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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, 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 {
/// 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
}
/// 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
}
}
/// Enables traversing selector components stored in various types
pub trait Visit {
/// The type parameter of selector component types.
type Impl: SelectorImpl;
/// Traverse selector components inside `self`.
///
/// Implementations of this method should call `SelectorVisitor` methods
/// or other impls of `Visit` as appropriate based on the fields of `Self`.
///
/// A return value of `false` indicates terminating the traversal.
/// It should be propagated with an early return.
/// On the contrary, `true` indicates that all fields of `self` have been traversed:
///
/// ```rust,ignore
/// if !visitor.visit_simple_selector(&self.some_simple_selector) {
/// return false;
/// }
/// if !self.some_component.visit(visitor) {
/// return false;
/// }
/// true
/// ```
fn visit<V>(&self, visitor: &mut V) -> bool
where
V: SelectorVisitor<Impl = Self::Impl>;
}