tor-browser

commit 6eb2a1b52bbbbdb43cc7ee8b64854f3e8a18b485
parent 67791fd91e9488c070eb9320a7e2ce049150c8f5
Author: David Shin <dshin@mozilla.com>
Date:   Mon,  8 Dec 2025 16:58:10 +0000

Bug 2004040: Properly nudge overflowing abspos elements into IMCB. r=layout-anchor-positioning-reviewers,layout-reviewers,emilio

Differential Revision: https://phabricator.services.mozilla.com/D275139

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
12
+++++++-----
D
testing/web-platform/meta/css/css-anchor-position/anchor-center-overflow-001.html.ini
 | 
2
--
D
testing/web-platform/meta/css/css-anchor-position/anchor-center-overflow-004.html.ini
 | 
2
--

3 files changed, 7 insertions(+), 9 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -867,17 +867,19 @@ static nscoord OffsetToAlignedStaticPos(
       // 1. We fit inside the IMCB, no action needed.
     } else if (kidSize <= overflowLimitRectEnd - overflowLimitRectStart) {
       // 2. We overflowed IMCB, try to cover IMCB completely, if it's not.
-      if (kidEnd < imcbEnd) {
-        offset += imcbEnd - kidEnd;
-      } else if (kidStart > imcbStart) {
-        offset -= kidStart - imcbStart;
-      } else {
+      if (kidStart <= imcbStart && kidEnd >= imcbEnd) {
         // IMCB already covered, ensure that we aren't escaping the limit rect.
         if (kidStart < overflowLimitRectStart) {
           offset += overflowLimitRectStart - kidStart;
         } else if (kidEnd > overflowLimitRectEnd) {
           offset -= kidEnd - overflowLimitRectEnd;
         }
+      } else if (kidEnd < imcbEnd && kidStart < imcbStart) {
+        // Space to end, overflowing on start - nudge to end.
+        offset += std::min(imcbStart - kidStart, imcbEnd - kidEnd);
+      } else if (kidStart > imcbStart && kidEnd > imcbEnd) {
+        // Space to start, overflowing on end - nudge to start.
+        offset -= std::min(kidEnd - imcbEnd, kidStart - imcbStart);
       }
     } else {
       // 3. We'll overflow the limit rect. Start align the subject int overflow
diff --git a/testing/web-platform/meta/css/css-anchor-position/anchor-center-overflow-001.html.ini b/testing/web-platform/meta/css/css-anchor-position/anchor-center-overflow-001.html.ini
@@ -1,2 +0,0 @@
-[anchor-center-overflow-001.html]
-  expected: FAIL
diff --git a/testing/web-platform/meta/css/css-anchor-position/anchor-center-overflow-004.html.ini b/testing/web-platform/meta/css/css-anchor-position/anchor-center-overflow-004.html.ini
@@ -1,2 +0,0 @@
-[anchor-center-overflow-004.html]
-  expected: FAIL