layout: Take sticky offsets into account for offset queries (#39385)

`offsetLeft` and `offsetTop` were ignoring that sticky positioned boxes
can be shifted out of their normal position.

Testing: Various test improvements.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/layout/fragment_tree/box_fragment.rs

@@ -569,4 +569,8 @@ impl BoxFragment {
             _ => false,
         }
     }
+
+    pub(crate) fn spatial_tree_node(&self) -> Option<ScrollTreeNodeId> {
+        *self.spatial_tree_node.borrow()
+    }
 }

components/layout/layout_impl.rs

@@ -322,7 +322,12 @@ impl Layout for LayoutThread {
     #[servo_tracing::instrument(skip_all)]
     fn query_offset_parent(&self, node: TrustedNodeAddress) -> OffsetParentResponse {
         let node = unsafe { ServoLayoutNode::new(&node) };
-        process_offset_parent_query(node).unwrap_or_default()
+        let stacking_context_tree = self.stacking_context_tree.borrow();
+        let stacking_context_tree = stacking_context_tree
+            .as_ref()
+            .expect("Should always have a StackingContextTree for offset parent queries");
+        process_offset_parent_query(&stacking_context_tree.compositor_info.scroll_tree, node)
+            .unwrap_or_default()
     }
 
     #[servo_tracing::instrument(skip_all)]
@@ -1608,26 +1613,26 @@ impl ReflowPhases {
     /// so [`ReflowPhases::empty()`] implies that.
     fn necessary(reflow_goal: &ReflowGoal) -> Self {
         match reflow_goal {
-            ReflowGoal::UpdateTheRendering | ReflowGoal::UpdateScrollNode(..) => {
-                Self::StackingContextTreeConstruction | Self::DisplayListConstruction
-            },
             ReflowGoal::LayoutQuery(query) => match query {
                 QueryMsg::NodesFromPointQuery => {
                     Self::StackingContextTreeConstruction | Self::DisplayListConstruction
                 },
                 QueryMsg::BoxArea |
                 QueryMsg::BoxAreas |
+                QueryMsg::ElementsFromPoint |
+                QueryMsg::OffsetParentQuery |
                 QueryMsg::ResolvedStyleQuery |
-                QueryMsg::ScrollingAreaOrOffsetQuery |
-                QueryMsg::ElementsFromPoint => Self::StackingContextTreeConstruction,
+                QueryMsg::ScrollingAreaOrOffsetQuery => Self::StackingContextTreeConstruction,
                 QueryMsg::ClientRectQuery |
                 QueryMsg::ElementInnerOuterTextQuery |
                 QueryMsg::InnerWindowDimensionsQuery |
-                QueryMsg::OffsetParentQuery |
-                QueryMsg::ScrollParentQuery |
                 QueryMsg::ResolvedFontStyleQuery |
-                QueryMsg::TextIndexQuery |
-                QueryMsg::StyleQuery => Self::empty(),
+                QueryMsg::ScrollParentQuery |
+                QueryMsg::StyleQuery |
+                QueryMsg::TextIndexQuery => Self::empty(),
+            },
+            ReflowGoal::UpdateScrollNode(..) | ReflowGoal::UpdateTheRendering => {
+                Self::StackingContextTreeConstruction | Self::DisplayListConstruction
             },
         }
     }

components/layout/query.rs

@@ -64,8 +64,7 @@ fn root_transform_for_layout_node(
         .first()
         .and_then(Fragment::retrieve_box_fragment)?
         .borrow();
-    let scroll_tree_node_id = box_fragment.spatial_tree_node.borrow();
-    let scroll_tree_node_id = (*scroll_tree_node_id)?;
+    let scroll_tree_node_id = box_fragment.spatial_tree_node()?;
     Some(scroll_tree.cumulative_node_to_root_transform(scroll_tree_node_id))
 }
 
@@ -565,7 +564,10 @@ fn offset_parent_fragments(node: ServoLayoutNode<'_>) -> Option<OffsetParentFrag
 }
 
 #[inline]
-pub fn process_offset_parent_query(node: ServoLayoutNode<'_>) -> Option<OffsetParentResponse> {
+pub fn process_offset_parent_query(
+    scroll_tree: &ScrollTree,
+    node: ServoLayoutNode<'_>,
+) -> Option<OffsetParentResponse> {
     // Only consider the first fragment of the node found as per a
     // possible interpretation of the specification: "[...] return the
     // y-coordinate of the top border edge of the first CSS layout box
@@ -588,6 +590,16 @@ pub fn process_offset_parent_query(node: ServoLayoutNode<'_>) -> Option<OffsetPa
         .first()
         .cloned()?;
     let mut border_box = fragment.cumulative_box_area_rect(BoxAreaType::Border)?;
+    let cumulative_sticky_offsets = fragment
+        .retrieve_box_fragment()
+        .and_then(|box_fragment| box_fragment.borrow().spatial_tree_node())
+        .map(|node_id| {
+            scroll_tree
+                .cumulative_sticky_offsets(node_id)
+                .map(Au::from_f32_px)
+                .cast_unit()
+        });
+    border_box = border_box.translate(cumulative_sticky_offsets.unwrap_or_default());
 
     // 2.  If the offsetParent of the element is null return the x-coordinate of the left
     //     border edge of the first CSS layout box associated with the element, relative to
@@ -638,7 +650,18 @@ pub fn process_offset_parent_query(node: ServoLayoutNode<'_>) -> Option<OffsetPa
         }
     } else {
         parent_fragment.offset_by_containing_block(&parent_fragment.padding_rect())
-    };
+    }
+    .translate(
+        cumulative_sticky_offsets
+            .and_then(|_| parent_fragment.spatial_tree_node())
+            .map(|node_id| {
+                scroll_tree
+                    .cumulative_sticky_offsets(node_id)
+                    .map(Au::from_f32_px)
+                    .cast_unit()
+            })
+            .unwrap_or_default(),
+    );
 
     border_box = border_box.translate(-parent_offset_rect.origin.to_vector());