tor-browser

commit 2786c0f5b896a22b0fd61f60d91bedb8177b9673
parent b6e55d9685d91621df92b8aad0c368e3d761ad94
Author: Tiaan Louw <tlouw@mozilla.com>
Date:   Fri, 17 Oct 2025 12:11:21 +0000

Bug 1924233 - Part 1 - Handle "position-visibility: no-overflow" r=emilio,layout-anchor-positioning-reviewers,layout-reviewers,dshin

Check for "no-overflow" after all fallbacks were tried and then "hide"
the frame if its still overflowing and value is set to "no-overflow".

This test is still failing and will be addressed in part 2 of this
patch:
css/css-anchor-position/position-visibility-no-overflow-scroll.html

Differential Revision: https://phabricator.services.mozilla.com/D268525

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
12
++++++++++++
D
testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-nested.html.ini
 | 
2
--
D
testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-stacked-child.html.ini
 | 
2
--
D
testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-without-anchor.html.ini
 | 
2
--
D
testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow.html.ini
 | 
2
--

5 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -935,6 +935,10 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
     }
   }
 
+  // Assume we *are* overflowing the CB and if we find a fallback that doesn't
+  // overflow, we set this to false and break the loop.
+  bool isOverflowingCB = true;
+
   do {
     AutoFallbackStyleSetter fallback(aKidFrame, currentFallbackStyle);
     const nsRect usedCb = [&] {
@@ -1184,6 +1188,7 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
 
     if (usedCb.Contains(aKidFrame->GetRect()) && aStatus.IsComplete()) {
       // We don't overflow our CB, no further fallback needed.
+      isOverflowingCB = false;
       break;
     }
 
@@ -1197,6 +1202,13 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
     aStatus.Reset();
   } while (true);
 
+  // If author asked for `position-visibility: no-overflow` and we overflow
+  // `usedCB`, treat as "strongly hidden".
+  aKidFrame->AddOrRemoveStateBits(
+      NS_FRAME_POSITION_VISIBILITY_HIDDEN,
+      isOverflowingCB && aKidFrame->StylePosition()->mPositionVisibility ==
+                             StylePositionVisibility::NO_OVERFLOW);
+
   if (currentFallbackIndex) {
     aKidFrame->SetProperty(nsIFrame::LastSuccessfulPositionFallback(),
                            *currentFallbackIndex);
diff --git a/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-nested.html.ini b/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-nested.html.ini
@@ -1,2 +0,0 @@
-[position-visibility-no-overflow-nested.html]
-  expected: FAIL
diff --git a/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-stacked-child.html.ini b/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-stacked-child.html.ini
@@ -1,2 +0,0 @@
-[position-visibility-no-overflow-stacked-child.html]
-  expected: FAIL
diff --git a/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-without-anchor.html.ini b/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow-without-anchor.html.ini
@@ -1,2 +0,0 @@
-[position-visibility-no-overflow-without-anchor.html]
-  expected: FAIL
diff --git a/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow.html.ini b/testing/web-platform/meta/css/css-anchor-position/position-visibility-no-overflow.html.ini
@@ -1,2 +0,0 @@
-[position-visibility-no-overflow.html]
-  expected: FAIL