Auto merge of #18037 - heycam:split-cascade-font-counter, r=emilio

style: Split collected @font-face / @counter-style rules per origin.

<!-- Please describe your changes on the following line: -->

More refactoring in preparation for rebuilding sheets only from the origin that changed.

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- [ ] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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3 files changed, 100 insertions, 44 deletions

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 26d1ef7bb41..9635e0b081d 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -114,7 +114,6 @@ use servo_url::ServoUrl;
 use std::borrow::ToOwned;
 use std::cell::{Cell, RefCell};
 use std::collections::HashMap;
-use std::marker::PhantomData;
 use std::mem as std_mem;
 use std::ops::{Deref, DerefMut};
 use std::process;
@@ -1207,9 +1206,7 @@ impl LayoutThread {
             author: &author_guard,
             ua_or_user: &ua_or_user_guard,
         };
-        let mut extra_data = ExtraStyleData {
-            marker: PhantomData,
-        };
+        let mut extra_data = ExtraStyleData;
         let needs_dirtying = self.stylist.update(
             StylesheetIterator(data.document_stylesheets.iter()),
             &guards,
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index 193ee928670..54dab9fe283 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -4,10 +4,8 @@
 
 //! Data needed to style a Gecko document.
 
-use Atom;
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use dom::TElement;
-use gecko::rules::{CounterStyleRule, FontFaceRule};
 use gecko_bindings::bindings::{self, RawServoStyleSet};
 use gecko_bindings::structs::{ServoStyleSheet, StyleSheetInfo, ServoStyleSheetInner};
 use gecko_bindings::structs::RawGeckoPresContextOwned;
@@ -16,11 +14,10 @@ use gecko_bindings::sugar::ownership::{HasArcFFI, HasBoxFFI, HasFFI, HasSimpleFF
 use invalidation::media_queries::{MediaListKey, ToMediaListKey};
 use media_queries::{Device, MediaList};
 use properties::ComputedValues;
-use selector_map::PrecomputedHashMap;
 use servo_arc::Arc;
 use shared_lock::{Locked, StylesheetGuards, SharedRwLockReadGuard};
 use stylesheet_set::StylesheetSet;
-use stylesheets::{Origin, StylesheetContents, StylesheetInDocument};
+use stylesheets::{StylesheetContents, StylesheetInDocument};
 use stylist::{ExtraStyleData, Stylist};
 
 /// Little wrapper to a Gecko style sheet.
@@ -120,11 +117,8 @@ pub struct PerDocumentStyleDataImpl {
     /// List of stylesheets, mirrored from Gecko.
     pub stylesheets: StylesheetSet<GeckoStyleSheet>,
 
-    /// List of effective font face rules.
-    pub font_faces: Vec<(Arc<Locked<FontFaceRule>>, Origin)>,
-
-    /// Map for effective counter style rules.
-    pub counter_styles: PrecomputedHashMap<Atom, Arc<Locked<CounterStyleRule>>>,
+    /// List of effective @font-face and @counter-style rules.
+    pub extra_style_data: ExtraStyleData,
 }
 
 /// The data itself is an `AtomicRefCell`, which guarantees the proper semantics
@@ -142,8 +136,7 @@ impl PerDocumentStyleData {
         PerDocumentStyleData(AtomicRefCell::new(PerDocumentStyleDataImpl {
             stylist: Stylist::new(device, quirks_mode.into()),
             stylesheets: StylesheetSet::new(),
-            font_faces: vec![],
-            counter_styles: PrecomputedHashMap::default(),
+            extra_style_data: Default::default(),
         }))
     }
 
@@ -169,11 +162,6 @@ impl PerDocumentStyleDataImpl {
             return;
         }
 
-        let mut extra_data = ExtraStyleData {
-            font_faces: &mut self.font_faces,
-            counter_styles: &mut self.counter_styles,
-        };
-
         let author_style_disabled = self.stylesheets.author_style_disabled();
         self.stylist.clear();
         let iter = self.stylesheets.flush(document_element);
@@ -183,7 +171,7 @@ impl PerDocumentStyleDataImpl {
             /* ua_sheets = */ None,
             /* stylesheets_changed = */ true,
             author_style_disabled,
-            &mut extra_data
+            &mut self.extra_style_data,
         );
     }
 
