Use ansi_colours package for better true-colour approximation

Cargo.toml

@@ -16,6 +16,7 @@ exclude = [
 [dependencies]
 atty = "0.2.2"
 ansi_term = "0.11"
+ansi_colours = "^1.0"
 console = "0.6"
 directories = "1.0"
 lazy_static = "1.0"

src/terminal.rs

@@ -1,32 +1,15 @@
+extern crate ansi_colours;
+
 use ansi_term::Colour::{Fixed, RGB};
 use ansi_term::{self, Style};
 
 use syntect::highlighting::{self, FontStyle};
 
-/// Approximate a 24 bit color value by a 8 bit ANSI code
-fn rgb2ansi(r: u8, g: u8, b: u8) -> u8 {
-    const BLACK: u8 = 16;
-    const WHITE: u8 = 231;
-
-    if r == g && g == b {
-        if r < 8 {
-            BLACK
-        } else if r > 248 {
-            WHITE
-        } else {
-            ((r - 8) as u16 * 24 / 247) as u8 + 232
-        }
-    } else {
-        36 * (r / 51) + 6 * (g / 51) + (b / 51) + 16
-    }
-}
-
 pub fn to_ansi_color(color: highlighting::Color, true_color: bool) -> ansi_term::Colour {
     if true_color {
         RGB(color.r, color.g, color.b)
     } else {
-        let ansi_code = rgb2ansi(color.r, color.g, color.b);
-        Fixed(ansi_code)
+        Fixed(ansi_colours::ansi256_from_rgb((color.r, color.g, color.b)))
     }
 }
 
@@ -54,27 +37,3 @@ pub fn as_terminal_escaped(
 
     style.paint(text).to_string()
 }
-
-#[test]
-fn test_rgb2ansi_black_white() {
-    assert_eq!(16, rgb2ansi(0x00, 0x00, 0x00));
-    assert_eq!(231, rgb2ansi(0xff, 0xff, 0xff));
-}
-
-#[test]
-fn test_rgb2ansi_gray() {
-    assert_eq!(241, rgb2ansi(0x6c, 0x6c, 0x6c));
-    assert_eq!(233, rgb2ansi(0x1c, 0x1c, 0x1c));
-}
-
-#[test]
-fn test_rgb2ansi_color() {
-    assert_eq!(96, rgb2ansi(0x87, 0x5f, 0x87));
-    assert_eq!(141, rgb2ansi(0xaf, 0x87, 0xff));
-    assert_eq!(193, rgb2ansi(0xd7, 0xff, 0xaf));
-}
-
-#[test]
-fn test_rgb2ansi_approx() {
-    assert_eq!(231, rgb2ansi(0xfe, 0xfe, 0xfe));
-}