servo: Merge #17078 - stylo: Avoid restyling the whole document when adding stylesheets (from emilio:stylesheet-invalidation-scopes); r=heycam

This is for bug 1357583.

Source-Repo: https://github.com/servo/servo
Source-Revision: 939716a7bc2ba2fbd8dcfe8b64d2f61edfa99c95

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : b25a23978bde1dc6abdaaa9621eca4903152efd2

servo/components/style/data.rs

@@ -388,6 +388,11 @@ impl StoredRestyleHint {
         self.0.insert(other.0)
     }
 
+    /// Contains whether the whole subtree is invalid.
+    pub fn contains_subtree(&self) -> bool {
+        self.0.contains(&RestyleHint::subtree())
+    }
+
     /// Insert another restyle hint, effectively resulting in the union of both.
     pub fn insert_from(&mut self, other: &Self) {
         self.0.insert_from(&other.0)

servo/components/style/gecko/data.rs

@@ -6,8 +6,10 @@
 
 use Atom;
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use dom::TElement;
 use fnv::FnvHashMap;
 use gecko::rules::{CounterStyleRule, FontFaceRule};
+use gecko::wrapper::GeckoElement;
 use gecko_bindings::bindings::RawServoStyleSet;
 use gecko_bindings::structs::RawGeckoPresContextOwned;
 use gecko_bindings::structs::nsIDocument;
@@ -72,13 +74,17 @@ impl PerDocumentStyleDataImpl {
     ///
     /// Implies also a stylesheet flush.
     pub fn reset_device(&mut self, guard: &SharedRwLockReadGuard) {
-        Arc::get_mut(self.stylist.device_mut()).unwrap().reset();
+        self.stylist.device_mut().reset();
         self.stylesheets.force_dirty();
-        self.flush_stylesheets(guard);
+        self.flush_stylesheets::<GeckoElement>(guard, None);
     }
 
     /// Recreate the style data if the stylesheets have changed.
-    pub fn flush_stylesheets(&mut self, guard: &SharedRwLockReadGuard) {
+    pub fn flush_stylesheets<E>(&mut self,
+                                guard: &SharedRwLockReadGuard,
+                                document_element: Option<E>)
+        where E: TElement,
+    {
         if !self.stylesheets.has_changed() {
             return;
         }
@@ -90,7 +96,8 @@ impl PerDocumentStyleDataImpl {
 
         let author_style_disabled = self.stylesheets.author_style_disabled();
         self.stylist.clear();
-        self.stylist.rebuild(self.stylesheets.flush(),
+        let iter = self.stylesheets.flush(document_element);
+        self.stylist.rebuild(iter,
                              &StylesheetGuards::same(guard),
                              /* ua_sheets = */ None,
                              /* stylesheets_changed = */ true,

servo/components/style/gecko/generated/bindings.rs

@@ -1804,7 +1804,9 @@ extern "C" {
                                                  before_unique_id: u64);
 }
 extern "C" {
-    pub fn Servo_StyleSet_FlushStyleSheets(set: RawServoStyleSetBorrowed);
+    pub fn Servo_StyleSet_FlushStyleSheets(set: RawServoStyleSetBorrowed,
+                                           doc_elem:
+                                               RawGeckoElementBorrowedOrNull);
 }
 extern "C" {
     pub fn Servo_StyleSet_NoteStyleSheetsChanged(set:

