Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 73f2c8612940176c11bc6312e3a7155a58b00b33
https://github.com/WebKit/WebKit/commit/73f2c8612940176c11bc6312e3a7155a58b00b33
Author: Christian Biesinger <[email protected]>
Date: 2026-10-14 (Wed, 14 Oct 2026)
Changed paths:
M LayoutTests/TestExpectations
A LayoutTests/fast/css-grid-layout/subgrid-continue-collapse-expected.html
A LayoutTests/fast/css-grid-layout/subgrid-continue-collapse.html
A LayoutTests/fast/css-grid-layout/subgrid-continue-discard-expected.html
A LayoutTests/fast/css-grid-layout/subgrid-continue-discard.html
M Source/WebCore/css/parser/CSSPropertyParserCustom.h
M Source/WebCore/rendering/LineClampUpdater.cpp
M Source/WebCore/rendering/LineClampUpdater.h
M Source/WebCore/rendering/RenderBlock.cpp
M Source/WebCore/rendering/RenderBlockFlow.cpp
Log Message:
-----------
[line-clamp] Make continue: collapse clamp, and set it from line-clamp
https://bugs.webkit.org/show_bug.cgi?id=327018
Reviewed by Alan Baradlay.
continue: collapse is parsed but behaves like the initial value, and the
line-clamp shorthand sets continue: discard
instead of collapse [1]. The line clamp implementation hides the content after
the clamp point and leaves it out of
the box's automatic block size, which is what collapse is specified to do [2],
while discard is specified to turn the
box into a fragmentation container.
Make collapse behave like discard does today, and have line-clamp set continue:
collapse as specified. This changes:
1. The computed value of continue when line-clamp is specified: it is now
collapse instead of discard. The rendering
of line-clamp does not change, since collapse and discard are now laid out
the same.
2. The behavior of continue: collapse when specified by the author, which used
to be ignored: the box establishes an
independent formatting context and is a line-clamp container, so it clamps
after max-lines lines, or at its
height or max-height when max-lines is auto.
Both changes are behind the CSSLineClampEnabled preference, since line-clamp
and continue are only parsed when it is enabled.
continue only applies to block containers (and multicol containers), so make
neither collapse nor discard establish an
independent formatting context on other boxes. Before, continue: discard on a
subgrid stopped it from being a subgrid.
This also lets continue: -webkit-legacy (as set by -webkit-line-clamp) be laid
out "identically to collapse" later on.
[1] https://drafts.csswg.org/css-overflow-4/#line-clamp
[2] https://drafts.csswg.org/css-overflow-4/#valdef-continue-collapse
* LayoutTests/TestExpectations: continue-001.html passes now.
* LayoutTests/fast/css-grid-layout/subgrid-continue-collapse-expected.html:
Added.
* LayoutTests/fast/css-grid-layout/subgrid-continue-collapse.html: Added.
* LayoutTests/fast/css-grid-layout/subgrid-continue-discard-expected.html:
Added.
* LayoutTests/fast/css-grid-layout/subgrid-continue-discard.html: Added.
* Source/WebCore/css/parser/CSSPropertyParserCustom.h:
(WebCore::PropertyParserCustom::consumeLineClampShorthand): Set continue:
collapse instead of discard.
* Source/WebCore/rendering/LineClampUpdater.cpp:
(WebCore::LineClampUpdater::shouldDiscardOverflow): Added. Both collapse and
discard hide the content after the clamp point.
(WebCore::LineClampUpdater::LineClampUpdater):
(WebCore::LineClampUpdater::isAutoLineClampRoot const):
(WebCore::LineClampUpdater::setMaximumLines):
(WebCore::LineClampUpdater::setClampAfterBox):
* Source/WebCore/rendering/LineClampUpdater.h:
* Source/WebCore/rendering/RenderBlock.cpp:
(WebCore::RenderBlock::establishesIndependentFormattingContextIgnoringDisplayType
const): continue: collapse and discard
establish an independent formatting context on a block container.
* Source/WebCore/rendering/RenderBlockFlow.cpp:
(WebCore::RenderBlockFlow::establishesLineClampContainer const): Use
LineClampUpdater::shouldDiscardOverflow so that
continue: collapse makes a line-clamp container too.
Canonical link: https://commits.webkit.org/323734@main
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