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diff --git a/servo/components/selectors/context.rs b/servo/components/selectors/context.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 https://mozilla.org/MPL/2.0/. */
+
+use crate::attr::CaseSensitivity;
+use crate::bloom::BloomFilter;
+use crate::nth_index_cache::{NthIndexCache, NthIndexCacheInner};
+use crate::parser::{Selector, SelectorImpl};
+use crate::tree::{Element, OpaqueElement};
+
+/// What kind of selector matching mode we should use.
+///
+/// There are two modes of selector matching. The difference is only noticeable
+/// in presence of pseudo-elements.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum MatchingMode {
+    /// Don't ignore any pseudo-element selectors.
+    Normal,
+
+    /// Ignores any stateless pseudo-element selectors in the rightmost sequence
+    /// of simple selectors.
+    ///
+    /// This is useful, for example, to match against ::before when you aren't a
+    /// pseudo-element yourself.
+    ///
+    /// For example, in presence of `::before:hover`, it would never match, but
+    /// `::before` would be ignored as in "matching".
+    ///
+    /// It's required for all the selectors you match using this mode to have a
+    /// pseudo-element.
+    ForStatelessPseudoElement,
+}
+
+/// The mode to use when matching unvisited and visited links.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum VisitedHandlingMode {
+    /// All links are matched as if they are unvisted.
+    AllLinksUnvisited,
+    /// All links are matched as if they are visited and unvisited (both :link
+    /// and :visited match).
+    ///
+    /// This is intended to be used from invalidation code, to be conservative
+    /// about whether we need to restyle a link.
+    AllLinksVisitedAndUnvisited,
+    /// A element's "relevant link" is the element being matched if it is a link
+    /// or the nearest ancestor link. The relevant link is matched as though it
+    /// is visited, and all other links are matched as if they are unvisited.
+    RelevantLinkVisited,
+}
+
+impl VisitedHandlingMode {
+    #[inline]
+    pub fn matches_visited(&self) -> bool {
+        matches!(
+            *self,
+            VisitedHandlingMode::RelevantLinkVisited |
+                VisitedHandlingMode::AllLinksVisitedAndUnvisited
+        )
+    }
+
+    #[inline]
+    pub fn matches_unvisited(&self) -> bool {
+        matches!(
+            *self,
+            VisitedHandlingMode::AllLinksUnvisited |
+                VisitedHandlingMode::AllLinksVisitedAndUnvisited
+        )
+    }
+}
+
+/// Whether we need to set selector invalidation flags on elements for this
+/// match request.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum NeedsSelectorFlags {
+    No,
+    Yes,
+}
+
+/// Which quirks mode is this document in.
+///
+/// See: https://quirks.spec.whatwg.org/
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub enum QuirksMode {
+    /// Quirks mode.
+    Quirks,
+    /// Limited quirks mode.
+    LimitedQuirks,
+    /// No quirks mode.
+    NoQuirks,
+}
+
+impl QuirksMode {
+    #[inline]
+    pub fn classes_and_ids_case_sensitivity(self) -> CaseSensitivity {
+        match self {
+            QuirksMode::NoQuirks | QuirksMode::LimitedQuirks => CaseSensitivity::CaseSensitive,
+            QuirksMode::Quirks => CaseSensitivity::AsciiCaseInsensitive,
+        }
+    }
+}
+
+/// Data associated with the matching process for a element.  This context is
+/// used across many selectors for an element, so it's not appropriate for
+/// transient data that applies to only a single selector.
+pub struct MatchingContext<'a, Impl>
+where
+    Impl: SelectorImpl,
+{
+    /// Input with the matching mode we should use when matching selectors.
+    matching_mode: MatchingMode,
+    /// Input with the bloom filter used to fast-reject selectors.
+    pub bloom_filter: Option<&'a BloomFilter>,
+    /// A cache to speed up nth-index-like selectors.
