         let partial = inline.start_layout(child.clone(), &mut ifc);
                         ifc.partial_inline_boxes_stack.push(partial)
@@ -283,8 +284,9 @@ impl InlineFormattingContext {
                     InlineLevelBox::TextRun(run) => run.layout(layout_context, &mut ifc),
                     InlineLevelBox::Atomic(a) => layout_atomic(layout_context, &mut ifc, a),
                     InlineLevelBox::OutOfFlowAbsolutelyPositionedBox(box_) => {
+                        let style = AtomicRef::map(box_.borrow(), |box_| &box_.contents.style);
                         let initial_start_corner =
-                            match Display::from(box_.contents.style.get_box().original_display) {
+                            match Display::from(style.get_box().original_display) {
                                 Display::GeneratingBox(DisplayGeneratingBox::OutsideInside {
                                     outside,
                                     inside: _,
@@ -313,7 +315,7 @@ impl InlineFormattingContext {
                             Fragment::AbsoluteOrFixedPositioned(
                                 AbsoluteOrFixedPositionedFragment {
                                     hoisted_fragment,
-                                    position: box_.contents.style.clone_position(),
+                                    position: style.clone_position(),
                                 },
                             ),
                         );
@@ -529,7 +531,7 @@ impl<'box_tree> PartialInlineBoxFragment<'box_tree> {
 fn layout_atomic(
     layout_context: &LayoutContext,
     ifc: &mut InlineFormattingContextState,
-    atomic: &IndependentFormattingContext,
+    atomic: &mut IndependentFormattingContext,
 ) {
     let pbm = atomic.style.padding_border_margin(&ifc.containing_block);
     let margin = pbm.margin.auto_is(Length::zero);

components/layout_2020/flow/mod.rs

@@ -52,7 +52,7 @@ pub(crate) enum BlockLevelBox {
         style: Arc<ComputedValues>,
         contents: BlockContainer,
     },
-    OutOfFlowAbsolutelyPositionedBox(Arc<AbsolutelyPositionedBox>),
+    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
     OutOfFlowFloatBox(FloatBox),
     Independent(IndependentFormattingContext),
 }
@@ -206,7 +206,7 @@ fn layout_block_level_children(
                 .iter()
                 .enumerate()
                 .map(|(tree_rank, box_)| {
-                    let mut fragment = box_.borrow().layout(
+                    let mut fragment = box_.borrow_mut().layout(
                         layout_context,
                         positioning_context,
                         containing_block,
@@ -226,7 +226,7 @@ fn layout_block_level_children(
                 .mapfold_reduce_into(
                     positioning_context,
                     |positioning_context, (tree_rank, box_)| {
-                        box_.borrow().layout(
+                        box_.borrow_mut().layout(
                             layout_context,
                             positioning_context,
                             containing_block,
@@ -259,7 +259,7 @@ fn layout_block_level_children(
 
 impl BlockLevelBox {
     fn layout(
-        &self,
+        &mut self,
         layout_context: &LayoutContext,
         positioning_context: &mut PositioningContext,
         containing_block: &ContainingBlock,
@@ -322,7 +322,7 @@ impl BlockLevelBox {
                 positioning_context.push(hoisted_box);
                 Fragment::AbsoluteOrFixedPositioned(AbsoluteOrFixedPositionedFragment {
                     hoisted_fragment,
-                    position: box_.contents.style.clone_position(),
+                    position: box_.borrow().contents.style.clone_position(),
                 })
             },
             BlockLevelBox::OutOfFlowFloatBox(_box_) => {

