style: Allow placeholder import sheets.

This is necessary because we can't create GeckoStyleSheets off-main-thread,
so we need a placeholder until it can be filled in.

Bug: 1454030
Reviewed-by: emilio
MozReview-Commit-ID: ssRme4fLYg

components/style/gecko/data.rs

@@ -5,6 +5,7 @@
 //! Data needed to style a Gecko document.
 
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use context::QuirksMode;
 use dom::TElement;
 use gecko_bindings::bindings::{self, RawServoStyleSet};
 use gecko_bindings::structs::{self, RawGeckoPresContextOwned, ServoStyleSetSizes, ServoStyleSheet};
@@ -17,7 +18,7 @@ use properties::ComputedValues;
 use selector_parser::SnapshotMap;
 use servo_arc::Arc;
 use shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
-use stylesheets::{StylesheetContents, StylesheetInDocument};
+use stylesheets::{CssRule, Origin, StylesheetContents, StylesheetInDocument};
 use stylist::Stylist;
 
 /// Little wrapper to a Gecko style sheet.
@@ -58,6 +59,16 @@ impl GeckoStyleSheet {
             &*(self.raw()._base.mInner as *const StyleSheetInfo as *const ServoStyleSheetInner)
         }
     }
+
+    /// Gets the StylesheetContents for this stylesheet.
+    pub fn contents(&self) -> &StylesheetContents {
+        debug_assert!(!self.inner().mContents.mRawPtr.is_null());
+        unsafe {
+            let contents =
+                (&**StylesheetContents::as_arc(&&*self.inner().mContents.mRawPtr)) as *const _;
+            &*contents
+        }
+    }
 }
 
 impl Drop for GeckoStyleSheet {
@@ -74,13 +85,12 @@ impl Clone for GeckoStyleSheet {
 }
 
 impl StylesheetInDocument for GeckoStyleSheet {
-    fn contents(&self, _: &SharedRwLockReadGuard) -> &StylesheetContents {
-        debug_assert!(!self.inner().mContents.mRawPtr.is_null());
-        unsafe {
-            let contents =
-                (&**StylesheetContents::as_arc(&&*self.inner().mContents.mRawPtr)) as *const _;
-            &*contents
-        }
+    fn origin(&self, _guard: &SharedRwLockReadGuard) -> Origin {
+        self.contents().origin
+    }
+
+    fn quirks_mode(&self, _guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.contents().quirks_mode
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
@@ -103,6 +113,11 @@ impl StylesheetInDocument for GeckoStyleSheet {
     fn enabled(&self) -> bool {
         true
     }
+
+    #[inline]
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.contents().rules(guard)
+    }
 }
 
 /// The container for data that a Servo-backed Gecko document needs to style

components/style/stylesheet_set.rs

@@ -478,7 +478,7 @@ where
         sheet: &S,
         guard: &SharedRwLockReadGuard,
     ) -> &mut SheetCollection<S> {
-        let origin = sheet.contents(guard).origin;
+        let origin = sheet.origin(guard);
         self.collections.borrow_mut_for_origin(&origin)
     }
 

components/style/stylesheets/import_rule.rs

@@ -6,20 +6,60 @@
 //!
 //! [import]: https://drafts.csswg.org/css-cascade-3/#at-import
 
+use context::QuirksMode;
 use cssparser::SourceLocation;
 use media_queries::MediaList;
 use shared_lock::{DeepCloneParams, DeepCloneWithLock};
 use shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt::{self, Write};
 use str::CssStringWriter;
 use style_traits::{CssWriter, ToCss};
-use stylesheets::{StylesheetContents, StylesheetInDocument};
+use stylesheets::{CssRule, Origin, StylesheetInDocument};
 use values::CssUrl;
 
+/// With asynchronous stylesheet parsing, we can't synchronously create a
+/// GeckoStyleSheet. So we use this placeholder instead.
+#[derive(Clone, Debug)]
+pub struct PendingSheet {
+    origin: Origin,
+    quirks_mode: QuirksMode,
+}
+
 /// A sheet that is held from an import rule.
 #[cfg(feature = "gecko")]
 #[derive(Debug)]
-pub struct ImportSheet(pub ::gecko::data::GeckoStyleSheet);
+pub enum ImportSheet {
+    /// A bonafide stylesheet.
+    Sheet(::gecko::data::GeckoStyleSheet),
+    /// An @import created while parsing off-main-thread, whose Gecko sheet has
+    /// yet to be created and attached.
+    Pending(PendingSheet),
+}
+
+#[cfg(feature = "gecko")]
+impl ImportSheet {
+    /// Creates a new ImportSheet from a GeckoStyleSheet.
+    pub fn new(sheet: ::gecko::data::GeckoStyleSheet) -> Self {
+        ImportSheet::Sheet(sheet)
+    }
+
+    /// Creates a pending ImportSheet for a load that has not started yet.
+    pub fn new_pending(origin: Origin, quirks_mode: QuirksMode) -> Self {
+        ImportSheet::Pending(PendingSheet {
+            origin,
+            quirks_mode,
+        })
+    }
+
+    /// Returns a reference to the GeckoStyleSheet in this ImportSheet, if it
+    /// exists.
+    pub fn as_sheet(&self) -> Option<&::gecko::data::GeckoStyleSheet> {
+        match *self {
+            ImportSheet::Sheet(ref s) => Some(s),
+            ImportSheet::Pending(_) => None,
+        }
+    }
+}
 
