improve arg comments, rename arg Match to Command

src/compl/arg.rs

@@ -1,24 +1,26 @@
-//! Module related to completion arguments.
+//! Module related to completion CLI.
 //!
-//! This module provides subcommands and an argument matcher related to completion.
+//! This module provides subcommands and a command matcher related to completion.
 
 use anyhow::Result;
 use clap::{self, App, Arg, ArgMatches, Shell, SubCommand};
 use log::debug;
 
-/// Enumeration of all possible matches.
-pub enum Match<'a> {
+type OptionShell<'a> = Option<&'a str>;
+
+/// Completion commands.
+pub enum Command<'a> {
     /// Generate completion script for the given shell slice.
-    Generate(&'a str),
+    Generate(OptionShell<'a>),
 }
 
-/// Completion arg matcher.
-pub fn matches<'a>(m: &'a ArgMatches) -> Result<Option<Match<'a>>> {
+/// Completion command matcher.
+pub fn matches<'a>(m: &'a ArgMatches) -> Result<Option<Command<'a>>> {
     if let Some(m) = m.subcommand_matches("completion") {
         debug!("completion command matched");
-        let shell = m.value_of("shell").unwrap();
-        debug!("shell: {}", shell);
-        return Ok(Some(Match::Generate(shell)));
+        let shell = m.value_of("shell");
+        debug!("shell: `{:?}`", shell);
+        return Ok(Some(Command::Generate(shell)));
     };
 
     Ok(None)

src/compl/handler.rs

@@ -7,8 +7,8 @@ use clap::{App, Shell};
 use std::{io, str::FromStr};
 
 /// Generate completion script from the given [`clap::App`] for the given shell slice.
-pub fn generate<'a>(shell: &'a str, mut app: App<'a, 'a>) -> Result<()> {
-    let shell = Shell::from_str(shell)
+pub fn generate<'a>(shell: Option<&'a str>, mut app: App<'a, 'a>) -> Result<()> {
+    let shell = Shell::from_str(shell.unwrap_or_default())
         .map_err(|err| anyhow!(err))
         .context("cannot parse shell")?;
     app.gen_completions_to("himalaya", shell, &mut io::stdout());