style: Add a struct to represent import rules, and parse them correctly.

components/style/stylesheets.rs

@@ -26,6 +26,7 @@ use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
 use style_traits::ToCss;
 use stylist::FnvHashMap;
+use values::specified::url::SpecifiedUrl;
 use viewport::ViewportRule;
 
 
@@ -79,7 +80,8 @@ impl CssRules {
     fn only_ns_or_import(&self) -> bool {
         self.0.iter().all(|r| {
             match *r {
-                CssRule::Namespace(..) /* | CssRule::Import(..) */ => true,
+                CssRule::Namespace(..) |
+                CssRule::Import(..) => true,
                 _ => false
             }
         })
@@ -180,6 +182,7 @@ pub enum CssRule {
     // https://drafts.csswg.org/cssom/#changes-from-5-december-2013
 
     Namespace(Arc<RwLock<NamespaceRule>>),
+    Import(Arc<RwLock<ImportRule>>),
     Style(Arc<RwLock<StyleRule>>),
     Media(Arc<RwLock<MediaRule>>),
     FontFace(Arc<RwLock<FontFaceRule>>),
@@ -235,6 +238,7 @@ impl CssRule {
     pub fn rule_type(&self) -> CssRuleType {
         match *self {
             CssRule::Style(_)     => CssRuleType::Style,
+            CssRule::Import(_)    => CssRuleType::Import,
             CssRule::Media(_)     => CssRuleType::Media,
             CssRule::FontFace(_)  => CssRuleType::FontFace,
             CssRule::Keyframes(_) => CssRuleType::Keyframes,
@@ -246,7 +250,7 @@ impl CssRule {
     fn rule_state(&self) -> State {
         match *self {
             // CssRule::Charset(..) => State::Start,
-            // CssRule::Import(..) => State::Imports,
+            CssRule::Import(..) => State::Imports,
             CssRule::Namespace(..) => State::Namespaces,
             _ => State::Body,
         }
@@ -254,10 +258,19 @@ 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.
+    /// Note that only some types of rules can contain rules. An empty slice is
+    /// used for others.
     pub fn with_nested_rules_and_mq<F, R>(&self, mut f: F) -> R
     where F: FnMut(&[CssRule], Option<&MediaList>) -> R {
         match *self {
+            CssRule::Import(ref lock) => {
+                let rule = lock.read();
+                let media = rule.stylesheet.media.read();
+                let rules = rule.stylesheet.rules.read();
+                // FIXME(emilio): Include the nested rules if the stylesheet is
+                // loaded.
+                f(&rules.0, Some(&media))
+            }
             CssRule::Namespace(_) |
             CssRule::Style(_) |
             CssRule::FontFace(_) |
@@ -315,6 +328,7 @@ impl ToCss for CssRule {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
         match *self {
             CssRule::Namespace(ref lock) => lock.read().to_css(dest),
+            CssRule::Import(ref lock) => lock.read().to_css(dest),
             CssRule::Style(ref lock) => lock.read().to_css(dest),
             CssRule::FontFace(ref lock) => lock.read().to_css(dest),
             CssRule::Viewport(ref lock) => lock.read().to_css(dest),
@@ -346,6 +360,34 @@ impl ToCss for NamespaceRule {
     }
 }
 