+    pub nth_index_cache: &'a mut NthIndexCache,
+    /// The element which is going to match :scope pseudo-class. It can be
+    /// either one :scope element, or the scoping element.
+    ///
+    /// Note that, although in theory there can be multiple :scope elements,
+    /// in current specs, at most one is specified, and when there is one,
+    /// scoping element is not relevant anymore, so we use a single field for
+    /// them.
+    ///
+    /// When this is None, :scope will match the root element.
+    ///
+    /// See https://drafts.csswg.org/selectors-4/#scope-pseudo
+    pub scope_element: Option<OpaqueElement>,
+
+    /// The current shadow host we're collecting :host rules for.
+    pub current_host: Option<OpaqueElement>,
+
+    /// Controls how matching for links is handled.
+    visited_handling: VisitedHandlingMode,
+
+    /// The current nesting level of selectors that we're matching.
+    nesting_level: usize,
+
+    /// Whether we're inside a negation or not.
+    in_negation: bool,
+
+    /// An optional hook function for checking whether a pseudo-element
+    /// should match when matching_mode is ForStatelessPseudoElement.
+    pub pseudo_element_matching_fn: Option<&'a dyn Fn(&Impl::PseudoElement) -> bool>,
+
+    /// Extra implementation-dependent matching data.
+    pub extra_data: Impl::ExtraMatchingData<'a>,
+
+    /// The current element we're anchoring on for evaluating the relative selector.
+    current_relative_selector_anchor: Option<OpaqueElement>,
+    pub considered_relative_selector: bool,
+
+    quirks_mode: QuirksMode,
+    needs_selector_flags: NeedsSelectorFlags,
+    classes_and_ids_case_sensitivity: CaseSensitivity,
+    _impl: ::std::marker::PhantomData<Impl>,
+}
+
+impl<'a, Impl> MatchingContext<'a, Impl>
+where
+    Impl: SelectorImpl,
+{
+    /// Constructs a new `MatchingContext`.
+    pub fn new(
+        matching_mode: MatchingMode,
+        bloom_filter: Option<&'a BloomFilter>,
+        nth_index_cache: &'a mut NthIndexCache,
+        quirks_mode: QuirksMode,
+        needs_selector_flags: NeedsSelectorFlags,
+    ) -> Self {
+        Self::new_for_visited(
+            matching_mode,
+            bloom_filter,
+            nth_index_cache,
+            VisitedHandlingMode::AllLinksUnvisited,
+            quirks_mode,
+            needs_selector_flags,
+        )
+    }
+
+    /// Constructs a new `MatchingContext` for use in visited matching.
+    pub fn new_for_visited(
+        matching_mode: MatchingMode,
+        bloom_filter: Option<&'a BloomFilter>,
+        nth_index_cache: &'a mut NthIndexCache,
+        visited_handling: VisitedHandlingMode,
+        quirks_mode: QuirksMode,
+        needs_selector_flags: NeedsSelectorFlags,
+    ) -> Self {
+        Self {
+            matching_mode,
+            bloom_filter,
+            visited_handling,
+            nth_index_cache,
+            quirks_mode,
+            classes_and_ids_case_sensitivity: quirks_mode.classes_and_ids_case_sensitivity(),
+            needs_selector_flags,
+            scope_element: None,
+            current_host: None,
+            nesting_level: 0,
+            in_negation: false,
+            pseudo_element_matching_fn: None,
+            extra_data: Default::default(),
+            current_relative_selector_anchor: None,
+            considered_relative_selector: false,
+            _impl: ::std::marker::PhantomData,
+        }
+    }
+
+    // Grab a reference to the appropriate cache.
+    #[inline]
+    pub fn nth_index_cache(
+        &mut self,
+        is_of_type: bool,
+        is_from_end: bool,
+        selectors: &[Selector<Impl>],
+    ) -> &mut NthIndexCacheInner {
+        self.nth_index_cache.get(is_of_type, is_from_end, selectors)
+    }
+
+    /// Whether we're matching a nested selector.
