292754 2025-05-08 18:40:08 -0700 [css-anchor-position-1] Wrong assumption that if an anchor doesn't exist, it will not exist again in the future 2025-07-23 13:18:22 -0700 1 1 1 Unclassified WebKit CSS WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED https://github.com/web-platform-tests/wpt/pull/53936 InRadar P2 Normal --- 291856 1 kiet.ho kiet.ho fantasai.bugs kiet.ho koivisto webkit-bug-importer oldest_to_newest 2116014 0 475172 kiet.ho 2025-05-08 18:40:08 -0700 Created attachment 475172 Test case Consider this pseudo-HTML (see attached HTML for a fully working test case) <div anchor-name: --a /> // A <div position-anchor: --a position-area: top left> // B <div anchor-name: --c ></div> // C </div> <div position-anchor: --c position-area: top right /> // D A is an anchor. B is anchor-positioned, and its child, C, is an anchor. D is anchor-positioned. Style/layout interleaving timeline: * First style resolution: A is discovered as an anchor. B is discovered as anchor-positioned to A. D is discovered as anchor-positioned to C. Crucially, there's an optimization where if an anchor-positioned element hasn't been resolved yet, we skip descending into its children until the next style resolution, when the anchor-positioned element has been resolved. So here, we don't discover C as an anchor (because its parent, B, is anchor-positioned and not resolved yet) * First layout: A is laid out. Post processing task links B to A, but doesn't link D to anything (because D depends on C, but the code hasn't seen C yet) * Second style resolution: B, D are marked as resolved. Since B is resolved, the code descends into B and discovers C as an anchor. BUT, since D are already marked as resolved, we don't go back and fix that C actually exists. * Second layout: B is laid out Result: the code treats C as if it doesn't exist. 2116015 1 webkit-bug-importer 2025-05-08 18:40:17 -0700 <rdar://problem/150975368> 2131316 2 kiet.ho 2025-07-18 19:09:05 -0700 Pull request: https://github.com/WebKit/WebKit/pull/48282 2132124 3 ews-feeder 2025-07-23 11:25:40 -0700 Committed 297797@main (1996b78d76bf): <https://commits.webkit.org/297797@main> Reviewed commits have been landed. Closing PR #48282 and removing active labels. 2132126 4 kiet.ho 2025-07-23 11:48:08 -0700 Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/53936 2132147 5 kiet.ho 2025-07-23 13:18:22 -0700 *** Bug 294642 has been marked as a duplicate of this bug. *** 475172 2025-05-08 18:40:08 -0700 2025-05-08 18:40:08 -0700 Test case position-area-display-change-anchor-positioned-in-anchor.html text/html 1980 kiet.ho