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 3000cd29e27..f3d79277a80 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -36,8 +36,6 @@ use servo_arc::{Arc, ArcBorrow};
 use shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
 use smallvec::VecLike;
 use std::fmt::Debug;
-#[cfg(feature = "servo")]
-use std::marker::PhantomData;
 use style_traits::viewport::ViewportConstraints;
 #[cfg(feature = "gecko")]
 use stylesheets::{CounterStyleRule, FontFaceRule};
@@ -112,27 +110,71 @@ pub struct Stylist {
     num_rebuilds: usize,
 }
 
-/// This struct holds data which user of Stylist may want to extract
+/// This struct holds data which users of Stylist may want to extract
+/// from stylesheets which can be done at the same time as updating.
+#[cfg(feature = "gecko")]
+#[derive(Default)]
+pub struct ExtraStyleData {
+    /// Extra data from user agent stylesheets
+    user_agent: PerOriginExtraStyleData,
+    /// Extra data from author stylesheets
+    author: PerOriginExtraStyleData,
+    /// Extra data from user stylesheets
+    user: PerOriginExtraStyleData,
+}
+
+/// This struct holds data which users of Stylist may want to extract
 /// from stylesheets which can be done at the same time as updating.
 #[cfg(feature = "gecko")]
-pub struct ExtraStyleData<'a> {
+#[derive(Default)]
+pub struct PerOriginExtraStyleData {
     /// A list of effective font-face rules and their origin.
-    pub font_faces: &'a mut Vec<(Arc<Locked<FontFaceRule>>, Origin)>,
+    pub font_faces: Vec<Arc<Locked<FontFaceRule>>>,
     /// A map of effective counter-style rules.
-    pub counter_styles: &'a mut PrecomputedHashMap<Atom, Arc<Locked<CounterStyleRule>>>,
+    pub counter_styles: PrecomputedHashMap<Atom, Arc<Locked<CounterStyleRule>>>,
 }
 
 #[cfg(feature = "gecko")]
-impl<'a> ExtraStyleData<'a> {
+impl ExtraStyleData {
     /// Clear the internal data.
+    pub fn clear(&mut self) {
+        self.user_agent.clear();
+        self.author.clear();
+        self.user.clear();
+    }
+
+    /// Returns a reference to the per-origin extra style data for
+    /// the specified origin.
+    #[inline]
+    pub fn borrow_mut_for_origin(&mut self, origin: &Origin) -> &mut PerOriginExtraStyleData {
+        match *origin {
+            Origin::UserAgent => &mut self.user_agent,
+            Origin::Author => &mut self.author,
+            Origin::User => &mut self.user,
+        }
+    }
+
+    /// Iterates over the per-origin extra style data, from highest level (user)
+    /// to lowest (user agent).
+    pub fn iter_origins(&self) -> ExtraStyleDataIter {
+        ExtraStyleDataIter {
+            extra_style_data: &self,
+            cur: 0,
+        }
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl PerOriginExtraStyleData {
+    /// Clears the stored @font-face and @counter-style rules.
     fn clear(&mut self) {
         self.font_faces.clear();
         self.counter_styles.clear();
     }
 
     /// Add the given @font-face rule.
-    fn add_font_face(&mut self, rule: &Arc<Locked<FontFaceRule>>, origin: Origin) {
-        self.font_faces.push((rule.clone(), origin));
+    fn add_font_face(&mut self, rule: &Arc<Locked<FontFaceRule>>) {
+        self.font_faces.push(rule.clone());
     }
 
     /// Add the given @counter-style rule.
@@ -145,12 +187,10 @@ impl<'a> ExtraStyleData<'a> {
 
 #[allow(missing_docs)]
 #[cfg(feature = "servo")]
-pub struct ExtraStyleData<'a> {
-    pub marker: PhantomData<&'a usize>,
-}
+pub struct ExtraStyleData;
 
 #[cfg(feature = "servo")]
-impl<'a> ExtraStyleData<'a> {
+impl ExtraStyleData {
     fn clear(&mut self) {}
 }
 
