Add a command to generate shell completions

Changelog.md

@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html) (for the cli, not for the crate).
 
+## Unreleased
+
+* Add `maturin completions <shell>` command to generate shell completions in [#586](https://github.com/PyO3/maturin/pull/586)
+
 ## 0.11.0 - 2021-07-04
 
 * Add support for reading metadata from [PEP 621](https://www.python.org/dev/peps/pep-0621/) project table in `pyproject.toml` in [#555](https://github.com/PyO3/maturin/pull/555)

src/main.rs

@@ -19,13 +19,13 @@ use maturin::{
     Metadata21, PathWriter, PlatformTag, PyProjectToml, PythonInterpreter, Target,
 };
 use std::env;
+use std::io;
 use std::path::PathBuf;
 use structopt::StructOpt;
 #[cfg(feature = "upload")]
 use {
     maturin::{upload, Registry, UploadError},
     reqwest::Url,
-    std::io,
 };
 
 /// Returns the password and a bool that states whether to ask for re-entering the password
@@ -283,6 +283,12 @@ enum Opt {
     /// The commands are meant to be called from the python PEP 517
     #[structopt(name = "pep517", setting = structopt::clap::AppSettings::Hidden)]
     Pep517(Pep517Command),
+    /// Generate shell completions
+    #[structopt(name = "completions", setting = structopt::clap::AppSettings::Hidden)]
+    Completions {
+        #[structopt(name = "SHELL", parse(try_from_str))]
+        shell: structopt::clap::Shell,
+    },
 }
 
 /// Backend for the PEP 517 integration. Not for human consumption
@@ -608,6 +614,9 @@ fn run() -> Result<()> {
 
             upload_ui(&files, &publish)?
         }
+        Opt::Completions { shell } => {
+            Opt::clap().gen_completions_to(env!("CARGO_BIN_NAME"), shell, &mut io::stdout());
+        }
     }
 
     Ok(())