Skip to content

Flexbox: apply transferred min/max sizes to flex base size and hypothetical sizes #989

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
nicoburns merged 2 commits into from
Jul 25, 2026
Merged

Flexbox: apply transferred min/max sizes to flex base size and hypothetical sizes #989

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
0974918
Apply transferred min/max sizes when determining flex base and hypoth…
nicoburns Jul 24, 2026
4708ca9
Add changelog entry
nicoburns Jul 24, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 2 additions & 0 deletions CHANGELOG.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@

### Fixed

- Flexbox: min/max sizes transferred through the aspect ratio now clamp the flex base size, the automatic minimum size, and the hypothetical main/cross sizes of flex items, instead of being baked into the item's used min/max sizes. This matches browser behaviour for replaced elements and items with `aspect-ratio` combined with min/max constraints in the opposite axis ([w3c/csswg-drafts#10997](https://github.com/w3c/csswg-drafts/issues/10997))

- Numeric style helpers (`length`, `percent`, `fr`, `flex`) now accept `Input: Into<f64>` instead of `Input: Into<f32>`. This allows bare float literals such as `length(800.0)` to be used without triggering the `float_literal_f32_fallback` future-compatibility lint, while widening the set of accepted numeric input types (#974)

## 0.12.2
Expand Down
44 changes: 33 additions & 11 deletions src/compute/flexbox.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,8 @@ struct FlexItem {
min_size: Size<Option<f32>>,
/// The maximum allowable size of this item
max_size: Size<Option<f32>>,
/// The aspect ratio of this item
aspect_ratio: Option<f32>,
/// The cross-alignment of this item
align_self: AlignSelf,

Expand Down Expand Up @@ -548,13 +550,12 @@ fn generate_anonymous_flex_items(
min_size: child_style
.min_size()
.maybe_resolve(constants.node_inner_size, |val, basis| tree.calc(val, basis))
.maybe_apply_aspect_ratio(aspect_ratio)
.maybe_add(box_sizing_adjustment),
max_size: child_style
.max_size()
.maybe_resolve(constants.node_inner_size, |val, basis| tree.calc(val, basis))
.maybe_apply_aspect_ratio(aspect_ratio)
.maybe_add(box_sizing_adjustment),
aspect_ratio,

inset: child_style
.inset()
Expand Down Expand Up @@ -676,9 +677,13 @@ fn determine_flex_base_size(
let child_parent_size = Size::from_cross(dir, cross_axis_parent_size);

// Available space for child sizing
// Min/max sizes transferred through the aspect ratio are taken into account here
// https://github.com/w3c/csswg-drafts/issues/10997
let cross_axis_margin_sum = constants.margin.cross_axis_sum(dir);
let child_min_cross = child.min_size.cross(dir).maybe_add(cross_axis_margin_sum);
let child_max_cross = child.max_size.cross(dir).maybe_add(cross_axis_margin_sum);
let transferred_min_size = child.min_size.maybe_apply_aspect_ratio(child.aspect_ratio);
let transferred_max_size = child.max_size.maybe_apply_aspect_ratio(child.aspect_ratio);
let child_min_cross = transferred_min_size.cross(dir).maybe_add(cross_axis_margin_sum);
let child_max_cross = transferred_max_size.cross(dir).maybe_add(cross_axis_margin_sum);

// Clamp available space by min- and max- size
let cross_axis_available_space: AvailableSpace = match available_space.cross(dir) {
Expand All @@ -698,6 +703,13 @@ fn determine_flex_base_size(
// Known dimensions for child sizing
let child_known_dimensions = {
let mut ckd = child.size.with_main(dir, None);
// Clamp the definite cross size by the cross min/max sizes so that sizes
// transferred through an intrinsic aspect ratio (e.g. for replaced elements)
// are based on the used cross size.
ckd.set_cross(
dir,
ckd.cross(dir).maybe_clamp(transferred_min_size.cross(dir), transferred_max_size.cross(dir)),
);
if child.align_self == AlignSelf::STRETCH
&& !child.margin_is_auto.cross_start(constants.dir)
&& !child.margin_is_auto.cross_end(constants.dir)
Expand Down Expand Up @@ -836,14 +848,19 @@ fn determine_flex_base_size(
// 4.5. Automatic Minimum Size of Flex Items
// https://www.w3.org/TR/css-flexbox-1/#min-size-auto
let clamped_min_content_size =
min_content_main_size.maybe_min(child.size.main(dir)).maybe_min(child.max_size.main(dir));
min_content_main_size.maybe_min(child.size.main(dir)).maybe_min(transferred_max_size.main(dir));
clamped_min_content_size.maybe_max(padding_border_axes_sums.main(dir))
});

let hypothetical_inner_min_main =
child.resolved_minimum_main_size.maybe_max(padding_border_axes_sums.main(constants.dir));
// Sizes transferred through the aspect ratio clamp the hypothetical main size,
// but do not participate in resolving flexible lengths or clamping the final size.
// https://github.com/w3c/csswg-drafts/issues/10997
let hypothetical_inner_min_main = child
.resolved_minimum_main_size
.maybe_max(transferred_min_size.main(constants.dir))
.maybe_max(padding_border_axes_sums.main(constants.dir));
let hypothetical_inner_size =
child.flex_basis.maybe_clamp(Some(hypothetical_inner_min_main), child.max_size.main(constants.dir));
child.flex_basis.maybe_clamp(Some(hypothetical_inner_min_main), transferred_max_size.main(constants.dir));
let hypothetical_outer_size = hypothetical_inner_size + child.margin.main_axis_sum(constants.dir);

child.hypothetical_inner_size.set_main(constants.dir, hypothetical_inner_size);
Expand Down Expand Up @@ -1394,15 +1411,20 @@ fn determine_hypothetical_cross_size(

let child_known_main = constants.container_size.main(constants.dir).into();

// Sizes transferred through the aspect ratio clamp the hypothetical cross size
// https://github.com/w3c/csswg-drafts/issues/10997
let transferred_min_cross = child.min_size.maybe_apply_aspect_ratio(child.aspect_ratio).cross(constants.dir);
let transferred_max_cross = child.max_size.maybe_apply_aspect_ratio(child.aspect_ratio).cross(constants.dir);

let child_cross = child
.size
.cross(constants.dir)
.maybe_clamp(child.min_size.cross(constants.dir), child.max_size.cross(constants.dir))
.maybe_clamp(transferred_min_cross, transferred_max_cross)
.maybe_max(padding_border_sum);

let child_available_cross = available_space
.cross(constants.dir)
.maybe_clamp(child.min_size.cross(constants.dir), child.max_size.cross(constants.dir))
.maybe_clamp(transferred_min_cross, transferred_max_cross)
.maybe_max(padding_border_sum);

let child_inner_cross = child_cross.unwrap_or_else(|| {
Expand All @@ -1421,7 +1443,7 @@ fn determine_hypothetical_cross_size(
constants.dir.cross_axis(),
Line::FALSE,
)
.maybe_clamp(child.min_size.cross(constants.dir), child.max_size.cross(constants.dir))
.maybe_clamp(transferred_min_cross, transferred_max_cross)
.max(padding_border_sum)
});
let child_outer_cross = child_inner_cross + child.margin.cross_axis_sum(constants.dir);
Expand Down