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layout: Fix interaction of margin and stretch size on block-level boxes (#35904)

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The CSSWG resolved that `block-size: stretch` on a block-level box
stretches the margin box to fill the parent. However, if the parent
doesn't have padding nor border, and doesn't establish an independent
formatting context, then we assume that the margins will collapse.
Therefore, we treat the margins as zero when resolving the stretch size,
regardless of whether they will actually end up collapsing.

https://github.com/w3c/csswg-drafts/issues/11044#issuecomment-2599101601
https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
This commit is contained in:
Oriol Brufau 2025-03-11 22:32:28 +01:00 • committed by GitHub
parent f7ddac249b
commit 9858ec81f9
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14 changed files with 379 additions and 120 deletions
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69
components/layout_2020/flow/mod.rs
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@ -32,8 +32,8 @@ use crate::fragment_tree::{
BaseFragmentInfo, BoxFragment, CollapsedBlockMargins, CollapsedMargin, Fragment, FragmentFlags,
};
use crate::geom::{
AuOrAuto, LogicalRect, LogicalSides, LogicalVec2, PhysicalPoint, PhysicalRect, PhysicalSides,
Size, Sizes, ToLogical, ToLogicalWithContainingBlock,
AuOrAuto, LogicalRect, LogicalSides, LogicalSides1D, LogicalVec2, PhysicalPoint, PhysicalRect,
PhysicalSides, Size, Sizes, ToLogical, ToLogicalWithContainingBlock,
};
use crate::layout_box_base::LayoutBoxBase;
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext, PositioningContextLength};
@ -278,12 +278,17 @@ impl OutsideMarker {
style: &self.marker_style,
};
// A ::marker can't have a stretch size (must be auto), so this doesn't matter.
// https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing
let ignore_block_margins_for_stretch = LogicalSides1D::new(false, false);
let flow_layout = self.block_container.layout(
layout_context,
positioning_context,
&containing_block_for_children,
sequential_layout_state,
collapsible_with_parent_start_margin.unwrap_or(CollapsibleWithParentStartMargin(false)),
ignore_block_margins_for_stretch,
);
let max_inline_size =
@ -364,12 +369,18 @@ impl BlockFormattingContext {
None
};
// Since this is an independent formatting context, we don't ignore block margins when
// resolving a stretch block size of the children.
// https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing
let ignore_block_margins_for_stretch = LogicalSides1D::new(false, false);
let flow_layout = self.contents.layout(
layout_context,
positioning_context,
containing_block,
sequential_layout_state.as_mut(),
CollapsibleWithParentStartMargin(false),
ignore_block_margins_for_stretch,
);
debug_assert!(
!flow_layout
@ -561,6 +572,7 @@ impl BlockContainer {
containing_block: &ContainingBlock,
sequential_layout_state: Option<&mut SequentialLayoutState>,
collapsible_with_parent_start_margin: CollapsibleWithParentStartMargin,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> FlowLayout {
match self {
BlockContainer::BlockLevelBoxes(child_boxes) => layout_block_level_children(
@ -570,6 +582,7 @@ impl BlockContainer {
containing_block,
sequential_layout_state,
collapsible_with_parent_start_margin,
ignore_block_margins_for_stretch,
),
BlockContainer::InlineFormattingContext(ifc) => ifc.layout(
layout_context,
@ -613,6 +626,7 @@ fn layout_block_level_children(
containing_block: &ContainingBlock,
mut sequential_layout_state: Option<&mut SequentialLayoutState>,
collapsible_with_parent_start_margin: CollapsibleWithParentStartMargin,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> FlowLayout {
let mut placement_state =
PlacementState::new(collapsible_with_parent_start_margin, containing_block);
@ -625,6 +639,7 @@ fn layout_block_level_children(
containing_block,
sequential_layout_state,
&mut placement_state,
ignore_block_margins_for_stretch,
),
None => layout_block_level_children_in_parallel(
layout_context,
@ -632,6 +647,7 @@ fn layout_block_level_children(
child_boxes,
containing_block,
&mut placement_state,
ignore_block_margins_for_stretch,
),
};
@ -659,6 +675,7 @@ fn layout_block_level_children_in_parallel(
child_boxes: &[ArcRefCell<BlockLevelBox>],
containing_block: &ContainingBlock,
placement_state: &mut PlacementState,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> Vec<Fragment> {
let collects_for_nearest_positioned_ancestor =
