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style: Document the restyle hints code, and make it operate on TElement
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This removes the annoying constraint of having to provide the current state from outside of the restyle hints code.
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4 changed files with 101 additions and 53 deletions
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@ -4,13 +4,16 @@
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//! Restyle hints: an optimization to avoid unnecessarily matching selectors.
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#![deny(missing_docs)]
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use Atom;
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use dom::TElement;
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use element_state::*;
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#[cfg(feature = "gecko")]
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use gecko_bindings::structs::nsRestyleHint;
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#[cfg(feature = "servo")]
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use heapsize::HeapSizeOf;
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use selector_parser::{AttrValue, ElementExt, NonTSPseudoClass, Snapshot, SelectorImpl};
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use selector_parser::{AttrValue, NonTSPseudoClass, Snapshot, SelectorImpl};
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use selectors::{Element, MatchAttr};
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use selectors::matching::{MatchingReason, StyleRelations};
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use selectors::matching::matches_complex_selector;
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@ -18,13 +21,14 @@ use selectors::parser::{AttrSelector, Combinator, ComplexSelector, SimpleSelecto
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use std::clone::Clone;
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use std::sync::Arc;
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/// When the ElementState of an element (like IN_HOVER_STATE) changes, certain
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/// pseudo-classes (like :hover) may require us to restyle that element, its
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/// siblings, and/or its descendants. Similarly, when various attributes of an
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/// element change, we may also need to restyle things with id, class, and
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/// attribute selectors. Doing this conservatively is expensive, and so we use
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/// RestyleHints to short-circuit work we know is unnecessary.
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bitflags! {
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/// When the ElementState of an element (like IN_HOVER_STATE) changes,
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/// certain pseudo-classes (like :hover) may require us to restyle that
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/// element, its siblings, and/or its descendants. Similarly, when various
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/// attributes of an element change, we may also need to restyle things with
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/// id, class, and attribute selectors. Doing this conservatively is
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/// expensive, and so we use RestyleHints to short-circuit work we know is
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/// unnecessary.
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pub flags RestyleHint: u32 {
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#[doc = "Rerun selector matching on the element."]
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const RESTYLE_SELF = 0x01,
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@ -99,26 +103,28 @@ pub trait ElementSnapshot : Sized + MatchAttr<Impl=SelectorImpl> {
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}
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struct ElementWrapper<'a, E>
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where E: ElementExt
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where E: TElement,
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{
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element: E,
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snapshot: Option<&'a Snapshot>,
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}
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impl<'a, E> ElementWrapper<'a, E>
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where E: ElementExt
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where E: TElement,
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{
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/// Trivially constructs an `ElementWrapper` without a snapshot.
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pub fn new(el: E) -> ElementWrapper<'a, E> {
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ElementWrapper { element: el, snapshot: None }
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}
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/// Trivially constructs an `ElementWrapper` with a snapshot.
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pub fn new_with_snapshot(el: E, snapshot: &'a Snapshot) -> ElementWrapper<'a, E> {
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ElementWrapper { element: el, snapshot: Some(snapshot) }
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}
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}
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impl<'a, E> MatchAttr for ElementWrapper<'a, E>
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where E: ElementExt,
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where E: TElement,
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{
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type Impl = SelectorImpl;
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@ -202,7 +208,7 @@ impl<'a, E> MatchAttr for ElementWrapper<'a, E>
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}
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impl<'a, E> Element for ElementWrapper<'a, E>
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where E: ElementExt<Impl=SelectorImpl>
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where E: TElement,
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{
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fn match_non_ts_pseudo_class(&self, pseudo_class: NonTSPseudoClass) -> bool {
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let flag = SelectorImpl::pseudo_class_state_flag(&pseudo_class);
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@ -393,6 +399,7 @@ impl DependencySet {
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}
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}
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/// Create an empty `DependencySet`.
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pub fn new() -> Self {
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DependencySet {
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state_deps: vec![],
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@ -401,10 +408,13 @@ impl DependencySet {
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}
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}
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/// Return the total number of dependencies that this set contains.
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pub fn len(&self) -> usize {
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self.common_deps.len() + self.attr_deps.len() + self.state_deps.len()
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}
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/// Create the needed dependencies that a given selector creates, and add
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/// them to the set.
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pub fn note_selector(&mut self, selector: &Arc<ComplexSelector<SelectorImpl>>) {
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let mut cur = selector;
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let mut combinator: Option<Combinator> = None;
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@ -434,18 +444,22 @@ impl DependencySet {
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}
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}
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/// Clear this dependency set.
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pub fn clear(&mut self) {
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self.common_deps.clear();
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self.attr_deps.clear();
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self.state_deps.clear();
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}
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pub fn compute_hint<E>(&self, el: &E,
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snapshot: &Snapshot,
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current_state: ElementState)
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/// Compute a restyle hint given an element and a snapshot, per the rules
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/// explained in the rest of the documentation.
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pub fn compute_hint<E>(&self,
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el: &E,
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snapshot: &Snapshot)
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-> RestyleHint
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where E: ElementExt + Clone
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where E: TElement + Clone,
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{
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let current_state = el.get_state();
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let state_changes = snapshot.state()
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.map_or_else(ElementState::empty, |old_state| current_state ^ old_state);
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let attrs_changed = snapshot.has_attrs();
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@ -483,7 +497,7 @@ impl DependencySet {
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state_changes: &ElementState,
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attrs_changed: bool,
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hint: &mut RestyleHint)
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where E: ElementExt
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where E: TElement,
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{
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if hint.is_all() {
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return;
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