Add --version switch

Add --version switch, which prints a short hash of the current
commit. Fix #612

src/bin/rustfmt.rs

@@ -23,6 +23,7 @@ use rustfmt::config::Config;
 use std::env;
 use std::fs::{self, File};
 use std::io::{self, Read, Write};
+use std::process::Command;
 use std::path::{Path, PathBuf};
 
 use getopts::{Matches, Options};
@@ -33,6 +34,8 @@ enum Operation {
     Format(Vec<PathBuf>, WriteMode),
     /// Print the help message.
     Help,
+    // Print version information
+    Version,
     /// Print detailed configuration help.
     ConfigHelp,
     /// Invalid program input, including reason.
@@ -82,6 +85,7 @@ fn update_config(config: &mut Config, matches: &Matches) {
 fn execute() -> i32 {
     let mut opts = Options::new();
     opts.optflag("h", "help", "show this message");
+    opts.optflag("", "version", "show version information");
     opts.optflag("v", "verbose", "show progress");
     opts.optopt("",
                 "write-mode",
@@ -111,6 +115,10 @@ fn execute() -> i32 {
             print_usage(&opts, "");
             0
         }
+        Operation::Version => {
+            print_version();
+            0
+        }
         Operation::ConfigHelp => {
             Config::print_docs();
             0
@@ -168,6 +176,18 @@ fn print_usage(opts: &Options, reason: &str) {
     println!("{}", opts.usage(&reason));
 }
 
+fn print_version() {
+    let cmd = Command::new("git")
+                  .arg("rev-parse")
+                  .arg("--short")
+                  .arg("HEAD")
+                  .output();
+    match cmd {
+        Ok(output) => print!("{}", String::from_utf8(output.stdout).unwrap()),
+        Err(e) => panic!("Unable te get version: {}", e),
+    }
+}
+
 fn determine_operation(matches: &Matches) -> Operation {
     if matches.opt_present("h") {
         return Operation::Help;
@@ -177,6 +197,10 @@ fn determine_operation(matches: &Matches) -> Operation {
         return Operation::ConfigHelp;
     }
 
+    if matches.opt_present("version") {
+        return Operation::Version;
+    }
+
     // if no file argument is supplied, read from stdin
     if matches.free.len() == 0 {