/
matching.rs
470 lines (436 loc) · 17.7 KB
/
matching.rs
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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 http://mozilla.org/MPL/2.0/. */
use bloom::BloomFilter;
use parser::{CaseSensitivity, Combinator, ComplexSelector, Component, LocalName};
use parser::{Selector, SelectorInner, SelectorIter};
use std::borrow::Borrow;
use tree::Element;
// The bloom filter for descendant CSS selectors will have a <1% false
// positive rate until it has this many selectors in it, then it will
// rapidly increase.
pub static RECOMMENDED_SELECTOR_BLOOM_FILTER_SIZE: usize = 4096;
bitflags! {
/// Set of flags that determine the different kind of elements affected by
/// the selector matching process.
///
/// This is used to implement efficient sharing.
pub flags StyleRelations: usize {
/// Whether this element is affected by an ID selector.
const AFFECTED_BY_ID_SELECTOR = 1 << 0,
/// Whether this element has a style attribute. Computed
/// externally.
const AFFECTED_BY_STYLE_ATTRIBUTE = 1 << 1,
/// Whether this element is affected by presentational hints. This is
/// computed externally (that is, in Servo).
const AFFECTED_BY_PRESENTATIONAL_HINTS = 1 << 2,
/// Whether this element has pseudo-element styles. Computed externally.
const AFFECTED_BY_PSEUDO_ELEMENTS = 1 << 3,
}
}
bitflags! {
/// Set of flags that are set on either the element or its parent (depending
/// on the flag) if the element could potentially match a selector.
pub flags ElementSelectorFlags: usize {
/// When a child is added or removed from the parent, all the children
/// must be restyled, because they may match :nth-last-child,
/// :last-of-type, :nth-last-of-type, or :only-of-type.
const HAS_SLOW_SELECTOR = 1 << 0,
/// When a child is added or removed from the parent, any later
/// children must be restyled, because they may match :nth-child,
/// :first-of-type, or :nth-of-type.
const HAS_SLOW_SELECTOR_LATER_SIBLINGS = 1 << 1,
/// When a child is added or removed from the parent, the first and
/// last children must be restyled, because they may match :first-child,
/// :last-child, or :only-child.
const HAS_EDGE_CHILD_SELECTOR = 1 << 2,
/// The element has an empty selector, so when a child is appended we
/// might need to restyle the parent completely.
const HAS_EMPTY_SELECTOR = 1 << 3,
}
}
impl ElementSelectorFlags {
/// Returns the subset of flags that apply to the element.
pub fn for_self(self) -> ElementSelectorFlags {
self & (HAS_EMPTY_SELECTOR)
}
/// Returns the subset of flags that apply to the parent.
pub fn for_parent(self) -> ElementSelectorFlags {
self & (HAS_SLOW_SELECTOR | HAS_SLOW_SELECTOR_LATER_SIBLINGS | HAS_EDGE_CHILD_SELECTOR)
}
}
pub fn matches_selector_list<E>(selector_list: &[Selector<E::Impl>],
element: &E,
parent_bf: Option<&BloomFilter>)
-> bool
where E: Element
{
selector_list.iter().any(|selector| {
selector.pseudo_element.is_none() &&
matches_selector(&selector.inner,
element,
parent_bf,
&mut StyleRelations::empty(),
&mut |_, _| {})
})
}
fn may_match<E>(sel: &SelectorInner<E::Impl>,
bf: &BloomFilter)
-> bool
where E: Element,
{
// Check against the list of precomputed hashes.
for hash in sel.ancestor_hashes.iter() {
// If we hit the 0 sentinel hash, that means the rest are zero as well.
if *hash == 0 {
break;
}
if !bf.might_contain_hash(*hash) {
return false;
}
}
true
}
/// Determines whether the given element matches the given complex selector.
pub fn matches_selector<E, F>(selector: &SelectorInner<E::Impl>,
element: &E,
parent_bf: Option<&BloomFilter>,
relations: &mut StyleRelations,
flags_setter: &mut F)
-> bool
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
// Use the bloom filter to fast-reject.
if let Some(filter) = parent_bf {
if !may_match::<E>(selector, filter) {
return false;
}
}
// Match the selector.
matches_complex_selector(&selector.complex, element, relations, flags_setter)
}
/// A result of selector matching, includes 3 failure types,
///
/// NotMatchedAndRestartFromClosestLaterSibling
/// NotMatchedAndRestartFromClosestDescendant
/// NotMatchedGlobally
///
/// When NotMatchedGlobally appears, stop selector matching completely since
/// the succeeding selectors never matches.
/// It is raised when
/// Child combinator cannot find the candidate element.
/// Descendant combinator cannot find the candidate element.
///
/// When NotMatchedAndRestartFromClosestDescendant appears, the selector
/// matching does backtracking and restarts from the closest Descendant
/// combinator.
/// It is raised when
/// NextSibling combinator cannot find the candidate element.
