feat: support shorthand hex colors

README.md

@@ -135,7 +135,8 @@ println!("{}", "Back to plain text".red().bold().clear());
 
 - RGB values must be in range 0-255 (enforced at compile time via `u8` type)
 - Attempting to use RGB values > 255 will result in a compile error
-- Hex color codes can be provided with or without the '#' prefix
+- Hex color codes can be provided with or without the '#' prefix in either
+  3-character shorthand or 6-character full form
 - Invalid hex codes (wrong length, invalid characters) will result in plain
   unstyled text
 - All color methods are guaranteed to return a valid string, never panicking
@@ -153,10 +154,11 @@ println!("{}", "Gray".hsl(0.0, 0.0, 50.0));      // 50% gray
 // Hex colors work with or without #
 println!("{}", "Hex color".hex("#ff8000"));
 println!("{}", "Also valid".hex("ff8000"));
+println!("{}", "Shorthand".hex("#f80"));
 
 // Invalid hex codes return uncolored text
 println!("{}", "Invalid".hex("xyz")); // Returns uncolored text
-println!("{}", "Too short".hex("#f8")); // Returns uncolored text
+println!("{}", "Wrong length".hex("#1234")); // Returns uncolored text
 ```
 
 ## NO_COLOR Support

TODO.md

@@ -2,5 +2,3 @@
 
 - Revisit whether to add `rust-version` to `Cargo.toml` once we want to commit
   to an explicit MSRV policy.
-- Support 3-character shorthand hex colors like `#f80` in addition to 6-digit
-  hex input.

examples/basic.rs

@@ -45,6 +45,9 @@ fn main() {
     println!("{}", "HSL Background".on_hsl(200.0, 100.0, 50.0));
 
     println!("{}", "Hex color (#ff8000)".hex("#ff8000"));
+    println!("{}", "Hex without # (ff8000)".hex("ff8000"));
+    println!("{}", "Hex shorthand (#f80)".hex("#f80"));
+    println!("{}", "Hex shorthand without # (f80)".hex("f80"));
     println!("{}", "Hex background (#0080ff)".on_hex("#0080ff"));
 
     // Chaining styles

src/color.rs

@@ -30,13 +30,22 @@ pub(crate) fn hsl_to_rgb(h: f32, s: f32, l: f32) -> (u8, u8, u8) {
 
 pub(crate) fn hex_to_rgb(hex: &str) -> Option<(u8, u8, u8)> {
     let hex = hex.trim_start_matches('#');
-    if hex.len() != 6 {
-        return None;
-    }
+    let expanded = match hex.len() {
+        3 => {
+            let mut expanded = String::with_capacity(6);
+            for ch in hex.chars() {
+                expanded.push(ch);
+                expanded.push(ch);
+            }
+            expanded
+        }
+        6 => hex.to_string(),
+        _ => return None,
+    };
 
-    let r = u8::from_str_radix(&hex[0..2], 16).ok()?;
-    let g = u8::from_str_radix(&hex[2..4], 16).ok()?;
-    let b = u8::from_str_radix(&hex[4..6], 16).ok()?;
+    let r = u8::from_str_radix(&expanded[0..2], 16).ok()?;
+    let g = u8::from_str_radix(&expanded[2..4], 16).ok()?;
+    let b = u8::from_str_radix(&expanded[4..6], 16).ok()?;
 
     Some((r, g, b))
 }

src/lib.rs

@@ -48,7 +48,8 @@
 //!
 //! - RGB values must be in range 0-255 (enforced at compile time via `u8` type)
 //! - Attempting to use RGB values > 255 will result in a compile error
-//! - Hex color codes can be provided with or without the `#` prefix
+//! - Hex color codes can be provided with or without the `#` prefix in 3-digit
+//!   shorthand or 6-digit full form
 //! - Invalid hex codes (wrong length or invalid characters) return plain
 //!   unstyled text
 //! - All color methods are guaranteed to return a valid string, never panicking
@@ -59,10 +60,11 @@
 //! // Valid hex codes (with or without #)
 //! println!("{}", "Valid hex".hex("#ff8000"));
 //! println!("{}", "Also valid".hex("ff8000"));
+//! println!("{}", "Shorthand".hex("#f80"));
 //!
 //! // Invalid hex codes return plain text
 //! println!("{}", "Invalid hex".hex("xyz")); // Returns plain text
-//! println!("{}", "Too short".hex("#f8")); // Returns plain text
+//! println!("{}", "Wrong length".hex("#1234")); // Returns plain text
 //! ```
 //!
 //! # Runtime Color Control

src/tests.rs

@@ -194,7 +194,9 @@ fn test_rgb_colors(#[case] r: u8, #[case] g: u8, #[case] b: u8) {
 
 #[rstest]
 #[case("#ff8000", 255, 128, 0)]
+#[case("#f80", 255, 136, 0)]
 #[case("#00ff00", 0, 255, 0)]
+#[case("0f8", 0, 255, 136)]
 #[case("#808080", 128, 128, 128)]
 #[case("#000000", 0, 0, 0)]
 #[case("#ffffff", 255, 255, 255)]
@@ -224,6 +226,8 @@ fn test_hex_colors(#[case] hex: &str, #[case] r: u8, #[case] g: u8, #[case] b: u
 #[rstest]
 #[case("invalid")]
 #[case("#12")]
+#[case("#1234")]
+#[case("#12345678")]
 #[case("not-a-color")]
 #[case("#12345")]
 #[case("#1234567")]