Add support for nerd font glyphs in languages info

CONTRIBUTING.md

@@ -48,7 +48,7 @@ CSharp: # required, this will be the name of the enum variant for the language a
       - "#803788"
       - "#FFFFFF"
     chip: "#178600" # required, this is used for the language breakdown bar, its value can be found in linguist (link 2).
-  icon: "\uE648" # optional, the UTF-16 code point of the nerd font icon if supported (link 3).
+  icon: "\\uE648" # optional, the UTF-16 code point of the nerd font icon if supported (link 3).
   serialization: c# # required only if the Enum name `CSharp` doesn't match the display name `C#`
 ```
 

build.rs

@@ -18,6 +18,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     let mut tera = Tera::default();
     tera.register_filter("strip_color_tokens", strip_color_tokens_filter);
     tera.register_filter("hex_to_rgb", hex_to_rgb_filter);
+    tera.register_filter("unicode_escape", unicode_escape_filter);
 
     let lang_data: serde_json::Value = serde_yaml::from_reader(File::open("languages.yaml")?)?;
 
@@ -32,6 +33,25 @@ fn main() -> Result<(), Box<dyn Error>> {
     Ok(())
 }
 
+/// Convert unicode escapes into ECMAScript 6-style
+/// https://rust-lang.github.io/rfcs/0446-es6-unicode-escapes.html
+fn unicode_escape_filter(
+    value: &tera::Value,
+    _args: &HashMap<String, tera::Value>,
+) -> tera::Result<tera::Value> {
+    lazy_static! {
+        static ref UNICODE_ESCAPE_REGEX: Regex = Regex::new(r"\\u([0-9A-Fa-f]+)").unwrap();
+    }
+    let s = match value {
+        tera::Value::String(s) => s,
+        _ => return Err(tera::Error::msg("expected string")),
+    };
+
+    return Ok(tera::Value::String(
+        UNICODE_ESCAPE_REGEX.replace_all(s, "\\u{$1}").to_string(),
+    ));
+}
+
 /// Strips out `{n}` from the given string.
 fn strip_color_tokens_filter(
     value: &tera::Value,