/// LaterSibling combinator cannot find the candidate element.
/// Child combinator doesn't match on the found element.
///
/// When NotMatchedAndRestartFromClosestLaterSibling appears, the selector
/// matching does backtracking and restarts from the closest LaterSibling
/// combinator.
/// It is raised when
/// NextSibling combinator doesn't match on the found element.
///
/// For example, when the selector "d1 d2 a" is provided and we cannot *find*
/// an appropriate ancestor element for "d1", this selector matching raises
/// NotMatchedGlobally since even if "d2" is moved to more upper element, the
/// candidates for "d1" becomes less than before and d1 .
///
/// The next example is siblings. When the selector "b1 + b2 ~ d1 a" is
/// provided and we cannot *find* an appropriate brother element for b1,
/// the selector matching raises NotMatchedAndRestartFromClosestDescendant.
/// The selectors ("b1 + b2 ~") doesn't match and matching restart from "d1".
///
/// The additional example is child and sibling. When the selector
/// "b1 + c1 > b2 ~ d1 a" is provided and the selector "b1" doesn't match on
/// the element, this "b1" raises NotMatchedAndRestartFromClosestLaterSibling.
/// However since the selector "c1" raises
/// NotMatchedAndRestartFromClosestDescendant. So the selector
/// "b1 + c1 > b2 ~ " doesn't match and restart matching from "d1".
#[derive(PartialEq, Eq, Copy, Clone)]
enum SelectorMatchingResult {
Matched,
NotMatchedAndRestartFromClosestLaterSibling,
NotMatchedAndRestartFromClosestDescendant,
NotMatchedGlobally,
}
/// Matches a complex selector.
pub fn matches_complex_selector<E, F>(selector: &ComplexSelector<E::Impl>,
element: &E,
relations: &mut StyleRelations,
flags_setter: &mut F)
-> bool
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
match matches_complex_selector_internal(selector.iter(),
element,
relations,
flags_setter) {
SelectorMatchingResult::Matched => true,
_ => false
}
}
fn matches_complex_selector_internal<E, F>(mut selector_iter: SelectorIter<E::Impl>,
element: &E,
relations: &mut StyleRelations,
flags_setter: &mut F)
-> SelectorMatchingResult
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
let matches_all_simple_selectors = selector_iter.all(|simple| {
matches_simple_selector(simple, element, relations, flags_setter)
});
let combinator = selector_iter.next_sequence();
let siblings = combinator.map_or(false, |c| c.is_sibling());
if siblings {
flags_setter(element, HAS_SLOW_SELECTOR_LATER_SIBLINGS);
}
if !matches_all_simple_selectors {
return SelectorMatchingResult::NotMatchedAndRestartFromClosestLaterSibling;
}
match combinator {
None => SelectorMatchingResult::Matched,
Some(c) => {
let (mut next_element, candidate_not_found) = if siblings {
(element.prev_sibling_element(),
SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant)
} else {
(element.parent_element(),
SelectorMatchingResult::NotMatchedGlobally)
};
loop {
let element = match next_element {
None => return candidate_not_found,
Some(next_element) => next_element,
};
let result = matches_complex_selector_internal(selector_iter.clone(),
&element,
relations,
flags_setter);
match (result, c) {
// Return the status immediately.
(SelectorMatchingResult::Matched, _) => return result,
(SelectorMatchingResult::NotMatchedGlobally, _) => return result,
// Upgrade the failure status to
// NotMatchedAndRestartFromClosestDescendant.
(_, Combinator::Child) => return SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant,
// Return the status directly.
(_, Combinator::NextSibling) => return result,
// If the failure status is NotMatchedAndRestartFromClosestDescendant
// and combinator is Combinator::LaterSibling, give up this Combinator::LaterSibling matching
// and restart from the closest descendant combinator.
(SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant, Combinator::LaterSibling)
=> return result,
// The Combinator::Descendant combinator and the status is
// NotMatchedAndRestartFromClosestLaterSibling or
// NotMatchedAndRestartFromClosestDescendant,
// or the Combinator::LaterSibling combinator and the status is
// NotMatchedAndRestartFromClosestDescendant
// can continue to matching on the next candidate element.
_ => {},
}
next_element = if siblings {
element.prev_sibling_element()
} else {
element.parent_element()
};
}
}
}
}
/// Determines whether the given element matches the given single selector.
