[librsvg] Color::from_color_spec() - Turn a ColorSpec from C back into a Result<Color>

[Federico Mena Quintero <federico src gnome org>]

commit 4fa9b849994a11e0bf53528b19f8dac9373e520b
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed May 31 12:59:14 2017 -0500

    Color::from_color_spec() - Turn a ColorSpec from C back into a Result<Color>
    
    We'll use this to think only in Rustic terms, instead of having to piece
    out a ColorSpec which can indicate a ParseError.

 rust/src/color.rs |   39 +++++++++++++++++++++++++++++++++++++++
 1 files changed, 39 insertions(+), 0 deletions(-)
---
diff --git a/rust/src/color.rs b/rust/src/color.rs
index 56cf10f..9a25005 100644
--- a/rust/src/color.rs
+++ b/rust/src/color.rs
@@ -85,6 +85,25 @@ impl Color {
             }
         }
     }
+
+    pub fn from_color_spec (spec: &ColorSpec) -> Result <Color, AttributeError> {
+        match *spec {
+            ColorSpec { kind: ColorKind::Inherit, .. }      => Ok (Color::Inherit),
+
+            ColorSpec { kind: ColorKind::CurrentColor, .. } => Ok (Color::CurrentColor),
+
+            ColorSpec { kind: ColorKind::ARGB, argb } => Ok (Color::RGBA (rgba_from_argb (argb))),
+
+            ColorSpec { kind: ColorKind::ParseError, .. } => Err (AttributeError::Parse (ParseError::new 
("parse error")))
+        }
+    }
+}
+
+fn rgba_from_argb (argb: u32) -> cssparser::RGBA {
+    cssparser::RGBA::new (((argb & 0x00ff0000) >> 16) as u8,
+                          ((argb & 0x0000ff00) >> 8) as u8,
+                          ((argb & 0x000000ff) as u8),
+                          ((argb & 0xff000000) >> 24) as u8)
 }
 
 impl From<cssparser::Color> for Color {
@@ -207,4 +226,24 @@ mod tests {
         assert_eq! (ColorSpec::from (Color::parse ("inherit", AllowInherit::No, AllowCurrentColor::Yes)),
                     make_error ());
     }
+
+    fn test_roundtrip (s: &str) {
+        let result = Color::parse (s, AllowInherit::Yes, AllowCurrentColor::Yes);
+        let result2 = result.clone ();
+        let spec = ColorSpec::from (result2);
+
+        if result.is_ok () {
+            assert_eq! (Color::from_color_spec (&spec), result);
+        } else {
+            assert! (Color::from_color_spec (&spec).is_err ());
+        }
+    }
+
+    #[test]
+    fn roundtrips () {
+        test_roundtrip ("inherit");
+        test_roundtrip ("currentColor");
+        test_roundtrip ("#aabbccdd");
+        test_roundtrip ("papadzul");
+    }
 }