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LibWeb: Make foreignObject establish a containing block for abspos

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Absolutely positioned elements inside SVG foreignObject were being
positioned relative to an ancestor containing block outside the SVG,
instead of relative to the foreignObject itself. Per a W3C resolution
and the behavior of other browsers, foreignObject should establish a
containing block for absolutely and fixed positioned elements.

With this fix, the `has_abspos_with_external_containing_block` check
in `set_needs_layout_update()` and the abspos preservation loop in
`relayout_svg_root()` become dead code — remove both and simplify the
ancestor loops. Rename related tests to reflect the new behavior.

Fixes https://github.com/LadybirdBrowser/ladybird/issues/3241
This commit is contained in:
Aliaksandr Kalenik
2026-02-17 04:59:31 +01:00
committed by Alexander Kalenik
parent fa49de8956
commit b3231ea2a0
Notes: github-actions[bot] 2026-02-17 15:49:36 +00:00 
Author: https://github.com/kalenikaliaksandr
Commit: https://github.com/LadybirdBrowser/ladybird/commit/b3231ea2a04
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/7993
Reviewed-by: https://github.com/gmta
8 changed files with 61 additions and 50 deletions
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23
Libraries/LibWeb/Layout/Node.cpp
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@@ -160,6 +160,11 @@ bool Node::establishes_an_absolute_positioning_containing_block() const
if (is<Viewport>(*this))
return true;
// https://github.com/w3c/fxtf-drafts/issues/307#issuecomment-499612420
// foreignObject establishes a containing block for absolutely and fixed positioned elements.
if (is_svg_foreign_object_box())
return true;
return computed_values_establish_absolute_positioning_containing_block();
}
@@ -1467,29 +1472,11 @@ void Node::set_needs_layout_update(DOM::SetNeedsLayoutReason reason)
return IterationDecision::Continue;
});
auto has_abspos_with_external_containing_block = [](SVGSVGBox const& svg_box) {
for (auto const* ancestor = svg_box.parent(); ancestor; ancestor = ancestor->parent()) {
auto const* box = as_if<Box>(ancestor);
if (!box)
continue;
for (auto const& abspos_child : box->contained_abspos_children()) {
if (svg_box.is_inclusive_ancestor_of(abspos_child))
return true;
}
}
return false;
};
for (auto* ancestor = parent(); ancestor; ancestor = ancestor->parent()) {
if (ancestor->m_needs_layout_update)
break;
ancestor->m_needs_layout_update = true;
if (auto* svg_box = as_if<SVGSVGBox>(ancestor)) {
// Absolutely positioned elements inside the SVG subtree whose containing
// block is outside the SVG can't be properly relaid out during partial SVG
// relayout — their layout depends on formatting contexts outside the subtree.
if (has_abspos_with_external_containing_block(*svg_box))
continue;
document().mark_svg_root_as_needing_relayout(*svg_box);
break;
}