Look for relevant links while matching

Adjust the matching process to look for a "relevant link" while matching.  A
"relevant link" is the element being matched if it is a link or the nearest
ancestor link.

Matching for links now depends on the `VisitedHandlingMode`, which determines
whether all links match as if they are unvisited (the default) or if the
relevant link matches as visited (and all others remain unvisited).

If a relevant link is ever found for any selector, track this as part of the
`MatchingContext` object.  This is used in the next patch to determine if an
additional match and cascade should be performed to compute the styles when
visited.

MozReview-Commit-ID: 3xUbRo7vpuD

components/script/dom/element.rs

@@ -87,8 +87,9 @@ use ref_filter_map::ref_filter_map;
 use script_layout_interface::message::ReflowQueryType;
 use script_thread::Runnable;
 use selectors::attr::{AttrSelectorOperation, NamespaceConstraint};
-use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode, matches_selector_list};
+use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode};
 use selectors::matching::{HAS_EDGE_CHILD_SELECTOR, HAS_SLOW_SELECTOR, HAS_SLOW_SELECTOR_LATER_SIBLINGS};
+use selectors::matching::{RelevantLinkStatus, matches_selector_list};
 use servo_atoms::Atom;
 use std::ascii::AsciiExt;
 use std::borrow::Cow;
@@ -2429,6 +2430,7 @@ impl<'a> ::selectors::Element for Root<Element> {
     fn match_non_ts_pseudo_class<F>(&self,
                                     pseudo_class: &NonTSPseudoClass,
                                     _: &mut MatchingContext,
+                                    _: &RelevantLinkStatus,
                                     _: &mut F)
                                     -> bool
         where F: FnMut(&Self, ElementSelectorFlags),
@@ -2478,6 +2480,20 @@ impl<'a> ::selectors::Element for Root<Element> {
         }
     }
 
+    fn is_link(&self) -> bool {
+        // FIXME: This is HTML only.
+        let node = self.upcast::<Node>();
+        match node.type_id() {
+            // https://html.spec.whatwg.org/multipage/#selector-link
+            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAnchorElement)) |
+            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAreaElement)) |
+            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLLinkElement)) => {
+                self.has_attribute(&local_name!("href"))
+            },
+            _ => false,
+        }
+    }
+
     fn get_id(&self) -> Option<Atom> {
         self.id_attribute.borrow().clone()
     }
@@ -2592,20 +2608,6 @@ impl Element {
         }
     }
 
-    fn is_link(&self) -> bool {
-        // FIXME: This is HTML only.
-        let node = self.upcast::<Node>();
-        match node.type_id() {
-            // https://html.spec.whatwg.org/multipage/#selector-link
-            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAnchorElement)) |
-            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAreaElement)) |
-            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLLinkElement)) => {
-                self.has_attribute(&local_name!("href"))
-            },
-            _ => false,
-        }
-    }
-
     /// Please call this method *only* for real click events
     ///
     /// https://html.spec.whatwg.org/multipage/#run-authentic-click-activation-steps

components/script/layout_wrapper.rs

@@ -51,7 +51,7 @@ use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutD
 use script_layout_interface::wrapper_traits::{DangerousThreadSafeLayoutNode, GetLayoutData, LayoutNode};
 use script_layout_interface::wrapper_traits::{PseudoElementType, ThreadSafeLayoutElement, ThreadSafeLayoutNode};
 use selectors::attr::{AttrSelectorOperation, NamespaceConstraint};
-use selectors::matching::{ElementSelectorFlags, MatchingContext};
+use selectors::matching::{ElementSelectorFlags, MatchingContext, RelevantLinkStatus};
 use servo_atoms::Atom;
 use servo_url::ServoUrl;
 use std::fmt;
@@ -680,6 +680,7 @@ impl<'le> ::selectors::Element for ServoLayoutElement<'le> {
     fn match_non_ts_pseudo_class<F>(&self,
                                     pseudo_class: &NonTSPseudoClass,
                                     _: &mut MatchingContext,
+                                    _: &RelevantLinkStatus,
                                     _: &mut F)
                                     -> bool
         where F: FnMut(&Self, ElementSelectorFlags),
@@ -687,16 +688,7 @@ impl<'le> ::selectors::Element for ServoLayoutElement<'le> {
         match *pseudo_class {
             // https://github.com/servo/servo/issues/8718
             NonTSPseudoClass::Link |
-            NonTSPseudoClass::AnyLink => unsafe {
-                match self.as_node().script_type_id() {
-                    // https://html.spec.whatwg.org/multipage/#selector-link
-                    NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAnchorElement)) |
-                    NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAreaElement)) |
-                    NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLLinkElement)) =>
-                        (*self.element.unsafe_get()).get_attr_val_for_layout(&ns!(), &local_name!("href")).is_some(),
-                    _ => false,
-                }
-            },
+            NonTSPseudoClass::AnyLink => self.is_link(),
             NonTSPseudoClass::Visited => false,
 
