tor-browser

checks.rs (6241B)

---

/* 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/. */

//! Different checks done during the style sharing process in order to determine
//! quickly whether it's worth to share style, and whether two different
//! elements can indeed share the same style.

use crate::bloom::StyleBloom;
use crate::context::SharedStyleContext;
use crate::dom::TElement;
use crate::sharing::{StyleSharingCandidate, StyleSharingTarget};
use selectors::matching::SelectorCaches;

/// Determines whether a target and a candidate have compatible parents for
/// sharing.
pub fn parents_allow_sharing<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
) -> bool
where
   E: TElement,
{
   // If the identity of the parent style isn't equal, we can't share. We check
   // this first, because the result is cached.
   if target.parent_style_identity() != candidate.parent_style_identity() {
       return false;
   }

   // Siblings can always share.
   let parent = target.inheritance_parent().unwrap();
   let candidate_parent = candidate.element.inheritance_parent().unwrap();
   if parent == candidate_parent {
       return true;
   }

   // If a parent element was already styled and we traversed past it without
   // restyling it, that may be because our clever invalidation logic was able
   // to prove that the styles of that element would remain unchanged despite
   // changes to the id or class attributes. However, style sharing relies in
   // the strong guarantee that all the classes and ids up the respective parent
   // chains are identical. As such, if we skipped styling for one (or both) of
   // the parents on this traversal, we can't share styles across cousins.
   //
   // This is a somewhat conservative check. We could tighten it by having the
   // invalidation logic explicitly flag elements for which it ellided styling.
   let parent_data = parent.borrow_data().unwrap();
   let candidate_parent_data = candidate_parent.borrow_data().unwrap();
   if !parent_data.safe_for_cousin_sharing() || !candidate_parent_data.safe_for_cousin_sharing() {
       return false;
   }

   true
}

/// Whether two elements have the same style attribute.
///
/// First checks pointer identity (fast path), then falls back to value comparison.
pub fn have_same_style_attribute<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
   shared_context: &SharedStyleContext,
) -> bool
where
   E: TElement,
{
   match (target.style_attribute(), candidate.style_attribute()) {
       (None, None) => true,
       (Some(_), None) | (None, Some(_)) => false,
       (Some(a), Some(b)) => {
           if std::ptr::eq(&*a, &*b) {
               return true;
           }
           let guard = shared_context.guards.author;
           *a.read_with(guard) == *b.read_with(guard)
       },
   }
}

/// Whether two elements have the same same presentational attributes.
pub fn have_same_presentational_hints<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
) -> bool
where
   E: TElement,
{
   target.pres_hints() == candidate.pres_hints()
}

/// Whether a given element has the same class attribute as a given candidate.
///
/// We don't try to share style across elements with different class attributes.
pub fn have_same_class<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
) -> bool
where
   E: TElement,
{
   target.class_list() == candidate.class_list()
}

/// Whether a given element has the same part attribute as a given candidate.
///
/// We don't try to share style across elements with different part attributes.
pub fn have_same_parts<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
) -> bool
where
   E: TElement,
{
   target.part_list() == candidate.part_list()
}

/// Whether a given element and a candidate match the same set of "revalidation"
/// selectors.
///
/// Revalidation selectors are those that depend on the DOM structure, like
/// :first-child, etc, or on attributes that we don't check off-hand (pretty
/// much every attribute selector except `id` and `class`.
#[inline]
pub fn revalidate<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
   shared_context: &SharedStyleContext,
   bloom: &StyleBloom<E>,
   selector_caches: &mut SelectorCaches,
) -> bool
where
   E: TElement,
{
   let stylist = &shared_context.stylist;

   let for_element = target.revalidation_match_results(stylist, bloom, selector_caches);

   let for_candidate = candidate.revalidation_match_results(stylist, bloom, selector_caches);

   for_element == for_candidate
}

/// Whether a given element and a candidate share a set of scope activations
/// for revalidation.
#[inline]
pub fn revalidate_scope<E>(
   target: &mut StyleSharingTarget<E>,
   candidate: &mut StyleSharingCandidate<E>,
   shared_context: &SharedStyleContext,
   selector_caches: &mut SelectorCaches,
) -> bool
where
   E: TElement,
{
   let stylist = &shared_context.stylist;
   let for_element = target.scope_revalidation_results(stylist, selector_caches);
   let for_candidate = candidate.scope_revalidation_results(stylist, selector_caches);

   for_element == for_candidate
}

/// Checks whether we might have rules for either of the two ids.
#[inline]
pub fn may_match_different_id_rules<E>(
   shared_context: &SharedStyleContext,
   element: E,
   candidate: E,
) -> bool
where
   E: TElement,
{
   let element_id = element.id();
   let candidate_id = candidate.id();

   if element_id == candidate_id {
       return false;
   }

   let stylist = &shared_context.stylist;

   let may_have_rules_for_element = match element_id {
       Some(id) => stylist.may_have_rules_for_id(id, element),
       None => false,
   };

   if may_have_rules_for_element {
       return true;
   }

   match candidate_id {
       Some(id) => stylist.may_have_rules_for_id(id, candidate),
       None => false,
   }
}