Give PositioningContext more responsibilities

Iits details are now private to the module.

It has a couple methods that take closures to make sure that "before" and "after" steps are done together:

* In an absolutely positioned box, take care of nested abspos (establish a new containing block, etc.)
* For a box that *might* be `position: relative`, optionally take care of the same.

components/layout_2020/flow/inline.rs

@@ -245,7 +245,6 @@ impl InlineFormattingContext {
                                 },
                             };
                         ifc.positioning_context
-                            .abspos
                             .push(box_.layout(initial_start_corner, tree_rank));
                     },
                     InlineLevelBox::OutOfFlowFloatBox(_box_) => {

components/layout_2020/flow/mod.rs

@@ -18,7 +18,6 @@ use crate::{relative_adjustement, ContainingBlock};
 use rayon::iter::{IndexedParallelIterator, IntoParallelRefIterator, ParallelIterator};
 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, LengthOrAuto};
 use style::Zero;
@@ -235,8 +234,8 @@ fn layout_block_level_children<'a>(
                             /* float_context = */ None,
                         )
                     },
-                    Default::default,
-                    |left, right| left.append(right),
+                    PositioningContext::new,
+                    PositioningContext::append,
                 )
                 .collect();
             for fragment in &mut fragments {
@@ -317,9 +316,7 @@ impl BlockLevelBox {
                 )),
             },
             BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(box_) => {
-                positioning_context
-                    .abspos
-                    .push(box_.layout(Vec2::zero(), tree_rank));
+                positioning_context.push(box_.layout(Vec2::zero(), tree_rank));
                 Fragment::Anonymous(AnonymousFragment::no_op(
                     containing_block.style.writing_mode,
                 ))
@@ -433,80 +430,70 @@ fn layout_in_flow_non_replaced_block_level<'a>(
         min_box_size.block == Length::zero() &&
         pb.block_end == Length::zero() &&
         block_level_kind == BlockLevelKind::SameFormattingContextBlock;
-    let mut nested_positioning_context = PositioningContext { abspos: Vec::new() };
-    let mut flow_layout = layout_contents(
-        if style.get_box().position == Position::Relative {
-            &mut nested_positioning_context
-        } else {
-            positioning_context
-        },
-        &containing_block_for_children,
-        this_start_margin_can_collapse_with_children,
-    );
-    let mut block_margins_collapsed_with_children = CollapsedBlockMargins::from_margin(&margin);
-    if this_start_margin_can_collapse_with_children.0 {
-        block_margins_collapsed_with_children
-            .start
-            .adjoin_assign(&flow_layout.collapsible_margins_in_children.start);
-        if flow_layout
-            .collapsible_margins_in_children
-            .collapsed_through
-        {
+
+    positioning_context.for_maybe_position_relative(layout_context, style, |positioning_context| {
+        let mut flow_layout = layout_contents(
+            positioning_context,
+            &containing_block_for_children,
+            this_start_margin_can_collapse_with_children,
+        );
+        let mut block_margins_collapsed_with_children = CollapsedBlockMargins::from_margin(&margin);
+        if this_start_margin_can_collapse_with_children.0 {
             block_margins_collapsed_with_children
                 .start
-                .adjoin_assign(&std::mem::replace(
-                    &mut flow_layout.collapsible_margins_in_children.end,
-                    CollapsedMargin::zero(),
-                ));
-        }
-    }
-    if this_end_margin_can_collapse_with_children {
-        block_margins_collapsed_with_children
-            .end
-            .adjoin_assign(&flow_layout.collapsible_margins_in_children.end);
-    } else {
-        flow_layout.content_block_size += flow_layout.collapsible_margins_in_children.end.solve();
-    }
-    block_margins_collapsed_with_children.collapsed_through =
-        this_start_margin_can_collapse_with_children.0 &&
-            this_end_margin_can_collapse_with_children &&
-            flow_layout
+                .adjoin_assign(&flow_layout.collapsible_margins_in_children.start);
+            if flow_layout
                 .collapsible_margins_in_children
-                .collapsed_through;
-    let relative_adjustement = relative_adjustement(style, inline_size, block_size);
-    let block_size = block_size.auto_is(|| {
-        flow_layout
-            .content_block_size
-            .clamp_between_extremums(min_box_size.block, max_box_size.block)
-    });
-    let content_rect = Rect {
-        start_corner: Vec2 {
-            block: pb.block_start + relative_adjustement.block,
-            inline: pb.inline_start + relative_adjustement.inline + margin.inline_start,
-        },
-        size: Vec2 {
-            block: block_size,
-            inline: inline_size,
-        },
-    };
-    if style.get_box().position == Position::Relative {
-        nested_positioning_context.layout_abspos(
-            layout_context,
-            &mut flow_layout.fragments,
-            &content_rect.size,
-            &padding,
-            style,
-        )
-    }
-    BoxFragment {
-        style: style.clone(),
-        children: flow_layout.fragments,
-        content_rect,
-        padding,
-        border,
-        margin,
-        block_margins_collapsed_with_children,
-    }
+                .collapsed_through
+            {
+                block_margins_collapsed_with_children
+                    .start
+                    .adjoin_assign(&std::mem::replace(
+                        &mut flow_layout.collapsible_margins_in_children.end,
+                        CollapsedMargin::zero(),
+                    ));
+            }
+        }
+        if this_end_margin_can_collapse_with_children {
+            block_margins_collapsed_with_children
+                .end
+                .adjoin_assign(&flow_layout.collapsible_margins_in_children.end);
+        } else {
+            flow_layout.content_block_size +=
+                flow_layout.collapsible_margins_in_children.end.solve();
+        }
+        block_margins_collapsed_with_children.collapsed_through =
+            this_start_margin_can_collapse_with_children.0 &&
+                this_end_margin_can_collapse_with_children &&
+                flow_layout
+                    .collapsible_margins_in_children
+                    .collapsed_through;
+        let relative_adjustement = relative_adjustement(style, inline_size, block_size);
+        let block_size = block_size.auto_is(|| {
+            flow_layout
+                .content_block_size
+                .clamp_between_extremums(min_box_size.block, max_box_size.block)
+        });
+        let content_rect = Rect {
+            start_corner: Vec2 {
+                block: pb.block_start + relative_adjustement.block,
+                inline: pb.inline_start + relative_adjustement.inline + margin.inline_start,
+            },
+            size: Vec2 {
+                block: block_size,
+                inline: inline_size,
+            },
+        };
+        BoxFragment {
+            style: style.clone(),
+            children: flow_layout.fragments,
+            content_rect,
+            padding,
+            border,
+            margin,
+            block_margins_collapsed_with_children,
+        }
+    })
 }
 
