From beec17e55d2a1ddf8dc052c546b88f90b935e7c0 Mon Sep 17 00:00:00 2001
From: Alexandru Macovei <alexnmaco@gmail.com>
Date: Mon, 4 Jan 2021 23:51:02 +0200
Subject: [PATCH] Add ability to generate shell completions via clap

---
 src/main.rs | 71 +++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 50 insertions(+), 21 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 76a46fa6..fefddf3b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,8 +3,9 @@ extern crate clap;
 #[macro_use]
 extern crate log;
 
+use anyhow::anyhow;
 use chrono::Local;
-use clap::{App, AppSettings, ArgMatches};
+use clap::{App, AppSettings, Arg, ArgMatches, Shell, SubCommand};
 use env_logger::Builder;
 use log::LevelFilter;
 use mdbook::utils;
@@ -20,7 +21,40 @@ const VERSION: &str = concat!("v", crate_version!());
 fn main() {
     init_logger();
 
-    // Create a list of valid arguments and sub-commands
+    let app = create_clap_app();
+
+    // Check which subcomamnd the user ran...
+    let res = match app.get_matches().subcommand() {
+        ("init", Some(sub_matches)) => cmd::init::execute(sub_matches),
+        ("build", Some(sub_matches)) => cmd::build::execute(sub_matches),
+        ("clean", Some(sub_matches)) => cmd::clean::execute(sub_matches),
+        #[cfg(feature = "watch")]
+        ("watch", Some(sub_matches)) => cmd::watch::execute(sub_matches),
+        #[cfg(feature = "serve")]
+        ("serve", Some(sub_matches)) => cmd::serve::execute(sub_matches),
+        ("test", Some(sub_matches)) => cmd::test::execute(sub_matches),
+        ("completions", Some(sub_matches)) => (|| {
+            let shell: Shell = sub_matches
+                .value_of("shell")
+                .ok_or_else(|| anyhow!("Shell name missing."))?
+                .parse()
+                .map_err(|s| anyhow!("Invalid shell: {}", s))?;
+
+            create_clap_app().gen_completions_to("mdbook", shell, &mut std::io::stdout().lock());
+            Ok(())
+        })(),
+        (_, _) => unreachable!(),
+    };
+
+    if let Err(e) = res {
+        utils::log_backtrace(&e);
+
+        std::process::exit(101);
+    }
+}
+
+/// Create a list of valid arguments and sub-commands
+fn create_clap_app<'a, 'b>() -> App<'a, 'b> {
     let app = App::new(crate_name!())
         .about(crate_description!())
         .author("Mathieu David <mathieudavid@mathieudavid.org>")
@@ -35,31 +69,26 @@ fn main() {
         .subcommand(cmd::init::make_subcommand())
         .subcommand(cmd::build::make_subcommand())
         .subcommand(cmd::test::make_subcommand())
-        .subcommand(cmd::clean::make_subcommand());
+        .subcommand(cmd::clean::make_subcommand())
+        .subcommand(
+            SubCommand::with_name("completions")
+                .about("Generate shell completions for your shell to stdout")
+                .arg(
+                    Arg::with_name("shell")
+                        .takes_value(true)
+                        .possible_values(&Shell::variants())
+                        .help("the shell to generate completions for")
+                        .value_name("SHELL")
+                        .required(true),
+                ),
+        );
 
     #[cfg(feature = "watch")]
     let app = app.subcommand(cmd::watch::make_subcommand());
     #[cfg(feature = "serve")]
     let app = app.subcommand(cmd::serve::make_subcommand());
 
-    // Check which subcomamnd the user ran...
-    let res = match app.get_matches().subcommand() {
-        ("init", Some(sub_matches)) => cmd::init::execute(sub_matches),
-        ("build", Some(sub_matches)) => cmd::build::execute(sub_matches),
-        ("clean", Some(sub_matches)) => cmd::clean::execute(sub_matches),
-        #[cfg(feature = "watch")]
-        ("watch", Some(sub_matches)) => cmd::watch::execute(sub_matches),
-        #[cfg(feature = "serve")]
-        ("serve", Some(sub_matches)) => cmd::serve::execute(sub_matches),
-        ("test", Some(sub_matches)) => cmd::test::execute(sub_matches),
-        (_, _) => unreachable!(),
-    };
-
-    if let Err(e) = res {
-        utils::log_backtrace(&e);
-
-        std::process::exit(101);
-    }
+    app
 }
 
 fn init_logger() {