             // FIXME(#15746): This is wrong, we need to instead use extended filtering as per RFC4647
@@ -731,6 +723,20 @@ impl<'le> ::selectors::Element for ServoLayoutElement<'le> {
         }
     }
 
+    #[inline]
+    fn is_link(&self) -> bool {
+        unsafe {
+            match self.as_node().script_type_id() {
+                // https://html.spec.whatwg.org/multipage/#selector-link
+                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAnchorElement)) |
+                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAreaElement)) |
+                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLLinkElement)) =>
+                    (*self.element.unsafe_get()).get_attr_val_for_layout(&ns!(), &local_name!("href")).is_some(),
+                _ => false,
+            }
+        }
+    }
+
     #[inline]
     fn get_id(&self) -> Option<Atom> {
         unsafe {
@@ -1187,6 +1193,7 @@ impl<'le> ::selectors::Element for ServoThreadSafeLayoutElement<'le> {
     fn match_non_ts_pseudo_class<F>(&self,
                                     _: &NonTSPseudoClass,
                                     _: &mut MatchingContext,
+                                    _: &RelevantLinkStatus,
                                     _: &mut F)
                                     -> bool
         where F: FnMut(&Self, ElementSelectorFlags),
@@ -1196,6 +1203,11 @@ impl<'le> ::selectors::Element for ServoThreadSafeLayoutElement<'le> {
         false
     }
 
+    fn is_link(&self) -> bool {
+        warn!("ServoThreadSafeLayoutElement::is_link called");
+        false
+    }
+
     fn get_id(&self) -> Option<Atom> {
         debug!("ServoThreadSafeLayoutElement::get_id called");
         None

components/selectors/matching.rs

@@ -94,6 +94,16 @@ pub enum MatchingMode {
     ForStatelessPseudoElement,
 }
 
+/// The mode to use when matching unvisited and visited links.
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+pub enum VisitedHandlingMode {
+    /// All links are matched as if they are unvisted.
+    AllLinksUnvisited,
+    /// 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,
+}
 
 /// 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
@@ -106,6 +116,13 @@ pub struct MatchingContext<'a> {
     pub matching_mode: MatchingMode,
     /// The bloom filter used to fast-reject selectors.
     pub bloom_filter: Option<&'a BloomFilter>,
+    /// Input that controls how matching for links is handled.
+    pub visited_handling: VisitedHandlingMode,
+    /// Output that records whether we encountered a "relevant link" while
+    /// matching _any_ selector for this element. (This differs from
+    /// `RelevantLinkStatus` which tracks the status for the _current_ selector
+    /// only.)
+    relevant_link_found: bool,
 }
 
 impl<'a> MatchingContext<'a> {
@@ -118,6 +135,8 @@ impl<'a> MatchingContext<'a> {
             relations: StyleRelations::empty(),
             matching_mode: matching_mode,
             bloom_filter: bloom_filter,
+            visited_handling: VisitedHandlingMode::AllLinksUnvisited,
+            relevant_link_found: false,
         }
     }
 }
@@ -156,6 +175,100 @@ fn may_match<E>(sel: &SelectorInner<E::Impl>,
     true
 }
 