components/layout_2020/flow/root.rs

@@ -207,7 +207,7 @@ impl BoxTree {
                 let contents = ReplacedContent::for_element(dirty_node)
                     .map_or(Contents::OfElement, Contents::Replaced);
                 let info = NodeAndStyleInfo::new(dirty_node, Arc::clone(&primary_style));
-                let out_of_flow_absolutely_positioned_box = Arc::new(
+                let out_of_flow_absolutely_positioned_box = ArcRefCell::new(
                     AbsolutelyPositionedBox::construct(context, &info, display_inside, contents),
                 );
                 match update_point {
@@ -267,7 +267,7 @@ fn construct_for_root_element<'dom>(
     let (contains_floats, root_box) = if box_style.position.is_absolutely_positioned() {
         (
             ContainsFloats::No,
-            BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(Arc::new(
+            BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(ArcRefCell::new(
                 AbsolutelyPositionedBox::construct(context, &info, display_inside, contents),
             )),
         )

components/layout_2020/positioned.rs

@@ -12,9 +12,8 @@ use crate::geom::{LengthOrAuto, LengthPercentageOrAuto};
 use crate::sizing::ContentSizesRequest;
 use crate::style_ext::{ComputedValuesExt, DisplayInside};
 use crate::{ContainingBlock, DefiniteContainingBlock};
-use rayon::iter::{IntoParallelRefIterator, ParallelExtend};
+use rayon::iter::{IntoParallelRefMutIterator, ParallelExtend};
 use rayon_croissant::ParallelIteratorExt;
-use servo_arc::Arc;
 use style::computed_values::position::T as Position;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthPercentage};
@@ -36,7 +35,7 @@ pub(crate) struct PositioningContext {
 }
 
 pub(crate) struct HoistedAbsolutelyPositionedBox {
-    absolutely_positioned_box: Arc<AbsolutelyPositionedBox>,
+    absolutely_positioned_box: ArcRefCell<AbsolutelyPositionedBox>,
 
     /// The rank of the child from which this absolutely positioned fragment
     /// came from, when doing the layout of a block container. Used to compute
@@ -98,14 +97,14 @@ impl AbsolutelyPositionedBox {
     }
 
     pub(crate) fn to_hoisted(
-        self_: Arc<Self>,
+        self_: ArcRefCell<Self>,
         initial_start_corner: Vec2<Length>,
         tree_rank: usize,
     ) -> HoistedAbsolutelyPositionedBox {
         fn absolute_box_offsets(
             initial_static_start: Length,
-            start: LengthPercentageOrAuto,
-            end: LengthPercentageOrAuto,
+            start: LengthPercentageOrAuto<'_>,
+            end: LengthPercentageOrAuto<'_>,
         ) -> AbsoluteBoxOffsets {
             match (start.non_auto(), end.non_auto()) {
                 (None, None) => AbsoluteBoxOffsets::StaticStart {
@@ -122,10 +121,10 @@ impl AbsolutelyPositionedBox {
             }
         }
 
-        let box_offsets = self_.contents.style.box_offsets();
-        HoistedAbsolutelyPositionedBox {
-            tree_rank,
-            box_offsets: Vec2 {
+        let box_offsets = {
+            let box_ = self_.borrow();
+            let box_offsets = box_.contents.style.box_offsets();
+            Vec2 {
                 inline: absolute_box_offsets(
                     initial_start_corner.inline,
                     box_offsets.inline_start,
@@ -136,7 +135,11 @@ impl AbsolutelyPositionedBox {
                     box_offsets.block_start,
                     box_offsets.block_end,
                 ),
-            },
+            }
+        };
+        HoistedAbsolutelyPositionedBox {
+            tree_rank,
+            box_offsets,
             fragment: ArcRefCell::new(None),
             absolutely_positioned_box: self_,
         }
@@ -268,7 +271,7 @@ impl PositioningContext {
         while !hoisted_boxes.is_empty() {
             HoistedAbsolutelyPositionedBox::layout_many(
                 layout_context,
-                &hoisted_boxes,
+                &mut hoisted_boxes,
                 &mut laid_out_child_fragments,
                 &mut self.for_nearest_containing_block_for_all_descendants,
                 &containing_block,
@@ -281,12 +284,13 @@ impl PositioningContext {
 
