main.rs: Add `-h` help flag

Print usage information with `-h`.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/main.rs b/src/main.rs
index 4d810b0..efe4477 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,6 +13,7 @@ fn main() {
     let args: Vec<String> = env::args().collect();
 
     let mut opts = Options::new();
+    opts.optflag("h", "help", "print this help menu");
 
     let matches = match opts.parse(&args[1..]) {
         Ok(m) => m,
@@ -22,6 +23,11 @@ fn main() {
         },
     };
 
+    if matches.opt_present("h") {
+        print_usage(&opts);
+        process::exit(exitcode::USAGE);
+    }
+
     let repo = match Repository::open(".") {
         Ok(r) => r,
         Err(e) => {
@@ -70,6 +76,12 @@ fn main() {
     };
 }
 
+/// Print command line usage.
+fn print_usage(opts: &Options) {
+    let brief = "usage: git todo [<commit>]";
+    print!("{}", opts.usage(&brief));
+}
+
 /// Print to standard error with a program-specific prefix.
 fn eprintln<D: std::fmt::Display>(error: &D) {
     eprintln!("error: {}", error);