tor-browser

commit 326431509879e00fc49a1040c76e6416ea4866b3
parent 64788e622c1ef22e73a15dee35034ee4364a000e
Author: Jonathan Kew <jkew@mozilla.com>
Date:   Mon,  5 Jan 2026 17:56:37 +0000

Bug 2008537 - Use "safe" behavior by default when applying implicit anchor-center alignment. r=layout-anchor-positioning-reviewers,layout-reviewers,emilio,dshin

Differential Revision: https://phabricator.services.mozilla.com/D277892

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
6
++++--

1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -865,11 +865,13 @@ static nscoord OffsetToAlignedStaticPos(
           ? aKidReflowInput.mStylePosition->mJustifySelf._0
           : aKidReflowInput.mStylePosition->mAlignSelf._0;
   if (aNonAutoAlignParams && !safetyBits &&
-      rawAlignConst != StyleAlignFlags::AUTO) {
+      (rawAlignConst != StyleAlignFlags::AUTO ||
+       alignConst == StyleAlignFlags::ANCHOR_CENTER)) {
     // No `safe` or `unsafe` specified - "in-between" behaviour for relevant
     // alignment values: https://drafts.csswg.org/css-position-3/#abspos-layout
     // Skip if the raw self alignment for this element is `auto` to preserve
-    // legacy behaviour.
+    // legacy behaviour, except in the case where the resolved value is
+    // anchor-center (where "legacy behavior" is not a concern).
     // Follows https://drafts.csswg.org/css-align-3/#auto-safety-position
     const auto cbSize = aAbsPosCBSize.Size(aAbsPosCBAxis, aAbsPosCBWM);
     // IMCB stands for "Inset-Modified Containing Block."