Add Shell completions (#1226)

* feat(cli): add subcommand to generate shell completions

* Update src/cli.rs

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

---------

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

src/cli.rs

@@ -2,6 +2,7 @@ use std::ffi::OsString;
 use std::path::PathBuf;
 
 use clap::{Parser, Subcommand};
+use clap_complete::Shell;
 use niri_ipc::{Action, OutputAction};
 
 use crate::utils::version;
@@ -54,6 +55,8 @@ pub enum Sub {
     },
     /// Cause a panic to check if the backtraces are good.
     Panic,
+    /// Generate shell completions.
+    Completions { shell: Shell },
 }
 
 #[derive(Subcommand)]

src/main.rs

@@ -9,7 +9,7 @@ use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::{env, mem};
 
-use clap::Parser;
+use clap::{CommandFactory, Parser};
 use directories::ProjectDirs;
 use niri::cli::{Cli, Sub};
 #[cfg(feature = "dbus")]
@@ -106,6 +106,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                 return Ok(());
             }
             Sub::Panic => cause_panic(),
+            Sub::Completions { shell } => {
+                clap_complete::generate(shell, &mut Cli::command(), "niri", &mut io::stdout());
+                return Ok(());
+            }
         }
     }