Auto merge of #13453 - metajack:media-query-list, r=jdm

Implement matchMedia and MediaQueryList

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #13376 (github issue number if applicable).

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

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Fixes #13376.

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This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/13453)

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components/style/lib.rs

@@ -137,6 +137,8 @@ pub mod values;
 pub mod viewport;
 pub mod workqueue;
 
+use cssparser::ToCss;
+use std::fmt;
 use std::sync::Arc;
 
 /// The CSS properties supported by the style system.
@@ -176,3 +178,16 @@ pub fn arc_ptr_eq<T: 'static>(a: &Arc<T>, b: &Arc<T>) -> bool {
     let b: &T = &**b;
     (a as *const T) == (b as *const T)
 }
+
+pub fn serialize_comma_separated_list<W, T>(dest: &mut W, list: &[T])
+                                            -> fmt::Result where W: fmt::Write, T: ToCss {
+    if list.len() > 0 {
+        for item in &list[..list.len()-1] {
+            try!(item.to_css(dest));
+            try!(write!(dest, ", "));
+        }
+        list[list.len()-1].to_css(dest)
+    } else {
+        Ok(())
+    }
+}

components/style/media_queries.rs

@@ -7,9 +7,12 @@
 //! [mq]: https://drafts.csswg.org/mediaqueries/
 
 use app_units::Au;
-use cssparser::{Delimiter, Parser, Token};
+use cssparser::{Delimiter, Parser, ToCss, Token};
 use euclid::size::{Size2D, TypedSize2D};
 use properties::longhands;
+use serialize_comma_separated_list;
+use std::fmt::{self, Write};
+use string_cache::Atom;
 use style_traits::ViewportPx;
 use values::specified;
 
@@ -20,6 +23,14 @@ pub struct MediaQueryList {
     pub media_queries: Vec<MediaQuery>
 }
 
+impl ToCss for MediaQueryList {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write
+    {
+        serialize_comma_separated_list(dest, &self.media_queries)
+    }
+}
+
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub enum Range<T> {
@@ -104,20 +115,58 @@ impl MediaQuery {
     }
 }
 
+impl ToCss for MediaQuery {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write
+    {
+        if self.qualifier == Some(Qualifier::Not) {
+            try!(write!(dest, "not "));
+        }
+
+        let mut type_ = String::new();
+        match self.media_type {
+            MediaQueryType::All => try!(write!(type_, "all")),
+            MediaQueryType::MediaType(MediaType::Screen) => try!(write!(type_, "screen")),
+            MediaQueryType::MediaType(MediaType::Print) => try!(write!(type_, "print")),
+            MediaQueryType::MediaType(MediaType::Unknown(ref desc)) => try!(write!(type_, "{}", desc)),
+        };
+        if self.expressions.is_empty() {
+            return write!(dest, "{}", type_)
+        } else if type_ != "all" || self.qualifier == Some(Qualifier::Not) {
+            try!(write!(dest, "{} and ", type_));
+        }
+        for (i, &e) in self.expressions.iter().enumerate() {
+            try!(write!(dest, "("));
+            let (mm, l) = match e {
+                Expression::Width(Range::Min(ref l)) => ("min", l),
+                Expression::Width(Range::Max(ref l)) => ("max", l),
+            };
+            try!(write!(dest, "{}-width: ", mm));
+            try!(l.to_css(dest));
+            if i == self.expressions.len() - 1 {
+                try!(write!(dest, ")"));
+            } else {
+                try!(write!(dest, ") and "));
+            }
+        }
+        Ok(())
+    }
+}
+
 /// http://dev.w3.org/csswg/mediaqueries-3/#media0
-#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub enum MediaQueryType {
     All,  // Always true
     MediaType(MediaType),
 }
 
-#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub enum MediaType {
     Screen,
     Print,
-    Unknown,
+    Unknown(Atom),
 }
 
 #[derive(Debug)]
@@ -181,7 +230,7 @@ impl MediaQuery {
                 "screen" => MediaQueryType::MediaType(MediaType::Screen),
                 "print" => MediaQueryType::MediaType(MediaType::Print),
                 "all" => MediaQueryType::All,
-                _ => MediaQueryType::MediaType(MediaType::Unknown)
+                _ => MediaQueryType::MediaType(MediaType::Unknown(Atom::from(&*ident)))
             }
         } else {
             // Media type is only optional if qualifier is not specified.
@@ -233,8 +282,8 @@ impl MediaQueryList {
         self.media_queries.iter().any(|mq| {
             // Check if media matches. Unknown media never matches.
             let media_match = match mq.media_type {
-                MediaQueryType::MediaType(MediaType::Unknown) => false,
-                MediaQueryType::MediaType(media_type) => media_type == device.media_type,
+                MediaQueryType::MediaType(MediaType::Unknown(_)) => false,
+                MediaQueryType::MediaType(ref media_type) => *media_type == device.media_type,
                 MediaQueryType::All => true,
             };