1 files changed, 111 insertions, 0 deletions
diff --git a/servo/components/selectors/visitor.rs b/servo/components/selectors/visitor.rs
new file mode 100644
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+++ b/servo/components/selectors/visitor.rs
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+/* 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/. */
+
+//! Visitor traits for selectors.
+
+#![deny(missing_docs)]
+
+use crate::attr::NamespaceConstraint;
+use crate::parser::{Combinator, Component, Selector, SelectorImpl};
+
+/// A trait to visit selector properties.
+///
+/// All the `visit_foo` methods return a boolean indicating whether the
+/// traversal should continue or not.
+pub trait SelectorVisitor: Sized {
+    /// The selector implementation this visitor wants to visit.
+    type Impl: SelectorImpl;
+
+    /// Visit an attribute selector that may match (there are other selectors
+    /// that may never match, like those containing whitespace or the empty
+    /// string).
+    fn visit_attribute_selector(
+        &mut self,
+        _namespace: &NamespaceConstraint<&<Self::Impl as SelectorImpl>::NamespaceUrl>,
+        _local_name: &<Self::Impl as SelectorImpl>::LocalName,
+        _local_name_lower: &<Self::Impl as SelectorImpl>::LocalName,
+    ) -> bool {
+        true
+    }
+
+    /// Visit a simple selector.
+    fn visit_simple_selector(&mut self, _: &Component<Self::Impl>) -> bool {
+        true
+    }
+
+    /// Visit a nested selector list. The caller is responsible to call visit
+    /// into the internal selectors if / as needed.
+    ///
+    /// The default implementation does this.
+    fn visit_selector_list(
+        &mut self,
+        _list_kind: SelectorListKind,
+        list: &[Selector<Self::Impl>],
+    ) -> bool {
+        for nested in list {
+            if !nested.visit(self) {
+                return false;
+            }
+        }
+        true
+    }
+
+    /// Visits a complex selector.
+    ///
+    /// Gets the combinator to the right of the selector, or `None` if the
+    /// selector is the rightmost one.
+    fn visit_complex_selector(&mut self, _combinator_to_right: Option<Combinator>) -> bool {
+        true
+    }
+}
+
+bitflags! {
+    /// The kinds of components the visitor is visiting the selector list of, if any
+    #[derive(Clone, Copy, Default)]
+    pub struct SelectorListKind: u8 {
+        /// The visitor is inside :not(..)
+        const NEGATION = 1 << 0;
+        /// The visitor is inside :is(..)
+        const IS = 1 << 1;
+        /// The visitor is inside :where(..)
+        const WHERE = 1 << 2;
+        /// The visitor is inside :nth-child(.. of <selector list>) or
+        /// :nth-last-child(.. of <selector list>)
+        const NTH_OF = 1 << 3;
+    }
+}
+
+impl SelectorListKind {
+    /// Construct a SelectorListKind for the corresponding component.
+    pub fn from_component<Impl: SelectorImpl>(component: &Component<Impl>) -> Self {
+        match component {
+            Component::Negation(_) => SelectorListKind::NEGATION,
+            Component::Is(_) => SelectorListKind::IS,
+            Component::Where(_) => SelectorListKind::WHERE,
+            Component::NthOf(_) => SelectorListKind::NTH_OF,
+            _ => SelectorListKind::empty(),
+        }
+    }
+
+    /// Whether the visitor is inside :not(..)
+    pub fn in_negation(&self) -> bool {
+        self.intersects(SelectorListKind::NEGATION)
+    }
+
+    /// Whether the visitor is inside :is(..)
+    pub fn in_is(&self) -> bool {
+        self.intersects(SelectorListKind::IS)
+    }
+
+    /// Whether the visitor is inside :where(..)
+    pub fn in_where(&self) -> bool {
+        self.intersects(SelectorListKind::WHERE)
+    }
+
+    /// Whether the visitor is inside :nth-child(.. of <selector list>) or
+    /// :nth-last-child(.. of <selector list>)
+    pub fn in_nth_of(&self) -> bool {
+        self.intersects(SelectorListKind::NTH_OF)
+    }
+}