     pub(crate) fn push(&mut self, box_: HoistedAbsolutelyPositionedBox) {
         if let Some(nearest) = &mut self.for_nearest_positioned_ancestor {
-            match box_
+            let position = box_
                 .absolutely_positioned_box
+                .borrow()
                 .contents
                 .style
-                .clone_position()
-            {
+                .clone_position();
+            match position {
                 Position::Fixed => {}, // fall through
                 Position::Absolute => return nearest.push(box_),
                 Position::Static | Position::Relative => unreachable!(),
@@ -357,7 +361,7 @@ impl PositioningContext {
         {
             HoistedAbsolutelyPositionedBox::layout_many(
                 layout_context,
-                &std::mem::take(&mut self.for_nearest_containing_block_for_all_descendants),
+                &mut std::mem::take(&mut self.for_nearest_containing_block_for_all_descendants),
                 fragments,
                 &mut self.for_nearest_containing_block_for_all_descendants,
                 initial_containing_block,
@@ -369,13 +373,13 @@ impl PositioningContext {
 impl HoistedAbsolutelyPositionedBox {
     pub(crate) fn layout_many(
         layout_context: &LayoutContext,
-        boxes: &[Self],
+        boxes: &mut [Self],
         fragments: &mut Vec<ArcRefCell<Fragment>>,
         for_nearest_containing_block_for_all_descendants: &mut Vec<HoistedAbsolutelyPositionedBox>,
         containing_block: &DefiniteContainingBlock,
     ) {
         if layout_context.use_rayon {
-            fragments.par_extend(boxes.par_iter().mapfold_reduce_into(
+            fragments.par_extend(boxes.par_iter_mut().mapfold_reduce_into(
                 for_nearest_containing_block_for_all_descendants,
                 |for_nearest_containing_block_for_all_descendants, box_| {
                     let new_fragment = ArcRefCell::new(Fragment::Box(box_.layout(
@@ -391,7 +395,7 @@ impl HoistedAbsolutelyPositionedBox {
                 vec_append_owned,
             ))
         } else {
-            fragments.extend(boxes.iter().map(|box_| {
+            fragments.extend(boxes.iter_mut().map(|box_| {
                 let new_fragment = ArcRefCell::new(Fragment::Box(box_.layout(
                     layout_context,
                     for_nearest_containing_block_for_all_descendants,
@@ -404,19 +408,20 @@ impl HoistedAbsolutelyPositionedBox {
     }
 
     pub(crate) fn layout(
-        &self,
+        &mut self,
         layout_context: &LayoutContext,
         for_nearest_containing_block_for_all_descendants: &mut Vec<HoistedAbsolutelyPositionedBox>,
         containing_block: &DefiniteContainingBlock,
     ) -> BoxFragment {
         let cbis = containing_block.size.inline;
         let cbbs = containing_block.size.block;
-        let style = &self.absolutely_positioned_box.contents.style;
+        let absolutely_positioned_box = self.absolutely_positioned_box.borrow_mut();
+        let style = &absolutely_positioned_box.contents.style;
         let pbm = style.padding_border_margin(&containing_block.into());
 
         let size;
         let replaced_used_size;
-        match self.absolutely_positioned_box.contents.as_replaced() {
+        match absolutely_positioned_box.contents.as_replaced() {
             Ok(replaced) => {
                 // https://drafts.csswg.org/css2/visudet.html#abs-replaced-width
                 // https://drafts.csswg.org/css2/visudet.html#abs-replaced-height
@@ -468,11 +473,11 @@ impl HoistedAbsolutelyPositionedBox {
             |positioning_context| {
                 let size;
                 let fragments;
-                match self.absolutely_positioned_box.contents.as_replaced() {
+                match absolutely_positioned_box.contents.as_replaced() {
                     Ok(replaced) => {
                         // https://drafts.csswg.org/css2/visudet.html#abs-replaced-width
                         // https://drafts.csswg.org/css2/visudet.html#abs-replaced-height
-                        let style = &self.absolutely_positioned_box.contents.style;
+                        let style = &absolutely_positioned_box.contents.style;
                         size = replaced_used_size.unwrap();
                         fragments = replaced.make_fragments(style, size.clone());
                     },
@@ -488,7 +493,7 @@ impl HoistedAbsolutelyPositionedBox {
                                 anchor -
                                 pbm.padding_border_sums.inline -
                                 margin.inline_sum();
-                            self.absolutely_positioned_box
+                            absolutely_positioned_box
                                 .contents
                                 .content_sizes
                                 .shrink_to_fit(available_size)
@@ -544,7 +549,7 @@ impl HoistedAbsolutelyPositionedBox {
                 };
 
