whattsreply/build.rs

//! Build script: embeds the short git commit hash as `WH_GIT_HASH` and the commit count
//! (build number) as `WH_BUILD_NUMBER`.

use std::process::Command;

/// Name of the compile-time environment variable holding the commit hash.
const GIT_HASH_ENV: &str = "WH_GIT_HASH";
/// Name of the compile-time environment variable holding the build number (commit count).
const BUILD_NUMBER_ENV: &str = "WH_BUILD_NUMBER";
/// Value used when the hash cannot be read (no git, not a repository).
const UNKNOWN_HASH: &str = "unknown";
/// Value used when the build number cannot be read (no git, not a repository).
const UNKNOWN_BUILD_NUMBER: &str = "0";

/// Purpose: export the short commit hash and the build number (commit count) to the crate
/// and rebuild when the commit changes.
/// Inputs: none (runs `git` in the package directory).
/// Output: none.
/// Side effects: prints cargo directives on stdout.
fn main() {
    println!("cargo:rerun-if-changed=.git/HEAD");
    println!("cargo:rerun-if-changed=.git/refs");
    println!("cargo:rerun-if-changed=.git/packed-refs");
    let hash =
        git_output(&["rev-parse", "--short", "HEAD"]).unwrap_or_else(|| UNKNOWN_HASH.to_owned());
    println!("cargo:rustc-env={GIT_HASH_ENV}={hash}");
    let build_number = git_output(&["rev-list", "--count", "HEAD"])
        .unwrap_or_else(|| UNKNOWN_BUILD_NUMBER.to_owned());
    println!("cargo:rustc-env={BUILD_NUMBER_ENV}={build_number}");
}

/// Purpose: run `git` with the given arguments and return its trimmed output.
/// Inputs: `args` - the arguments passed to `git`.
/// Output: the trimmed stdout, or `None` when git is missing, fails or prints nothing.
/// Side effects: runs the `git` command.
fn git_output(args: &[&str]) -> Option<String> {
    let output = Command::new("git").args(args).output().ok()?;
    if !output.status.success() {
        return None;
    }
    let text = String::from_utf8(output.stdout).ok()?.trim().to_owned();
    (!text.is_empty()).then_some(text)
}