build.rs

// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::{Path, PathBuf};
use std::process::Command;

fn main() {
    // Only check .git/HEAD dirty status if it exists - doing so when
    // building dependent crates may lead to false positives and rebuilds
    if Path::new(".git/HEAD").exists() {
        println!("cargo:rerun-if-changed=.git/HEAD");
    }

    println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");

    let out_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());

    File::create(out_dir.join("commit-info.txt"))
        .unwrap()
        .write_all(commit_info().as_bytes())
        .unwrap();
}

// Try to get hash and date of the last commit on a best effort basis. If anything goes wrong
// (git not installed or if this is not a git repository) just return an empty string.
fn commit_info() -> String {
    match (channel(), commit_hash(), commit_date()) {
        (channel, Some(hash), Some(date)) => {
            format!("{} ({} {})", channel, hash.trim_end(), date)
        }
        _ => String::new(),
    }
}

fn channel() -> String {
    if let Ok(channel) = env::var("CFG_RELEASE_CHANNEL") {
        channel
    } else {
        "nightly".to_owned()
    }
}

fn commit_hash() -> Option<String> {
    Command::new("git")
        .args(&["rev-parse", "--short", "HEAD"])
        .output()
        .ok()
        .and_then(|r| String::from_utf8(r.stdout).ok())
}

fn commit_date() -> Option<String> {
    Command::new("git")
        .args(&["log", "-1", "--date=short", "--pretty=format:%cd"])
        .output()
        .ok()
        .and_then(|r| String::from_utf8(r.stdout).ok())
}