Main: Add command line option to make the process idle indefinitely

src/main.rs

@@ -1,6 +1,7 @@
 use std::env;
 use std::fs;
 use std::path::PathBuf;
+use std::thread;
 
 use anyhow::Result;
 
@@ -18,12 +19,18 @@ struct Arguments {
 
     /// The path to write the built secret file to
     output_path: PathBuf,
+
+    /// If the process should keep running without doing anything. This is used to keep a systemd service
+    /// running this and the associated RuntimeDirectory alive.
+    #[clap(long, default_value_t = false)]
+    idle: bool,
 }
 
 fn main() -> Result<()> {
     let Arguments {
         contents_path,
         output_path,
+        idle
     } = Arguments::parse();
 
     let mut handlebars = Handlebars::new();
@@ -91,5 +98,11 @@ fn main() -> Result<()> {
     fs::write(&output_path, output)
         .expect(format!("To be able to write to '{}'", output_path.to_string_lossy()).as_str());
 
+    if idle {
+        loop {
+            thread::park();
+        }
+    }
+
     Ok(())
 }