gnu_legacy: with GNU, write foreground first, else background first.

Fixes:
sharkdp/lscolors#77

src/ansi.rs

@@ -64,21 +64,42 @@ impl Style {
         // The foreground and background colors, if specified, need to be
         // handled specially because the number codes are more complicated.
         // (see `write_background_code` and `write_foreground_code`)
-        if let Some(bg) = self.background {
-            if written_anything {
-                write!(f, ";")?;
+
+        #[cfg(feature = "gnu_legacy")]
+        // write foreground first, else background first.
+        {
+            if let Some(fg) = self.foreground {
+                if written_anything {
+                    write!(f, ";")?;
+                }
+                written_anything = true;
+                fg.write_foreground_code(f)?;
             }
-            written_anything = true;
-            bg.write_background_code(f)?;
-        }
 
-        if let Some(fg) = self.foreground {
-            if written_anything {
-                write!(f, ";")?;
+            if let Some(bg) = self.background {
+                if written_anything {
+                    write!(f, ";")?;
+                }
+                bg.write_background_code(f)?;
             }
-            fg.write_foreground_code(f)?;
         }
+        #[cfg(not(feature = "gnu_legacy"))]
+        {
+            if let Some(bg) = self.background {
+                if written_anything {
+                    write!(f, ";")?;
+                }
+                written_anything = true;
+                bg.write_background_code(f)?;
+            }
 
+            if let Some(fg) = self.foreground {
+                if written_anything {
+                    write!(f, ";")?;
+                }
+                fg.write_foreground_code(f)?;
+            }
+        }
         // All the codes end with an `m`, because reasons.
         write!(f, "m")?;
 
@@ -397,6 +418,8 @@ macro_rules! test {
 mod test {
     use crate::style::Color::*;
     use crate::style::Style;
+    use crate::Color;
+    use std::default::Default;
 
     test!(plain:                 Style::default();                  "text/plain" => "text/plain");
     test!(red:                   Red;                               "hi" => "\x1B[31mhi\x1B[0m");
@@ -452,13 +475,28 @@ mod test {
         assert_eq!(White.normal().infix(Blue.normal()).to_string(), "\x1B[34m");
         assert_eq!(Blue.bold().infix(Blue.bold()).to_string(), "");
     }
+
+    #[test]
+    fn test_write_prefix_no_gnu_compat_order() {
+        let style = Style {
+            foreground: Some(Color::Red),
+            background: Some(Color::Blue),
+            ..Default::default()
+        };
+        assert_eq!(
+            style.paint("file").to_string(),
+            "\u{1b}[44;31mfile\u{1b}[0m".to_string()
+        );
+    }
 }
 
 #[cfg(test)]
 #[cfg(feature = "gnu_legacy")]
 mod gnu_legacy_test {
     use crate::style::Color::*;
     use crate::style::Style;
+    use crate::Color;
+    use std::default::Default;
 
     test!(plain:                 Style::default();                  "text/plain" => "text/plain");
     test!(red:                   Red;                               "hi" => "\x1B[31mhi\x1B[0m");
@@ -499,4 +537,17 @@ mod gnu_legacy_test {
     test!(hidden:                Style::new().hidden();             "hi" => "\x1B[08mhi\x1B[0m");
     test!(stricken:              Style::new().strikethrough();      "hi" => "\x1B[09mhi\x1B[0m");
     test!(lr_on_lr:              LightRed.on(LightRed);             "hi" => "\x1B[101;91mhi\x1B[0m");
+
+    #[test]
+    fn test_write_prefix_gnu_compat_order() {
+        let style = Style {
+            foreground: Some(Color::Red),
+            background: Some(Color::Blue),
+            ..Default::default()
+        };
+        assert_eq!(
+            style.paint("file").to_string(),
+            "\u{1b}[31;44mfile\u{1b}[0m".to_string()
+        );
+    }
 }