 #[cfg(feature = "gecko")]
 impl DeepCloneWithLock for ImportSheet {
@@ -31,10 +71,15 @@ impl DeepCloneWithLock for ImportSheet {
     ) -> Self {
         use gecko::data::GeckoStyleSheet;
         use gecko_bindings::bindings;
-        let clone = unsafe {
-            bindings::Gecko_StyleSheet_Clone(self.0.raw() as *const _, params.reference_sheet)
-        };
-        ImportSheet(unsafe { GeckoStyleSheet::from_addrefed(clone) })
+        match *self {
+            ImportSheet::Sheet(ref s) => {
+                let clone = unsafe {
+                    bindings::Gecko_StyleSheet_Clone(s.raw() as *const _, params.reference_sheet)
+                };
+                ImportSheet::Sheet(unsafe { GeckoStyleSheet::from_addrefed(clone) })
+            },
+            ImportSheet::Pending(ref p) => ImportSheet::Pending(p.clone()),
+        }
     }
 }
 
@@ -44,17 +89,39 @@ impl DeepCloneWithLock for ImportSheet {
 pub struct ImportSheet(pub ::servo_arc::Arc<::stylesheets::Stylesheet>);
 
 impl StylesheetInDocument for ImportSheet {
-    /// Get the media associated with this stylesheet.
-    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
-        self.0.media(guard)
+    fn origin(&self, _guard: &SharedRwLockReadGuard) -> Origin {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.contents().origin,
+            ImportSheet::Pending(ref p) => p.origin,
+        }
     }
 
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents {
-        self.0.contents(guard)
+    fn quirks_mode(&self, _guard: &SharedRwLockReadGuard) -> QuirksMode {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.contents().quirks_mode,
+            ImportSheet::Pending(ref p) => p.quirks_mode,
+        }
     }
 
     fn enabled(&self) -> bool {
-        self.0.enabled()
+        match *self {
+            ImportSheet::Sheet(ref s) => s.enabled(),
+            ImportSheet::Pending(_) => true,
+        }
+    }
+
+    fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.media(guard),
+            ImportSheet::Pending(_) => None,
+        }
+    }
+
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        match *self {
+            ImportSheet::Sheet(ref s) => s.contents().rules(guard),
+            ImportSheet::Pending(_) => &[],
+        }
     }
 }
 

components/style/stylesheets/rules_iterator.rs

@@ -9,8 +9,9 @@ use media_queries::Device;
 use shared_lock::SharedRwLockReadGuard;
 use smallvec::SmallVec;
 use std::slice;
-use stylesheets::{CssRule, CssRules, DocumentRule, ImportRule, MediaRule, SupportsRule};
+use stylesheets::{CssRule, DocumentRule, ImportRule, MediaRule, SupportsRule};
 use stylesheets::StylesheetInDocument;
+use stylesheets::import_rule::ImportSheet;
 
 /// An iterator over a list of rules.
 pub struct RulesIterator<'a, 'b, C>
@@ -35,10 +36,10 @@ where
         device: &'a Device,
         quirks_mode: QuirksMode,
         guard: &'a SharedRwLockReadGuard<'b>,
-        rules: &'a CssRules,
+        rules: &'a [CssRule],
     ) -> Self {
         let mut stack = SmallVec::new();
-        stack.push(rules.0.iter());
+        stack.push(rules.iter());
         Self {
             device: device,
             quirks_mode: quirks_mode,
@@ -102,10 +103,7 @@ where
                         }
                         import_rule
                             .stylesheet
-                            .contents(self.guard)
-                            .rules
-                            .read_with(self.guard)
-                            .0
+                            .rules(self.guard)
                             .iter()
                     },
                     CssRule::Document(ref doc_rule) => {

components/style/stylesheets/stylesheet.rs

@@ -103,22 +103,10 @@ impl StylesheetContents {
         }
     }
 
-    /// Return an iterator using the condition `C`.
+    /// Returns a reference to the list of rules.
     #[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),
-        )
+    pub fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        &self.rules.read_with(guard).0
     }
 
