selectors/visitor.rs

/* 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<'i>: Sized {
  /// The selector implementation this visitor wants to visit.
  type Impl: SelectorImpl<'i>;

  /// 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<'i>>::NamespaceUrl>,
    _local_name: &<Self::Impl as SelectorImpl<'i>>::LocalName,
    _local_name_lower: &<Self::Impl as SelectorImpl<'i>>::LocalName,
  ) -> bool {
    true
  }

  /// Visit a simple selector.
  fn visit_simple_selector(&mut self, _: &Component<'i, 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: &[Selector<'i, 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
  }
}