feat: add codex completion to generate shell completions (#1491)

Once this lands, we can update our brew formula to use
`generate_completions_from_executable()` like so:


905238ff7f/Formula/h/hgrep.rb (L21-L25)

codex-rs/cli/Cargo.toml

@@ -17,6 +17,7 @@ workspace = true
 [dependencies]
 anyhow = "1"
 clap = { version = "4", features = ["derive"] }
+clap_complete = "4"
 codex-core = { path = "../core" }
 codex-common = { path = "../common", features = ["cli"] }
 codex-exec = { path = "../exec" }

codex-rs/cli/src/main.rs

@@ -1,4 +1,7 @@
+use clap::CommandFactory;
 use clap::Parser;
+use clap_complete::Shell;
+use clap_complete::generate;
 use codex_cli::LandlockCommand;
 use codex_cli::SeatbeltCommand;
 use codex_cli::login::run_login_with_chatgpt;
@@ -47,10 +50,20 @@ enum Subcommand {
     #[clap(visible_alias = "p")]
     Proto(ProtoCli),
 
+    /// Generate shell completion scripts.
+    Completion(CompletionCommand),
+
     /// Internal debugging commands.
     Debug(DebugArgs),
 }
 
+#[derive(Debug, Parser)]
+struct CompletionCommand {
+    /// Shell to generate completions for
+    #[clap(value_enum, default_value_t = Shell::Bash)]
+    shell: Shell,
+}
+
 #[derive(Debug, Parser)]
 struct DebugArgs {
     #[command(subcommand)]
@@ -103,6 +116,9 @@ async fn cli_main(codex_linux_sandbox_exe: Option<PathBuf>) -> anyhow::Result<()
             prepend_config_flags(&mut proto_cli.config_overrides, cli.config_overrides);
             proto::run_main(proto_cli).await?;
         }
+        Some(Subcommand::Completion(completion_cli)) => {
+            print_completion(completion_cli);
+        }
         Some(Subcommand::Debug(debug_args)) => match debug_args.cmd {
             DebugCommand::Seatbelt(mut seatbelt_cli) => {
                 prepend_config_flags(&mut seatbelt_cli.config_overrides, cli.config_overrides);
@@ -136,3 +152,9 @@ fn prepend_config_flags(
         .raw_overrides
         .splice(0..0, cli_config_overrides.raw_overrides);
 }
+
+fn print_completion(cmd: CompletionCommand) {
+    let mut app = MultitoolCli::command();
+    let name = app.get_name().to_string();
+    generate(cmd.shell, &mut app, name, &mut std::io::stdout());
+}