feat: add shell completions subcommand (#106)

Adds a subcommand "completions" which can generate shell completions for
a few supported shells, namely bash, zsh and Nushell.
You can use it like this: `koji completions <SHELL> >
<CUSTOM_COMPLETIONS_DIR>/_koji`.
I consider this feature necessary for eventually publishing koji to
other package registries, such as the AUR.

Cargo.toml

@@ -31,6 +31,7 @@ indexmap = "2.1"
 serde = { version = "1.0", features = ["derive"] }
 toml = "0.8"
 inquire = "0.7.5"
+clap_complete_command = { version = "0.6.1", features = ["nushell"]}
 
 [features]
 vendored-openssl = ["git2/vendored-openssl"]

README.md

@@ -58,6 +58,8 @@ koji
 
 See `koji --help` for more options.
 
+Use `koji completions <SHELL>` to generate completion scripts for your shell.
+
 ## Using as a git hook
 
 An alternative way to use koji is as a [git hook](https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks),

src/bin/main.rs

@@ -1,7 +1,7 @@
 use std::fs::read_to_string;
 
 use anyhow::{Context, Result};
-use clap::Parser;
+use clap::{CommandFactory, Parser, Subcommand};
 use cocogitto::command::commit::CommitOptions;
 use conventional_commit_parser::parse;
 use git2::Repository;
@@ -16,6 +16,9 @@ use koji::questions::create_prompt;
     version
 )]
 struct Args {
+    #[command(subcommand)]
+    command: Option<SubCmds>,
+
     #[arg(
         long,
         default_missing_value = "true",
@@ -86,10 +89,17 @@ struct Args {
     all: bool,
 }
 
+#[derive(Debug, Subcommand)]
+enum SubCmds {
+    #[command(about = "Generate shell completions")]
+    Completions { shell: clap_complete_command::Shell },
+}
+
 #[cfg(not(tarpaulin_include))]
 fn main() -> Result<()> {
     // Get CLI args
     let Args {
+        command,
         autocomplete,
         breaking_changes,
         config,
@@ -100,6 +110,15 @@ fn main() -> Result<()> {
         all,
     } = Args::parse();
 
+    if command.is_some() {
+        match command.unwrap() {
+            SubCmds::Completions { shell } => {
+                shell.generate(&mut Args::command(), &mut std::io::stdout());
+            }
+        }
+        return Ok(());
+    }
+
     // Find repo
     let repo =
         Repository::discover(std::env::current_dir()?).context("could not find git repository")?;