+
+/// The [`@import`][import] at-rule.
+///
+/// [import]: https://drafts.csswg.org/css-cascade-3/#at-import
+#[derive(Debug)]
+pub struct ImportRule {
+    pub url: SpecifiedUrl,
+
+    /// The stylesheet is always present.
+    ///
+    /// It contains an empty list of rules and namespace set that is updated
+    /// when it loads.
+    pub stylesheet: Arc<Stylesheet>,
+}
+
+impl ToCss for ImportRule {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        try!(dest.write_str("@import "));
+        try!(self.url.to_css(dest));
+        let media = self.stylesheet.media.read();
+        if !media.is_empty() {
+            try!(dest.write_str(" "));
+            try!(media.to_css(dest));
+        }
+        Ok(())
+    }
+}
+
 #[derive(Debug)]
 pub struct KeyframesRule {
     pub name: Atom,
@@ -612,8 +654,32 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
             "import" => {
                 if self.state.get() <= State::Imports {
                     self.state.set(State::Imports);
-                    // TODO: support @import
+                    let url = try!(input.expect_url_or_string());
-                    return Err(())  // "@import is not supported yet"
+                    let url =
+                        try!(SpecifiedUrl::parse_from_string(url,
+                                                             &self.context));
+
+                    let media =
+                        Arc::new(RwLock::new(parse_media_query_list(input)));
+
+                    let is_valid_url = url.url().is_some();
+
+                    let import_rule = Arc::new(RwLock::new(
+                        ImportRule {
+                            url: url,
+                            stylesheet: Arc::new(Stylesheet {
+                                rules: Arc::new(RwLock::new(CssRules(vec![]))),
+                                media: media,
+                                origin: self.context.stylesheet_origin,
+                                base_url: self.context.base_url.clone(),
+                                namespaces: RwLock::new(Namespaces::default()),
+                                dirty_on_viewport_size_change: AtomicBool::new(false),
+                                disabled: AtomicBool::new(false),
+                            })
+                        }
+                    ));
+
+                    return Ok(AtRuleType::WithoutBlock(CssRule::Import(import_rule)))
                 } else {
                     self.state.set(State::Invalid);
                     return Err(())  // "@import must be before any rule but @charset"

components/style/stylist.rs

@@ -165,6 +165,25 @@ impl Stylist {
             self.add_stylesheet(stylesheet);
         }
 
+        debug!("Stylist stats:");
+        debug!(" - Got {} sibling-affecting selectors",
+               self.sibling_affecting_selectors.len());
+        debug!(" - Got {} non-common-style-attribute-affecting selectors",
+               self.non_common_style_affecting_attributes_selectors.len());
+        debug!(" - Got {} deps for style-hint calculation",
+               self.state_deps.len());
+
+        SelectorImpl::each_precomputed_pseudo_element(|pseudo| {
+            // TODO: Consider not doing this and just getting the rules on the
+            // fly. It should be a bit slower, but we'd take rid of the
+            // extra field, and avoid this precomputation entirely.
+            if let Some(map) = self.pseudos_map.remove(&pseudo) {
+                let mut declarations = vec![];
+                map.user_agent.get_universal_rules(&mut declarations);
+                self.precomputed_pseudo_element_decls.insert(pseudo, declarations);
+            }
+        });
+
         self.is_device_dirty = false;
         true
     }
@@ -211,6 +230,10 @@ impl Stylist {
                         }
                     }
                 }
+                CssRule::Import(ref import) => {
+                    let import = import.read();
+                    self.add_stylesheet(&import.stylesheet)
+                }
                 CssRule::Keyframes(ref keyframes_rule) => {
                     let keyframes_rule = keyframes_rule.read();
                     debug!("Found valid keyframes rule: {:?}", *keyframes_rule);
@@ -250,6 +273,7 @@ impl Stylist {
         });
     }
 
+
     /// Computes the style for a given "precomputed" pseudo-element, taking the
     /// universal rules and applying them.
     ///

components/style/values/specified/url.rs

@@ -11,6 +11,7 @@ use parser::{Parse, ParserContext};
 #[cfg(feature = "gecko")]
 use parser::ParserContextExtraData;
 use servo_url::ServoUrl;
+use std::borrow::Cow;
 use std::fmt::{self, Write};
 use std::ptr;
 use std::sync::Arc;
@@ -76,7 +77,14 @@ pub struct SpecifiedUrl {
 impl Parse for SpecifiedUrl {
     fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
         let url = try!(input.expect_url());
+        Self::parse_from_string(url, context)
+    }
+}
 
+impl SpecifiedUrl {
+    pub fn parse_from_string<'a>(url: Cow<'a, str>,
+                                 context: &ParserContext)
+                                 -> Result<Self, ()> {
         let extra_data = match UrlExtraData::make_from(context) {
             Some(extra_data) => extra_data,
             None => {
@@ -96,9 +104,7 @@ impl Parse for SpecifiedUrl {
             extra_data: extra_data,
         })
     }
-}
 
-impl SpecifiedUrl {
     pub fn extra_data(&self) -> &UrlExtraData {
         &self.extra_data
     }