@@ -277,17 +317,17 @@ impl Stylist {
     /// This method resets all the style data each time the stylesheets change
     /// (which is indicated by the `stylesheets_changed` parameter), or the
     /// device is dirty, which means we need to re-evaluate media queries.
-    pub fn rebuild<'a, 'b, I, S>(
+    pub fn rebuild<'a, I, S>(
         &mut self,
         doc_stylesheets: I,
         guards: &StylesheetGuards,
         ua_stylesheets: Option<&UserAgentStylesheets>,
         stylesheets_changed: bool,
         author_style_disabled: bool,
-        extra_data: &mut ExtraStyleData<'a>
+        extra_data: &mut ExtraStyleData
     ) -> bool
     where
-        I: Iterator<Item = &'b S> + Clone,
+        I: Iterator<Item = &'a S> + Clone,
         S: StylesheetInDocument + ToMediaListKey + 'static,
     {
         debug_assert!(!self.is_cleared || self.is_device_dirty);
@@ -357,17 +397,17 @@ impl Stylist {
 
     /// clear the stylist and then rebuild it.  Chances are, you want to use
     /// either clear() or rebuild(), with the latter done lazily, instead.
-    pub fn update<'a, 'b, I, S>(
+    pub fn update<'a, I, S>(
         &mut self,
         doc_stylesheets: I,
         guards: &StylesheetGuards,
         ua_stylesheets: Option<&UserAgentStylesheets>,
         stylesheets_changed: bool,
         author_style_disabled: bool,
-        extra_data: &mut ExtraStyleData<'a>
+        extra_data: &mut ExtraStyleData
     ) -> bool
     where
-        I: Iterator<Item = &'b S> + Clone,
+        I: Iterator<Item = &'a S> + Clone,
         S: StylesheetInDocument + ToMediaListKey + 'static,
     {
         debug_assert!(!self.is_cleared || self.is_device_dirty);
@@ -382,11 +422,11 @@ impl Stylist {
                      author_style_disabled, extra_data)
     }
 
-    fn add_stylesheet<'a, S>(
+    fn add_stylesheet<S>(
         &mut self,
         stylesheet: &S,
         guard: &SharedRwLockReadGuard,
-        _extra_data: &mut ExtraStyleData<'a>
+        _extra_data: &mut ExtraStyleData
     )
     where
         S: StylesheetInDocument + ToMediaListKey + 'static,
@@ -506,11 +546,15 @@ impl Stylist {
                 }
                 #[cfg(feature = "gecko")]
                 CssRule::FontFace(ref rule) => {
-                    _extra_data.add_font_face(&rule, origin);
+                    _extra_data
+                        .borrow_mut_for_origin(&origin)
+                        .add_font_face(&rule);
                 }
                 #[cfg(feature = "gecko")]
                 CssRule::CounterStyle(ref rule) => {
-                    _extra_data.add_counter_style(guard, &rule);
+                    _extra_data
+                        .borrow_mut_for_origin(&origin)
+                        .add_counter_style(guard, &rule);
                 }
                 // We don't care about any other rule.
                 _ => {}
@@ -1628,6 +1672,33 @@ impl<'a> Iterator for CascadeDataIter<'a> {
     }
 }
 
+/// Iterator over `PerOriginExtraStyleData`, from highest level (user) to lowest
+/// (user agent).
+///
+/// We rely on this specific order for correctly looking up the @font-face
+/// and @counter-style rules.
+#[cfg(feature = "gecko")]
+pub struct ExtraStyleDataIter<'a> {
+    extra_style_data: &'a ExtraStyleData,
+    cur: usize,
+}
+
+#[cfg(feature = "gecko")]
+impl<'a> Iterator for ExtraStyleDataIter<'a> {
+    type Item = (&'a PerOriginExtraStyleData, Origin);
+
+    fn next(&mut self) -> Option<(&'a PerOriginExtraStyleData, Origin)> {
+        let result = match self.cur {
+            0 => (&self.extra_style_data.user, Origin::User),
+            1 => (&self.extra_style_data.author, Origin::Author),
+            2 => (&self.extra_style_data.user_agent, Origin::UserAgent),
+            _ => return None,
+        };
+        self.cur += 1;
+        Some(result)
+    }
+}
+
 /// Data resulting from performing the CSS cascade that is specific to a given
 /// origin.
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]