Border collapse problem with rowspan/colspan cells by karlcow · Pull Request #57402 · WebKit/WebKit

karlcow · 2026-01-28T12:57:04Z

`c9af451`

Border collapse problem with rowspan/colspan cells
https://bugs.webkit.org/show_bug.cgi?id=5515
rdar://94163960

Reviewed by Alan Baradlay.

Currently for a table of 2 columns and 4 rows.
* the first column has a rowspan = 3
(so 2 cells with one covering the first 3 rows)
* the second column has 4 cells on 4 rows
When specifiying a different bottom border color for each first 3 rows,
WebKit is adopting the color of the first cell defined in the second
colum for the bottom color of the rowspanned cell instead of the color
of the third row like Gecko and Blink do.

This patch is fixing and only this. It doesn't fix the more general
issue for vertical border shared in between the rowspanned cell and the
second column cells.
This will need to be fixed in https://webkit.org/b/20260 as it requires
a larger architectural change on border segmenting.

This didn't have WPT tests before, this is adding one covering this
behavior.

Tests: imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color-ref.html
imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color.html

* LayoutTests/imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color-ref.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color.html: Added.
* Source/WebCore/rendering/RenderTableCell.cpp:
(WebCore::RenderTableCell::computeCollapsedAfterBorder const):

Canonical link: https://commits.webkit.org/306471@main

ef1a9cd

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	~~🛠 win~~	✅ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	~~🧪 win-tests~~	✅ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		✅ 🛠 vision-apple
	~~🧪 ios-wk2-wpt~~	✅ 🧪 api-mac-debug	✅ 🛠 wpe-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 vision	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🧪 vision-wk2	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
✅ 🛠 🧪 unsafe-merge	✅ 🛠 tv	~~🧪 mac-intel-wk2~~
	✅ 🛠 tv-sim	~~🛠 mac-safer-cpp~~
	✅ 🛠 watch
	✅ 🛠 watch-sim

webkit-early-warning-system · 2026-01-28T12:57:12Z

EWS run on previous version of this PR (hash e4ede84)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	❌ 🧪 win-tests	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	⏳ wpe-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 vision	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🧪 vision-wk2	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🛠 tv	⏳ 🧪 mac-intel-wk2
	✅ 🛠 tv-sim	✅ 🛠 mac-safer-cpp
	✅ 🛠 watch
	✅ 🛠 watch-sim

karlcow · 2026-01-28T13:00:44Z

If no WPT tests is being progressed by this, I will amend the patch to add one.

Source/WebCore/rendering/RenderTableCell.cpp

webkit-early-warning-system · 2026-01-28T23:52:13Z

EWS run on previous version of this PR (hash c910942)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	~~🛠 win~~	⏳ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2	~~🧪 win-tests~~	⏳ 🛠 mac-apple
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	⏳ 🧪 api-mac	✅ 🧪 api-wpe		⏳ 🛠 vision-apple
	⏳ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	⏳ wpe-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	~~🛠 vision~~	⏳ 🧪 mac-wk2	❌ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🧪 vision-wk2	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
	✅ 🛠 tv	⏳ 🧪 mac-intel-wk2
	✅ 🛠 tv-sim	~~🛠 mac-safer-cpp~~
	~~🛠 watch~~
	✅ 🛠 watch-sim

karlcow · 2026-01-28T23:54:51Z

If no WPT tests is being progressed by this, I will amend the patch to add one.

I addressed comments by @annevk
I added a WPT test case to cover this.
And WebKit is matching Gecko and Blink.

Review time for @alanbaradlay 🙏

karlcow · 2026-01-29T01:47:12Z

Maybe I should have put the expected above. 🤦

webkit-early-warning-system · 2026-01-29T02:00:49Z

EWS run on previous version of this PR (hash e089c10)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	~~🛠 win~~	✅ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2	~~🧪 win-tests~~	✅ 🛠 mac-apple
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	⏳ 🧪 api-mac	✅ 🧪 api-wpe		✅ 🛠 vision-apple
	~~🧪 ios-wk2-wpt~~	✅ 🧪 api-mac-debug	⏳ wpe-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 vision	⏳ 🧪 mac-wk2	❌ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🧪 vision-wk2	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🛠 tv	⏳ 🧪 mac-intel-wk2
	✅ 🛠 tv-sim	~~🛠 mac-safer-cpp~~
	✅ 🛠 watch
	✅ 🛠 watch-sim

webkit-early-warning-system · 2026-01-29T05:35:10Z

EWS run on previous version of this PR (hash 375f819)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	❌ 🧪 win-tests	🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		🛠 vision-apple
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	⏳ 🛠 wpe-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 vision	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🧪 vision-wk2	✅ 🧪 mac-wk2-stress	✅ 🛠 playstation
	✅ 🛠 tv	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv-sim	✅ 🛠 mac-safer-cpp
	✅ 🛠 watch
	✅ 🛠 watch-sim

alanbaradlay

we should really stop committing tree dumps and use ref tests instead.(I had to rebaseline close to 10K the other day and it was not fun)

