Auto merge of #14192 - gterzian:support_equality_constraints, r=emilio

implement support for the width query

<!-- Please describe your changes on the following line: -->
implement support for the `width` media query

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #https://github.com/servo/servo/issues/13670 (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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1 files changed, 10 insertions, 6 deletions

diff --git a/components/style/media_queries.rs b/components/style/media_queries.rs
index 569265b323f..522a252a05b 100644
--- a/components/style/media_queries.rs
+++ b/components/style/media_queries.rs
@@ -42,7 +42,7 @@ impl Default for MediaList {
 pub enum Range<T> {
     Min(T),
     Max(T),
-    //Eq(T),    // FIXME: Implement parsing support for equality then re-enable this.
+    Eq(T),
 }
 
 impl Range<specified::Length> {
@@ -54,7 +54,7 @@ impl Range<specified::Length> {
         match *self {
             Range::Min(ref width) => Range::Min(width.to_computed_value(&context)),
             Range::Max(ref width) => Range::Max(width.to_computed_value(&context)),
-            //Range::Eq(ref width) => Range::Eq(compute_width(width))
+            Range::Eq(ref width) => Range::Eq(width.to_computed_value(&context))
         }
     }
 }
@@ -64,7 +64,7 @@ impl<T: Ord> Range<T> {
         match *self {
             Range::Min(ref width) => { value >= *width },
             Range::Max(ref width) => { value <= *width },
-            //Range::Eq(ref width) => { value == *width },
+            Range::Eq(ref width) => { value == *width },
         }
     }
 }
@@ -127,10 +127,11 @@ impl ToCss for MediaQuery {
         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),
+                Expression::Width(Range::Min(ref l)) => ("min-", l),
+                Expression::Width(Range::Max(ref l)) => ("max-", l),
+                Expression::Width(Range::Eq(ref l)) => ("", l),
             };
-            try!(write!(dest, "{}-width: ", mm));
+            try!(write!(dest, "{}width: ", mm));
             try!(l.to_css(dest));
             if i == self.expressions.len() - 1 {
                 try!(write!(dest, ")"));
@@ -195,6 +196,9 @@ impl Expression {
                 "max-width" => {
                     Ok(Expression::Width(Range::Max(try!(specified::Length::parse_non_negative(input)))))
                 },
+                "width" => {
+                    Ok(Expression::Width(Range::Eq(try!(specified::Length::parse_non_negative(input)))))
+                },
                 _ => Err(())
             }
         })