servo/components/style/invalidation/mod.rs

@@ -0,0 +1,296 @@
+/* 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/. */
+
+//! A collection of invalidations due to changes in which stylesheets affect a
+//! document.
+
+#![deny(unsafe_code)]
+
+use Atom;
+use data::StoredRestyleHint;
+use dom::{TElement, TNode};
+use fnv::FnvHashSet;
+use selector_parser::SelectorImpl;
+use selectors::parser::{Component, Selector};
+use shared_lock::SharedRwLockReadGuard;
+use stylesheets::{CssRule, Stylesheet};
+use stylist::Stylist;
+
+/// An invalidation scope represents a kind of subtree that may need to be
+/// restyled.
+#[derive(Debug, Hash, Eq, PartialEq)]
+enum InvalidationScope {
+    /// All the descendants of an element with a given id.
+    ID(Atom),
+    /// All the descendants of an element with a given class name.
+    Class(Atom),
+}
+
+impl InvalidationScope {
+    fn is_id(&self) -> bool {
+        matches!(*self, InvalidationScope::ID(..))
+    }
+
+    fn matches<E>(&self, element: E) -> bool
+        where E: TElement,
+    {
+        match *self {
+            InvalidationScope::Class(ref class) => {
+                element.has_class(class)
+            }
+            InvalidationScope::ID(ref id) => {
+                match element.get_id() {
+                    Some(element_id) => element_id == *id,
+                    None => false,
+                }
+            }
+        }
+    }
+}
+
+/// A set of invalidations due to stylesheet additions.
+///
+/// TODO(emilio): We might be able to do the same analysis for removals and
+/// media query changes too?
+pub struct StylesheetInvalidationSet {
+    /// The style scopes we know we have to restyle so far.
+    invalid_scopes: FnvHashSet<InvalidationScope>,
+    /// Whether the whole document should be invalid.
+    fully_invalid: bool,
+}
+
+impl StylesheetInvalidationSet {
+    /// Create an empty `StylesheetInvalidationSet`.
+    pub fn new() -> Self {
+        Self {
+            invalid_scopes: FnvHashSet::default(),
+            fully_invalid: false,
+        }
+    }
+
+    /// Mark the DOM tree styles' as fully invalid.
+    pub fn invalidate_fully(&mut self) {
+        debug!("StylesheetInvalidationSet::invalidate_fully");
+        self.invalid_scopes.clear();
+        self.fully_invalid = true;
+    }
+
+    /// Analyze the given stylesheet, and collect invalidations from their
+    /// rules, in order to avoid doing a full restyle when we style the document
+    /// next time.
+    pub fn collect_invalidations_for(
+        &mut self,
+        stylist: &Stylist,
+        stylesheet: &Stylesheet,
+        guard: &SharedRwLockReadGuard)
+    {
+        debug!("StylesheetInvalidationSet::collect_invalidations_for");
+        if self.fully_invalid {
+            debug!(" > Fully invalid already");
+            return;
+        }
+
+        if stylesheet.disabled() ||
+           !stylesheet.is_effective_for_device(stylist.device(), guard) {
+            debug!(" > Stylesheet was not effective");
+            return; // Nothing to do here.
+        }
+
+        for rule in stylesheet.effective_rules(stylist.device(), guard) {
+            self.collect_invalidations_for_rule(rule, guard);
+            if self.fully_invalid {
+                self.invalid_scopes.clear();
+                break;
+            }
+        }
+
+        debug!(" > resulting invalidations: {:?}", self.invalid_scopes);
+        debug!(" > fully_invalid: {}", self.fully_invalid);
+    }
+
+    /// Clears the invalidation set, invalidating elements as needed if
+    /// `document_element` is provided.
+    pub fn flush<E>(&mut self, document_element: Option<E>)
+        where E: TElement,
+    {
+        if let Some(e) = document_element {
+            self.process_invalidations_in_subtree(e);
+        }
+        self.invalid_scopes.clear();
+        self.fully_invalid = false;
+    }
+
+    /// Process style invalidations in a given subtree, that is, look for all
+    /// the relevant scopes in the subtree, and mark as dirty only the relevant
+    /// ones.
+    ///
+    /// Returns whether it invalidated at least one element's style.
+    #[allow(unsafe_code)]
+    fn process_invalidations_in_subtree<E>(&self, element: E) -> bool
+        where E: TElement,
+    {
+        let mut data = match element.mutate_data() {
+            Some(data) => data,
+            None => return false,
+        };
+
+        if !data.has_styles() {
+            return false;
+        }
+
+        if let Some(ref r) = data.get_restyle() {
+            if r.hint.contains_subtree() {
+                debug!("process_invalidations_in_subtree: {:?} was already invalid",
+                       element);
+                return false;
+            }
+        }
+
+        if self.fully_invalid {
+            debug!("process_invalidations_in_subtree: fully_invalid({:?})",
+                   element);
+            data.ensure_restyle().hint.insert(StoredRestyleHint::subtree());
+            return true;
+        }
+
+        for scope in &self.invalid_scopes {
+            if scope.matches(element) {
+                debug!("process_invalidations_in_subtree: {:?} matched {:?}",
+                       element, scope);
+                data.ensure_restyle().hint.insert(StoredRestyleHint::subtree());
+                return true;
+            }
+        }
+
+
+        let mut any_children_invalid = false;
+
+        for child in element.as_node().children() {
+            let child = match child.as_element() {
+                Some(e) => e,
+                None => continue,
+            };
+
+            any_children_invalid |= self.process_invalidations_in_subtree(child);
+        }
+
+        if any_children_invalid {
+            debug!("Children of {:?} changed, setting dirty descendants",
+                   element);
+            unsafe { element.set_dirty_descendants() }
+        }
+
+        return any_children_invalid
+    }
+
+    fn scan_component(
+        component: &Component<SelectorImpl>,
+        scope: &mut Option<InvalidationScope>)
+    {
+        match *component {
+            Component::Class(ref class) => {
+                if scope.as_ref().map_or(true, |s| !s.is_id()) {
+                    *scope = Some(InvalidationScope::Class(class.clone()));
+                }
+            }
+            Component::ID(ref id) => {
+                if scope.is_none() {
+                    *scope = Some(InvalidationScope::ID(id.clone()));
+                }
+            }
+            _ => {
+                // Ignore everything else, at least for now.
+            }
+        }
+    }
+
+    /// Collect a style scopes for a given selector.
+    ///
+    /// We look at the outermost class or id selector to the left of an ancestor
+    /// combinator, in order to restyle only a given subtree.
+    ///
+    /// We prefer id scopes to class scopes, and outermost scopes to innermost
+    /// scopes (to reduce the amount of traversal we need to do).
+    fn collect_scopes(&mut self, selector: &Selector<SelectorImpl>) {
+        debug!("StylesheetInvalidationSet::collect_scopes({:?})", selector);
+
+        let mut scope: Option<InvalidationScope> = None;
+
+        let mut scan = true;
+        let mut iter = selector.inner.complex.iter();
+
+        loop {
+            for component in &mut iter {
+                if scan {
+                    Self::scan_component(component, &mut scope);
+                }
+            }
+            match iter.next_sequence() {
+                None => break,
+                Some(combinator) => {
+                    scan = combinator.is_ancestor();
+                }
+            }
+        }
+
+        match scope {
+            Some(s) => {
+                debug!(" > Found scope: {:?}", s);
+                self.invalid_scopes.insert(s);
+            }
+            None => {
+                debug!(" > Scope not found");
+
+                // If we didn't find a scope, any element could match this, so
+                // let's just bail out.
+                self.fully_invalid = true;
+            }
+        }
+    }
+
+    /// Collects invalidations for a given CSS rule.
+    fn collect_invalidations_for_rule(
+        &mut self,
+        rule: &CssRule,
+        guard: &SharedRwLockReadGuard)
+    {
+        use stylesheets::CssRule::*;
+        debug!("StylesheetInvalidationSet::collect_invalidations_for_rule");
+        debug_assert!(!self.fully_invalid, "Not worth to be here!");
+
+        match *rule {
+            Style(ref lock) => {
+                let style_rule = lock.read_with(guard);
+                for selector in &style_rule.selectors.0 {
+                    self.collect_scopes(selector);
+                    if self.fully_invalid {
+                        return;
+                    }
+                }
+            }
+            Document(..) |
+            Namespace(..) |
+            Import(..) |
+            Media(..) |
+            Supports(..) => {
+                // Do nothing, relevant nested rules are visited as part of the
+                // iteration.
+            }
+            FontFace(..) |
+            CounterStyle(..) |
+            Keyframes(..) |
+            Page(..) |
+            Viewport(..) => {
+                debug!(" > Found unsupported rule, marking the whole subtree \
+                       invalid.");
+
+                // TODO(emilio): Can we do better here?
+                //
+                // At least in `@page`, we could check the relevant media, I
+                // guess.
+                self.fully_invalid = true;
+            }
+        }
+    }
+}

servo/components/style/lib.rs

@@ -110,6 +110,7 @@ pub mod font_face;
 pub mod font_metrics;
 #[cfg(feature = "gecko")] #[allow(unsafe_code)] pub mod gecko;
 #[cfg(feature = "gecko")] #[allow(unsafe_code)] pub mod gecko_bindings;
+pub mod invalidation;
 pub mod keyframes;
 #[allow(missing_docs)] // TODO.
 pub mod logical_geometry;

servo/components/style/restyle_hints.rs

@@ -368,7 +368,7 @@ impl RestyleHint {
     /// Returns whether this `RestyleHint` represents at least as much restyle
     /// work as the specified one.
     #[inline]
-    pub fn contains(&mut self, other: &Self) -> bool {
+    pub fn contains(&self, other: &Self) -> bool {
         self.match_under_self.contains(other.match_under_self) &&
         (self.match_later_siblings & other.match_later_siblings) == other.match_later_siblings &&
         self.replacements.contains(other.replacements)

servo/components/style/stylesheet_set.rs

@@ -4,9 +4,13 @@
 
 //! A centralized set of stylesheets for a document.
 
