layout: Simplify and generalize the usage of pseudo-elements (#36202)

- Remove the last remaining Servo-specific PseudoElement enum from
  layout. This was made to select `::before` and `::after` (both eager
  pseudo-elements), but now `traverse_pseudo_element` is called
  `traverse_eager_pseudo_element` and should work on any eager pseudo
  element.
- Expose a single way of getting psuedo-element variants of
  ThreadSafeLayoutElement in the Layout DOM, which returns `None` when
  the pseudo-element doesn't apply (not defined for eager
  pseudo-elements or when trying to get `<details>` related
  pseudo-elements on elements that they don't apply to).
- Ensure that NodeAndStyleInfo always refers to a node. This is done by
  making sure that anonymous boxes are all associated with their
  originating node.

These changes are prepatory work for implementation of the `::marker`
pseudo-element as well as ensuring that all anonymous boxes can be
cached into the box tree eventually.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

1 files changed, 19 insertions, 11 deletions

diff --git a/components/layout_2020/dom.rs b/components/layout_2020/dom.rs
index b0323a4e56b..f8b3d6f9c29 100644
--- a/components/layout_2020/dom.rs
+++ b/components/layout_2020/dom.rs
@@ -17,10 +17,10 @@ use script_layout_interface::{
 };
 use servo_arc::Arc as ServoArc;
 use style::properties::ComputedValues;
+use style::selector_parser::PseudoElement;
 
 use crate::cell::ArcRefCell;
 use crate::context::LayoutContext;
-use crate::dom_traversal::WhichPseudoElement;
 use crate::flexbox::FlexLevelBox;
 use crate::flow::BlockLevelBox;
 use crate::flow::inline::InlineItem;
@@ -108,8 +108,8 @@ pub(crate) trait NodeExt<'dom>: 'dom + LayoutNode<'dom> {
     fn layout_data_mut(self) -> AtomicRefMut<'dom, InnerDOMLayoutData>;
     fn layout_data(self) -> Option<AtomicRef<'dom, InnerDOMLayoutData>>;
     fn element_box_slot(&self) -> BoxSlot<'dom>;
-    fn pseudo_element_box_slot(&self, which: WhichPseudoElement) -> BoxSlot<'dom>;
-    fn unset_pseudo_element_box(self, which: WhichPseudoElement);
+    fn pseudo_element_box_slot(&self, which: PseudoElement) -> BoxSlot<'dom>;
+    fn unset_pseudo_element_box(self, which: PseudoElement);
 
     /// Remove boxes for the element itself, and its `:before` and `:after` if any.
     fn unset_all_boxes(self);
@@ -217,20 +217,28 @@ where
         BoxSlot::new(self.layout_data_mut().self_box.clone())
     }
 
-    fn pseudo_element_box_slot(&self, which: WhichPseudoElement) -> BoxSlot<'dom> {
+    fn pseudo_element_box_slot(&self, pseudo_element_type: PseudoElement) -> BoxSlot<'dom> {
         let data = self.layout_data_mut();
-        let cell = match which {
-            WhichPseudoElement::Before => &data.pseudo_before_box,
-            WhichPseudoElement::After => &data.pseudo_after_box,
+        let cell = match pseudo_element_type {
+            PseudoElement::Before => &data.pseudo_before_box,
+            PseudoElement::After => &data.pseudo_after_box,
+            _ => unreachable!(
+                "Asked for box slot for unsupported pseudo-element: {:?}",
+                pseudo_element_type
+            ),
         };
         BoxSlot::new(cell.clone())
     }
 
-    fn unset_pseudo_element_box(self, which: WhichPseudoElement) {
+    fn unset_pseudo_element_box(self, pseudo_element_type: PseudoElement) {
         let data = self.layout_data_mut();
-        let cell = match which {
-            WhichPseudoElement::Before => &data.pseudo_before_box,
-            WhichPseudoElement::After => &data.pseudo_after_box,
+        let cell = match pseudo_element_type {
+            PseudoElement::Before => &data.pseudo_before_box,
+            PseudoElement::After => &data.pseudo_after_box,
+            _ => unreachable!(
+                "Asked for box slot for unsupported pseudo-element: {:?}",
+                pseudo_element_type
+            ),
         };
         *cell.borrow_mut() = None;
     }