tor-browser

commit 94b9e3475381144051ccf17b900895817cb50dc9
parent 827aa14e00b3b4003214d95aed3a39876d5ece72
Author: Timothy Nikkel <tnikkel@gmail.com>
Date:   Wed, 26 Nov 2025 13:55:42 +0000

Bug 1988032. Assign the ASR of the anchor to the anchored content. r=hiro,layout-reviewers,layout-anchor-positioning-reviewers,emilio

Differential Revision: https://phabricator.services.mozilla.com/D271807

Diffstat:
M
layout/generic/nsIFrame.cpp
 | 
38
++++++++++++++++++++++++++++++++++++--

1 file changed, 36 insertions(+), 2 deletions(-)
diff --git a/layout/generic/nsIFrame.cpp b/layout/generic/nsIFrame.cpp
@@ -4421,6 +4421,41 @@ void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
   if (savedOutOfFlowData) {
     aBuilder->SetBuildingInvisibleItems(false);
 
+    nsIFrame* scrollsWithAnchor = nullptr;
+    if (aBuilder->IsPaintingToWindow() &&
+        // If we are in view transition capture we get a null asr no matter
+        // what, so don't bother checking for async scrolling with a CSS anchor
+        // pos anchor.
+        !aBuilder->IsInViewTransitionCapture() &&
+        child->IsAbsolutelyPositioned(disp)) {
+      scrollsWithAnchor =
+          AnchorPositioningUtils::GetAnchorThatFrameScrollsWith(child);
+    }
+
+    const ActiveScrolledRoot* asr =
+        savedOutOfFlowData->mContainingBlockActiveScrolledRoot;
+
+#ifdef DEBUG
+    if (aBuilder->IsPaintingToWindow()) {
+      if (savedOutOfFlowData->mContainingBlockInViewTransitionCapture) {
+        MOZ_ASSERT(asr == nullptr);
+        MOZ_ASSERT(aBuilder->IsInViewTransitionCapture());
+      } else {
+        MOZ_ASSERT(
+            (asr ? asr->mFrame : nullptr) ==
+            nsLayoutUtils::GetASRAncestorFrame(child->GetParent(), aBuilder));
+      }
+    }
+#endif
+
+    if (scrollsWithAnchor) {
+      asr = DisplayPortUtils::ActivateDisplayportOnASRAncestors(
+          scrollsWithAnchor, child->GetParent(), asr, aBuilder);
+
+      // TODO should we set the scroll parent id too?
+      // https://github.com/w3c/csswg-drafts/issues/12042
+    }
+
     if (aBuilder->IsInViewTransitionCapture()) {
       if (!savedOutOfFlowData->mContainingBlockInViewTransitionCapture) {
         clipState.Clear();
@@ -4432,8 +4467,7 @@ void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
     } else {
       clipState.SetClipChainForContainingBlockDescendants(
           savedOutOfFlowData->mContainingBlockClipChain);
-      asrSetter.SetCurrentActiveScrolledRoot(
-          savedOutOfFlowData->mContainingBlockActiveScrolledRoot);
+      asrSetter.SetCurrentActiveScrolledRoot(asr);
       asrSetter.SetCurrentScrollParentId(savedOutOfFlowData->mScrollParentId);
     }
     MOZ_ASSERT(awayFromCommonPath,