selectors/nth_index_cache.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/. */

use crate::tree::OpaqueElement;
use rustc_hash::FxHashMap;

/// A cache to speed up matching of nth-index-like selectors.
///
/// See [1] for some discussion around the design tradeoffs.
///
/// [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1401855#c3
#[derive(Default)]
pub struct NthIndexCache {
  nth: NthIndexCacheInner,
  nth_last: NthIndexCacheInner,
  nth_of_type: NthIndexCacheInner,
  nth_last_of_type: NthIndexCacheInner,
}

impl NthIndexCache {
  /// Gets the appropriate cache for the given parameters.
  pub fn get(&mut self, is_of_type: bool, is_from_end: bool) -> &mut NthIndexCacheInner {
    match (is_of_type, is_from_end) {
      (false, false) => &mut self.nth,
      (false, true) => &mut self.nth_last,
      (true, false) => &mut self.nth_of_type,
      (true, true) => &mut self.nth_last_of_type,
    }
  }
}

/// The concrete per-pseudo-class cache.
#[derive(Default)]
pub struct NthIndexCacheInner(FxHashMap<OpaqueElement, i32>);

impl NthIndexCacheInner {
  /// Does a lookup for a given element in the cache.
  pub fn lookup(&mut self, el: OpaqueElement) -> Option<i32> {
    self.0.get(&el).copied()
  }

  /// Inserts an entry into the cache.
  pub fn insert(&mut self, element: OpaqueElement, index: i32) {
    self.0.insert(element, index);
  }

  /// Returns whether the cache is empty.
  pub fn is_empty(&self) -> bool {
    self.0.is_empty()
  }
}