style: Add a StylesheetLoader abstraction, and make it a no-op on Geckolib.

Servo doesn't compile at this stage.

components/layout_thread/lib.rs

@@ -1542,6 +1542,7 @@ fn get_ua_stylesheets() -> Result<UserAgentStylesheets, &'static str> {
             None,
             Origin::UserAgent,
             Default::default(),
+            None,
             Box::new(StdoutErrorReporter),
             ParserContextExtraData::default()))
     }
@@ -1555,7 +1556,8 @@ fn get_ua_stylesheets() -> Result<UserAgentStylesheets, &'static str> {
     for &(ref contents, ref url) in &opts::get().user_stylesheets {
         user_or_user_agent_stylesheets.push(Stylesheet::from_bytes(
             &contents, url.clone(), None, None, Origin::User, Default::default(),
-            Box::new(StdoutErrorReporter), ParserContextExtraData::default()));
+            None, Box::new(StdoutErrorReporter),
+            ParserContextExtraData::default()));
     }
 
     let quirks_mode_stylesheet = try!(parse_ua_stylesheet("quirks-mode.css"));

components/style/stylesheets.rs

@@ -307,6 +307,7 @@ impl CssRule {
         let mut rule_parser = TopLevelRuleParser {
             stylesheet_origin: parent_stylesheet.origin,
             context: context,
+            loader: None,
             state: Cell::new(state),
             namespaces: &mut namespaces,
         };
@@ -605,9 +606,20 @@ rule_filter! {
     effective_keyframes_rules(Keyframes => KeyframesRule),
 }
 
+/// The stylesheet loader is the abstraction used to trigger network requests
+/// for `@import` rules.
+pub trait StylesheetLoader {
+    /// Request a stylesheet after parsing a given `@import` rule.
+    ///
+    /// The called code is responsible to update the `stylesheet` rules field
+    /// when the sheet is done loading.
+    fn request_stylesheet(&self, import: &Arc<RwLock<ImportRule>>);
+}
+
 struct TopLevelRuleParser<'a> {
     stylesheet_origin: Origin,
     namespaces: &'a mut Namespaces,
+    loader: Option<&'a StylesheetLoader>,
     context: ParserContext<'a>,
     state: Cell<State>,
 }
@@ -679,6 +691,12 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
                         }
                     ));
 
+                    if is_valid_url {
+                        let loader = self.loader
+                            .expect("Expected a stylesheet loader for @import");
+                        loader.request_stylesheet(&import_rule);
+                    }
+
                     return Ok(AtRuleType::WithoutBlock(CssRule::Import(import_rule)))
                 } else {
                     self.state.set(State::Invalid);

ports/geckolib/glue.rs

@@ -60,6 +60,7 @@ use style::thread_state;
 use style::timer::Timer;
 use style::traversal::{recalc_style_at, DomTraversalContext, PerLevelTraversalData};
 use style_traits::ToCss;
+use stylesheet_loader::StylesheetLoader;
 
 /*
  * For Gecko->Servo function calls, we need to redeclare the same signature that was declared in
@@ -232,8 +233,10 @@ pub extern "C" fn Servo_StyleSheet_Empty(mode: SheetParsingMode) -> RawServoStyl
         SheetParsingMode::eUserSheetFeatures => Origin::User,
         SheetParsingMode::eAgentSheetFeatures => Origin::UserAgent,
     };
+    let loader = StylesheetLoader::new();
     let sheet = Arc::new(Stylesheet::from_str(
-        "", url, origin, Default::default(), Box::new(StdoutErrorReporter), extra_data));
+        "", url, origin, Default::default(), Some(&loader),
+        Box::new(StdoutErrorReporter), extra_data));
     unsafe {
         transmute(sheet)
     }
@@ -262,8 +265,10 @@ pub extern "C" fn Servo_StyleSheet_FromUTF8Bytes(data: *const nsACString,
         referrer: Some(GeckoArcURI::new(referrer)),
         principal: Some(GeckoArcPrincipal::new(principal)),
     }};
+    let loader = StylesheetLoader::new();
     let sheet = Arc::new(Stylesheet::from_str(
-        input, url, origin, Default::default(), Box::new(StdoutErrorReporter), extra_data));
+        input, url, origin, Default::default(), Some(&loader),
+        Box::new(StdoutErrorReporter), extra_data));
     unsafe {
         transmute(sheet)
     }

ports/geckolib/lib.rs

@@ -18,6 +18,7 @@ extern crate style_traits;
 
