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layout: Use overflow: visible if overflow was propagated to viewport (#38598)

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The `overflow-*` values of either the root element or the `<body>` get
propagated to the viewport. However, we were missing this part:
> The element from which the value is propagated must then have a used
`overflow` value of `visible`.

See https://drafts.csswg.org/css-overflow/#overflow-propagation

Testing:
 - `css/cssom-view/scrolling-quirks-vs-nonquirks.html`
 - `css/css-overflow/overflow-body-propagation-007.html`
 - `css/css-overflow/overflow-body-propagation-008.html`
 - `css/css-overflow/overflow-body-propagation-009.html`
 - `css/css-overflow/scrollable-overflow-with-nested-elements-001.html` 
 - `css/css-overflow/scrollable-overflow-with-nested-elements-002.html` 
 - `css/css-overflow/scrollable-overflow-with-nested-elements-003.html`
 - `css/css-overflow/scrollable-overflow-with-nested-elements-004.html`
 - `css/css-overflow/scrollbar-gutter-scroll-into-view.html`

Failures:
 - `css/css-overflow/overflow-body-propagation-010.html`
   Failing because of missing support for `contain: paint`.
- `css/css-overflow/scrollable-overflow-with-nested-elements-005.html`
Failing because of wrong `data-expected-height`, but correct
`data-expected-scroll-height` which is core of this PR.
`data-expected-height` can be dealt separately.


Fixes: #38248

---------

Signed-off-by: Shubham Gupta <shubham13297@gmail.com>
Signed-off-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
This commit is contained in:
Shubham Gupta 2025-08-20 22:21:51 +08:00 • committed by GitHub
parent 37088aa4c3
commit d8ff9c7a08
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22 changed files with 373 additions and 72 deletions
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23
components/layout/flow/root.rs
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@ -26,7 +26,7 @@ use crate::flow::float::FloatBox;
use crate::flow::inline::InlineItem;
use crate::flow::{BlockContainer, BlockFormattingContext, BlockLevelBox};
use crate::formatting_contexts::IndependentFormattingContext;
use crate::fragment_tree::FragmentTree;
use crate::fragment_tree::{FragmentFlags, FragmentTree};
use crate::geom::{LogicalVec2, PhysicalSize};
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
use crate::replaced::ReplacedContents;
@ -48,10 +48,6 @@ impl BoxTree {
#[servo_tracing::instrument(name = "Box Tree Construction", skip_all)]
pub(crate) fn construct(context: &LayoutContext, root_element: ServoLayoutNode<'_>) -> Self {
let root_element = root_element.to_threadsafe();
let boxes = construct_for_root_element(context, root_element);
// Zero box for `:root { display: none }`, one for the root element otherwise.
assert!(boxes.len() <= 1);
// From https://www.w3.org/TR/css-overflow-3/#overflow-propagation:
// > UAs must apply the overflow-* values set on the root element to the viewport when the
@ -65,6 +61,7 @@ impl BoxTree {
let mut viewport_overflow_x = root_style.clone_overflow_x();
let mut viewport_overflow_y = root_style.clone_overflow_y();
let mut element_propagating_overflow = root_element;
if viewport_overflow_x == Overflow::Visible &&
viewport_overflow_y == Overflow::Visible &&
!root_style.get_box().display.is_none()
@ -81,12 +78,28 @@ impl BoxTree {
if !style.get_box().display.is_none() {
viewport_overflow_x = style.clone_overflow_x();
viewport_overflow_y = style.clone_overflow_y();
element_propagating_overflow = child;
break;
}
}
}
let boxes = construct_for_root_element(context, root_element);
// Zero box for `:root { display: none }`, one for the root element otherwise.
assert!(boxes.len() <= 1);
if let Some(layout_data) = element_propagating_overflow.inner_layout_data() {
if let Some(ref mut layout_box) = *layout_data.self_box.borrow_mut() {
layout_box.with_base_mut(|base| {
base.base_fragment_info
.flags
.insert(FragmentFlags::PROPAGATED_OVERFLOW_TO_VIEWPORT)
});
}
}
let contents = BlockContainer::BlockLevelBoxes(boxes);
let contains_floats = contents.contains_floats();
Self {