Add a subcommand to generate shell completions (benfred#427)

src/config.rs

@@ -1,4 +1,4 @@
-use clap::{App, Arg, crate_description, crate_name, crate_version, arg_enum, value_t};
+use clap::{App, AppSettings, Arg, crate_description, crate_name, crate_version, arg_enum, value_t};
 use remoteprocess::Pid;
 
 /// Options on how to collect samples from a python process
@@ -229,6 +229,13 @@ impl Config {
                 .long("json")
                 .help("Format output as JSON"));
 
+        let completions = clap::SubCommand::with_name("completions")
+            .about("Generate shell completions")
+            .setting(AppSettings::Hidden)
+            .arg(Arg::with_name("shell")
+                .possible_values(&clap::Shell::variants())
+                .help("Shell type"));
+
         // add native unwinding if appropiate
         #[cfg(unwind)]
         let record = record.arg(native.clone());
@@ -253,7 +260,7 @@ impl Config {
         #[cfg(not(target_os="freebsd"))]
         let dump = dump.arg(nonblocking.clone());
 
-        let matches = App::new(crate_name!())
+        let mut app = App::new(crate_name!())
             .version(crate_version!())
             .about(crate_description!())
             .setting(clap::AppSettings::InferSubcommands)
@@ -263,7 +270,8 @@ impl Config {
             .subcommand(record)
             .subcommand(top)
             .subcommand(dump)
-            .get_matches_from_safe(args)?;
+            .subcommand(completions);
+        let matches = app.clone().get_matches_from_safe(args)?;
         info!("Command line args: {:?}", matches);
 
         let mut config = Config::default();
@@ -284,6 +292,11 @@ impl Config {
             "top" => {
                 config.sampling_rate = value_t!(matches, "rate", u64)?;
             }
+            "completions" => {
+                let shell = value_t!(matches.value_of("shell"), clap::Shell).unwrap_or_else(|e| e.exit());
+                app.gen_completions_to(crate_name!(), shell, &mut std::io::stdout());
+                std::process::exit(0);
+            }
             _ => {}
         }
         config.command = subcommand.to_owned();