Auto merge of #26012 - mrobinson:scrolling-overflow-cb, r=nox

layout_2020: Use the containing block more when calculating scrolling overflow

When calculating scrolling overflow calculation we cannot currently use
the actual containing block in all cases. This change increases the
amount that we do use the containing block.

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---
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- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they should not change behavior.

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components/layout_2020/display_list/stacking_context.rs

@@ -580,7 +580,8 @@ impl BoxFragment {
             builder.current_space_and_clip = builder.wr.define_scroll_frame(
                 &original_scroll_and_clip_info,
                 Some(external_id),
-                self.scrollable_overflow().to_webrender(),
+                self.scrollable_overflow(&containing_block_info.rect)
+                    .to_webrender(),
                 padding_rect,
                 vec![], // complex_clips
                 None,   // image_mask

components/layout_2020/flow/root.rs

@@ -163,7 +163,7 @@ impl BoxTreeRoot {
                 .fragments
                 .iter()
                 .fold(PhysicalRect::zero(), |acc, child| {
-                    let child_overflow = child.scrollable_overflow();
+                    let child_overflow = child.scrollable_overflow(&physical_containing_block);
 
                     // https://drafts.csswg.org/css-overflow/#scrolling-direction
                     // We want to clip scrollable overflow on box-start and inline-start

components/layout_2020/fragments.rs

@@ -132,10 +132,10 @@ impl Fragment {
         }
     }
 
-    pub fn scrollable_overflow(&self) -> PhysicalRect<Length> {
-        // FIXME(mrobinson, bug 25564): We should be using the containing block
-        // here to properly convert scrollable overflow to physical geometry.
-        let containing_block = PhysicalRect::zero();
+    pub fn scrollable_overflow(
+        &self,
+        containing_block: &PhysicalRect<Length>,
+    ) -> PhysicalRect<Length> {
         match self {
             Fragment::Box(fragment) => fragment.scrollable_overflow_for_parent(&containing_block),
             Fragment::AbsoluteOrFixedPositioned(_) => PhysicalRect::zero(),
@@ -182,11 +182,14 @@ impl AnonymousFragment {
     }
 
     pub fn new(rect: Rect<Length>, children: Vec<Fragment>, mode: WritingMode) -> Self {
+        // FIXME(mrobinson, bug 25564): We should be using the containing block
+        // here to properly convert scrollable overflow to physical geometry.
+        let containing_block = PhysicalRect::zero();
         let content_origin = rect.start_corner.to_physical(mode);
         let scrollable_overflow = children.iter().fold(PhysicalRect::zero(), |acc, child| {
             acc.union(
                 &child
-                    .scrollable_overflow()
+                    .scrollable_overflow(&containing_block)
                     .translate(content_origin.to_vector()),
             )
         });
@@ -226,9 +229,12 @@ impl BoxFragment {
         block_margins_collapsed_with_children: CollapsedBlockMargins,
         hoisted_fragment_id: Option<HoistedFragmentId>,
     ) -> BoxFragment {
+        // FIXME(mrobinson, bug 25564): We should be using the containing block
+        // here to properly convert scrollable overflow to physical geometry.
+        let containing_block = PhysicalRect::zero();
         let scrollable_overflow_from_children =
             children.iter().fold(PhysicalRect::zero(), |acc, child| {
-                acc.union(&child.scrollable_overflow())
+                acc.union(&child.scrollable_overflow(&containing_block))
             });
         BoxFragment {
             tag,
@@ -245,12 +251,13 @@ impl BoxFragment {
         }
     }
 
-    pub fn scrollable_overflow(&self) -> PhysicalRect<Length> {
-        // FIXME(mrobinson, bug 25564): We should be using the containing block
-        // here to properly convert scrollable overflow to physical geometry.
+    pub fn scrollable_overflow(
+        &self,
+        containing_block: &PhysicalRect<Length>,
+    ) -> PhysicalRect<Length> {
         let physical_padding_rect = self
             .padding_rect()
-            .to_physical(self.style.writing_mode, &PhysicalRect::zero());
+            .to_physical(self.style.writing_mode, containing_block);
 
         let content_origin = self
             .content_rect
@@ -284,7 +291,7 @@ impl BoxFragment {
             self.content_rect,
             self.padding_rect(),
             self.border_rect(),
-            self.scrollable_overflow(),
+            self.scrollable_overflow(&PhysicalRect::zero()),
             self.style.get_box().overflow_x,
             self.style.get_box().overflow_y,
             self.style,
@@ -313,7 +320,7 @@ impl BoxFragment {
 
         // https://www.w3.org/TR/css-overflow-3/#scrollable
         // Only include the scrollable overflow of a child box if it has overflow: visible.
-        let scrollable_overflow = self.scrollable_overflow();
+        let scrollable_overflow = self.scrollable_overflow(&containing_block);
         let bottom_right = PhysicalPoint::new(
             overflow.max_x().max(scrollable_overflow.max_x()),
             overflow.max_y().max(scrollable_overflow.max_y()),