Split FlowChildren in IndependentLayout and FlowLayout

The result of doing the layout of an independent formatting context
should be unconcerned with margin collapsing.

components/layout_2020/flow/inline.rs

@@ -4,7 +4,7 @@
 
 use crate::context::LayoutContext;
 use crate::flow::float::FloatBox;
-use crate::flow::FlowChildren;
+use crate::flow::FlowLayout;
 use crate::fragments::{
     AnonymousFragment, BoxFragment, CollapsedBlockMargins, Fragment, TextFragment,
 };
@@ -88,7 +88,7 @@ impl InlineFormattingContext {
         containing_block: &ContainingBlock,
         tree_rank: usize,
         absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
-    ) -> FlowChildren {
+    ) -> FlowLayout {
         let mut ifc = InlineFormattingContextState {
             containing_block,
             partial_inline_boxes_stack: Vec::new(),
@@ -156,9 +156,9 @@ impl InlineFormattingContext {
             } else {
                 ifc.line_boxes
                     .finish_line(&mut ifc.current_nesting_level, containing_block);
-                return FlowChildren {
+                return FlowLayout {
                     fragments: ifc.line_boxes.boxes,
-                    block_size: ifc.line_boxes.next_line_block_position,
+                    content_block_size: ifc.line_boxes.next_line_block_position,
                     collapsible_margins_in_children: CollapsedBlockMargins::zero(),
                 };
             }

components/layout_2020/flow/mod.rs

@@ -7,11 +7,11 @@
 use crate::context::LayoutContext;
 use crate::flow::float::{FloatBox, FloatContext};
 use crate::flow::inline::InlineFormattingContext;
-use crate::formatting_contexts::IndependentFormattingContext;
+use crate::formatting_contexts::{IndependentFormattingContext, IndependentLayout};
 use crate::fragments::{
     AnonymousFragment, BoxFragment, CollapsedBlockMargins, CollapsedMargin, Fragment,
 };
-use crate::geom::flow_relative::{Rect, Vec2};
+use crate::geom::flow_relative::{Rect, Sides, Vec2};
 use crate::positioned::{
     adjust_static_positions, AbsolutelyPositionedBox, AbsolutelyPositionedFragment,
 };
@@ -54,9 +54,9 @@ pub(crate) enum BlockLevelBox {
     Independent(IndependentFormattingContext),
 }
 
-pub(super) struct FlowChildren {
+struct FlowLayout {
     pub fragments: Vec<Fragment>,
-    pub block_size: Length,
+    pub content_block_size: Length,
     pub collapsible_margins_in_children: CollapsedBlockMargins,
 }
 
@@ -70,7 +70,7 @@ impl BlockFormattingContext {
         containing_block: &ContainingBlock,
         tree_rank: usize,
         absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
-    ) -> FlowChildren {
+    ) -> IndependentLayout {
         let mut float_context;
         let float_context = if self.contains_floats {
             float_context = FloatContext::new();
@@ -78,7 +78,7 @@ impl BlockFormattingContext {
         } else {
             None
         };
-        let mut flow_children = self.contents.layout(
+        let flow_layout = self.contents.layout(
             layout_context,
             containing_block,
             tree_rank,
@@ -86,12 +86,16 @@ impl BlockFormattingContext {
             float_context,
             CollapsibleWithParentStartMargin(false),
         );
-        flow_children.block_size += flow_children.collapsible_margins_in_children.end.solve();
-        flow_children
-            .collapsible_margins_in_children
-            .collapsed_through = false;
-        flow_children.collapsible_margins_in_children.end = CollapsedMargin::zero();
-        flow_children
+        assert!(
+            !flow_layout
+                .collapsible_margins_in_children
+                .collapsed_through
+        );
+        IndependentLayout {
+            fragments: flow_layout.fragments,
+            content_block_size: flow_layout.content_block_size +
+                flow_layout.collapsible_margins_in_children.end.solve(),
+        }
     }
 }
 
@@ -104,7 +108,7 @@ impl BlockContainer {
         absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
         float_context: Option<&mut FloatContext>,
         collapsible_with_parent_start_margin: CollapsibleWithParentStartMargin,
-    ) -> FlowChildren {
+    ) -> FlowLayout {
         match self {
             BlockContainer::BlockLevelBoxes(child_boxes) => layout_block_level_children(
                 layout_context,
@@ -133,7 +137,7 @@ fn layout_block_level_children<'a>(
     absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
     float_context: Option<&mut FloatContext>,
     collapsible_with_parent_start_margin: CollapsibleWithParentStartMargin,
-) -> FlowChildren {
+) -> FlowLayout {
     fn place_block_level_fragment(fragment: &mut Fragment, placement_state: &mut PlacementState) {
         match fragment {
             Fragment::Box(fragment) => {
@@ -249,9 +253,9 @@ fn layout_block_level_children<'a>(
         tree_rank,
     );
 