 /// https://drafts.csswg.org/css2/visudet.html#block-replaced-width

components/layout_2020/flow/root.rs

@@ -12,13 +12,12 @@ use crate::formatting_contexts::IndependentFormattingContext;
 use crate::fragments::Fragment;
 use crate::geom;
 use crate::geom::flow_relative::Vec2;
+use crate::positioned::AbsolutelyPositionedBox;
 use crate::positioned::PositioningContext;
-use crate::positioned::{AbsolutelyPositionedBox, CollectedAbsolutelyPositionedBox};
 use crate::replaced::ReplacedContent;
 use crate::sizing::ContentSizesRequest;
 use crate::style_ext::{Display, DisplayGeneratingBox, DisplayInside};
 use crate::DefiniteContainingBlock;
-use rayon::iter::{IntoParallelRefIterator, ParallelExtend, ParallelIterator};
 use script_layout_interface::wrapper_traits::LayoutNode;
 use servo_arc::Arc;
 use style::properties::ComputedValues;
@@ -111,7 +110,7 @@ impl BoxTreeRoot {
         };
 
         let dummy_tree_rank = 0;
-        let mut positioning_context = PositioningContext { abspos: Vec::new() };
+        let mut positioning_context = PositioningContext::new();
         let mut independent_layout = self.0.layout(
             layout_context,
             &mut positioning_context,
@@ -119,18 +118,11 @@ impl BoxTreeRoot {
             dummy_tree_rank,
         );
 
-        let map = |a: &CollectedAbsolutelyPositionedBox| {
-            a.layout(layout_context, &initial_containing_block)
-        };
-        if layout_context.use_rayon {
-            independent_layout
-                .fragments
-                .par_extend(positioning_context.abspos.par_iter().map(map))
-        } else {
-            independent_layout
-                .fragments
-                .extend(positioning_context.abspos.iter().map(map))
-        }
+        positioning_context.layout_in_initial_containing_block(
+            layout_context,
+            &initial_containing_block,
+            &mut independent_layout.fragments,
+        );
 