+use dom::TElement;
+use invalidation::StylesheetInvalidationSet;
+use shared_lock::SharedRwLockReadGuard;
 use std::slice;
 use stylearc::Arc;
 use stylesheets::Stylesheet;
+use stylist::Stylist;
 
 /// Entry for a StylesheetSet. We don't bother creating a constructor, because
 /// there's no sensible defaults for the member variables.
@@ -40,6 +44,9 @@ pub struct StylesheetSet {
 
     /// Has author style been disabled?
     author_style_disabled: bool,
+
+    /// The style invalidations that we still haven't processed.
+    invalidations: StylesheetInvalidationSet,
 }
 
 impl StylesheetSet {
@@ -49,6 +56,7 @@ impl StylesheetSet {
             entries: vec![],
             dirty: false,
             author_style_disabled: false,
+            invalidations: StylesheetInvalidationSet::new(),
         }
     }
 
@@ -63,32 +71,57 @@ impl StylesheetSet {
     }
 
     /// Appends a new stylesheet to the current set.
-    pub fn append_stylesheet(&mut self, sheet: &Arc<Stylesheet>,
-                             unique_id: u64) {
+    pub fn append_stylesheet(
+        &mut self,
+        stylist: &Stylist,
+        sheet: &Arc<Stylesheet>,
+        unique_id: u64,
+        guard: &SharedRwLockReadGuard)
+    {
+        debug!("StylesheetSet::append_stylesheet");
         self.remove_stylesheet_if_present(unique_id);
         self.entries.push(StylesheetSetEntry {
             unique_id: unique_id,
             sheet: sheet.clone(),
         });
         self.dirty = true;
+        self.invalidations.collect_invalidations_for(
+            stylist,
+            sheet,
+            guard)
     }
 
     /// Prepend a new stylesheet to the current set.
-    pub fn prepend_stylesheet(&mut self, sheet: &Arc<Stylesheet>,
-                              unique_id: u64) {
+    pub fn prepend_stylesheet(
+        &mut self,
+        stylist: &Stylist,
+        sheet: &Arc<Stylesheet>,
+        unique_id: u64,
+        guard: &SharedRwLockReadGuard)
+    {
+        debug!("StylesheetSet::prepend_stylesheet");
         self.remove_stylesheet_if_present(unique_id);
         self.entries.insert(0, StylesheetSetEntry {
             unique_id: unique_id,
             sheet: sheet.clone(),
         });
         self.dirty = true;
+        self.invalidations.collect_invalidations_for(
+            stylist,
+            sheet,
+            guard)
     }
 
     /// Insert a given stylesheet before another stylesheet in the document.
-    pub fn insert_stylesheet_before(&mut self,
+    pub fn insert_stylesheet_before(
+        &mut self,
+        stylist: &Stylist,
         sheet: &Arc<Stylesheet>,
         unique_id: u64,
-                                    before_unique_id: u64) {
+        before_unique_id: u64,
+        guard: &SharedRwLockReadGuard)
+    {
+        debug!("StylesheetSet::insert_stylesheet_before");
         self.remove_stylesheet_if_present(unique_id);
         let index = self.entries.iter().position(|x| {
             x.unique_id == before_unique_id
@@ -98,21 +131,30 @@ impl StylesheetSet {
             sheet: sheet.clone(),
         });
         self.dirty = true;
+        self.invalidations.collect_invalidations_for(
+            stylist,
+            sheet,
+            guard)
     }
 
     /// Remove a given stylesheet from the set.
     pub fn remove_stylesheet(&mut self, unique_id: u64) {
+        debug!("StylesheetSet::remove_stylesheet");
         self.remove_stylesheet_if_present(unique_id);
         self.dirty = true;
+        // FIXME(emilio): We can do better!
+        self.invalidations.invalidate_fully();
     }
 
     /// Notes that the author style has been disabled for this document.
     pub fn set_author_style_disabled(&mut self, disabled: bool) {
+        debug!("StylesheetSet::set_author_style_disabled");
         if self.author_style_disabled == disabled {
             return;
         }
         self.author_style_disabled = disabled;
         self.dirty = true;
+        self.invalidations.invalidate_fully();
     }
 
     /// Returns whether the given set has changed from the last flush.
@@ -122,8 +164,17 @@ impl StylesheetSet {
 
     /// Flush the current set, unmarking it as dirty, and returns an iterator
     /// over the new stylesheet list.
-    pub fn flush(&mut self) -> StylesheetIterator {
+    pub fn flush<E>(&mut self,
+                    document_element: Option<E>)
+                    -> StylesheetIterator
+        where E: TElement,
+    {
+        debug!("StylesheetSet::flush");
+        debug_assert!(self.dirty);
+
         self.dirty = false;
+        self.invalidations.flush(document_element);
+
         StylesheetIterator(self.entries.iter())
     }
 
@@ -133,5 +184,6 @@ impl StylesheetSet {
     /// FIXME(emilio): Make this more granular.
     pub fn force_dirty(&mut self) {
         self.dirty = true;
+        self.invalidations.invalidate_fully();
     }
 }

servo/components/style/stylesheets.rs

@@ -37,11 +37,13 @@ use servo_config::prefs::PREFS;
 #[cfg(not(feature = "gecko"))]
 use servo_url::ServoUrl;
 use shared_lock::{SharedRwLock, Locked, ToCssWithGuard, SharedRwLockReadGuard};
+use smallvec::SmallVec;
 use std::borrow::Borrow;
 use std::cell::Cell;
 use std::fmt;
 use std::mem::align_of;
 use std::os::raw::c_void;
+use std::slice;
 use std::sync::atomic::{AtomicBool, Ordering};
 use str::starts_with_ignore_ascii_case;
 use style_traits::ToCss;
@@ -432,16 +434,6 @@ pub enum CssRuleType {
     Viewport            = 15,
 }
 
-/// Result type for with_nested_rules_mq_and_doc_rule()
-pub enum NestedRulesResult<'a> {
-    /// Only rules
-    Rules(&'a [CssRule]),
-    /// Rules with media queries
-    RulesWithMediaQueries(&'a [CssRule], &'a MediaList),
-    /// Rules with document rule
-    RulesWithDocument(&'a [CssRule], &'a DocumentRule)
-}
-
 #[allow(missing_docs)]
 pub enum SingleRuleParseError {
     Syntax,
@@ -475,60 +467,6 @@ impl CssRule {
         }
     }
 