+    #[inline]
+    pub fn is_nested(&self) -> bool {
+        self.nesting_level != 0
+    }
+
+    /// Whether we're matching inside a :not(..) selector.
+    #[inline]
+    pub fn in_negation(&self) -> bool {
+        self.in_negation
+    }
+
+    /// The quirks mode of the document.
+    #[inline]
+    pub fn quirks_mode(&self) -> QuirksMode {
+        self.quirks_mode
+    }
+
+    /// The matching-mode for this selector-matching operation.
+    #[inline]
+    pub fn matching_mode(&self) -> MatchingMode {
+        self.matching_mode
+    }
+
+    /// Whether we need to set selector flags.
+    #[inline]
+    pub fn needs_selector_flags(&self) -> bool {
+        self.needs_selector_flags == NeedsSelectorFlags::Yes
+    }
+
+    /// The case-sensitivity for class and ID selectors
+    #[inline]
+    pub fn classes_and_ids_case_sensitivity(&self) -> CaseSensitivity {
+        self.classes_and_ids_case_sensitivity
+    }
+
+    /// Runs F with a deeper nesting level.
+    #[inline]
+    pub fn nest<F, R>(&mut self, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R,
+    {
+        self.nesting_level += 1;
+        let result = f(self);
+        self.nesting_level -= 1;
+        result
+    }
+
+    /// Runs F with a deeper nesting level, and marking ourselves in a negation,
+    /// for a :not(..) selector, for example.
+    #[inline]
+    pub fn nest_for_negation<F, R>(&mut self, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R,
+    {
+        let old_in_negation = self.in_negation;
+        self.in_negation = true;
+        let result = self.nest(f);
+        self.in_negation = old_in_negation;
+        result
+    }
+
+    #[inline]
+    pub fn visited_handling(&self) -> VisitedHandlingMode {
+        self.visited_handling
+    }
+
+    /// Runs F with a different VisitedHandlingMode.
+    #[inline]
+    pub fn with_visited_handling_mode<F, R>(
+        &mut self,
+        handling_mode: VisitedHandlingMode,
+        f: F,
+    ) -> R
+    where
+        F: FnOnce(&mut Self) -> R,
+    {
+        let original_handling_mode = self.visited_handling;
+        self.visited_handling = handling_mode;
+        let result = f(self);
+        self.visited_handling = original_handling_mode;
+        result
+    }
+
+    /// Runs F with a given shadow host which is the root of the tree whose
+    /// rules we're matching.
+    #[inline]
+    pub fn with_shadow_host<F, E, R>(&mut self, host: Option<E>, f: F) -> R
+    where
+        E: Element,
+        F: FnOnce(&mut Self) -> R,
+    {
+        let original_host = self.current_host.take();
+        self.current_host = host.map(|h| h.opaque());
+        let result = f(self);
+        self.current_host = original_host;
+        result
+    }
+
+    /// Returns the current shadow host whose shadow root we're matching rules
+    /// against.
+    #[inline]
+    pub fn shadow_host(&self) -> Option<OpaqueElement> {
+        self.current_host
+    }
+
+    /// Runs F with a deeper nesting level, with the given element as the anchor,
+    /// for a :has(...) selector, for example.
+    #[inline]
+    pub fn nest_for_relative_selector<F, R>(&mut self, anchor: OpaqueElement, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R,
+    {
+        // TODO(dshin): Nesting should be rejected at parse time.
+        let original_relative_selector_anchor = self.current_relative_selector_anchor.take();
+        self.current_relative_selector_anchor = Some(anchor);
+        let result = self.nest(f);
+        self.current_relative_selector_anchor = original_relative_selector_anchor;
+        self.considered_relative_selector = true;
+        result
+    }
+
+    /// Returns the current anchor element to evaluate the relative selector against.
+    #[inline]
+    pub fn relative_selector_anchor(&self) -> Option<OpaqueElement> {
+        self.current_relative_selector_anchor
+    }
+}