Source/WebCore/rendering/RenderTableCell.cpp

webkit-early-warning-system · 2026-01-30T03:26:18Z

EWS run on current version of this PR (hash ef1a9cd)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	~~🛠 win~~	✅ 🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	~~🧪 win-tests~~	✅ 🛠 mac-apple
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe		✅ 🛠 vision-apple
	~~🧪 ios-wk2-wpt~~	✅ 🧪 api-mac-debug	✅ 🛠 wpe-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 vision	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision-sim	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🧪 vision-wk2	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
✅ 🛠 🧪 unsafe-merge	✅ 🛠 tv	~~🧪 mac-intel-wk2~~
	✅ 🛠 tv-sim	~~🛠 mac-safer-cpp~~
	✅ 🛠 watch
	✅ 🛠 watch-sim

karlcow · 2026-01-30T03:26:56Z

we should really stop committing tree dumps and use ref tests instead.(I had to rebaseline close to 10K the other day and it was not fun)

I was missing an -expected.html I removed the tree dumps and added the expected. Thanks for spotting it.

karlcow · 2026-01-30T04:45:38Z

TODO: export the test to WPT.

https://bugs.webkit.org/show_bug.cgi?id=5515 rdar://94163960 Reviewed by Alan Baradlay. Currently for a table of 2 columns and 4 rows. * the first column has a rowspan = 3 (so 2 cells with one covering the first 3 rows) * the second column has 4 cells on 4 rows When specifiying a different bottom border color for each first 3 rows, WebKit is adopting the color of the first cell defined in the second colum for the bottom color of the rowspanned cell instead of the color of the third row like Gecko and Blink do. This patch is fixing and only this. It doesn't fix the more general issue for vertical border shared in between the rowspanned cell and the second column cells. This will need to be fixed in https://webkit.org/b/20260 as it requires a larger architectural change on border segmenting. This didn't have WPT tests before, this is adding one covering this behavior. Tests: imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color-ref.html imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color.html * LayoutTests/imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color-expected.html: Added. * LayoutTests/imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color-ref.html: Added. * LayoutTests/imported/w3c/web-platform-tests/css/css-tables/rowspan-cell-border-after-color.html: Added. * Source/WebCore/rendering/RenderTableCell.cpp: (WebCore::RenderTableCell::computeCollapsedAfterBorder const): Canonical link: https://commits.webkit.org/306471@main

webkit-commit-queue · 2026-01-30T05:26:59Z

Committed 306471@main (c9af451): https://commits.webkit.org/306471@main

Reviewed commits have been landed. Closing PR #57402 and removing active labels.

karlcow · 2026-01-30T05:41:22Z

I also opened w3c/csswg-drafts#13417
because it is not really specified.

karlcow self-assigned this Jan 28, 2026

karlcow added the Tables For bugs specific to tables (both the DOM and rendering issues). label Jan 28, 2026

karlcow requested a review from alanbaradlay January 28, 2026 12:59

karlcow commented Jan 28, 2026

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annevk reviewed Jan 28, 2026

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karlcow force-pushed the 5515-border-collapse-cells branch from e4ede84 to c910942 Compare January 28, 2026 23:52

webkit-ews-buildbot added the merging-blocked Applied to prevent a change from being merged label Jan 29, 2026

karlcow removed the merging-blocked Applied to prevent a change from being merged label Jan 29, 2026

karlcow force-pushed the 5515-border-collapse-cells branch from c910942 to e089c10 Compare January 29, 2026 02:00

webkit-ews-buildbot added the merging-blocked Applied to prevent a change from being merged label Jan 29, 2026

karlcow removed the merging-blocked Applied to prevent a change from being merged label Jan 29, 2026

karlcow force-pushed the 5515-border-collapse-cells branch from e089c10 to 375f819 Compare January 29, 2026 05:35

alanbaradlay approved these changes Jan 30, 2026

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karlcow force-pushed the 5515-border-collapse-cells branch from 375f819 to ef1a9cd Compare January 30, 2026 03:26

karlcow added the unsafe-merge-queue Applied to send a pull request to merge-queue, but skip building and testing label Jan 30, 2026

webkit-commit-queue force-pushed the 5515-border-collapse-cells branch from ef1a9cd to c9af451 Compare January 30, 2026 05:26

webkit-commit-queue merged commit c9af451 into WebKit:main Jan 30, 2026

webkit-commit-queue removed the unsafe-merge-queue Applied to send a pull request to merge-queue, but skip building and testing label Jan 30, 2026

karlcow mentioned this pull request Jan 30, 2026

[css-borders][css-tables] The rowspan cell bottom-border takes the color of the last border shared adjacent cell w3c/csswg-drafts#13417

Open

karlcow mentioned this pull request Jan 30, 2026

WebKit export of https://bugs.webkit.org/show_bug.cgi?id=5515 (#281) web-platform-tests/wpt#57442

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