-    /// Call `f` with the slice of rules directly contained inside this rule.
-    ///
-    /// Note that only some types of rules can contain rules. An empty slice is
-    /// used for others.
-    ///
-    /// This will not recurse down unsupported @supports rules
-    pub fn with_nested_rules_mq_and_doc_rule<F, R>(&self, guard: &SharedRwLockReadGuard, mut f: F) -> R
-    where F: FnMut(NestedRulesResult) -> R {
-        match *self {
-            CssRule::Import(ref lock) => {
-                let rule = lock.read_with(guard);
-                let media = rule.stylesheet.media.read_with(guard);
-                let rules = rule.stylesheet.rules.read_with(guard);
-                // FIXME(emilio): Include the nested rules if the stylesheet is
-                // loaded.
-                f(NestedRulesResult::RulesWithMediaQueries(&rules.0, &media))
-            }
-            CssRule::Namespace(_) |
-            CssRule::Style(_) |
-            CssRule::FontFace(_) |
-            CssRule::CounterStyle(_) |
-            CssRule::Viewport(_) |
-            CssRule::Keyframes(_) |
-            CssRule::Page(_) => {
-                f(NestedRulesResult::Rules(&[]))
-            }
-            CssRule::Media(ref lock) => {
-                let media_rule = lock.read_with(guard);
-                let mq = media_rule.media_queries.read_with(guard);
-                let rules = &media_rule.rules.read_with(guard).0;
-                f(NestedRulesResult::RulesWithMediaQueries(rules, &mq))
-            }
-            CssRule::Supports(ref lock) => {
-                let supports_rule = lock.read_with(guard);
-                let enabled = supports_rule.enabled;
-                if enabled {
-                    let rules = &supports_rule.rules.read_with(guard).0;
-                    f(NestedRulesResult::Rules(rules))
-                } else {
-                    f(NestedRulesResult::Rules(&[]))
-                }
-            }
-            CssRule::Document(ref lock) => {
-                if cfg!(feature = "gecko") {
-                    let document_rule = lock.read_with(guard);
-                    let rules = &document_rule.rules.read_with(guard).0;
-                    f(NestedRulesResult::RulesWithDocument(rules, &document_rule))
-                } else {
-                    unimplemented!()
-                }
-            }
-        }
-    }
-
     // input state is None for a nested rule
     // Returns a parsed CSS rule and the final state of the parser
     #[allow(missing_docs)]
@@ -1003,6 +941,263 @@ impl DocumentRule {
     }
 }
 
+/// A trait that describes statically which rules are iterated for a given
+/// RulesIterator.
+pub trait NestedRuleIterationCondition {
+    /// Whether we should process the nested rules in a given `@import` rule.
+    fn process_import(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &ImportRule)
+        -> bool;
+
+    /// Whether we should process the nested rules in a given `@media` rule.
+    fn process_media(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &MediaRule)
+        -> bool;
+
+    /// Whether we should process the nested rules in a given `@-moz-document` rule.
+    fn process_document(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &DocumentRule)
+        -> bool;
+
+    /// Whether we should process the nested rules in a given `@supports` rule.
+    fn process_supports(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &SupportsRule)
+        -> bool;
+}
+
+/// A struct that represents the condition that a rule applies to the document.
+pub struct EffectiveRules;
+
+impl NestedRuleIterationCondition for EffectiveRules {
+    fn process_import(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &ImportRule)
+        -> bool
+    {
+        rule.stylesheet.media.read_with(guard).evaluate(device, quirks_mode)
+    }
+
+    fn process_media(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &MediaRule)
+        -> bool
+    {
+        rule.media_queries.read_with(guard).evaluate(device, quirks_mode)
+    }
+
+    fn process_document(
+        _: &SharedRwLockReadGuard,
+        device: &Device,
+        _: QuirksMode,
+        rule: &DocumentRule)
+        -> bool
+    {
+        rule.condition.evaluate(device)
+    }
+
+    fn process_supports(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        rule: &SupportsRule)
+        -> bool
+    {
+        rule.enabled
+    }
+}
+
+/// A filter that processes all the rules in a rule list.
+pub struct AllRules;
+
+impl NestedRuleIterationCondition for AllRules {
+    fn process_import(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        _: &ImportRule)
+        -> bool
+    {
+        true
+    }
+
+    /// Whether we should process the nested rules in a given `@media` rule.
+    fn process_media(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        _: &MediaRule)
+        -> bool
+    {
+        true
+    }
+
+    /// Whether we should process the nested rules in a given `@-moz-document` rule.
+    fn process_document(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        _: &DocumentRule)
+        -> bool
+    {
+        true
+    }
+
+    /// Whether we should process the nested rules in a given `@supports` rule.
+    fn process_supports(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        _: &SupportsRule)
+        -> bool
+    {
+        true
+    }
+}
+
+/// An iterator over all the effective rules of a stylesheet.
+///
+/// NOTE: This iterator recurses into `@import` rules.
+pub type EffectiveRulesIterator<'a, 'b> = RulesIterator<'a, 'b, EffectiveRules>;
+
+/// An iterator over a list of rules.
+pub struct RulesIterator<'a, 'b, C>
+    where 'b: 'a,
+          C: NestedRuleIterationCondition + 'static,
+{
+    device: &'a Device,
+    quirks_mode: QuirksMode,
+    guard: &'a SharedRwLockReadGuard<'b>,
+    stack: SmallVec<[slice::Iter<'a, CssRule>; 3]>,
+    _phantom: ::std::marker::PhantomData<C>,
+}
+
+impl<'a, 'b, C> RulesIterator<'a, 'b, C>
+    where 'b: 'a,
+          C: NestedRuleIterationCondition + 'static,
+{
+    /// Creates a new `RulesIterator` to iterate over `rules`.
+    pub fn new(
+        device: &'a Device,
+        quirks_mode: QuirksMode,
+        guard: &'a SharedRwLockReadGuard<'b>,
+        rules: &'a CssRules)
+        -> Self
+    {
+        let mut stack = SmallVec::new();
+        stack.push(rules.0.iter());
+        Self {
+            device: device,
+            quirks_mode: quirks_mode,
+            guard: guard,
+            stack: stack,
+            _phantom: ::std::marker::PhantomData,
+        }
+    }
+
+    /// Skips all the remaining children of the last nested rule processed.
+    pub fn skip_children(&mut self) {
+        self.stack.pop();
+    }
+}
+
+impl<'a, 'b, C> Iterator for RulesIterator<'a, 'b, C>
+    where 'b: 'a,
+          C: NestedRuleIterationCondition + 'static,
+{
+    type Item = &'a CssRule;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut nested_iter_finished = false;
+        while !self.stack.is_empty() {
+            if nested_iter_finished {
+                self.stack.pop();
+                nested_iter_finished = false;
+                continue;
+            }
+
+            let rule;
+            let sub_iter;
+            {
+                let mut nested_iter = self.stack.last_mut().unwrap();
+                rule = match nested_iter.next() {
+                    Some(r) => r,
+                    None => {
+                        nested_iter_finished = true;
+                        continue
+                    }
+                };
+
+                sub_iter = match *rule {
+                    CssRule::Import(ref import_rule) => {
+                        let import_rule = import_rule.read_with(self.guard);
+
+                        if C::process_import(self.guard, self.device, self.quirks_mode, import_rule) {
+                            Some(import_rule.stylesheet.rules.read_with(self.guard).0.iter())
+                        } else {
+                            None
+                        }
+                    }
+                    CssRule::Document(ref doc_rule) => {
+                        let doc_rule = doc_rule.read_with(self.guard);
+                        if C::process_document(self.guard, self.device, self.quirks_mode, doc_rule) {
+                            Some(doc_rule.rules.read_with(self.guard).0.iter())
+                        } else {
+                            None
+                        }
+                    }
+                    CssRule::Media(ref lock) => {
+                        let media_rule = lock.read_with(self.guard);
+                        if C::process_media(self.guard, self.device, self.quirks_mode, media_rule) {
+                            Some(media_rule.rules.read_with(self.guard).0.iter())
+                        } else {
+                            None
+                        }
+                    }
+                    CssRule::Supports(ref lock) => {
+                        let supports_rule = lock.read_with(self.guard);
+                        if C::process_supports(self.guard, self.device, self.quirks_mode, supports_rule) {
+                            Some(supports_rule.rules.read_with(self.guard).0.iter())
+                        } else {
+                            None
+                        }
+                    }
+                    CssRule::Namespace(_) |
+                    CssRule::Style(_) |
+                    CssRule::FontFace(_) |
+                    CssRule::CounterStyle(_) |
+                    CssRule::Viewport(_) |
+                    CssRule::Keyframes(_) |
+                    CssRule::Page(_) => None,
+                };
+            }
+
+            if let Some(sub_iter) = sub_iter {
+                self.stack.push(sub_iter);
+            }
+
+            return Some(rule);
+        }
+
+        None
+    }
+}
+
 impl Stylesheet {
     /// Updates an empty stylesheet from a given string of text.
     pub fn update_from_str(existing: &Stylesheet,
@@ -1132,14 +1327,30 @@ impl Stylesheet {
 
