Add layout support for list markers

components/layout_2020/flow/construct.rs

@@ -20,6 +20,7 @@ use rayon_croissant::ParallelIteratorExt;
 use servo_arc::Arc;
 use std::borrow::Cow;
 use std::convert::{TryFrom, TryInto};
+use style::properties::longhands::list_style_position::computed_value::T as ListStylePosition;
 use style::properties::ComputedValues;
 use style::selector_parser::PseudoElement;
 use style::values::specified::text::TextDecorationLine;
@@ -192,7 +193,21 @@ impl BlockContainer {
         };
 
         if is_list_item {
-            // FIXME: generate a box for the list marker
+            if let Some(marker_contents) = crate::lists::make_marker(context, info) {
+                let _position = info.style.clone_list_style_position();
+                // FIXME: implement support for `outside` and remove this:
+                let position = ListStylePosition::Inside;
+                match position {
+                    ListStylePosition::Inside => {
+                        builder.handle_list_item_marker_inside(info, marker_contents)
+                    },
+                    ListStylePosition::Outside => {
+                        // FIXME: implement layout for this case
+                        // https://github.com/servo/servo/issues/27383
+                        // and enable `list-style-position` and the `list-style` shorthand in Stylo.
+                    },
+                }
+            }
         }
 
         contents.traverse(context, info, &mut builder);
@@ -399,6 +414,29 @@ where
         }
     }
 
+    fn handle_list_item_marker_inside(
+        &mut self,
+        info: &NodeAndStyleInfo<Node>,
+        contents: Vec<crate::dom_traversal::PseudoElementContentItem>,
+    ) {
+        let marker_style = self
+            .context
+            .shared_context()
+            .stylist
+            .style_for_anonymous::<Node::ConcreteElement>(
+                &self.context.shared_context().guards,
+                &PseudoElement::ServoText, // FIMXE: use `PseudoElement::Marker` when we add it
+                &info.style,
+            );
+        self.handle_inline_level_element(
+            &info.new_replacing_style(marker_style),
+            DisplayInside::Flow {
+                is_list_item: false,
+            },
+            Contents::OfPseudoElement(contents),
+        );
+    }
+
     fn handle_inline_level_element(
         &mut self,
         info: &NodeAndStyleInfo<Node>,
@@ -420,7 +458,12 @@ where
             });
 
             if is_list_item {
-                // FIXME: generate a box for the list marker
+                if let Some(marker_contents) = crate::lists::make_marker(self.context, info) {
+                    // Ignore `list-style-position` here:
+                    // “If the list item is an inline box: this value is equivalent to `inside`.”
+                    // https://drafts.csswg.org/css-lists/#list-style-position-outside
+                    self.handle_list_item_marker_inside(info, marker_contents)
+                }
             }
 
             // `unwrap` doesn’t panic here because `is_replaced` returned `false`.

components/layout_2020/lib.rs

@@ -22,6 +22,7 @@ mod fragments;
 pub mod geom;
 #[macro_use]
 pub mod layout_debug;
+mod lists;
 mod opaque_node;
 mod positioned;
 pub mod query;

components/layout_2020/lists.rs

@@ -0,0 +1,50 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use crate::context::LayoutContext;
+use crate::dom_traversal::{NodeAndStyleInfo, NodeExt, PseudoElementContentItem};
+use crate::replaced::ReplacedContent;
+use style::properties::longhands::list_style_type::computed_value::T as ListStyleType;
+use style::properties::style_structs;
+use style::values::computed::url::UrlOrNone;
+
+/// https://drafts.csswg.org/css-lists/#content-property
+pub(crate) fn make_marker<'dom, Node>(
+    context: &LayoutContext,
+    info: &NodeAndStyleInfo<Node>,
+) -> Option<Vec<PseudoElementContentItem>>
+where
+    Node: NodeExt<'dom>,
+{
+    let style = info.style.get_list();
+
+    // https://drafts.csswg.org/css-lists/#marker-image
+    let marker_image = || match &style.list_style_image {
+        UrlOrNone::Url(url) => Some(vec![
+            PseudoElementContentItem::Replaced(ReplacedContent::from_image_url(
+                info.node, context, url,
+            )?),
+            PseudoElementContentItem::Text(" ".into()),
+        ]),
+        UrlOrNone::None => None,
+    };
+    marker_image().or_else(|| {
+        Some(vec![PseudoElementContentItem::Text(
+            marker_string(style)?.into(),
+        )])
+    })
+}
+
+/// https://drafts.csswg.org/css-lists/#marker-string
+fn marker_string(style: &style_structs::List) -> Option<&'static str> {
+    // FIXME: add support for counters and other style types
+    match style.list_style_type {
+        ListStyleType::None => None,
+        ListStyleType::Disc => Some("• "),
+        ListStyleType::Circle => Some("◦ "),
+        ListStyleType::Square => Some("▪ "),
+        ListStyleType::DisclosureOpen => Some("▾ "),
+        ListStyleType::DisclosureClosed => Some("‣ "),
+    }
+}