         FragmentTreeRoot(independent_layout.fragments)
     }

components/layout_2020/positioned.rs

@@ -10,8 +10,9 @@ use crate::geom::flow_relative::{Rect, Sides, Vec2};
 use crate::sizing::ContentSizesRequest;
 use crate::style_ext::{ComputedValuesExt, DisplayInside};
 use crate::{ContainingBlock, DefiniteContainingBlock};
-use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
+use rayon::iter::{IntoParallelRefIterator, ParallelExtend, ParallelIterator};
 use servo_arc::Arc;
+use style::computed_values::position::T as Position;
 use style::properties::ComputedValues;
 use style::values::computed::{Length, LengthOrAuto, LengthPercentage, LengthPercentageOrAuto};
 use style::Zero;
@@ -21,10 +22,8 @@ pub(crate) struct AbsolutelyPositionedBox {
     pub contents: IndependentFormattingContext,
 }
 
-#[derive(Default)]
 pub(crate) struct PositioningContext<'box_tree> {
-    /// With `position: absolute`
-    pub abspos: Vec<CollectedAbsolutelyPositionedBox<'box_tree>>,
+    boxes: Vec<CollectedAbsolutelyPositionedBox<'box_tree>>,
 }
 
 #[derive(Debug)]
@@ -83,8 +82,8 @@ impl AbsolutelyPositionedBox {
         }
     }
 
-    pub(crate) fn layout<'a>(
-        &'a self,
+    pub(crate) fn layout(
+        &self,
         initial_start_corner: Vec2<Length>,
         tree_rank: usize,
     ) -> CollectedAbsolutelyPositionedBox {
@@ -123,73 +122,143 @@ impl AbsolutelyPositionedBox {
     }
 }
 
-impl PositioningContext<'_> {
-    /// Unlike `Vec::append`, this takes ownership of the other value.
-    pub(crate) fn append(&mut self, mut other: Self) {
-        if self.abspos.is_empty() {
-            self.abspos = other.abspos
-        } else {
-            self.abspos.append(&mut other.abspos)
+impl<'box_tree> PositioningContext<'box_tree> {
+    pub(crate) fn new() -> Self {
+        Self {
+            boxes: Vec::new(),
         }
     }
 
+    pub(crate) fn for_maybe_position_relative(
+        &mut self,
+        layout_context: &LayoutContext,
+        style: &ComputedValues,
+        f: impl FnOnce(&mut Self) -> BoxFragment,
+    ) -> BoxFragment {
+        if style.clone_position() == Position::Relative {
+            Self::for_positioned(layout_context, f)
+        } else {
+            f(self)
+        }
+    }
+
+    fn for_positioned(
+        layout_context: &LayoutContext,
+        f: impl FnOnce(&mut Self) -> BoxFragment,
+    ) -> BoxFragment {
+        let mut new = Self::new();
+        let mut positioned_box_fragment = f(&mut new);
+        new.layout_in_positioned_ancestor(layout_context, &mut positioned_box_fragment);
+        positioned_box_fragment
+    }
+
+    pub(crate) fn push(&mut self, box_: CollectedAbsolutelyPositionedBox<'box_tree>) {
+        self.boxes.push(box_)
+    }
+
+    pub(crate) fn append(&mut self, other: Self) {
+        vec_append_owned(
+            &mut self.boxes,
+            other.boxes,
+        );
+    }
+
     pub(crate) fn adjust_static_positions(
         &mut self,
         tree_rank_in_parent: usize,
         f: impl FnOnce(&mut Self) -> Vec<Fragment>,
     ) -> Vec<Fragment> {
-        let abspos_so_far = self.abspos.len();
+        let so_far = self.boxes.len();
+
         let fragments = f(self);
+
         adjust_static_positions(
-            &mut self.abspos[abspos_so_far..],
+            &mut self.boxes[so_far..],
             &fragments,
             tree_rank_in_parent,
         );
         fragments
     }
 