+/// Tracks whether we are currently looking for relevant links for a given
+/// complex selector. A "relevant link" is the element being matched if it is a
+/// link or the nearest ancestor link.
+///
+/// `matches_complex_selector` creates a new instance of this for each complex
+/// selector we try to match for an element. This is done because `is_visited`
+/// and `is_unvisited` are based on relevant link state of only the current
+/// complex selector being matched (not the global relevant link status for all
+/// selectors in `MatchingContext`).
+#[derive(PartialEq, Eq, Copy, Clone)]
+pub enum RelevantLinkStatus {
+    /// Looking for a possible relevant link.  This is the initial mode when
+    /// matching a selector.
+    Looking,
+    /// Not looking for a relevant link.  We transition to this mode if we
+    /// encounter a sibiling combinator (since only ancestor combinators are
+    /// allowed for this purpose).
+    NotLooking,
+    /// Found a relevant link for the element being matched.
+    Found,
+}
+
+impl Default for RelevantLinkStatus {
+    fn default() -> Self {
+        RelevantLinkStatus::NotLooking
+    }
+}
+
+impl RelevantLinkStatus {
+    /// If we found the relevant link for this element, record that in the
+    /// overall matching context for the element as a whole and stop looking for
+    /// addtional links.
+    fn examine_potential_link<E>(&self, element: &E, context: &mut MatchingContext)
+                                 -> RelevantLinkStatus
+        where E: Element,
+    {
+        if *self != RelevantLinkStatus::Looking {
+            return *self
+        }
+
+        if !element.is_link() {
+            return *self
+        }
+
+        // We found a relevant link. Record this in the `MatchingContext`,
+        // where we track whether one was found for _any_ selector (meaning
+        // this field might already be true from a previous selector).
+        context.relevant_link_found = true;
+        // Also return `Found` to update the relevant link status for _this_
+        // specific selector's matching process.
+        RelevantLinkStatus::Found
+    }
+
+    /// Returns whether an element is considered visited for the purposes of
+    /// matching.  This is true only if the element is a link, an relevant link
+    /// exists for the element, and the visited handling mode is set to accept
+    /// relevant links as visited.
+    pub fn is_visited<E>(&self, element: &E, context: &MatchingContext) -> bool
+        where E: Element,
+    {
+        if !element.is_link() {
+            return false
+        }
+
+        // Non-relevant links are always unvisited.
+        if *self != RelevantLinkStatus::Found {
+            return false
+        }
+
+        context.visited_handling == VisitedHandlingMode::RelevantLinkVisited
+    }
+
+    /// Returns whether an element is considered unvisited for the purposes of
+    /// matching.  Assuming the element is a link, this is always true for
+    /// non-relevant links, since only relevant links can potentially be treated
+    /// as visited.  If this is a relevant link, then is it unvisited if the
+    /// visited handling mode is set to treat all links as unvisted (including
+    /// relevant links).
+    pub fn is_unvisited<E>(&self, element: &E, context: &MatchingContext) -> bool
+        where E: Element,
+    {
+        if !element.is_link() {
+            return false
+        }
+
+        // Non-relevant links are always unvisited.
+        if *self != RelevantLinkStatus::Found {
+            return true
+        }
+
+        context.visited_handling == VisitedHandlingMode::AllLinksUnvisited
+    }
+}
+
 /// A result of selector matching, includes 3 failure types,
 ///
 ///   NotMatchedAndRestartFromClosestLaterSibling
@@ -267,6 +380,7 @@ pub fn matches_complex_selector<E, F>(complex_selector: &ComplexSelector<E::Impl
     match matches_complex_selector_internal(iter,
                                             element,
                                             context,
+                                            RelevantLinkStatus::Looking,
                                             flags_setter) {
         SelectorMatchingResult::Matched => true,
         _ => false
@@ -276,13 +390,16 @@ pub fn matches_complex_selector<E, F>(complex_selector: &ComplexSelector<E::Impl
 fn matches_complex_selector_internal<E, F>(mut selector_iter: SelectorIter<E::Impl>,
                                            element: &E,
                                            context: &mut MatchingContext,
+                                           relevant_link: RelevantLinkStatus,
                                            flags_setter: &mut F)
                                            -> SelectorMatchingResult
      where E: Element,
            F: FnMut(&E, ElementSelectorFlags),
 {
+    let mut relevant_link = relevant_link.examine_potential_link(element, context);
+
     let matches_all_simple_selectors = selector_iter.all(|simple| {
-        matches_simple_selector(simple, element, context, flags_setter)
+        matches_simple_selector(simple, element, context, &relevant_link, flags_setter)
     });
 
     let combinator = selector_iter.next_sequence();
@@ -300,6 +417,9 @@ fn matches_complex_selector_internal<E, F>(mut selector_iter: SelectorIter<E::Im
         Some(c) => {
             let (mut next_element, candidate_not_found) = match c {
                 Combinator::NextSibling | Combinator::LaterSibling => {
+                    // Only ancestor combinators are allowed while looking for
+                    // relevant links, so switch to not looking.
+                    relevant_link = RelevantLinkStatus::NotLooking;
                     (element.prev_sibling_element(),
                      SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant)
                 }
@@ -321,6 +441,7 @@ fn matches_complex_selector_internal<E, F>(mut selector_iter: SelectorIter<E::Im
                 let result = matches_complex_selector_internal(selector_iter.clone(),
                                                                &element,
                                                                context,
+                                                               relevant_link,
                                                                flags_setter);
                 match (result, c) {
                     // Return the status immediately.
@@ -365,6 +486,7 @@ fn matches_simple_selector<E, F>(
         selector: &Component<E::Impl>,
         element: &E,
         context: &mut MatchingContext,
+        relevant_link: &RelevantLinkStatus,
         flags_setter: &mut F)
         -> bool
     where E: Element,
@@ -465,7 +587,7 @@ fn matches_simple_selector<E, F>(
             )
         }
         Component::NonTSPseudoClass(ref pc) => {
-            element.match_non_ts_pseudo_class(pc, context, flags_setter)
+            element.match_non_ts_pseudo_class(pc, context, relevant_link, flags_setter)
         }
         Component::FirstChild => {
             matches_first_child(element, flags_setter)
@@ -509,7 +631,7 @@ fn matches_simple_selector<E, F>(
             matches_generic_nth_child(element, 0, 1, true, true, flags_setter)
         }
         Component::Negation(ref negated) => {
-            !negated.iter().all(|ss| matches_simple_selector(ss, element, context, flags_setter))
+            !negated.iter().all(|ss| matches_simple_selector(ss, element, context, relevant_link, flags_setter))
         }
     }
 }

