tor-browser

commit 81f86c8b2f7e9ac0b65eeb9e066176a35843a78a
parent 11aa87560528683e19d203586ca6fc6fac68c8e8
Author: Jonathan Kew <jkew@mozilla.com>
Date:   Tue, 30 Dec 2025 19:10:22 +0000

Bug 2006959 - Even if there's no anchor-positioning cache, we need to save and potentially restore the target's firstTryNormalPosition. r=layout-anchor-positioning-reviewers,layout-reviewers,emilio

Differential Revision: https://phabricator.services.mozilla.com/D277619

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
21
+++++++++++----------
D
testing/web-platform/meta/css/css-anchor-position/try-tactic-back-to-base.html.ini
 | 
3
---

2 files changed, 11 insertions(+), 13 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -1634,6 +1634,10 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
     aKidFrame->DidReflow(aPresContext, &kidReflowInput);
 
     [&]() {
+      const auto position = aKidFrame->GetPosition();
+      if (!firstTryNormalPosition) {
+        firstTryNormalPosition = Some(position);
+      }
       if (!aAnchorPosResolutionCache) {
         return;
       }
@@ -1653,12 +1657,8 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
             aAnchorPosResolutionCache->mDefaultAnchorCache);
       }();
       // Apply the hypothetical scroll offset.
-      const auto position = aKidFrame->GetPosition();
       // Set initial scroll position. TODO(dshin, bug 1987962): Need
       // additional work for remembered scroll offset here.
-      if (!firstTryNormalPosition) {
-        firstTryNormalPosition = Some(position);
-      }
       aKidFrame->SetProperty(nsIFrame::NormalPositionProperty(), position);
       if (offset != nsPoint{}) {
         aKidFrame->SetPosition(position - offset);
@@ -1728,14 +1728,13 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
       }
     }
 
-    // Try with the next  fallback.
+    // Try with the next fallback.
     aKidFrame->AddStateBits(NS_FRAME_IS_DIRTY);
     aStatus.Reset();
   } while (true);
 
   [&]() {
-    if (!isOverflowingCB || !aAnchorPosResolutionCache ||
-        !firstTryNormalPosition) {
+    if (!isOverflowingCB || !firstTryNormalPosition) {
       return;
     }
     // We gave up applying fallbacks. Recover previous values, if changed, and
@@ -1749,9 +1748,11 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
       aKidFrame->SetProperty(nsIFrame::NormalPositionProperty(),
                              normalPosition);
     }
-    const auto position =
-        normalPosition -
-        aAnchorPosResolutionCache->mReferenceData->mDefaultScrollShift;
+    auto position = normalPosition;
+    if (aAnchorPosResolutionCache) {
+      position -=
+          aAnchorPosResolutionCache->mReferenceData->mDefaultScrollShift;
+    }
     const auto oldPosition = aKidFrame->GetPosition();
     if (position == oldPosition) {
       return;
diff --git a/testing/web-platform/meta/css/css-anchor-position/try-tactic-back-to-base.html.ini b/testing/web-platform/meta/css/css-anchor-position/try-tactic-back-to-base.html.ini
@@ -1,3 +0,0 @@
-[try-tactic-back-to-base.html]
-  [Should use base values when nothing fits]
-    expected: FAIL