#[inline]
fn matches_simple_selector<E, F>(
selector: &Component<E::Impl>,
element: &E,
relations: &mut StyleRelations,
flags_setter: &mut F)
-> bool
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
macro_rules! relation_if {
($ex:expr, $flag:ident) => {
if $ex {
*relations |= $flag;
true
} else {
false
}
}
}
match *selector {
Component::Combinator(_) => unreachable!(),
Component::LocalName(LocalName { ref name, ref lower_name }) => {
let name = if element.is_html_element_in_html_document() { lower_name } else { name };
element.get_local_name() == name.borrow()
}
Component::Namespace(ref namespace) => {
element.get_namespace() == namespace.url.borrow()
}
// TODO: case-sensitivity depends on the document type and quirks mode
Component::ID(ref id) => {
relation_if!(element.get_id().map_or(false, |attr| attr == *id),
AFFECTED_BY_ID_SELECTOR)
}
Component::Class(ref class) => {
element.has_class(class)
}
Component::AttrExists(ref attr) => {
element.match_attr_has(attr)
}
Component::AttrEqual(ref attr, ref value, case_sensitivity) => {
match case_sensitivity {
CaseSensitivity::CaseSensitive => element.match_attr_equals(attr, value),
CaseSensitivity::CaseInsensitive => element.match_attr_equals_ignore_ascii_case(attr, value),
}
}
Component::AttrIncludes(ref attr, ref value) => {
element.match_attr_includes(attr, value)
}
Component::AttrDashMatch(ref attr, ref value) => {
element.match_attr_dash(attr, value)
}
Component::AttrPrefixMatch(ref attr, ref value) => {
element.match_attr_prefix(attr, value)
}
Component::AttrSubstringMatch(ref attr, ref value) => {
element.match_attr_substring(attr, value)
}
Component::AttrSuffixMatch(ref attr, ref value) => {
element.match_attr_suffix(attr, value)
}
Component::AttrIncludesNeverMatch(..) |
Component::AttrPrefixNeverMatch(..) |
Component::AttrSubstringNeverMatch(..) |
Component::AttrSuffixNeverMatch(..) => {
false
}
Component::NonTSPseudoClass(ref pc) => {
element.match_non_ts_pseudo_class(pc, relations, flags_setter)
}
Component::FirstChild => {
matches_first_child(element, flags_setter)
}
Component::LastChild => {
matches_last_child(element, flags_setter)
}
Component::OnlyChild => {
matches_first_child(element, flags_setter) &&
matches_last_child(element, flags_setter)
}
Component::Root => {
// We never share styles with an element with no parent, so no point
// in creating a new StyleRelation.
element.is_root()
}
Component::Empty => {
flags_setter(element, HAS_EMPTY_SELECTOR);
element.is_empty()
}
Component::NthChild(a, b) => {
matches_generic_nth_child(element, a, b, false, false, flags_setter)
}
Component::NthLastChild(a, b) => {
matches_generic_nth_child(element, a, b, false, true, flags_setter)
}
Component::NthOfType(a, b) => {
matches_generic_nth_child(element, a, b, true, false, flags_setter)
}
Component::NthLastOfType(a, b) => {
matches_generic_nth_child(element, a, b, true, true, flags_setter)
}
Component::FirstOfType => {
matches_generic_nth_child(element, 0, 1, true, false, flags_setter)
}
Component::LastOfType => {
matches_generic_nth_child(element, 0, 1, true, true, flags_setter)
}
Component::OnlyOfType => {
matches_generic_nth_child(element, 0, 1, true, false, flags_setter) &&
matches_generic_nth_child(element, 0, 1, true, true, flags_setter)
}
Component::Negation(ref negated) => {
!negated.iter().all(|s| {
match matches_complex_selector_internal(s.iter(),
element,
relations,
flags_setter) {
SelectorMatchingResult::Matched => true,
_ => false,
}
})
}
}
}
#[inline]
fn matches_generic_nth_child<E, F>(element: &E,
a: i32,
b: i32,
is_of_type: bool,
is_from_end: bool,
flags_setter: &mut F)
-> bool
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
flags_setter(element, if is_from_end {
HAS_SLOW_SELECTOR
} else {
HAS_SLOW_SELECTOR_LATER_SIBLINGS
});
let mut index = 1;
let mut next_sibling = if is_from_end {
element.next_sibling_element()
} else {
element.prev_sibling_element()
};
loop {
let sibling = match next_sibling {
None => break,
Some(next_sibling) => next_sibling
};
if is_of_type {
if element.get_local_name() == sibling.get_local_name() &&
element.get_namespace() == sibling.get_namespace() {
index += 1;
}
} else {
index += 1;
}
next_sibling = if is_from_end {
sibling.next_sibling_element()
} else {
sibling.prev_sibling_element()
};
}
if a == 0 {
b == index
} else {
(index - b) / a >= 0 &&
(index - b) % a == 0
}
}
#[inline]
fn matches_first_child<E, F>(element: &E, flags_setter: &mut F) -> bool
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
flags_setter(element, HAS_EDGE_CHILD_SELECTOR);
element.prev_sibling_element().is_none()
}
#[inline]
fn matches_last_child<E, F>(element: &E, flags_setter: &mut F) -> bool
where E: Element,
F: FnMut(&E, ElementSelectorFlags),
{
flags_setter(element, HAS_EDGE_CHILD_SELECTOR);
element.next_sibling_element().is_none()
}