positioning_context.collects_for_nearest_positioned_ancestor();
@ -676,6 +693,7 @@ fn layout_block_level_children_in_parallel(
containing_block,
/* sequential_layout_state = */ None,
/* collapsible_with_parent_start_margin = */ None,
ignore_block_margins_for_stretch,
);
(fragment, child_positioning_context)
})
@ -702,6 +720,7 @@ fn layout_block_level_children_sequentially(
containing_block: &ContainingBlock,
sequential_layout_state: &mut SequentialLayoutState,
placement_state: &mut PlacementState,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> Vec<Fragment> {
// Because floats are involved, we do layout for this block formatting context in tree
// order without parallelism. This enables mutable access to a `SequentialLayoutState` that
@ -718,6 +737,7 @@ fn layout_block_level_children_sequentially(
Some(CollapsibleWithParentStartMargin(
placement_state.next_in_flow_margin_collapses_with_parent_start_margin,
)),
ignore_block_margins_for_stretch,
);
placement_state
@ -740,6 +760,7 @@ impl BlockLevelBox {
containing_block: &ContainingBlock,
sequential_layout_state: Option<&mut SequentialLayoutState>,
collapsible_with_parent_start_margin: Option<CollapsibleWithParentStartMargin>,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> Fragment {
match self {
BlockLevelBox::SameFormattingContextBlock { base, contents, .. } => Fragment::Box(
@ -756,6 +777,7 @@ impl BlockLevelBox {
contents,
sequential_layout_state,
collapsible_with_parent_start_margin,
ignore_block_margins_for_stretch,
)
},
)),
@ -771,6 +793,7 @@ impl BlockLevelBox {
positioning_context,
containing_block,
sequential_layout_state,
ignore_block_margins_for_stretch,
)
},
),
@ -842,6 +865,7 @@ fn layout_in_flow_non_replaced_block_level_same_formatting_context(
contents: &BlockContainer,
mut sequential_layout_state: Option<&mut SequentialLayoutState>,
collapsible_with_parent_start_margin: Option<CollapsibleWithParentStartMargin>,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> BoxFragment {
let style = &base.style;
let layout_style = contents.layout_style(base);
@ -860,6 +884,7 @@ fn layout_in_flow_non_replaced_block_level_same_formatting_context(
containing_block,
&layout_style,
get_inline_content_sizes,
ignore_block_margins_for_stretch,
);
let ResolvedMargins {
margin,
@ -951,12 +976,23 @@ fn layout_in_flow_non_replaced_block_level_same_formatting_context(
},
};
// https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing
// > If this is a block axis size, and the element is in a Block Layout formatting context,
// > and the parent element does not have a block-start border or padding and is not an
// > independent formatting context, treat the element’s block-start margin as zero
// > for the purpose of calculating this size. Do the same for the block-end margin.
let ignore_block_margins_for_stretch = LogicalSides1D::new(
pbm.border.block_start.is_zero() && pbm.padding.block_start.is_zero(),
pbm.border.block_end.is_zero() && pbm.padding.block_end.is_zero(),
);
let flow_layout = contents.layout(
layout_context,
positioning_context,
&containing_block_for_children,
sequential_layout_state.as_deref_mut(),
CollapsibleWithParentStartMargin(start_margin_can_collapse_with_children),
ignore_block_margins_for_stretch,
);
let mut content_block_size: Au = flow_layout.content_block_size;
@ -1078,6 +1114,7 @@ impl IndependentNonReplacedContents {
positioning_context: &mut PositioningContext,
containing_block: &ContainingBlock,
sequential_layout_state: Option<&mut SequentialLayoutState>,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> BoxFragment {
if let Some(sequential_layout_state) = sequential_layout_state {
return self.layout_in_flow_block_level_sequentially(
@ -1086,6 +1123,7 @@ impl IndependentNonReplacedContents {
positioning_context,
containing_block,
sequential_layout_state,
ignore_block_margins_for_stretch,
);
}
@ -1104,6 +1142,7 @@ impl IndependentNonReplacedContents {
containing_block,
&layout_style,
get_inline_content_sizes,
ignore_block_margins_for_stretch,
);
let layout = self.layout(
@ -1177,6 +1216,7 @@ impl IndependentNonReplacedContents {
positioning_context: &mut PositioningContext,
containing_block: &ContainingBlock<'_>,
sequential_layout_state: &mut SequentialLayoutState,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> BoxFragment {
let style = &base.style;
let containing_block_writing_mode = containing_block.style.writing_mode;
@ -1218,13 +1258,12 @@ impl IndependentNonReplacedContents {
});
// Then compute a tentative block size, only taking extrinsic values into account.