 #[allow(non_snake_case)]
 pub mod glue;
+mod stylesheet_loader;
 
 // FIXME(bholley): This should probably go away once we harmonize the allocators.
 #[no_mangle]

ports/geckolib/stylesheet_loader.rs

@@ -0,0 +1,21 @@
+/* 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/. */
+
+use parking_lot::RwLock;
+use std::sync::Arc;
+use style::stylesheets::{ImportRule, StylesheetLoader as StyleStylesheetLoader};
+
+pub struct StylesheetLoader;
+
+impl StylesheetLoader {
+    pub fn new() -> Self {
+        StylesheetLoader
+    }
+}
+
+impl StyleStylesheetLoader for StylesheetLoader {
+    fn request_stylesheet(&self, _import: &Arc<RwLock<ImportRule>>) {
+        // FIXME(emilio): Implement `@import` in stylo.
+    }
+}

tests/unit/style/media_queries.rs

@@ -29,7 +29,8 @@ fn test_media_rule<F>(css: &str, callback: F) where F: Fn(&MediaList, &str) {
     let url = ServoUrl::parse("http://localhost").unwrap();
     let stylesheet = Stylesheet::from_str(
         css, url, Origin::Author, Default::default(),
-        Box::new(CSSErrorReporterTest), ParserContextExtraData::default());
+        None, Box::new(CSSErrorReporterTest),
+        ParserContextExtraData::default());
     let mut rule_count = 0;
     media_queries(&stylesheet.rules.read().0, &mut |mq| {
         rule_count += 1;
@@ -53,7 +54,8 @@ fn media_query_test(device: &Device, css: &str, expected_rule_count: usize) {
     let url = ServoUrl::parse("http://localhost").unwrap();
     let ss = Stylesheet::from_str(
         css, url, Origin::Author, Default::default(),
-        Box::new(CSSErrorReporterTest), ParserContextExtraData::default());
+        None, Box::new(CSSErrorReporterTest),
+        ParserContextExtraData::default());
     let mut rule_count = 0;
     ss.effective_style_rules(device, |_| rule_count += 1);
     assert!(rule_count == expected_rule_count, css.to_owned());

tests/unit/style/stylesheets.rs

@@ -52,6 +52,7 @@ fn test_parse_stylesheet() {
         }";
     let url = ServoUrl::parse("about::test").unwrap();
     let stylesheet = Stylesheet::from_str(css, url.clone(), Origin::UserAgent, Default::default(),
+                                          None,
                                           Box::new(CSSErrorReporterTest),
                                           ParserContextExtraData::default());
     let mut namespaces = Namespaces::default();
@@ -332,7 +333,9 @@ fn test_report_error_stylesheet() {
 
     let errors = error_reporter.errors.clone();
 
-    Stylesheet::from_str(css, url, Origin::UserAgent, Default::default(), error_reporter,
+    Stylesheet::from_str(css, url, Origin::UserAgent, Default::default(),
+                         None,
+                         error_reporter,
                          ParserContextExtraData::default());
 
     let mut errors = errors.lock().unwrap();

tests/unit/style/viewport.rs

@@ -25,6 +25,7 @@ macro_rules! stylesheet {
             ServoUrl::parse("http://localhost").unwrap(),
             Origin::$origin,
             Default::default(),
+            None,
             $error_reporter,
             ParserContextExtraData::default()
         ))

tests/unit/stylo/lib.rs

@@ -16,5 +16,8 @@ extern crate style_traits;
 
 mod sanity_checks;
 
+#[path = "../../../ports/geckolib/stylesheet_loader.rs"]
+mod stylesheet_loader;
+
 mod servo_function_signatures;