tor-browser

commit 7cd59a61c6a01fdd88254a2d880191ebcd3865ab
parent e53645f574d4cccad40a679ab9cb3cf0fbbcf110
Author: Timothy Nikkel <tnikkel@gmail.com>
Date:   Wed, 26 Nov 2025 13:04:52 +0000

Bug 1988030. Allow passing a limit ancestor to DisplayPortUtils::OneStepInASRChain that we don't walk past. r=hiro,layout-reviewers

With CSS anchor pos we know that the anchor is in the containing block of the anchored content. We use that to limit a walk up the frame tree in subsequent patches and make the computation simpler. So we need OneStepInASRChain to obey that limit too.

Differential Revision: https://phabricator.services.mozilla.com/D271804

Diffstat:
M
layout/base/DisplayPortUtils.cpp
 | 
14
++++++++++++--
M
layout/base/DisplayPortUtils.h
 | 
6
++++--

2 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/layout/base/DisplayPortUtils.cpp b/layout/base/DisplayPortUtils.cpp
@@ -856,7 +856,8 @@ nsIFrame* DisplayPortUtils::OneStepInAsyncScrollableAncestorChain(
   return nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
 }
 
-nsIFrame* DisplayPortUtils::OneStepInASRChain(nsIFrame* aFrame) {
+nsIFrame* DisplayPortUtils::OneStepInASRChain(
+    nsIFrame* aFrame, nsIFrame* aLimitAncestor /* = nullptr */) {
   // This mirrors one iteration of GetNearestScrollableOrOverflowClipFrame in
   // nsLayoutUtils.cpp as called by nsLayoutUtils::GetASRAncestorFrame. They
   // should be kept in sync. See that function for comments about the structure
@@ -867,9 +868,18 @@ nsIFrame* DisplayPortUtils::OneStepInASRChain(nsIFrame* aFrame) {
   nsIFrame* anchor = nullptr;
   while ((anchor =
               AnchorPositioningUtils::GetAnchorThatFrameScrollsWith(aFrame))) {
+    MOZ_ASSERT_IF(aLimitAncestor,
+                  nsLayoutUtils::IsProperAncestorFrameConsideringContinuations(
+                      aLimitAncestor, anchor));
     aFrame = anchor;
   }
-  return nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
+  nsIFrame* parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(aFrame);
+  if (aLimitAncestor && parent &&
+      (parent == aLimitAncestor ||
+       parent->FirstContinuation() == aLimitAncestor->FirstContinuation())) {
+    return nullptr;
+  }
+  return parent;
 }
 
 void DisplayPortUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(
diff --git a/layout/base/DisplayPortUtils.h b/layout/base/DisplayPortUtils.h
@@ -294,9 +294,11 @@ class DisplayPortUtils {
    * ASR frame to the next. Rather this walks all frame types, taking only one
    * ancestor step per call. Note that a frame returned from this function could
    * generate two ASRs: an inner one corresponding to an activated scroll frame,
-   * and an outer one corresponding to sticky pos.
+   * and an outer one corresponding to sticky pos. Returns null if we hit
+   * aLimitAncestor.
    */
-  static nsIFrame* OneStepInASRChain(nsIFrame* aFrame);
+  static nsIFrame* OneStepInASRChain(nsIFrame* aFrame,
+                                     nsIFrame* aLimitAncestor = nullptr);
 
   /**
    * Sets a zero margin display port on all proper ancestors of aFrame that