layout: Add a basic support for list-style-position: outside (#32114)

This change adds very basic support for `list-style-position`.
Currently, the marker does not do any kind of baseline alignment with
the rest
of the list item contents and it also doesn't force the list item to be
at least as tall as the marker.

This adds a few new failures:

- Four failures because markers do not ensure that list-items have at
least the same block size as they do:
  - FAIL [expected PASS] /css/CSS2/lists/list-style-applies-to-012.xht
  - FAIL [expected PASS] /css/CSS2/lists/list-style-applies-to-014.xht
- FAIL [expected PASS]
/css/CSS2/lists/list-style-type-applies-to-012.xht
- FAIL [expected PASS]
/css/CSS2/lists/list-style-type-applies-to-014.xht
- One failure because we don't yet support the `::marker`
pseudo-selector:
- FAIL [expected PASS]
/css/css-position/position-absolute-dynamic-list-marker.html
- One failure because we don't support the list item exception for the
line height quirk:
  - FAIL [expected PASS] /quirks/line-height-in-list-item.tentative.html

Co-authored-by: Oriol Brufau <obrufau@igalia.com>

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Fixes #27383.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #27383.
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/layout_2020/flow/mod.rs

@@ -71,6 +71,10 @@ impl BlockContainer {
 
 #[derive(Debug, Serialize)]
 pub(crate) enum BlockLevelBox {
+    Independent(IndependentFormattingContext),
+    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
+    OutOfFlowFloatBox(FloatBox),
+    OutsideMarker(OutsideMarker),
     SameFormattingContextBlock {
         base_fragment_info: BaseFragmentInfo,
         #[serde(skip_serializing)]
@@ -78,9 +82,6 @@ pub(crate) enum BlockLevelBox {
         contents: BlockContainer,
         contains_floats: bool,
     },
-    OutOfFlowAbsolutelyPositionedBox(ArcRefCell<AbsolutelyPositionedBox>),
-    OutOfFlowFloatBox(FloatBox),
-    Independent(IndependentFormattingContext),
 }
 
 impl BlockLevelBox {
@@ -103,6 +104,7 @@ impl BlockLevelBox {
             BlockLevelBox::SameFormattingContextBlock { ref style, .. } => style,
             BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(_) |
             BlockLevelBox::OutOfFlowFloatBox(_) => return true,
+            BlockLevelBox::OutsideMarker(_) => return false,
             BlockLevelBox::Independent(ref context) => {
                 // FIXME: If the element doesn't fit next to floats, it will get clearance.
                 // In that case this should be returning false.
@@ -205,6 +207,81 @@ struct FlowLayout {
 #[derive(Clone, Copy)]
 struct CollapsibleWithParentStartMargin(bool);
 
+/// The contentes of a BlockContainer created to render a list marker
+/// for a list that has `list-style-position: outside`.
+#[derive(Debug, Serialize)]
+pub(crate) struct OutsideMarker {
+    #[serde(skip_serializing)]
+    pub style: Arc<ComputedValues>,
+    pub block_container: BlockContainer,
+}
+
+impl OutsideMarker {
+    fn layout(
+        &self,
+        layout_context: &LayoutContext<'_>,
+        containing_block: &ContainingBlock<'_>,
+        positioning_context: &mut PositioningContext,
+        sequential_layout_state: Option<&mut SequentialLayoutState>,
+        collapsible_with_parent_start_margin: Option<CollapsibleWithParentStartMargin>,
+    ) -> Fragment {
+        let content_sizes = self
+            .block_container
+            .inline_content_sizes(layout_context, containing_block.style.writing_mode);
+        let containing_block = ContainingBlock {
+            inline_size: content_sizes.max_content,
+            block_size: AuOrAuto::auto(),
+            style: &self.style,
+        };
+        let flow_layout = self.block_container.layout(
+            layout_context,
+            positioning_context,
+            &containing_block,
+            sequential_layout_state,
+            collapsible_with_parent_start_margin.unwrap_or(CollapsibleWithParentStartMargin(false)),
+        );
+        let max_inline_size = flow_layout.fragments.iter().fold(
+            Length::zero(),
+            |current_max, fragment| match fragment {
+                Fragment::Text(text) => current_max.max(text.rect.max_inline_position()),
+                Fragment::Image(image) => current_max.max(image.rect.max_inline_position()),
+                Fragment::Positioning(positioning) => {
+                    current_max.max(positioning.rect.max_inline_position())
+                },
+                Fragment::Box(_) |
+                Fragment::Float(_) |
+                Fragment::AbsoluteOrFixedPositioned(_) |
+                Fragment::IFrame(_) => {
+                    unreachable!("Found unexpected fragment type in outside list marker!");
+                },
+            },
+        );
+
+        let content_rect = LogicalRect {
+            start_corner: LogicalVec2 {
+                inline: -max_inline_size,
+                block: Zero::zero(),
+            },
+            size: LogicalVec2 {
+                inline: max_inline_size,
+                block: Zero::zero(),
+            },
+        };
+
+        Fragment::Box(BoxFragment::new(
+            BaseFragmentInfo::anonymous(),
+            self.style.clone(),
+            flow_layout.fragments,
+            content_rect,
+            LogicalSides::zero(),
+            LogicalSides::zero(),
+            LogicalSides::zero(),
+            None,
+            CollapsedBlockMargins::zero(),
+        ))
+    }
+}
+
 impl BlockFormattingContext {
     pub(super) fn layout(
         &self,
@@ -261,7 +338,8 @@ fn calculate_inline_content_size_for_block_level_boxes(
 ) -> ContentSizes {
     let get_box_info = |box_: &ArcRefCell<BlockLevelBox>| {
         match &mut *box_.borrow_mut() {
-            BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(_) => None,
+            BlockLevelBox::OutOfFlowAbsolutelyPositionedBox(_) |
+            BlockLevelBox::OutsideMarker { .. } => None,
             BlockLevelBox::OutOfFlowFloatBox(ref mut float_box) => {
                 let size = float_box
                     .contents
@@ -603,6 +681,13 @@ impl BlockLevelBox {
                 positioning_context,
                 containing_block,
             )),
+            BlockLevelBox::OutsideMarker(outside_marker) => outside_marker.layout(
+                layout_context,
+                containing_block,
+                positioning_context,
+                sequential_layout_state,
+                collapsible_with_parent_start_margin,
+            ),
         }
     }
 }