components/selectors/tree.rs

@@ -2,11 +2,11 @@
  * 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/. */
 
-//! Traits that nodes must implement. Breaks the otherwise-cyclic dependency between layout and
-//! style.
+//! Traits that nodes must implement. Breaks the otherwise-cyclic dependency
+//! between layout and style.
 
 use attr::{AttrSelectorOperation, NamespaceConstraint};
-use matching::{ElementSelectorFlags, MatchingContext};
+use matching::{ElementSelectorFlags, MatchingContext, RelevantLinkStatus};
 use parser::SelectorImpl;
 
 pub trait Element: Sized {
@@ -50,6 +50,7 @@ pub trait Element: Sized {
     fn match_non_ts_pseudo_class<F>(&self,
                                     pc: &<Self::Impl as SelectorImpl>::NonTSPseudoClass,
                                     context: &mut MatchingContext,
+                                    relevant_link: &RelevantLinkStatus,
                                     flags_setter: &mut F) -> bool
         where F: FnMut(&Self, ElementSelectorFlags);
 
@@ -58,6 +59,9 @@ pub trait Element: Sized {
                             context: &mut MatchingContext)
                             -> bool;
 
+    /// Whether this element is a `link`.
+    fn is_link(&self) -> bool;
+
     fn get_id(&self) -> Option<<Self::Impl as SelectorImpl>::Identifier>;
 
     fn has_class(&self, name: &<Self::Impl as SelectorImpl>::ClassName) -> bool;

components/style/gecko/wrapper.rs

@@ -65,7 +65,7 @@ use rule_tree::CascadeLevel as ServoCascadeLevel;
 use selector_parser::ElementExt;
 use selectors::Element;
 use selectors::attr::{AttrSelectorOperation, AttrSelectorOperator, CaseSensitivity, NamespaceConstraint};
-use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode};
+use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode, RelevantLinkStatus};
 use shared_lock::Locked;
 use sink::Push;
 use std::cell::RefCell;
@@ -1236,6 +1236,7 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
     fn match_non_ts_pseudo_class<F>(&self,
                                     pseudo_class: &NonTSPseudoClass,
                                     context: &mut MatchingContext,
+                                    relevant_link: &RelevantLinkStatus,
                                     flags_setter: &mut F)
                                     -> bool
         where F: FnMut(&Self, ElementSelectorFlags),
@@ -1243,8 +1244,6 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
         use selectors::matching::*;
         match *pseudo_class {
             NonTSPseudoClass::AnyLink |
-            NonTSPseudoClass::Link |
-            NonTSPseudoClass::Visited |
             NonTSPseudoClass::Active |
             NonTSPseudoClass::Focus |
             NonTSPseudoClass::Hover |
@@ -1293,6 +1292,8 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
                 // here, to handle `:any-link` correctly.
                 self.get_state().intersects(pseudo_class.state_flag())
             },
+            NonTSPseudoClass::Link => relevant_link.is_unvisited(self, context),
+            NonTSPseudoClass::Visited => relevant_link.is_visited(self, context),
             NonTSPseudoClass::MozFirstNode => {
                 flags_setter(self, HAS_EDGE_CHILD_SELECTOR);
                 let mut elem = self.as_node();
@@ -1369,6 +1370,15 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
         }
     }
 