     /// Return an iterator over the effective rules within the style-sheet, as
     /// according to the supplied `Device`.
-    ///
-    /// If a condition does not hold, its associated conditional group rule and
-    /// nested rules will be skipped. Use `rules` if all rules need to be
-    /// examined.
     #[inline]
-    pub fn effective_rules<F>(&self, device: &Device, guard: &SharedRwLockReadGuard, mut f: F)
-    where F: FnMut(&CssRule) {
-        effective_rules(&self.rules.read_with(guard).0, device, self.quirks_mode, guard, &mut f);
+    pub fn effective_rules<'a, 'b>(
+        &'a self,
+        device: &'a Device,
+        guard: &'a SharedRwLockReadGuard<'b>)
+        -> EffectiveRulesIterator<'a, 'b>
+    {
+        self.iter_rules::<'a, 'b, EffectiveRules>(device, guard)
+    }
+
+    /// Return an iterator using the condition `C`.
+    #[inline]
+    pub fn iter_rules<'a, 'b, C>(
+        &'a self,
+        device: &'a Device,
+        guard: &'a SharedRwLockReadGuard<'b>)
+        -> RulesIterator<'a, 'b, C>
+        where C: NestedRuleIterationCondition,
+    {
+        RulesIterator::new(
+            device,
+            self.quirks_mode,
+            guard,
+            &self.rules.read_with(guard))
     }
 
     /// Returns whether the stylesheet has been explicitly disabled through the
@@ -1189,51 +1400,20 @@ impl Clone for Stylesheet {
     }
 }
 
-fn effective_rules<F>(rules: &[CssRule],
-                      device: &Device,
-                      quirks_mode: QuirksMode,
-                      guard: &SharedRwLockReadGuard,
-                      f: &mut F)
-    where F: FnMut(&CssRule)
-{
-    for rule in rules {
-        f(rule);
-        rule.with_nested_rules_mq_and_doc_rule(guard, |result| {
-            let rules = match result {
-                NestedRulesResult::Rules(rules) => {
-                    rules
-                },
-                NestedRulesResult::RulesWithMediaQueries(rules, media_queries) => {
-                    if !media_queries.evaluate(device, quirks_mode) {
-                        return;
-                    }
-                    rules
-                },
-                NestedRulesResult::RulesWithDocument(rules, doc_rule) => {
-                    if !doc_rule.condition.evaluate(device) {
-                        return;
-                    }
-                    rules
-                },
-            };
-            effective_rules(rules, device, quirks_mode, guard, f)
-        })
-    }
-}
-
 macro_rules! rule_filter {
     ($( $method: ident($variant:ident => $rule_type: ident), )+) => {
         impl Stylesheet {
             $(
                 #[allow(missing_docs)]
                 pub fn $method<F>(&self, device: &Device, guard: &SharedRwLockReadGuard, mut f: F)
-                where F: FnMut(&$rule_type) {
-                    self.effective_rules(device, guard, |rule| {
+                    where F: FnMut(&$rule_type),
+                {
+                    for rule in self.effective_rules(device, guard) {
                         if let CssRule::$variant(ref lock) = *rule {
                             let rule = lock.read_with(guard);
                             f(&rule)
                         }
-                    })
+                    }
                 }
             )+
         }

servo/components/style/stylist.rs

@@ -39,10 +39,9 @@ use style_traits::viewport::ViewportConstraints;
 use stylearc::Arc;
 #[cfg(feature = "gecko")]
 use stylesheets::{CounterStyleRule, FontFaceRule};
-use stylesheets::{CssRule, Origin};
-use stylesheets::{StyleRule, Stylesheet, UserAgentStylesheets};
-#[cfg(feature = "servo")]
-use stylesheets::NestedRulesResult;
+use stylesheets::{CssRule, DocumentRule, ImportRule, MediaRule, StyleRule, SupportsRule};
+use stylesheets::{Stylesheet, Origin, UserAgentStylesheets};
+use stylesheets::NestedRuleIterationCondition;
 use thread_state;
 use viewport::{self, MaybeNew, ViewportRule};
 
@@ -79,10 +78,7 @@ pub struct Stylist {
     /// On Servo, on the other hand, the device is a really cheap representation
     /// that is recreated each time some constraint changes and calling
     /// `set_device`.
-    ///
-    /// In both cases, the device is actually _owned_ by the Stylist, and it's
-    /// only an `Arc` so we can implement `add_stylesheet` more idiomatically.
-    device: Arc<Device>,
+    device: Device,
 
