Auto merge of #17471 - aethanyc:fix-pseudo-element-matching-xbl, r=emilio

stylo: Fix pseudo element matching for rules in XBL stylesheets

This change was reviewed in https://bugzilla.mozilla.org/show_bug.cgi?id=1372876

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3 files changed, 22 insertions, 21 deletions

diff --git a/components/style/dom.rs b/components/style/dom.rs
index f4031c1d6f7..de736e291c6 100644
--- a/components/style/dom.rs
+++ b/components/style/dom.rs
@@ -602,6 +602,21 @@ pub trait TElement : Eq + PartialEq + Debug + Hash + Sized + Copy + Clone +
         None
     }
 
+    /// Returns the rule hash target given an element.
+    fn rule_hash_target(&self) -> Self {
+        let is_implemented_pseudo =
+            self.implemented_pseudo_element().is_some();
+
+        // NB: This causes use to rule has pseudo selectors based on the
+        // properties of the originating element (which is fine, given the
+        // find_first_from_right usage).
+        if is_implemented_pseudo {
+            self.closest_non_native_anonymous_ancestor().unwrap()
+        } else {
+            *self
+        }
+    }
+
     /// Gets declarations from XBL bindings from the element. Only gecko element could have this.
     fn get_declarations_from_xbl_bindings<V>(&self,
                                              _pseudo_element: Option<&PseudoElement>,
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index b97a7fc1081..9f2169028ca 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -1019,7 +1019,9 @@ impl<'le> TElement for GeckoElement<'le> {
         where V: Push<ApplicableDeclarationBlock> + VecLike<ApplicableDeclarationBlock> {
         // Walk the binding scope chain, starting with the binding attached to our content, up
         // till we run out of scopes or we get cut off.
-        let mut current = Some(*self);
+
+        // If we are NAC, we want to get rules from our rule_hash_target.
+        let mut current = Some(self.rule_hash_target());
 
         while let Some(element) = current {
             if let Some(binding) = element.get_xbl_binding() {
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 80a15c14081..2825e6c1088 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -957,22 +957,6 @@ impl Stylist {
         }
     }
 
-    /// Returns the rule hash target given an element.
-    fn rule_hash_target<E>(&self, element: E) -> E
-        where E: TElement
-    {
-        let is_implemented_pseudo =
-            element.implemented_pseudo_element().is_some();
-
-        // NB: This causes use to rule has pseudo selectors based on the
-        // properties of the originating element (which is fine, given the
-        // find_first_from_right usage).
-        if is_implemented_pseudo {
-            element.closest_non_native_anonymous_ancestor().unwrap()
-        } else {
-            element
-        }
-    }
 
     /// Returns the applicable CSS declarations for the given element by
     /// treating us as an XBL stylesheet-only stylist.
@@ -991,7 +975,7 @@ impl Stylist {
             Some(map) => map,
             None => return,
         };
-        let rule_hash_target = self.rule_hash_target(*element);
+        let rule_hash_target = element.rule_hash_target();
 
         // nsXBLPrototypeResources::ComputeServoStyleSet() added XBL stylesheets under author
         // (doc) level.
@@ -1037,7 +1021,7 @@ impl Stylist {
             Some(map) => map,
             None => return,
         };
-        let rule_hash_target = self.rule_hash_target(*element);
+        let rule_hash_target = element.rule_hash_target();
 
         debug!("Determining if style is shareable: pseudo: {}",
                pseudo_element.is_some());
@@ -1099,8 +1083,8 @@ impl Stylist {
 
         // Step 3b: XBL rules.
         let cut_off_inheritance =
-            rule_hash_target.get_declarations_from_xbl_bindings(pseudo_element,
-                                                                applicable_declarations);
+            element.get_declarations_from_xbl_bindings(pseudo_element,
+                                                       applicable_declarations);
         debug!("XBL: {:?}", context.relations);
 
         if rule_hash_target.matches_user_and_author_rules() && !only_default_rules {