-    FlowChildren {
+    FlowLayout {
         fragments,
-        block_size: placement_state.current_block_direction_position,
+        content_block_size: placement_state.current_block_direction_position,
         collapsible_margins_in_children: CollapsedBlockMargins {
             collapsed_through: placement_state
                 .next_in_flow_margin_collapses_with_parent_start_margin,
@@ -302,12 +306,17 @@ impl BlockLevelBox {
                     &contents.style,
                     BlockLevelKind::EstablishesAnIndependentFormattingContext,
                     |containing_block, nested_abspos, _| {
-                        non_replaced.layout(
+                        let independent_layout = non_replaced.layout(
                             layout_context,
                             containing_block,
                             tree_rank,
                             nested_abspos,
-                        )
+                        );
+                        FlowLayout {
+                            fragments: independent_layout.fragments,
+                            content_block_size: independent_layout.content_block_size,
+                            collapsible_margins_in_children: CollapsedBlockMargins::zero(),
+                        }
                     },
                 )),
             },
@@ -341,7 +350,7 @@ fn layout_in_flow_non_replaced_block_level<'a>(
         &ContainingBlock,
         &mut Vec<AbsolutelyPositionedFragment<'a>>,
         CollapsibleWithParentStartMargin,
-    ) -> FlowChildren,
+    ) -> FlowLayout,
 ) -> BoxFragment {
     let cbis = containing_block.inline_size;
     let padding = style.padding().percentages_relative_to(cbis);
@@ -400,7 +409,7 @@ fn layout_in_flow_non_replaced_block_level<'a>(
             LengthOrAuto::Auto,
         );
     let mut nested_abspos = vec![];
-    let mut flow_children = layout_contents(
+    let mut flow_layout = layout_contents(
         &containing_block_for_children,
         if style.get_box().position == Position::Relative {
             &mut nested_abspos
@@ -412,15 +421,15 @@ fn layout_in_flow_non_replaced_block_level<'a>(
     if this_start_margin_can_collapse_with_children.0 {
         block_margins_collapsed_with_children
             .start
-            .adjoin_assign(&flow_children.collapsible_margins_in_children.start);
-        if flow_children
+            .adjoin_assign(&flow_layout.collapsible_margins_in_children.start);
+        if flow_layout
             .collapsible_margins_in_children
             .collapsed_through
         {
             block_margins_collapsed_with_children
                 .start
                 .adjoin_assign(&std::mem::replace(
-                    &mut flow_children.collapsible_margins_in_children.end,
+                    &mut flow_layout.collapsible_margins_in_children.end,
                     CollapsedMargin::zero(),
                 ));
         }
@@ -428,18 +437,18 @@ fn layout_in_flow_non_replaced_block_level<'a>(
     if this_end_margin_can_collapse_with_children {
         block_margins_collapsed_with_children
             .end
-            .adjoin_assign(&flow_children.collapsible_margins_in_children.end);
+            .adjoin_assign(&flow_layout.collapsible_margins_in_children.end);
     } else {
-        flow_children.block_size += flow_children.collapsible_margins_in_children.end.solve();
+        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_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_children.block_size);
+    let block_size = block_size.auto_is(|| flow_layout.content_block_size);
     let content_rect = Rect {
         start_corner: Vec2 {
             block: pb.block_start + relative_adjustement.block,
@@ -454,7 +463,7 @@ fn layout_in_flow_non_replaced_block_level<'a>(
         AbsolutelyPositionedFragment::in_positioned_containing_block(
             layout_context,
             &nested_abspos,
-            &mut flow_children.fragments,
+            &mut flow_layout.fragments,
             &content_rect.size,
             &padding,
             containing_block_for_children.mode,
@@ -462,7 +471,7 @@ fn layout_in_flow_non_replaced_block_level<'a>(
     }
     BoxFragment {
         style: style.clone(),
-        children: flow_children.fragments,
+        children: flow_layout.fragments,
         content_rect,
         padding,
         border,

components/layout_2020/flow/root.rs

@@ -31,10 +31,7 @@ pub struct BoxTreeRoot(BlockFormattingContext);
 pub struct FragmentTreeRoot(Vec<Fragment>);
 
 impl BoxTreeRoot {
-    pub fn construct<'dom, Node>(
-        context: &SharedStyleContext<'_>,
-        root_element: Node,
-    ) -> Self
+    pub fn construct<'dom, Node>(context: &SharedStyleContext<'_>, root_element: Node) -> Self
     where
         Node: 'dom + Copy + LayoutNode + Send + Sync,
     {
@@ -124,7 +121,7 @@ impl BoxTreeRoot {
         };
         let dummy_tree_rank = 0;
         let mut absolutely_positioned_fragments = vec![];
-        let mut flow_children = self.0.layout(
+        let mut independent_layout = self.0.layout(
             layout_context,
             &initial_containing_block,
             dummy_tree_rank,
@@ -135,12 +132,12 @@ impl BoxTreeRoot {
             size: initial_containing_block_size,
             mode: initial_containing_block.mode,
         };
-        flow_children.fragments.par_extend(
+        independent_layout.fragments.par_extend(
             absolutely_positioned_fragments
                 .par_iter()
                 .map(|a| a.layout(layout_context, &initial_containing_block)),
         );
-        FragmentTreeRoot(flow_children.fragments)
+        FragmentTreeRoot(independent_layout.fragments)
     }
 }
 