PCFET0NUWVBFIGh0bWw+Cgo8dGl0bGU+VGVzdHMgdGhhdCBYWFg8L3RpdGxlPgoKPGxpbmsgcmVs PSJoZWxwIiBocmVmPSJodHRwczovL2RyYWZ0cy5jc3N3Zy5vcmcvY3NzLWFuY2hvci1wb3NpdGlv bi0xLyNwb3NpdGlvbi1hcmVhIj4KPGxpbmsgcmVsPSJhdXRob3IiIGhyZWY9Im1haWx0bzpraWV0 LmhvQGFwcGxlLmNvbSI+CjxsaW5rIHJlbD0ibWF0Y2giIGhyZWY9InJlZmVyZW5jZS9wb3NpdGlv bi1hcmVhLWRpc3BsYXktY2hhbmdlLXJlZi5odG1sIj4KCjxzY3JpcHQgc3JjPSIvY29tbW9uL3Jl ZnRlc3Qtd2FpdC5qcyI+PC9zY3JpcHQ+CjxzY3JpcHQgc3JjPSIvY29tbW9uL3JlbmRlcmluZy11 dGlscy5qcyI+PC9zY3JpcHQ+Cgo8c3R5bGU+CiAgLmNvbnRhaW5pbmctYmxvY2sgewogICAgcG9z aXRpb246IHJlbGF0aXZlOwogICAgd2lkdGg6IDE1MHB4OwogICAgaGVpZ2h0OiAxNTBweDsKICB9 CgogIC5jZWxsIHsKICAgIHdpZHRoOiA1MHB4OwogICAgaGVpZ2h0OiA1MHB4OwogIH0KCiAgI2Fu Y2hvci1jZWxsLTEgewogICAgcG9zaXRpb246IGFic29sdXRlOwogICAgdG9wOiA1MHB4OwogICAg bGVmdDogNTBweDsKCiAgICBhbmNob3ItbmFtZTogLS1hbmNob3I7CgogICAgYmFja2dyb3VuZDog Z3JlZW47CiAgfQoKICAjYW5jaG9yLWNlbGwtMiB7CiAgICBhbmNob3ItbmFtZTogLS1hbmNob3It MjsKICB9CgogIC5hbmNob3ItcG9zaXRpb25lZC1jZWxsIHsKICAgIHBvc2l0aW9uOiBhYnNvbHV0 ZTsKICB9CgogICN0YXJnZXQtMSB7CiAgICBwb3NpdGlvbi1hbmNob3I6IC0tYW5jaG9yOwogICAg cG9zaXRpb24tYXJlYTogdG9wIHJpZ2h0OwoKICAgIC8qIFdpbGwgYmUgY2hhbmdlZCB0byAnYmxv Y2snICovCiAgICAvKiBkaXNwbGF5OiBub25lOyAqLwogIH0KCiAgI3RhcmdldC0yIHsKICAgIHBv c2l0aW9uLWFuY2hvcjogLS1hbmNob3ItMjsKICAgIHBvc2l0aW9uLWFyZWE6IGJvdHRvbSByaWdo dDsKCiAgICAvKiBXaWxsIGJlIGNoYW5nZWQgdG8gJ3Zpc2libGUnICovCiAgICAvKiB2aXNpYmls aXR5OiBoaWRkZW47ICovCiAgfQoKICAuYmx1ZS1iYWNrZ3JvdW5kIHsKICAgIGJhY2tncm91bmQ6 IGJsdWU7CiAgfQoKICAuY3lhbi1iYWNrZ3JvdW5kIHsKICAgIGJhY2tncm91bmQ6IGN5YW47CiAg fQo8L3N0eWxlPgoKPGJvZHk+CiAgPHA+VGhlcmUgc2hvdWxkIGJlIFhYWDwvcD4KCiAgPGRpdiBj bGFzcz0iY29udGFpbmluZy1ibG9jayI+CiAgICA8ZGl2IGNsYXNzPSJjZWxsIiBpZD0iYW5jaG9y LWNlbGwtMSI+PC9kaXY+CgogICAgPGRpdiBjbGFzcz0iY2VsbCBhbmNob3ItcG9zaXRpb25lZC1j ZWxsIiBpZD0idGFyZ2V0LTEiPgogICAgICA8ZGl2IGNsYXNzPSJjZWxsIGJsdWUtYmFja2dyb3Vu ZCIgaWQ9ImFuY2hvci1jZWxsLTIiPjwvZGl2PgogICAgPC9kaXY+CgogICAgPGRpdiBjbGFzcz0i Y2VsbCBhbmNob3ItcG9zaXRpb25lZC1jZWxsIiBpZD0idGFyZ2V0LTIiPgogICAgICAgIDxkaXYg Y2xhc3M9ImNlbGwgY3lhbi1iYWNrZ3JvdW5kIj48L2Rpdj4KICAgIDwvZGl2PgogIDwvZGl2PgoK ICA8IS0tIDxzY3JpcHQ+CiAgICAvLyBBbGwgdGFyZ2V0cyBzaG91bGQgaW5pdGlhbGx5IGJlIGhp ZGRlbi4KICAgIHdhaXRGb3JBdExlYXN0T25lRnJhbWUoKS50aGVuKCgpID0+IHsKICAgICAgLy8g Q2hhbmdlIHRhcmdldHMgdG8gYmUgdmlzaWJsZS4KICAgICAgZG9jdW1lbnQuZ2V0RWxlbWVudEJ5 SWQoJ3RhcmdldC0xJykuc3R5bGUuZGlzcGxheSA9ICdibG9jayc7CiAgICAgIGRvY3VtZW50Lmdl dEVsZW1lbnRCeUlkKCd0YXJnZXQtMicpLnN0eWxlLnZpc2liaWxpdHkgPSAndmlzaWJsZSc7Cgog ICAgICB3YWl0Rm9yQXRMZWFzdE9uZUZyYW1lKCkudGhlbigoKSA9PiB7CiAgICAgICAgLy8gQWxs IHRhcmdldHMgc2hvdWxkIGJlIHZpc2libGUgbm93LgogICAgICAgIHRha2VTY3JlZW5zaG90KCk7 CiAgICAgIH0pOwogICAgfSk7CiAgPC9zY3JpcHQ+IC0tPgo8L2JvZHk+