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layout: Inform child layout about final block size (#36980)

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Before this patch it wasn't possibly to simultaneously support intrinsic
min/max sizes and content alignment in the block axis. For example,
block containers only support the former, and flex containers only the
latter.

The reason is that the final block size was decided by the parent
formatting context *after* performing layout, while content alignment is
performed *during* layout.

To address the problem, this introduces the struct `LazySize`, which
contains the data to resolve the final size, except for the intrinsic
size. Thus the parent formatting context can first create a `LazySize`,
then pass it to the child layout so that (if necessary) it can compute
the final size once the intrinsic one is known, and after layout the
parent formatting context uses it to actually size the child.

This PR just provides the functionality that will be used by follow-ups,
but at this point no layout is using the `LazySize` provided by the
parent, so there shouldn't be any behavior change yet.

Testing: Unnecessary (no behavior change)
This is part of #36981 and #36982

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
This commit is contained in:
Oriol Brufau 2025-05-14 13:35:49 -07:00 • committed by GitHub
parent 1499e2a874
commit 1cceb5f6a0
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6 changed files with 194 additions and 81 deletions
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42
components/layout/flexbox/layout.rs
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@ -32,7 +32,7 @@ use crate::formatting_contexts::{Baselines, IndependentFormattingContextContents
use crate::fragment_tree::{
BoxFragment, CollapsedBlockMargins, Fragment, FragmentFlags, SpecificLayoutInfo,
};
use crate::geom::{AuOrAuto, LogicalRect, LogicalSides, LogicalVec2, Size, Sizes};
use crate::geom::{AuOrAuto, LazySize, LogicalRect, LogicalSides, LogicalVec2, Size, Sizes};
use crate::layout_box_base::CacheableLayoutResult;
use crate::positioned::{
AbsolutelyPositionedBox, PositioningContext, PositioningContextLength, relative_adjustement,
@ -1936,6 +1936,27 @@ impl FlexItem<'_> {
}
}
let lazy_block_size = if cross_axis_is_item_block_axis {
// This means that an auto size with stretch alignment will behave different than
// a stretch size. That's not what the spec says, but matches other browsers.
// To be discussed in https://github.com/w3c/csswg-drafts/issues/11784.
let stretch_size = containing_block
.size
.block
.to_definite()
.map(|size| Au::zero().max(size - self.pbm_auto_is_zero.cross));
LazySize::new(
&self.content_cross_sizes,
Direction::Block,
Size::FitContent,
Au::zero,
stretch_size,
self.is_table(),
)
} else {
used_main_size.into()
};
let layout = non_replaced.layout(
flex_context.layout_context,
&mut positioning_context,
@ -1945,6 +1966,7 @@ impl FlexItem<'_> {
flex_axis == FlexAxis::Column ||
self.cross_size_stretches_to_line ||
self.depends_on_block_constraints,
&lazy_block_size,
);
let CacheableLayoutResult {
fragments,
@ -1962,22 +1984,7 @@ impl FlexItem<'_> {
});
let hypothetical_cross_size = if cross_axis_is_item_block_axis {
// This means that an auto size with stretch alignment will behave different than
// a stretch size. That's not what the spec says, but matches other browsers.
// To be discussed in https://github.com/w3c/csswg-drafts/issues/11784.
let stretch_size = containing_block
.size
.block
.to_definite()
.map(|size| Au::zero().max(size - self.pbm_auto_is_zero.cross));
self.content_cross_sizes.resolve(
Direction::Block,
Size::FitContent,
Au::zero,
stretch_size,
|| content_block_size.into(),
self.is_table(),
)
lazy_block_size.resolve(|| content_block_size)
} else {
inline_size
};
@ -2687,6 +2694,7 @@ impl FlexItemBox {
flex_context.containing_block,
&self.independent_formatting_context.base,
false, /* depends_on_block_constraints */
&LazySize::intrinsic(),
)
.content_block_size
};