-    pub(crate) fn layout_abspos(
-        self,
+    pub(crate) fn layout_in_initial_containing_block(
+        &mut self,
         layout_context: &LayoutContext,
+        initial_containing_block: &DefiniteContainingBlock,
         fragments: &mut Vec<Fragment>,
-        content_rect_size: &Vec2<Length>,
-        padding: &Sides<Length>,
-        style: &ComputedValues,
     ) {
-        if self.abspos.is_empty() {
-            return;
+        CollectedAbsolutelyPositionedBox::layout_many(
+            layout_context,
+            &self.boxes,
+            fragments,
+            initial_containing_block,
+        )
+    }
+
+    fn layout_in_positioned_ancestor(
+        &mut self,
+        layout_context: &LayoutContext,
+        positioned_box_fragment: &mut BoxFragment,
+    ) {
+        if !self.boxes.is_empty() {
+            let padding_rect = Rect {
+                size: positioned_box_fragment.content_rect.size.clone(),
+                // Ignore the content rect’s position in its own containing block:
+                start_corner: Vec2::zero(),
+            }
+            .inflate(&positioned_box_fragment.padding);
+            let containing_block = DefiniteContainingBlock {
+                size: padding_rect.size.clone(),
+                style: &positioned_box_fragment.style,
+            };
+            let mut children = Vec::new();
+            CollectedAbsolutelyPositionedBox::layout_many(
+                layout_context,
+                &self.boxes,
+                &mut children,
+                &containing_block,
+            );
+            positioned_box_fragment
+                .children
+                .push(Fragment::Anonymous(AnonymousFragment {
+                    children,
+                    rect: padding_rect,
+                    mode: positioned_box_fragment.style.writing_mode,
+                }))
         }
-        let padding_rect = Rect {
-            size: content_rect_size.clone(),
-            // Ignore the content rect’s position in its own containing block:
-            start_corner: Vec2::zero(),
-        }
-        .inflate(&padding);
-        let containing_block = DefiniteContainingBlock {
-            size: padding_rect.size.clone(),
-            style,
-        };
-        let map =
-            |a: &CollectedAbsolutelyPositionedBox| a.layout(layout_context, &containing_block);
-        let children = if layout_context.use_rayon {
-            self.abspos.par_iter().map(map).collect()
-        } else {
-            self.abspos.iter().map(map).collect()
-        };
-        fragments.push(Fragment::Anonymous(AnonymousFragment {
-            children,
-            rect: padding_rect,
-            mode: style.writing_mode,
-        }))
     }
 }
 
-impl CollectedAbsolutelyPositionedBox<'_> {
+impl<'box_tree> CollectedAbsolutelyPositionedBox<'box_tree> {
+    pub(crate) fn layout_many(
+        layout_context: &LayoutContext,
+        boxes: &[Self],
+        fragments: &mut Vec<Fragment>,
+        containing_block: &DefiniteContainingBlock,
+    ) {
+        if layout_context.use_rayon {
+            fragments.par_extend(boxes.par_iter().map(
+                |box_| {
+                    Fragment::Box(box_.layout(
+                        layout_context,
+                        containing_block,
+                    ))
+                }
+            ))
+        } else {
+            fragments.extend(boxes.iter().map(|box_| {
+                Fragment::Box(box_.layout(
+                    layout_context,
+                    containing_block,
+                ))
+            }))
+        }
+    }
+
     pub(crate) fn layout(
         &self,
         layout_context: &LayoutContext,
         containing_block: &DefiniteContainingBlock,
-    ) -> Fragment {
+    ) -> BoxFragment {
         let style = &self.absolutely_positioned_box.contents.style;
         let cbis = containing_block.size.inline;
         let cbbs = containing_block.size.block;
@@ -249,94 +318,88 @@ impl CollectedAbsolutelyPositionedBox<'_> {
             block_end: block_axis.margin_end,
         };
 
-        let mut positioning_context = PositioningContext { abspos: Vec::new() };
-        let (size, mut fragments) = match self.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 size = replaced_used_size.unwrap();
-                let fragments = replaced.make_fragments(style, size.clone());
-                (size, fragments)
-            },
-            Err(non_replaced) => {
-                // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-width
-                // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-height
-                let inline_size = inline_axis.size.auto_is(|| {
-                    let available_size = match inline_axis.anchor {
-                        Anchor::Start(start) => {
-                            cbis - start - pb.inline_sum() - margin.inline_sum()
-                        },
-                        Anchor::End(end) => cbis - end - pb.inline_sum() - margin.inline_sum(),
+        PositioningContext::for_positioned(layout_context, |positioning_context| {
+            let size;
+            let fragments;
+            match self.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;
+                    size = replaced_used_size.unwrap();
+                    fragments = replaced.make_fragments(style, size.clone());
+                },
+                Err(non_replaced) => {
+                    // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-width
+                    // https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-height
+                    let inline_size = inline_axis.size.auto_is(|| {
+                        let available_size = match inline_axis.anchor {
+                            Anchor::Start(start) => {
+                                cbis - start - pb.inline_sum() - margin.inline_sum()
+                            },
+                            Anchor::End(end) => cbis - end - pb.inline_sum() - margin.inline_sum(),
+                        };
+                        self.absolutely_positioned_box
+                            .contents
+                            .content_sizes
+                            .shrink_to_fit(available_size)
+                    });
+
+                    let containing_block_for_children = ContainingBlock {
+                        inline_size,
+                        block_size: block_axis.size,
+                        style,
                     };
-                    self.absolutely_positioned_box
-                        .contents
-                        .content_sizes
-                        .shrink_to_fit(available_size)
-                });
+                    // https://drafts.csswg.org/css-writing-modes/#orthogonal-flows
+                    assert_eq!(
+                        containing_block.style.writing_mode,
+                        containing_block_for_children.style.writing_mode,
+                        "Mixed writing modes are not supported yet"
+                    );
+                    let dummy_tree_rank = 0;
+                    let independent_layout = non_replaced.layout(
+                        layout_context,
+                        positioning_context,
+                        &containing_block_for_children,
+                        dummy_tree_rank,
+                    );
 