+    #[inline]
+    fn is_link(&self) -> bool {
+        let mut context = MatchingContext::new(MatchingMode::Normal, None);
+        self.match_non_ts_pseudo_class(&NonTSPseudoClass::AnyLink,
+                                       &mut context,
+                                       &RelevantLinkStatus::default(),
+                                       &mut |_, _| {})
+    }
+
     fn get_id(&self) -> Option<Atom> {
         if !self.has_id() {
             return None;
@@ -1420,14 +1430,6 @@ impl<'a> NamespaceConstraintHelpers for NamespaceConstraint<&'a Namespace> {
 }
 
 impl<'le> ElementExt for GeckoElement<'le> {
-    #[inline]
-    fn is_link(&self) -> bool {
-        let mut context = MatchingContext::new(MatchingMode::Normal, None);
-        self.match_non_ts_pseudo_class(&NonTSPseudoClass::AnyLink,
-                                       &mut context,
-                                       &mut |_, _| {})
-    }
-
     #[inline]
     fn matches_user_and_author_rules(&self) -> bool {
         self.flags() & (NODE_IS_IN_NATIVE_ANONYMOUS_SUBTREE as u32) == 0

components/style/restyle_hints.rs

@@ -20,7 +20,7 @@ use selector_map::{SelectorMap, SelectorMapEntry};
 use selector_parser::{NonTSPseudoClass, PseudoElement, SelectorImpl, Snapshot, SnapshotMap, AttrValue};
 use selectors::Element;
 use selectors::attr::{AttrSelectorOperation, NamespaceConstraint};
-use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode};
+use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode, RelevantLinkStatus};
 use selectors::matching::matches_selector;
 use selectors::parser::{Combinator, Component, Selector, SelectorInner, SelectorMethods};
 use selectors::visitor::SelectorVisitor;
@@ -535,6 +535,7 @@ impl<'a, E> Element for ElementWrapper<'a, E>
     fn match_non_ts_pseudo_class<F>(&self,
                                     pseudo_class: &NonTSPseudoClass,
                                     context: &mut MatchingContext,
+                                    relevant_link: &RelevantLinkStatus,
                                     _setter: &mut F)
                                     -> bool
         where F: FnMut(&Self, ElementSelectorFlags),
@@ -580,6 +581,7 @@ impl<'a, E> Element for ElementWrapper<'a, E>
         if flag.is_empty() {
             return self.element.match_non_ts_pseudo_class(pseudo_class,
                                                           context,
+                                                          relevant_link,
                                                           &mut |_, _| {})
         }
         match self.snapshot().and_then(|s| s.state()) {
@@ -587,6 +589,7 @@ impl<'a, E> Element for ElementWrapper<'a, E>
             None => {
                 self.element.match_non_ts_pseudo_class(pseudo_class,
                                                        context,
+                                                       relevant_link,
                                                        &mut |_, _| {})
             }
         }
@@ -600,6 +603,14 @@ impl<'a, E> Element for ElementWrapper<'a, E>
         self.element.match_pseudo_element(pseudo_element, context)
     }
 
+    fn is_link(&self) -> bool {
+        let mut context = MatchingContext::new(MatchingMode::Normal, None);
+        self.match_non_ts_pseudo_class(&NonTSPseudoClass::AnyLink,
+                                       &mut context,
+                                       &RelevantLinkStatus::default(),
+                                       &mut |_, _| {})
+    }
+
     fn parent_element(&self) -> Option<Self> {
         self.element.parent_element()
             .map(|e| ElementWrapper::new(e, self.snapshot_map))

components/style/selector_parser.rs

@@ -103,9 +103,6 @@ pub enum PseudoElementCascadeType {
 
 /// An extension to rust-selector's `Element` trait.
 pub trait ElementExt: Element<Impl=SelectorImpl> + Debug {
-    /// Whether this element is a `link`.
-    fn is_link(&self) -> bool;
-
     /// Whether this element should match user and author rules.
     ///
     /// We use this for Native Anonymous Content in Gecko.

components/style/servo/selector_parser.rs

@@ -16,7 +16,6 @@ use restyle_hints::ElementSnapshot;
 use selector_parser::{ElementExt, PseudoElementCascadeType, SelectorParser};
 use selectors::Element;
 use selectors::attr::{AttrSelectorOperation, NamespaceConstraint};
-use selectors::matching::{MatchingContext, MatchingMode};
 use selectors::parser::SelectorMethods;
 use selectors::visitor::SelectorVisitor;
 use std::borrow::Cow;
@@ -601,13 +600,6 @@ impl ServoElementSnapshot {
 }
 
 impl<E: Element<Impl=SelectorImpl> + Debug> ElementExt for E {
-    fn is_link(&self) -> bool {
-        let mut context = MatchingContext::new(MatchingMode::Normal, None);
-        self.match_non_ts_pseudo_class(&NonTSPseudoClass::AnyLink,
-                                       &mut context,
-                                       &mut |_, _| {})
-    }
-
     #[inline]
     fn matches_user_and_author_rules(&self) -> bool {
         true