Ensure serialization takes precision into account.

Author: tiaanl

src/color.rs

@@ -16,7 +16,7 @@ const OPAQUE: f32 = 1.0;
 #[inline]
 fn serialize_alpha(dest: &mut impl fmt::Write, alpha: f32, legacy_syntax: bool) -> fmt::Result {
     // If the alpha component is full opaque, don't emit the alpha value in CSS.
-    if alpha == OPAQUE {
+    if clamp_unit_f32(alpha) == 255 {
         return Ok(());
     }
 
@@ -159,7 +159,7 @@ impl ToCss for RGBA {
     where
         W: fmt::Write,
     {
-        let has_alpha = self.alpha != OPAQUE;
+        let has_alpha = clamp_unit_f32(self.alpha) != 255;
 
         dest.write_str(if has_alpha { "rgba(" } else { "rgb(" })?;
         self.red.to_css(dest)?;

src/tests.rs

@@ -572,6 +572,13 @@ fn serialize_rgb_full_alpha() {
 fn serialize_rgba() {
     let c = rgba(26, 51, 77, 0.125);
     assert_eq!(c.to_css_string(), "rgba(26, 51, 77, 0.125)");
+
+    let c = rgba(26, 51, 77, 0.99);
+    assert_eq!(c.to_css_string(), "rgba(26, 51, 77, 0.99)");
+    let c = rgba(26, 51, 77, 0.999);
+    assert_eq!(c.to_css_string(), "rgb(26, 51, 77)");
+    let c = rgba(26, 51, 77, 0.9999);
+    assert_eq!(c.to_css_string(), "rgb(26, 51, 77)");
 }
 
 #[test]