style: Add simple parsing and matching support for :has

Parsing is behind a config value `layout.css.has-selectors.enabled`. This
change does not support p:has(> a) combinators, but will handle them
gracefully, just not matching on them.

Differential Revision: https://phabricator.services.mozilla.com/D149515

1 files changed, 22 insertions, 5 deletions

diff --git a/components/selectors/parser.rs b/components/selectors/parser.rs
index 2720d723568..2fc5ad02d39 100644
--- a/components/selectors/parser.rs
+++ b/components/selectors/parser.rs
@@ -261,6 +261,11 @@ pub trait Parser<'i> {
         false
     }
 
+    /// Whether to parse the :has pseudo-class.
+    fn parse_has(&self) -> bool {
+        false
+    }
+
     /// Whether the given function name is an alias for the `:is()` function.
     fn is_is_alias(&self, _name: &str) -> bool {
         false
@@ -1116,6 +1121,12 @@ pub enum Component<Impl: SelectorImpl> {
     ///
     /// Same comment as above re. the argument.
     Is(Box<[Selector<Impl>]>),
+    /// The `:has` pseudo-class.
+    ///
+    /// https://drafts.csswg.org/selectors/#has-pseudo
+    ///
+    /// Same comment as above re. the argument.
+    Has(Box<[Selector<Impl>]>),
     /// An implementation-dependent pseudo-element selector.
     PseudoElement(#[cfg_attr(feature = "shmem", shmem(field_bound))] Impl::PseudoElement),
 
@@ -1589,11 +1600,12 @@ impl<Impl: SelectorImpl> ToCss for Component<Impl> {
                 write_affine(dest, a, b)?;
                 dest.write_char(')')
             },
-            Is(ref list) | Where(ref list) | Negation(ref list) => {
+            Is(ref list) | Where(ref list) | Negation(ref list) | Has(ref list) => {
                 match *self {
                     Where(..) => dest.write_str(":where(")?,
                     Is(..) => dest.write_str(":is(")?,
                     Negation(..) => dest.write_str(":not(")?,
+                    Has(..) => dest.write_str(":has(")?,
                     _ => unreachable!(),
                 }
                 serialize_selector_list(list.iter(), dest)?;
@@ -2253,7 +2265,7 @@ where
     Ok(empty)
 }
 
-fn parse_is_or_where<'i, 't, P, Impl>(
+fn parse_is_where_has<'i, 't, P, Impl>(
     parser: &P,
     input: &mut CssParser<'i, 't>,
     state: SelectorParsingState,
@@ -2295,8 +2307,9 @@ where
         "nth-of-type" => return parse_nth_pseudo_class(parser, input, state, Component::NthOfType),
         "nth-last-child" => return parse_nth_pseudo_class(parser, input, state, Component::NthLastChild),
         "nth-last-of-type" => return parse_nth_pseudo_class(parser, input, state, Component::NthLastOfType),
-        "is" if parser.parse_is_and_where() => return parse_is_or_where(parser, input, state, Component::Is),
-        "where" if parser.parse_is_and_where() => return parse_is_or_where(parser, input, state, Component::Where),
+        "is" if parser.parse_is_and_where() => return parse_is_where_has(parser, input, state, Component::Is),
+        "where" if parser.parse_is_and_where() => return parse_is_where_has(parser, input, state, Component::Where),
+        "has" if parser.parse_has() => return parse_is_where_has(parser, input, state, Component::Has),
         "host" => {
             if !state.allows_tree_structural_pseudo_classes() {
                 return Err(input.new_custom_error(SelectorParseErrorKind::InvalidState));
@@ -2310,7 +2323,7 @@ where
     }
 
     if parser.parse_is_and_where() && parser.is_is_alias(&name) {
-        return parse_is_or_where(parser, input, state, Component::Is);
+        return parse_is_where_has(parser, input, state, Component::Is);
     }
 
     if !state.allows_custom_functional_pseudo_classes() {
@@ -2684,6 +2697,10 @@ pub mod tests {
             true
         }
 
+        fn parse_has(&self) -> bool {
+            true
+        }
+
         fn parse_part(&self) -> bool {
             true
         }