components/layout_2020/formatting_contexts.rs

@@ -4,7 +4,8 @@
 
 use crate::context::LayoutContext;
 use crate::dom_traversal::{Contents, NodeExt};
-use crate::flow::{BlockFormattingContext, FlowChildren};
+use crate::flow::BlockFormattingContext;
+use crate::fragments::Fragment;
 use crate::geom::flow_relative::Vec2;
 use crate::positioned::AbsolutelyPositionedFragment;
 use crate::replaced::ReplacedContent;
@@ -14,6 +15,7 @@ use servo_arc::Arc;
 use std::convert::TryInto;
 use style::context::SharedStyleContext;
 use style::properties::ComputedValues;
+use style::values::computed::Length;
 
 /// https://drafts.csswg.org/css-display/#independent-formatting-context
 #[derive(Debug)]
@@ -22,6 +24,11 @@ pub(crate) struct IndependentFormattingContext {
     contents: IndependentFormattingContextContents,
 }
 
+pub(crate) struct IndependentLayout {
+    pub fragments: Vec<Fragment>,
+    pub content_block_size: Length,
+}
+
 // Private so that code outside of this module cannot match variants.
 // It should got through methods instead.
 #[derive(Debug)]
@@ -74,7 +81,7 @@ impl IndependentFormattingContext {
         containing_block: &ContainingBlock,
         tree_rank: usize,
         absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
-    ) -> FlowChildren {
+    ) -> IndependentLayout {
         match self.as_replaced() {
             Ok(replaced) => match *replaced {},
             Err(ifc) => ifc.layout(
@@ -94,7 +101,7 @@ impl<'a> NonReplacedIFC<'a> {
         containing_block: &ContainingBlock,
         tree_rank: usize,
         absolutely_positioned_fragments: &mut Vec<AbsolutelyPositionedFragment<'a>>,
-    ) -> FlowChildren {
+    ) -> IndependentLayout {
         match &self.0 {
             NonReplacedIFCKind::Flow(bfc) => bfc.layout(
                 layout_context,

components/layout_2020/lib.rs

@@ -33,7 +33,7 @@ pub use flow::{BoxTreeRoot, FragmentTreeRoot};
 
 use crate::context::LayoutContext;
 use crate::dom_traversal::{Contents, NodeExt};
-use crate::flow::{BlockFormattingContext, FlowChildren};
+use crate::flow::BlockFormattingContext;
 use crate::geom::flow_relative::Vec2;
 use crate::positioned::AbsolutelyPositionedFragment;
 use crate::replaced::ReplacedContent;

components/layout_2020/positioned.rs

@@ -274,7 +274,7 @@ impl<'a> AbsolutelyPositionedFragment<'a> {
         );
         let dummy_tree_rank = 0;
         let mut absolutely_positioned_fragments = vec![];
-        let mut flow_children = self.absolutely_positioned_box.contents.layout(
+        let mut independent_layout = self.absolutely_positioned_box.contents.layout(
             layout_context,
             &containing_block_for_children,
             dummy_tree_rank,
@@ -286,7 +286,7 @@ impl<'a> AbsolutelyPositionedFragment<'a> {
             Anchor::End(end) => cbbs - end - pb.inline_end - margin.inline_end - inline_size,
         };
 
-        let block_size = block_size.auto_is(|| flow_children.block_size);
+        let block_size = block_size.auto_is(|| independent_layout.content_block_size);
         let block_start = match block_anchor {
             Anchor::Start(start) => start + pb.block_start + margin.block_start,
             Anchor::End(end) => cbbs - end - pb.block_end - margin.block_end - block_size,
@@ -306,7 +306,7 @@ impl<'a> AbsolutelyPositionedFragment<'a> {
         AbsolutelyPositionedFragment::in_positioned_containing_block(
             layout_context,
             &absolutely_positioned_fragments,
-            &mut flow_children.fragments,
+            &mut independent_layout.fragments,
             &content_rect.size,
             &padding,
             containing_block_for_children.mode,
@@ -314,7 +314,7 @@ impl<'a> AbsolutelyPositionedFragment<'a> {
 
         Fragment::Box(BoxFragment {
             style: style.clone(),
-            children: flow_children.fragments,
+            children: independent_layout.fragments,
             content_rect,
             padding,
             border,