color: Serialize floating point alpha two two decimal positions if it roundtrips instead of three.

Author: emilio

src/color.rs

@@ -96,11 +96,17 @@ impl ToCss for RGBA {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result
         where W: fmt::Write,
     {
+        // Try first with two decimal places, then with three.
+        let mut rounded_alpha = (self.alpha_f32() * 100.).round() / 100.;
+        if clamp_f32(rounded_alpha) != self.alpha {
+            rounded_alpha = (self.alpha_f32() * 1000.).round() / 1000.;
+        }
+
         if self.alpha == 255 {
             write!(dest, "rgb({}, {}, {})", self.red, self.green, self.blue)
         } else {
-            write!(dest, "rgba({}, {}, {}, {:.3})",
-                   self.red, self.green, self.blue, self.alpha_f32())
+            write!(dest, "rgba({}, {}, {}, {})",
+                   self.red, self.green, self.blue, rounded_alpha)
         }
     }
 }

src/tests.rs

@@ -100,7 +100,6 @@ fn assert_json_eq(results: json::Json, mut expected: json::Json, message: String
     }
 }
 
-
 fn run_raw_json_tests<F: Fn(Json, Json) -> ()>(json_data: &str, run: F) {
     let items = match Json::from_str(json_data) {
         Ok(Json::Array(items)) => items,
@@ -380,27 +379,30 @@ fn serializer(preserve_comments: bool) {
     });
 }
 
-
 #[test]
 fn serialize_current_color() {
     let c = Color::CurrentColor;
     assert!(c.to_css_string() == "currentColor");
 }
 
-
 #[test]
 fn serialize_rgb_full_alpha() {
     let c = Color::RGBA(RGBA::new(255, 230, 204, 255));
     assert_eq!(c.to_css_string(), "rgb(255, 230, 204)");
 }
 
-
 #[test]
 fn serialize_rgba() {
     let c = Color::RGBA(RGBA::new(26, 51, 77, 32));
     assert_eq!(c.to_css_string(), "rgba(26, 51, 77, 0.125)");
 }
 
+#[test]
+fn serialize_rgba_two_digit_float_if_roundtrips() {
+    let c = Color::RGBA(RGBA::from_floats(0., 0., 0., 0.5));
+    assert_eq!(c.to_css_string(), "rgba(0, 0, 0, 0.5)");
+}
+
 #[test]
 fn line_numbers() {
     let mut input = Parser::new("foo bar\nbaz\r\n\n\"a\\\r\nb\"");