     /// Viewport constraints based on the current device.
     viewport_constraints: Option<ViewportConstraints>,
@@ -226,6 +222,57 @@ impl From<StyleRuleInclusion> for RuleInclusion {
     }
 }
 
+/// A filter that filters over effective rules, but allowing all potentially
+/// effective `@media` rules.
+pub struct PotentiallyEffectiveMediaRules;
+
+impl NestedRuleIterationCondition for PotentiallyEffectiveMediaRules {
+    fn process_import(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        _: &ImportRule)
+        -> bool
+    {
+        true
+    }
+
+    fn process_media(
+        _: &SharedRwLockReadGuard,
+        _: &Device,
+        _: QuirksMode,
+        _: &MediaRule)
+        -> bool
+    {
+        true
+    }
+
+    /// Whether we should process the nested rules in a given `@-moz-document` rule.
+    fn process_document(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &DocumentRule)
+        -> bool
+    {
+        use stylesheets::EffectiveRules;
+        EffectiveRules::process_document(guard, device, quirks_mode, rule)
+    }
+
+    /// Whether we should process the nested rules in a given `@supports` rule.
+    fn process_supports(
+        guard: &SharedRwLockReadGuard,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        rule: &SupportsRule)
+        -> bool
+    {
+        use stylesheets::EffectiveRules;
+        EffectiveRules::process_supports(guard, device, quirks_mode, rule)
+    }
+}
+
+
 impl Stylist {
     /// Construct a new `Stylist`, using given `Device` and `QuirksMode`.
     /// If more members are added here, think about whether they should
@@ -234,7 +281,7 @@ impl Stylist {
     pub fn new(device: Device, quirks_mode: QuirksMode) -> Self {
         let mut stylist = Stylist {
             viewport_constraints: None,
-            device: Arc::new(device),
+            device: device,
             is_device_dirty: true,
             is_cleared: true,
             quirks_mode: quirks_mode,
@@ -364,8 +411,7 @@ impl Stylist {
             ViewportConstraints::maybe_new(&self.device, &cascaded_rule, self.quirks_mode);
 
         if let Some(ref constraints) = self.viewport_constraints {
-            Arc::get_mut(&mut self.device).unwrap()
-                .account_for_viewport_rule(constraints);
+            self.device.account_for_viewport_rule(constraints);
         }
 
         SelectorImpl::each_eagerly_cascaded_pseudo_element(|pseudo| {
@@ -431,31 +477,47 @@ impl Stylist {
     fn add_stylesheet<'a>(&mut self,
                           stylesheet: &Stylesheet,
                           guard: &SharedRwLockReadGuard,
-                          extra_data: &mut ExtraStyleData<'a>) {
+                          _extra_data: &mut ExtraStyleData<'a>) {
         if stylesheet.disabled() || !stylesheet.is_effective_for_device(&self.device, guard) {
             return;
         }
 
-        // Cheap `Arc` clone so that the closure below can borrow `&mut Stylist`.
-        let device = self.device.clone();
-
-        stylesheet.effective_rules(&device, guard, |rule| {
+        for rule in stylesheet.effective_rules(&self.device, guard) {
             match *rule {
                 CssRule::Style(ref locked) => {
                     let style_rule = locked.read_with(&guard);
                     self.num_declarations += style_rule.block.read_with(&guard).len();
                     for selector in &style_rule.selectors.0 {
                         self.num_selectors += 1;
-                        self.add_rule_to_map(selector, locked, stylesheet);
+
+                        let map = if let Some(pseudo) = selector.pseudo_element() {
+                            self.pseudos_map
+                                .entry(pseudo.canonical())
+                                .or_insert_with(PerPseudoElementSelectorMap::new)
+                                .borrow_for_origin(&stylesheet.origin)
+                        } else {
+                            self.element_map.borrow_for_origin(&stylesheet.origin)
+                        };
+
+                        map.insert(Rule::new(selector.clone(),
+                                             locked.clone(),
+                                             self.rules_source_order));
+
                         self.dependencies.note_selector(selector);
-                        self.note_for_revalidation(selector);
-                        self.note_attribute_and_state_dependencies(selector);
+                        if needs_revalidation(selector) {
+                            self.selectors_for_cache_revalidation.insert(selector.inner.clone());
+                        }
+                        selector.visit(&mut AttributeAndStateDependencyVisitor {
+                            attribute_dependencies: &mut self.attribute_dependencies,
+                            style_attribute_dependency: &mut self.style_attribute_dependency,
+                            state_dependencies: &mut self.state_dependencies,
+                        });
                     }
                     self.rules_source_order += 1;
                 }
-                CssRule::Import(ref import) => {
-                    let import = import.read_with(guard);
-                    self.add_stylesheet(&import.stylesheet, guard, extra_data)
+                CssRule::Import(..) => {
+                    // effective_rules visits the inner stylesheet if
+                    // appropriate.
                 }
                 CssRule::Keyframes(ref keyframes_rule) => {
                     let keyframes_rule = keyframes_rule.read_with(guard);
@@ -474,42 +536,15 @@ impl Stylist {
                 }
                 #[cfg(feature = "gecko")]
                 CssRule::FontFace(ref rule) => {
-                    extra_data.add_font_face(&rule, stylesheet.origin);
+                    _extra_data.add_font_face(&rule, stylesheet.origin);
                 }
                 #[cfg(feature = "gecko")]
                 CssRule::CounterStyle(ref rule) => {
-                    extra_data.add_counter_style(guard, &rule);
+                    _extra_data.add_counter_style(guard, &rule);
                 }
                 // We don't care about any other rule.
                 _ => {}
             }
-        });
-    }
-
-    #[inline]
-    fn add_rule_to_map(&mut self,
-                       selector: &Selector<SelectorImpl>,
-                       rule: &Arc<Locked<StyleRule>>,
-                       stylesheet: &Stylesheet)
-    {
-        let map = if let Some(pseudo) = selector.pseudo_element() {
-            self.pseudos_map
-                .entry(pseudo.canonical())
-                .or_insert_with(PerPseudoElementSelectorMap::new)
-                .borrow_for_origin(&stylesheet.origin)
-        } else {
-            self.element_map.borrow_for_origin(&stylesheet.origin)
-        };
-
-        map.insert(Rule::new(selector.clone(),
-                             rule.clone(),
-                             self.rules_source_order));
-    }
-
-    #[inline]
-    fn note_for_revalidation(&mut self, selector: &Selector<SelectorImpl>) {
-        if needs_revalidation(selector) {
-            self.selectors_for_cache_revalidation.insert(selector.inner.clone());
         }
     }
 