-                let containing_block_for_children = ContainingBlock {
-                    inline_size,
-                    block_size: block_axis.size,
-                    style,
-                };
-                // https://drafts.csswg.org/css-writing-modes/#orthogonal-flows
-                assert_eq!(
-                    containing_block.style.writing_mode,
-                    containing_block_for_children.style.writing_mode,
-                    "Mixed writing modes are not supported yet"
-                );
-                let dummy_tree_rank = 0;
-                let independent_layout = non_replaced.layout(
-                    layout_context,
-                    &mut positioning_context,
-                    &containing_block_for_children,
-                    dummy_tree_rank,
-                );
+                    size = Vec2 {
+                        inline: inline_size,
+                        block: block_axis
+                            .size
+                            .auto_is(|| independent_layout.content_block_size),
+                    };
+                    fragments = independent_layout.fragments
+                },
+            };
 
-                let size = Vec2 {
-                    inline: inline_size,
-                    block: block_axis
-                        .size
-                        .auto_is(|| independent_layout.content_block_size),
-                };
-                (size, independent_layout.fragments)
-            },
-        };
+            let inline_start = match inline_axis.anchor {
+                Anchor::Start(start) => start + pb.inline_start + margin.inline_start,
+                Anchor::End(end) => cbbs - end - pb.inline_end - margin.inline_end - size.inline,
+            };
+            let block_start = match block_axis.anchor {
+                Anchor::Start(start) => start + pb.block_start + margin.block_start,
+                Anchor::End(end) => cbbs - end - pb.block_end - margin.block_end - size.block,
+            };
 
-        let inline_start = match inline_axis.anchor {
-            Anchor::Start(start) => start + pb.inline_start + margin.inline_start,
-            Anchor::End(end) => cbbs - end - pb.inline_end - margin.inline_end - size.inline,
-        };
-        let block_start = match block_axis.anchor {
-            Anchor::Start(start) => start + pb.block_start + margin.block_start,
-            Anchor::End(end) => cbbs - end - pb.block_end - margin.block_end - size.block,
-        };
+            let content_rect = Rect {
+                start_corner: Vec2 {
+                    inline: inline_start,
+                    block: block_start,
+                },
+                size,
+            };
 
-        let content_rect = Rect {
-            start_corner: Vec2 {
-                inline: inline_start,
-                block: block_start,
-            },
-            size,
-        };
-
-        positioning_context.layout_abspos(
-            layout_context,
-            &mut fragments,
-            &content_rect.size,
-            &padding,
-            style,
-        );
-
-        Fragment::Box(BoxFragment {
-            style: style.clone(),
-            children: fragments,
-            content_rect,
-            padding,
-            border,
-            margin,
-            block_margins_collapsed_with_children: CollapsedBlockMargins::zero(),
+            BoxFragment {
+                style: style.clone(),
+                children: fragments,
+                content_rect,
+                padding,
+                border,
+                margin,
+                block_margins_collapsed_with_children: CollapsedBlockMargins::zero(),
+            }
         })
     }
 }
@@ -468,3 +531,11 @@ fn adjust_static_positions(
         }
     }
 }
+
+fn vec_append_owned<T>(a: &mut Vec<T>, mut b: Vec<T>) {
+    if a.is_empty() {
+        *a = b
+    } else {
+        a.append(&mut b)
+    }
+}