     /// Measure heap usage.
@@ -189,32 +177,20 @@ macro_rules! rule_filter {
 
 /// A trait to represent a given stylesheet in a document.
 pub trait StylesheetInDocument {
-    /// Get the contents of this stylesheet.
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents;
-
     /// Get the stylesheet origin.
-    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin {
-        self.contents(guard).origin
-    }
+    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin;
 
     /// Get the stylesheet quirks mode.
-    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode {
-        self.contents(guard).quirks_mode
-    }
+    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode;
+
+    /// Get whether this stylesheet is enabled.
+    fn enabled(&self) -> bool;
 
     /// Get the media associated with this stylesheet.
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList>;
 
-    /// Returns whether the style-sheet applies for the current device.
-    fn is_effective_for_device(&self, device: &Device, guard: &SharedRwLockReadGuard) -> bool {
-        match self.media(guard) {
-            Some(medialist) => medialist.evaluate(device, self.quirks_mode(guard)),
-            None => true,
-        }
-    }
-
-    /// Get whether this stylesheet is enabled.
-    fn enabled(&self) -> bool;
+    /// Returns a reference to the list of rules in this stylesheet.
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule];
 
     /// Return an iterator using the condition `C`.
     #[inline]
@@ -226,7 +202,15 @@ pub trait StylesheetInDocument {
     where
         C: NestedRuleIterationCondition,
     {
-        self.contents(guard).iter_rules(device, guard)
+        RulesIterator::new(device, self.quirks_mode(guard), guard, self.rules(guard))
+    }
+
+    /// Returns whether the style-sheet applies for the current device.
+    fn is_effective_for_device(&self, device: &Device, guard: &SharedRwLockReadGuard) -> bool {
+        match self.media(guard) {
+            Some(medialist) => medialist.evaluate(device, self.quirks_mode(guard)),
+            None => true,
+        }
     }
 
     /// Return an iterator over the effective rules within the style-sheet, as
@@ -255,8 +239,12 @@ pub trait StylesheetInDocument {
 }
 
 impl StylesheetInDocument for Stylesheet {
-    fn contents(&self, _: &SharedRwLockReadGuard) -> &StylesheetContents {
-        &self.contents
+    fn origin(&self, _guard: &SharedRwLockReadGuard) -> Origin {
+        self.contents.origin
+    }
+
+    fn quirks_mode(&self, _guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.contents.quirks_mode
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
@@ -266,6 +254,11 @@ impl StylesheetInDocument for Stylesheet {
     fn enabled(&self) -> bool {
         !self.disabled()
     }
+
+    #[inline]
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.contents.rules(guard)
+    }
 }
 
 /// A simple wrapper over an `Arc<Stylesheet>`, with pointer comparison, and
@@ -289,8 +282,12 @@ impl ToMediaListKey for DocumentStyleSheet {
 }
 
 impl StylesheetInDocument for DocumentStyleSheet {
-    fn contents(&self, guard: &SharedRwLockReadGuard) -> &StylesheetContents {
-        self.0.contents(guard)
+    fn origin(&self, guard: &SharedRwLockReadGuard) -> Origin {
+        self.0.origin(guard)
+    }
+
+    fn quirks_mode(&self, guard: &SharedRwLockReadGuard) -> QuirksMode {
+        self.0.quirks_mode(guard)
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
@@ -300,6 +297,11 @@ impl StylesheetInDocument for DocumentStyleSheet {
     fn enabled(&self) -> bool {
         self.0.enabled()
     }
+
+    #[inline]
+    fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {
+        self.0.rules(guard)
+    }
 }
 
 impl Stylesheet {

ports/geckolib/glue.rs

@@ -2048,7 +2048,7 @@ pub extern "C" fn Servo_ImportRule_GetSheet(
     rule: RawServoImportRuleBorrowed,
 ) -> *const ServoStyleSheet {
     read_locked_arc(rule, |rule: &ImportRule| {
-        rule.stylesheet.0.raw() as *const ServoStyleSheet
+        rule.stylesheet.as_sheet().unwrap().raw() as *const ServoStyleSheet
     })
 }
 

ports/geckolib/stylesheet_loader.rs

@@ -55,9 +55,8 @@ impl StyleStylesheetLoader for StylesheetLoader {
 
         debug_assert!(!child_sheet.is_null(),
                       "Import rules should always have a strong sheet");
-        let stylesheet = unsafe {
-            ImportSheet(GeckoStyleSheet::from_addrefed(child_sheet))
-        };
+        let sheet = unsafe { GeckoStyleSheet::from_addrefed(child_sheet) };
+        let stylesheet = ImportSheet::new(sheet);
         Arc::new(lock.wrap(ImportRule { url, source_location, stylesheet }))
     }
 }