style: Implement parsing / selector-matching for :is() and :where().

This implements the easy / straight-forward parts of the :where / :is
selectors.

The biggest missing piece is to handle properly invalidation when there
are combinators present inside the :where. That's the hard part of this,
actually.

But this is probably worth landing in the interim. This fixes some of
the visitors that were easy to fix.

Differential Revision: https://phabricator.services.mozilla.com/D70788

1 files changed, 9 insertions, 12 deletions

diff --git a/components/style/servo/selector_parser.rs b/components/style/servo/selector_parser.rs
index 2537cae9f83..75dd041b9c0 100644
--- a/components/style/servo/selector_parser.rs
+++ b/components/style/servo/selector_parser.rs
@@ -19,7 +19,7 @@ use crate::{Atom, CaseSensitivityExt, LocalName, Namespace, Prefix};
 use cssparser::{serialize_identifier, CowRcStr, Parser as CssParser, SourceLocation, ToCss};
 use fxhash::FxHashMap;
 use selectors::attr::{AttrSelectorOperation, CaseSensitivity, NamespaceConstraint};
-use selectors::parser::{SelectorParseErrorKind, Visit};
+use selectors::parser::SelectorParseErrorKind;
 use selectors::visitor::SelectorVisitor;
 use std::fmt;
 use std::mem;
@@ -315,8 +315,16 @@ impl ::selectors::parser::NonTSPseudoClass for NonTSPseudoClass {
     fn has_zero_specificity(&self) -> bool {
         false
     }
+
+    fn visit<V>(&self, _: &mut V) -> bool
+    where
+        V: SelectorVisitor<Impl = Self::Impl>,
+    {
+        true
+    }
 }
 
+
 impl ToCss for NonTSPseudoClass {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result
     where
@@ -352,17 +360,6 @@ impl ToCss for NonTSPseudoClass {
     }
 }
 
-impl Visit for NonTSPseudoClass {
-    type Impl = SelectorImpl;
-
-    fn visit<V>(&self, _: &mut V) -> bool
-    where
-        V: SelectorVisitor<Impl = Self::Impl>,
-    {
-        true
-    }
-}
-
 impl NonTSPseudoClass {
     /// Gets a given state flag for this pseudo-class. This is used to do
     /// selector matching, and it's set from the DOM.