build.rs: Font Subsetting

The build script (build.rs) runs at compile time and performs two tasks: Nerd Font subsetting and git hash extraction.

Font Subsetting

ashell uses Nerd Font symbols for icons (battery, WiFi, Bluetooth, volume, etc.). The full font files are ~4.8 MB. Since ashell only uses ~80 icons, the build script subsets the fonts to include only the needed glyphs.

How It Works

1. Parse icons: Read src/components/icons.rs and find all \u{XXXX} Unicode escape sequences.

2. Convert to characters: Each hex code is converted to its Unicode character.

3. Subset the font: Using the allsorts crate, create new TTF files containing only the needed glyphs.

4. Write output: Save the subsetted fonts to target/generated/:

   • SymbolsNerdFont-Regular-Subset.ttf
   • SymbolsNerdFontMono-Regular-Subset.ttf

Source Files

Adding a New Icon

To add a new icon to ashell:

1. Find the Unicode codepoint from the Nerd Fonts cheat sheet.
2. Add a constant to src/components/icons.rs:

   #![allow(unused)]
   fn main() {
   pub const MY_ICON: char = '\u{f0001}';
   }

3. Build — build.rs automatically detects the new codepoint and includes it in the subset.

No manual font editing is required.

Git Hash Extraction

The build script also extracts the current git commit hash:

#![allow(unused)]
fn main() {
let output = Command::new("git")
    .args(["rev-parse", "--short", "HEAD"])
    .output();

match output {
    Ok(output) if output.status.success() => {
        let git_hash = String::from_utf8(output.stdout)?;
        println!("cargo:rustc-env=GIT_HASH={}", git_hash.trim());
    }
    _ => {
        println!("cargo:rustc-env=GIT_HASH=unknown");
    }
}
}

This is used in the --version output via clap:

#![allow(unused)]
fn main() {
#[command(version = concat!(env!("CARGO_PKG_VERSION"), " (", env!("GIT_HASH"), ")"))]
}

Producing output like: ashell 0.7.0 (abc1234)

Font Loading at Runtime

The subsetted fonts are embedded in the binary at compile time:

#![allow(unused)]
fn main() {
// In main.rs
const NERD_FONT: &[u8] = include_bytes!("../target/generated/SymbolsNerdFont-Regular-Subset.ttf");
const NERD_FONT_MONO: &[u8] = include_bytes!("../target/generated/SymbolsNerdFontMono-Regular-Subset.ttf");
const CUSTOM_FONT: &[u8] = include_bytes!("../assets/AshellCustomIcon-Regular.otf");
}

These are loaded into iced’s font system at startup:

#![allow(unused)]
fn main() {
iced::daemon(/* ... */)
    .font(Cow::from(NERD_FONT))
    .font(Cow::from(NERD_FONT_MONO))
    .font(Cow::from(CUSTOM_FONT))
}