let margin = pbm.margin.auto_is(Au::zero);
let pbm_sums = pbm.padding + pbm.border + margin;
let pbm_sums = pbm.sums_auto_is_zero(ignore_block_margins_for_stretch);
let available_block_size = containing_block
.size
.block
.to_definite()
.map(|block_size| Au::zero().max(block_size - pbm_sums.block_sum()));
.map(|block_size| Au::zero().max(block_size - pbm_sums.block));
let (preferred_block_size, min_block_size, max_block_size) = content_box_sizes
.block
.resolve_each_extrinsic(Size::FitContent, Au::zero(), available_block_size);
@ -1478,6 +1517,7 @@ impl ReplacedContents {
layout_context: &LayoutContext,
containing_block: &ContainingBlock,
mut sequential_layout_state: Option<&mut SequentialLayoutState>,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> BoxFragment {
let content_box_sizes_and_pbm = self
.layout_style(base)
@ -1487,6 +1527,7 @@ impl ReplacedContents {
containing_block,
&base.style,
&content_box_sizes_and_pbm,
ignore_block_margins_for_stretch,
);
let margin_inline_start;
@ -1631,6 +1672,7 @@ fn solve_containing_block_padding_and_border_for_in_flow_box<'a>(
containing_block: &ContainingBlock<'_>,
layout_style: &'a LayoutStyle,
get_inline_content_sizes: impl FnOnce(&ConstraintSpace) -> ContentSizes,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> ContainingBlockPaddingAndBorder<'a> {
let style = layout_style.style();
if matches!(style.pseudo(), Some(PseudoElement::ServoAnonymousBox)) {
@ -1663,16 +1705,14 @@ fn solve_containing_block_padding_and_border_for_in_flow_box<'a>(
depends_on_block_constraints,
} = layout_style.content_box_sizes_and_padding_border_margin(&containing_block.into());
let margin = pbm.margin.auto_is(Au::zero);
let pbm_sums = pbm.padding + pbm.border + margin;
let pbm_sums = pbm.sums_auto_is_zero(ignore_block_margins_for_stretch);
let writing_mode = style.writing_mode;
let available_inline_size =
Au::zero().max(containing_block.size.inline - pbm_sums.inline_sum());
let available_inline_size = Au::zero().max(containing_block.size.inline - pbm_sums.inline);
let available_block_size = containing_block
.size
.block
.to_definite()
.map(|block_size| Au::zero().max(block_size - pbm_sums.block_sum()));
.map(|block_size| Au::zero().max(block_size - pbm_sums.block));
// https://drafts.csswg.org/css2/#the-height-property
// https://drafts.csswg.org/css2/visudet.html#min-max-heights
@ -2125,6 +2165,7 @@ impl IndependentFormattingContext {
positioning_context: &mut PositioningContext,
containing_block: &ContainingBlock,
sequential_layout_state: Option<&mut SequentialLayoutState>,
ignore_block_margins_for_stretch: LogicalSides1D<bool>,
) -> BoxFragment {
match &self.contents {
IndependentFormattingContextContents::NonReplaced(contents) => contents
@ -2134,6 +2175,7 @@ impl IndependentFormattingContext {
positioning_context,
containing_block,
sequential_layout_state,
ignore_block_margins_for_stretch,
),
IndependentFormattingContextContents::Replaced(contents) => contents
.layout_in_flow_block_level(
@ -2141,6 +2183,7 @@ impl IndependentFormattingContext {
layout_context,
containing_block,
sequential_layout_state,
ignore_block_margins_for_stretch,
),
}
}
@ -2161,6 +2204,11 @@ impl IndependentFormattingContext {
let (fragments, content_rect, baselines) = match &self.contents {
IndependentFormattingContextContents::Replaced(replaced) => {
// Floats and atomic inlines can't collapse margins with their parent,
// so don't ignore block margins when resolving a stretch block size.
// https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing
let ignore_block_margins_for_stretch = LogicalSides1D::new(false, false);
// https://drafts.csswg.org/css2/visudet.html#float-replaced-width
// https://drafts.csswg.org/css2/visudet.html#inline-replaced-height
let content_size = replaced
@ -2168,6 +2216,7 @@ impl IndependentFormattingContext {
containing_block,
style,
&content_box_sizes_and_pbm,
ignore_block_margins_for_stretch,
)
.to_physical_size(container_writing_mode);
let fragments = replaced.make_fragments(layout_context, style, content_size);