@@ -518,12 +553,7 @@ impl Stylist {
     pub fn might_have_attribute_dependency(&self,
                                            local_name: &LocalName)
                                            -> bool {
-        #[cfg(feature = "servo")]
-        let style_lower_name = local_name!("style");
-        #[cfg(feature = "gecko")]
-        let style_lower_name = atom!("style");
-
-        if *local_name == style_lower_name {
+        if *local_name == local_name!("style") {
             self.style_attribute_dependency
         } else {
             self.attribute_dependencies.might_contain(local_name)
@@ -536,11 +566,6 @@ impl Stylist {
         self.state_dependencies.intersects(state)
     }
 
-    #[inline]
-    fn note_attribute_and_state_dependencies(&mut self, selector: &Selector<SelectorImpl>) {
-        selector.visit(&mut AttributeAndStateDependencyVisitor(self));
-    }
-
     /// Computes the style for a given "precomputed" pseudo-element, taking the
     /// universal rules and applying them.
     ///
@@ -791,44 +816,62 @@ impl Stylist {
             device.account_for_viewport_rule(constraints);
         }
 
-        fn mq_eval_changed(guard: &SharedRwLockReadGuard, rules: &[CssRule],
-                           before: &Device, after: &Device, quirks_mode: QuirksMode) -> bool {
-            for rule in rules {
-                let changed = rule.with_nested_rules_mq_and_doc_rule(guard,
-                                                                     |result| {
-                    let rules = match result {
-                        NestedRulesResult::Rules(rules) => rules,
-                        NestedRulesResult::RulesWithMediaQueries(rules, mq) => {
-                            if mq.evaluate(before, quirks_mode) != mq.evaluate(after, quirks_mode) {
-                                return true;
-                            }
-                            rules
-                        },
-                        NestedRulesResult::RulesWithDocument(rules, doc_rule) => {
-                            if !doc_rule.condition.evaluate(before) {
-                                return false;
-                            }
-                            rules
-                        },
-                    };
-                    mq_eval_changed(guard, rules, before, after, quirks_mode)
-                });
-                if changed {
-                    return true
-                }
-            }
-            false
-        }
         self.is_device_dirty |= stylesheets.iter().any(|stylesheet| {
             let mq = stylesheet.media.read_with(guard);
             if mq.evaluate(&self.device, self.quirks_mode) != mq.evaluate(&device, self.quirks_mode) {
                 return true
             }
 
-            mq_eval_changed(guard, &stylesheet.rules.read_with(guard).0, &self.device, &device, self.quirks_mode)
+            let mut iter =
+                stylesheet.iter_rules::<PotentiallyEffectiveMediaRules>(
+                    &self.device,
+                    guard);
+
+            while let Some(rule) = iter.next() {
+                match *rule {
+                    CssRule::Style(..) |
+                    CssRule::Namespace(..) |
+                    CssRule::FontFace(..) |
+                    CssRule::CounterStyle(..) |
+                    CssRule::Supports(..) |
+                    CssRule::Keyframes(..) |
+                    CssRule::Page(..) |
+                    CssRule::Viewport(..) |
+                    CssRule::Document(..) => {
+                        // Not affected by device changes.
+                        continue;
+                    }
+                    CssRule::Import(ref lock) => {
+                        let import_rule = lock.read_with(guard);
+                        let mq = import_rule.stylesheet.media.read_with(guard);
+                        let effective_now = mq.evaluate(&self.device, self.quirks_mode);
+                        if effective_now != mq.evaluate(&device, self.quirks_mode) {
+                            return true;
+                        }
+
+                        if !effective_now {
+                            iter.skip_children();
+                        }
+                    }
+                    CssRule::Media(ref lock) => {
+                        let media_rule = lock.read_with(guard);
+                        let mq = media_rule.media_queries.read_with(guard);
+                        let effective_now = mq.evaluate(&self.device, self.quirks_mode);
+                        if effective_now != mq.evaluate(&device, self.quirks_mode) {
+                            return true;
+                        }
+
+                        if !effective_now {
+                            iter.skip_children();
+                        }
+                    }
+                }
+            }
+
+            return false;
         });
 
-        self.device = Arc::new(device);
+        self.device = device;
     }
 
     /// Returns the viewport constraints that apply to this document because of
@@ -1119,7 +1162,7 @@ impl Stylist {
     }
 
     /// Accessor for a mutable reference to the device.
-    pub fn device_mut(&mut self) -> &mut Arc<Device> {
+    pub fn device_mut(&mut self) -> &mut Device {
         &mut self.device
     }
 
@@ -1146,7 +1189,11 @@ impl Drop for Stylist {
 
 /// Visitor to collect names that appear in attribute selectors and any
 /// dependencies on ElementState bits.
-struct AttributeAndStateDependencyVisitor<'a>(&'a mut Stylist);
+struct AttributeAndStateDependencyVisitor<'a> {
+    attribute_dependencies: &'a mut BloomFilter,
+    style_attribute_dependency: &'a mut bool,
+    state_dependencies: &'a mut ElementState,
+}
 
 impl<'a> SelectorVisitor for AttributeAndStateDependencyVisitor<'a> {
     type Impl = SelectorImpl;
@@ -1160,17 +1207,17 @@ impl<'a> SelectorVisitor for AttributeAndStateDependencyVisitor<'a> {
         let style_lower_name = atom!("style");
 
         if *lower_name == style_lower_name {
-            self.0.style_attribute_dependency = true;
+            *self.style_attribute_dependency = true;
         } else {
-            self.0.attribute_dependencies.insert(&name);
-            self.0.attribute_dependencies.insert(&lower_name);
+            self.attribute_dependencies.insert(&name);
+            self.attribute_dependencies.insert(&lower_name);
         }
         true
     }
 
     fn visit_simple_selector(&mut self, s: &Component<SelectorImpl>) -> bool {
         if let Component::NonTSPseudoClass(ref p) = *s {
-            self.0.state_dependencies.insert(p.state_flag());
+            self.state_dependencies.insert(p.state_flag());
         }
         true
     }

