feat(man): add man page generation script (#35)

git-cliff/Cargo.toml

@@ -16,6 +16,10 @@ edition = "2021"
 name = "git-cliff-completions"
 path = "src/bin/completions.rs"
 
+[[bin]]
+name = "git-cliff-mangen"
+path = "src/bin/mangen.rs"
+
 [features]
 # check for new versions
 default = ["update-informer"]
@@ -25,6 +29,7 @@ pretty_env_logger = "0.4.0"
 log = "0.4.14"
 dirs-next = "2.0.0"
 clap_complete = "3.1.1"
+clap_mangen = "0.1.2"
 
 [dependencies.git-cliff-core]
 version = "0.6.1" # managed by release.sh

git-cliff/src/bin/mangen.rs

@@ -0,0 +1,24 @@
+use clap::CommandFactory;
+use clap_mangen::Man;
+use git_cliff::args::Opt;
+use std::env;
+use std::fs;
+use std::io::Result;
+use std::path::PathBuf;
+
+/// Man page can be created with:
+/// `cargo run --bin git-cliff-mangen`
+/// in a directory specified by the environment variable OUT_DIR.
+/// See <https://doc.rust-lang.org/cargo/reference/environment-variables.html>
+fn main() -> Result<()> {
+	let out_dir = env::var("OUT_DIR").expect("OUT_DIR is not set");
+	let out_path =
+		PathBuf::from(out_dir).join(format!("{}.1", env!("CARGO_PKG_NAME")));
+	let app = Opt::command();
+	let man = Man::new(app);
+	let mut buffer = Vec::<u8>::new();
+	man.render(&mut buffer)?;
+	fs::write(&out_path, buffer)?;
+	println!("Man page is generated at {:?}", out_path);
+	Ok(())
+}