print version information when -V or --version is issued

Cargo.toml

@@ -1,5 +1,6 @@
 [package]
 authors = ["Jorge Aparicio <japaricious@gmail.com>"]
+build = "build.rs"
 name = "cross"
 version = "0.1.0-dev"
 

build.rs

@@ -0,0 +1,55 @@
+use std::env;
+use std::error::Error;
+use std::fs::File;
+use std::io::Write;
+use std::path::PathBuf;
+use std::process::Command;
+
+struct Some {}
+
+impl<E> From<E> for Some
+    where E: Error
+{
+    fn from(_: E) -> Some {
+        Some {}
+    }
+}
+
+fn main() {
+    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();
+}
+
+fn commit_info() -> String {
+    match (commit_hash(), commit_date()) {
+        (Ok(hash), Ok(date)) => format!(" ({} {})", hash.trim(), date.trim()),
+        _ => String::new(),
+    }
+}
+
+fn commit_hash() -> Result<String, Some> {
+    let output = Command::new("git").args(&["rev-parse", "--short", "HEAD"])
+        .output()?;
+
+    if output.status.success() {
+        Ok(String::from_utf8(output.stdout)?)
+    } else {
+        Err(Some {})
+    }
+}
+
+fn commit_date() -> Result<String, Some> {
+    let output = Command::new("git")
+        .args(&["log", "-1", "--date=short", "--pretty=format:%cd"])
+        .output()?;
+
+    if output.status.success() {
+        Ok(String::from_utf8(output.stdout)?)
+    } else {
+        Err(Some {})
+    }
+}

src/main.rs

@@ -71,6 +71,11 @@ fn main() {
 fn run() -> Result<ExitStatus> {
     let args = cli::parse();
 
+    if args.all.iter().any(|a| a == "--version" || a == "-V") {
+        println!(concat!("cross ", env!("CARGO_PKG_VERSION"), "{}"),
+                 include_str!(concat!(env!("OUT_DIR"), "/commit-info.txt")));
+    }
+
     match args.subcommand.as_ref().map(|s| &**s) {
         Some("build") | Some("run") | Some("rustc") | Some("test") => {
             let host = rustc::host();