From 0f9f507b46ec416b4e05c876a329df33d3d7a48f Mon Sep 17 00:00:00 2001
From: Oriol Brufau <obrufau@igalia.com>
Date: Fri, 5 Sep 2025 16:49:21 +0200
Subject: [PATCH] layout: Fix `scrollParent` to skip ancestors with `display:
 contents` (#39153)

When encountering such an ancestor, we were returning null instead of
skipping it.

Testing: Adding new subtest for this. And while I'm at it, another one
for the root element, unrelated to this fix.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
---
 components/layout/query.rs                       | 7 +++++--
 tests/wpt/meta/MANIFEST.json                     | 2 +-
 tests/wpt/tests/css/cssom-view/scrollParent.html | 9 ++++++++-
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/components/layout/query.rs b/components/layout/query.rs
index 0a35c24e344..c4630f90f9a 100644
--- a/components/layout/query.rs
+++ b/components/layout/query.rs
@@ -701,10 +701,13 @@ pub(crate) fn process_scroll_parent_query(
             continue;
         };
 
-        let (ancestor_style, ancestor_flags) = ancestor_layout_box
+        let Some((ancestor_style, ancestor_flags)) = ancestor_layout_box
             .with_base_flat(|base| vec![(base.style.clone(), base.base_fragment_info.flags)])
             .first()
-            .cloned()?;
+            .cloned()
+        else {
+            continue;
+        };
 
         let is_containing_block = match current_position_value {
             Position::Static | Position::Relative | Position::Sticky => {
diff --git a/tests/wpt/meta/MANIFEST.json b/tests/wpt/meta/MANIFEST.json
index 08490dc7f0a..1edd12daeed 100644
--- a/tests/wpt/meta/MANIFEST.json
+++ b/tests/wpt/meta/MANIFEST.json
@@ -630047,7 +630047,7 @@
       ]
      ],
      "scrollParent.html": [
-      "344ee522ef2664e0b963e79812074f08f343f5bf",
+      "b1c6898af349691d357a3d39cc8fd8e578612d94",
       [
        null,
        {}
diff --git a/tests/wpt/tests/css/cssom-view/scrollParent.html b/tests/wpt/tests/css/cssom-view/scrollParent.html
index 344ee522ef2..b1c6898af34 100644
--- a/tests/wpt/tests/css/cssom-view/scrollParent.html
+++ b/tests/wpt/tests/css/cssom-view/scrollParent.html
@@ -57,6 +57,10 @@
           <div id="hidden" class="hidden">
             <div id="childOfHidden"></div>
           </div>
+          <!-- No box with `display: contents` -->
+          <div style="display: contents">
+            <div id="childOfDisplayContents"></div>
+          </div>
         </div>
       </div>
     </div>
@@ -82,6 +86,9 @@ test(() => { assert_equals(fixedContainedByRoot.scrollParent, document.scrolling
     "scrollParent of fixed element contained within root is document scrolling element.");
 test(() => { assert_equals(document.body.scrollParent, null); },
     "scrollParent of body is null.");
-
+test(() => { assert_equals(document.documentElement.scrollParent, null); },
+    "scrollParent of root is null.");
+test(() => { assert_equals(childOfDisplayContents.scrollParent, scroller1); },
+    "scrollParent skips ancestors with `display: contents`.");
 </script>
 </html>