windows: support the first 16 Ansi256

While the native Windows console APIs have very limited support
for colors, we can at least support the first 16 colors of the ANSI
spectrum by translating them to the standard Windows 8-bit palette,
along with toggling the intensity to make 16 total colors.

This fixes a bug that was reported against rustc.
See: rust-lang/rust#55788 (comment)

src/lib.rs

@@ -1511,17 +1511,12 @@ impl ColorSpec {
         &self,
         console: &mut wincolor::Console,
     ) -> io::Result<()> {
-        use wincolor::Intense;
-
-        let intense = if self.intense { Intense::Yes } else { Intense::No };
-
-        let fg_color = self.fg_color.as_ref().and_then(|c| c.to_windows());
-        if let Some(color) = fg_color {
+        let fg_color = self.fg_color.and_then(|c| c.to_windows(self.intense));
+        if let Some((intense, color)) = fg_color {
             console.fg(intense, color)?;
         }
-
-        let bg_color = self.bg_color.as_ref().and_then(|c| c.to_windows());
-        if let Some(color) = bg_color {
+        let bg_color = self.bg_color.and_then(|c| c.to_windows(self.intense));
+        if let Some((intense, color)) = bg_color {
             console.bg(intense, color)?;
         }
         Ok(())
@@ -1569,20 +1564,43 @@ pub enum Color {
 impl Color {
     /// Translate this color to a wincolor::Color.
     #[cfg(windows)]
-    fn to_windows(&self) -> Option<wincolor::Color> {
-        match *self {
-            Color::Black => Some(wincolor::Color::Black),
-            Color::Blue => Some(wincolor::Color::Blue),
-            Color::Green => Some(wincolor::Color::Green),
-            Color::Red => Some(wincolor::Color::Red),
-            Color::Cyan => Some(wincolor::Color::Cyan),
-            Color::Magenta => Some(wincolor::Color::Magenta),
-            Color::Yellow => Some(wincolor::Color::Yellow),
-            Color::White => Some(wincolor::Color::White),
-            Color::Ansi256(_) => None,
-            Color::Rgb(_, _, _) => None,
+    fn to_windows(
+        self,
+        intense: bool,
+    ) -> Option<(wincolor::Intense, wincolor::Color)> {
+        use wincolor::Intense::{Yes, No};
+
+        let color = match self {
+            Color::Black => wincolor::Color::Black,
+            Color::Blue => wincolor::Color::Blue,
+            Color::Green => wincolor::Color::Green,
+            Color::Red => wincolor::Color::Red,
+            Color::Cyan => wincolor::Color::Cyan,
+            Color::Magenta => wincolor::Color::Magenta,
+            Color::Yellow => wincolor::Color::Yellow,
+            Color::White => wincolor::Color::White,
+            Color::Ansi256(0) => return Some((No, wincolor::Color::Black)),
+            Color::Ansi256(1) => return Some((No, wincolor::Color::Red)),
+            Color::Ansi256(2) => return Some((No, wincolor::Color::Green)),
+            Color::Ansi256(3) => return Some((No, wincolor::Color::Yellow)),
+            Color::Ansi256(4) => return Some((No, wincolor::Color::Blue)),
+            Color::Ansi256(5) => return Some((No, wincolor::Color::Magenta)),
+            Color::Ansi256(6) => return Some((No, wincolor::Color::Cyan)),
+            Color::Ansi256(7) => return Some((No, wincolor::Color::White)),
+            Color::Ansi256(8) => return Some((Yes, wincolor::Color::Black)),
+            Color::Ansi256(9) => return Some((Yes, wincolor::Color::Red)),
+            Color::Ansi256(10) => return Some((Yes, wincolor::Color::Green)),
+            Color::Ansi256(11) => return Some((Yes, wincolor::Color::Yellow)),
+            Color::Ansi256(12) => return Some((Yes, wincolor::Color::Blue)),
+            Color::Ansi256(13) => return Some((Yes, wincolor::Color::Magenta)),
+            Color::Ansi256(14) => return Some((Yes, wincolor::Color::Cyan)),
+            Color::Ansi256(15) => return Some((Yes, wincolor::Color::White)),
+            Color::Ansi256(_) => return None,
+            Color::Rgb(_, _, _) => return None,
             Color::__Nonexhaustive => unreachable!(),
-        }
+        };
+        let intense = if intense { Yes } else { No };
+        Some((intense, color))
     }
 
     /// Parses a numeric color string, either ANSI or RGB.