servo/ports/geckolib/glue.rs

@@ -26,6 +26,7 @@ use style::gecko::selector_parser::PseudoElement;
 use style::gecko::traversal::RecalcStyleOnly;
 use style::gecko::wrapper::GeckoElement;
 use style::gecko_bindings::bindings;
+use style::gecko_bindings::bindings::{RawGeckoElementBorrowed, RawGeckoElementBorrowedOrNull};
 use style::gecko_bindings::bindings::{RawGeckoKeyframeListBorrowed, RawGeckoKeyframeListBorrowedMut};
 use style::gecko_bindings::bindings::{RawServoDeclarationBlockBorrowed, RawServoDeclarationBlockStrong};
 use style::gecko_bindings::bindings::{RawServoDocumentRule, RawServoDocumentRuleBorrowed};
@@ -50,7 +51,6 @@ use style::gecko_bindings::bindings::RawGeckoAnimationPropertySegmentBorrowed;
 use style::gecko_bindings::bindings::RawGeckoCSSPropertyIDListBorrowed;
 use style::gecko_bindings::bindings::RawGeckoComputedKeyframeValuesListBorrowedMut;
 use style::gecko_bindings::bindings::RawGeckoComputedTimingBorrowed;
-use style::gecko_bindings::bindings::RawGeckoElementBorrowed;
 use style::gecko_bindings::bindings::RawGeckoFontFaceRuleListBorrowedMut;
 use style::gecko_bindings::bindings::RawGeckoServoStyleRuleListBorrowedMut;
 use style::gecko_bindings::bindings::RawServoAnimationValueBorrowed;
@@ -732,9 +732,16 @@ pub extern "C" fn Servo_StyleSheet_ClearAndUpdate(stylesheet: RawServoStyleSheet
 pub extern "C" fn Servo_StyleSet_AppendStyleSheet(raw_data: RawServoStyleSetBorrowed,
                                                   raw_sheet: RawServoStyleSheetBorrowed,
                                                   unique_id: u64) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
+    let mut data = &mut *data;
     let sheet = HasArcFFI::as_arc(&raw_sheet);
-    data.stylesheets.append_stylesheet(sheet, unique_id);
+    let guard = global_style_data.shared_lock.read();
+    data.stylesheets.append_stylesheet(
+        &data.stylist,
+        sheet,
+        unique_id,
+        &guard);
     data.clear_stylist();
 }
 
@@ -742,9 +749,16 @@ pub extern "C" fn Servo_StyleSet_AppendStyleSheet(raw_data: RawServoStyleSetBorr
 pub extern "C" fn Servo_StyleSet_PrependStyleSheet(raw_data: RawServoStyleSetBorrowed,
                                                    raw_sheet: RawServoStyleSheetBorrowed,
                                                    unique_id: u64) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
+    let mut data = &mut *data;
     let sheet = HasArcFFI::as_arc(&raw_sheet);
-    data.stylesheets.prepend_stylesheet(sheet, unique_id);
+    let guard = global_style_data.shared_lock.read();
+    data.stylesheets.prepend_stylesheet(
+        &data.stylist,
+        sheet,
+        unique_id,
+        &guard);
     data.clear_stylist();
 }
 
@@ -753,9 +767,17 @@ pub extern "C" fn Servo_StyleSet_InsertStyleSheetBefore(raw_data: RawServoStyleS
                                                         raw_sheet: RawServoStyleSheetBorrowed,
                                                         unique_id: u64,
                                                         before_unique_id: u64) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
+    let mut data = &mut *data;
     let sheet = HasArcFFI::as_arc(&raw_sheet);
-    data.stylesheets.insert_stylesheet_before(sheet, unique_id, before_unique_id);
+    let guard = global_style_data.shared_lock.read();
+    data.stylesheets.insert_stylesheet_before(
+        &data.stylist,
+        sheet,
+        unique_id,
+        before_unique_id,
+        &guard);
     data.clear_stylist();
 }
 
@@ -768,16 +790,22 @@ pub extern "C" fn Servo_StyleSet_RemoveStyleSheet(raw_data: RawServoStyleSetBorr
 }
 
 #[no_mangle]
-pub extern "C" fn Servo_StyleSet_FlushStyleSheets(raw_data: RawServoStyleSetBorrowed) {
+pub extern "C" fn Servo_StyleSet_FlushStyleSheets(
+    raw_data: RawServoStyleSetBorrowed,
+    doc_element: RawGeckoElementBorrowedOrNull)
+{
     let global_style_data = &*GLOBAL_STYLE_DATA;
     let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
-    data.flush_stylesheets(&guard);
+    let doc_element = doc_element.map(GeckoElement);
+    data.flush_stylesheets(&guard, doc_element);
 }
 
 #[no_mangle]
-pub extern "C" fn Servo_StyleSet_NoteStyleSheetsChanged(raw_data: RawServoStyleSetBorrowed,
-                                                        author_style_disabled: bool) {
+pub extern "C" fn Servo_StyleSet_NoteStyleSheetsChanged(
+    raw_data: RawServoStyleSetBorrowed,
+    author_style_disabled: bool)
+{
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     data.stylesheets.force_dirty();
     data.stylesheets.set_author_style_disabled(author_style_disabled);

servo/tests/unit/style/media_queries.rs

@@ -13,7 +13,7 @@ use style::media_queries::*;
 use style::servo::media_queries::*;
 use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard};
 use style::stylearc::Arc;
-use style::stylesheets::{Stylesheet, Origin, CssRule, NestedRulesResult};
+use style::stylesheets::{AllRules, Stylesheet, Origin, CssRule};
 use style::values::specified;
 use style_traits::ToCss;
 
@@ -39,33 +39,18 @@ fn test_media_rule<F>(css: &str, callback: F)
     let stylesheet = Stylesheet::from_str(
         css, url, Origin::Author, media_list, lock,
         None, &CSSErrorReporterTest, QuirksMode::NoQuirks, 0u64);
+    let dummy = Device::new(MediaType::Screen, TypedSize2D::new(200.0, 100.0));
     let mut rule_count = 0;
     let guard = stylesheet.shared_lock.read();
-    media_queries(&guard, &stylesheet.rules.read_with(&guard).0, &mut |mq| {
+    for rule in stylesheet.iter_rules::<AllRules>(&dummy, &guard) {
+        if let CssRule::Media(ref lock) = *rule {
             rule_count += 1;
-        callback(mq, css);
-    });
+            callback(&lock.read_with(&guard).media_queries.read_with(&guard), css);
+        }
+    }
     assert!(rule_count > 0, css_str);
 }
 
-fn media_queries<F>(guard: &SharedRwLockReadGuard, rules: &[CssRule], f: &mut F)
-    where F: FnMut(&MediaList),
-{
-    for rule in rules {
-        rule.with_nested_rules_mq_and_doc_rule(guard, |result| {
-            match result {
-                NestedRulesResult::Rules(rules) |
-                NestedRulesResult::RulesWithDocument(rules, _) => {
-                    media_queries(guard, rules, f)
-                },
-                NestedRulesResult::RulesWithMediaQueries(_, mq) => {
-                    f(mq)
-                }
-            }
-        })
-    }
-}
-
 fn media_query_test(device: &Device, css: &str, expected_rule_count: usize) {
     let url = ServoUrl::parse("http://localhost").unwrap();
     let lock = SharedRwLock::new();