tor-browser

commit d8bd94aa646aa77a24a487be85480a479341d8eb
parent a804b5349956a4ce2002bebae629b152afd30ca2
Author: Emilio Cobos Álvarez <emilio@crisal.io>
Date:   Fri,  9 Jan 2026 16:00:07 +0000

Bug 2009424 - Make containing block adjustment work for default anchored frames. r=layout-anchor-positioning-reviewers,layout-reviewers,dshin

Differential Revision: https://phabricator.services.mozilla.com/D278497

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
29
+++++++++++++++--------------
D
testing/web-platform/meta/css/css-anchor-position/anchor-scroll-position-try-007.html.ini
 | 
5
-----

2 files changed, 15 insertions(+), 19 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -1326,6 +1326,7 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
       // The current containing block, with ongoing modifications.
       // Starts as a local containing block.
       nsRect containingBlock = aOriginalContainingBlockRect;
+      nsRect scrollableContainingBlock = aOriginalScrollableContainingBlockRect;
       const auto defaultAnchorInfo = [&]() -> Maybe<AnchorPosInfo> {
         if (!aAnchorPosResolutionCache) {
           return Nothing{};
@@ -1341,6 +1342,18 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
         containingBlock = aOriginalScrollableContainingBlockRect;
       }
 
+      if (ViewportFrame* viewport = do_QueryFrame(aDelegatingFrame)) {
+        if (IsSnapshotContainingBlock(aKidFrame)) {
+          return ContainingBlockRect{
+              dom::ViewTransition::SnapshotContainingBlockRect(
+                  viewport->PresContext())};
+        }
+        MOZ_ASSERT(aOriginalScrollableContainingBlockRect ==
+                   aOriginalContainingBlockRect);
+        containingBlock = scrollableContainingBlock =
+            viewport->GetContainingBlockAdjustedForScrollbars(aReflowInput);
+      }
+
       // https://drafts.csswg.org/css-position/#original-cb
       // Handle grid-based adjustment first...
       if (isGrid) {
@@ -1382,24 +1395,12 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
           aAnchorPosResolutionCache->mReferenceData->mScrollCompensatedSides =
               GetScrollCompensatedSidesFor(resolvedPositionArea);
           return ContainingBlockRect{
-              offset, resolvedPositionArea,
-              aOriginalScrollableContainingBlockRect,
+              offset, resolvedPositionArea, scrollableContainingBlock,
               // Unscroll the CB by canceling out the previously applied
               // scroll offset (See above), the offset will be applied later.
               scrolledAnchorCb + offset};
         }
-        return ContainingBlockRect{aOriginalScrollableContainingBlockRect,
-                                   containingBlock};
-      }
-
-      if (ViewportFrame* viewport = do_QueryFrame(aDelegatingFrame)) {
-        if (!IsSnapshotContainingBlock(aKidFrame)) {
-          return ContainingBlockRect{
-              viewport->GetContainingBlockAdjustedForScrollbars(aReflowInput)};
-        }
-        return ContainingBlockRect{
-            dom::ViewTransition::SnapshotContainingBlockRect(
-                viewport->PresContext())};
+        return ContainingBlockRect{scrollableContainingBlock, containingBlock};
       }
       return ContainingBlockRect{containingBlock};
     }();
diff --git a/testing/web-platform/meta/css/css-anchor-position/anchor-scroll-position-try-007.html.ini b/testing/web-platform/meta/css/css-anchor-position/anchor-scroll-position-try-007.html.ini
@@ -1,5 +0,0 @@
-[anchor-scroll-position-try-007.html]
-  [Should use the third position option with enough space left]
-    expected:
-      if os == "android": PASS
-      FAIL