[keygen] Implement '-v' with version info

Cargo.toml

@@ -16,7 +16,7 @@ openssl = ["domain/openssl"]
 ring    = ["domain/ring"]
 
 [dependencies]
-clap = { version = "4", features = ["derive"] }
+clap = { version = "4", features = ["cargo", "derive"] }
 domain = { git = "http://github.com/NLnetLabs/domain", branch = "main", features = ["unstable-sign"] }
 lexopt = "0.3.0"
 

src/commands/keygen.rs

@@ -108,7 +108,14 @@ impl LdnsCommand for Keygen {
                     force_symlinks = true;
                 }
 
-                // TODO: '-v' version argument?
+                Arg::Short('v') => {
+                    let version = clap::crate_version!();
+                    // NOTE: The outer version is the latest version of 'ldns-keygen' we are
+                    // compatible with.  This needs to be updated manually.
+                    println!("DNSSEC key generator version 1.8.4 (dnst version {version})");
+                    std::process::exit(0);
+                }
+
                 Arg::Value(value) => {
                     if name.is_some() {
                         return Err("cannot specify multiple domain names".into());