                 BoxFragment::new(
-                    self.absolutely_positioned_box.contents.tag,
+                    absolutely_positioned_box.contents.tag,
                     style.clone(),
                     fragments,
                     content_rect,

components/layout_2020/style_ext.rs

@@ -64,9 +64,9 @@ pub(crate) struct PaddingBorderMargin {
 pub(crate) trait ComputedValuesExt {
     fn inline_size_is_length(&self) -> bool;
     fn inline_box_offsets_are_both_non_auto(&self) -> bool;
-    fn box_offsets(&self) -> flow_relative::Sides<LengthPercentageOrAuto>;
-    fn box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto>;
-    fn min_box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto>;
+    fn box_offsets(&self) -> flow_relative::Sides<LengthPercentageOrAuto<'_>>;
+    fn box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto<'_>>;
+    fn min_box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto<'_>>;
     fn max_box_size(&self) -> flow_relative::Vec2<Option<&LengthPercentage>>;
     fn content_box_size(
         &self,
@@ -86,7 +86,7 @@ pub(crate) trait ComputedValuesExt {
     fn padding_border_margin(&self, containing_block: &ContainingBlock) -> PaddingBorderMargin;
     fn padding(&self) -> flow_relative::Sides<&LengthPercentage>;
     fn border_width(&self) -> flow_relative::Sides<Length>;
-    fn margin(&self) -> flow_relative::Sides<LengthPercentageOrAuto>;
+    fn margin(&self) -> flow_relative::Sides<LengthPercentageOrAuto<'_>>;
     fn has_transform_or_perspective(&self) -> bool;
     fn effective_z_index(&self) -> i32;
     fn establishes_stacking_context(&self) -> bool;
@@ -117,7 +117,7 @@ impl ComputedValuesExt for ComputedValues {
         !a.is_auto() && !b.is_auto()
     }
 
-    fn box_offsets(&self) -> flow_relative::Sides<LengthPercentageOrAuto> {
+    fn box_offsets(&self) -> flow_relative::Sides<LengthPercentageOrAuto<'_>> {
         let position = self.get_position();
         flow_relative::Sides::from_physical(
             &PhysicalSides::new(
@@ -130,7 +130,7 @@ impl ComputedValuesExt for ComputedValues {
         )
     }
 
-    fn box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto> {
+    fn box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto<'_>> {
         let position = self.get_position();
         flow_relative::Vec2::from_physical_size(
             &PhysicalSize::new(
@@ -141,7 +141,7 @@ impl ComputedValuesExt for ComputedValues {
         )
     }
 
-    fn min_box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto> {
+    fn min_box_size(&self) -> flow_relative::Vec2<LengthPercentageOrAuto<'_>> {
         let position = self.get_position();
         flow_relative::Vec2::from_physical_size(
             &PhysicalSize::new(
@@ -271,7 +271,7 @@ impl ComputedValuesExt for ComputedValues {
         )
     }
 
-    fn margin(&self) -> flow_relative::Sides<LengthPercentageOrAuto> {
+    fn margin(&self) -> flow_relative::Sides<LengthPercentageOrAuto<'_>> {
         let margin = self.get_margin();
         flow_relative::Sides::from_physical(
             &PhysicalSides::new(