Print help/version info when run w/ no subcommand

cli/build.rs

@@ -1,6 +1,32 @@
+use std::{io, env, fs};
+
 fn main() {
+    let git_sha = read_git_sha().unwrap();
+    println!("cargo:rustc-env={}={}", "BUILD_SHA", git_sha);
+
     println!(
         "cargo:rustc-env=BUILD_TARGET={}",
         std::env::var("TARGET").unwrap()
     );
 }
+
+fn read_git_sha() -> io::Result<String> {
+    let git_path = env::current_dir().unwrap().parent().unwrap().join(".git");
+    let git_head_path = git_path.join("HEAD");
+    println!("cargo:rerun-if-changed={}", git_head_path.to_str().unwrap());
+    let mut head_content = fs::read_to_string(&git_head_path)?;
+    assert!(head_content.ends_with("\n"));
+    head_content.pop();
+
+    if head_content.starts_with("ref: ") {
+        // We're on a branch. Read the SHA from the ref file.
+        head_content.replace_range(0.."ref: ".len(), "");
+        let ref_filename = git_path.join(&head_content);
+        println!("cargo:rerun-if-changed={}", ref_filename.to_str().unwrap());
+        fs::read_to_string(&ref_filename)
+    } else {
+        // We're not on a branch. The `HEAD` file itself contains the sha.
+        assert_eq!(head_content.len(), 40);
+        Ok(head_content)
+    }
+}

cli/src/main.rs

@@ -21,7 +21,7 @@ mod util;
 mod tests;
 
 use self::loader::Loader;
-use clap::{App, Arg, SubCommand};
+use clap::{App, AppSettings, Arg, SubCommand};
 use std::env;
 use std::fs;
 use std::path::Path;
@@ -37,7 +37,8 @@ fn main() {
 
 fn run() -> error::Result<()> {
     let matches = App::new("tree-sitter")
-        .version("0.1")
+        .version(concat!(env!("CARGO_PKG_VERSION"), " (", env!("BUILD_SHA"), ")"))
+        .setting(AppSettings::SubcommandRequiredElseHelp)
         .author("Max Brunsfeld <maxbrunsfeld@gmail.com>")
         .about("Generates and tests parsers")
         .subcommand(
@@ -77,6 +78,7 @@ fn run() -> error::Result<()> {
     let home_dir = dirs::home_dir().unwrap();
     let current_dir = env::current_dir().unwrap();
     let config_dir = home_dir.join(".tree-sitter");
+
     fs::create_dir_all(&config_dir).unwrap();
     let mut loader = Loader::new(config_dir);