From 72a31d38d6e719b337d23e3a73a5050bc9221d1c Mon Sep 17 00:00:00 2001
From: Robin Krahl <robin.krahl@ireas.org>
Date: Wed, 8 Jan 2020 11:35:19 +0000
Subject: Handle doc comments and empty variants in the Command! macro

This patch introduces two changes to the Command! macro:
- We allow variants without fields so that we no longer have to define
  empty *Args structs just for the Command! macro.
- We allow doc comments so that we can document commands without a
  separate *Args struct.
---
 nitrocli/src/arg_util.rs | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/nitrocli/src/arg_util.rs b/nitrocli/src/arg_util.rs
index cb75c52..bc1c02c 100644
--- a/nitrocli/src/arg_util.rs
+++ b/nitrocli/src/arg_util.rs
@@ -24,12 +24,21 @@ macro_rules! count {
   }
 }
 
+/// Translate an optional source into an optional destination.
+macro_rules! tr {
+  ($dst:tt, $src:tt) => {
+    $dst
+  };
+  ($dst:tt) => {};
+}
+
 macro_rules! Command {
-  ( $name:ident, [ $( $var:ident($inner:ident) => $exec:expr, ) *] ) => {
+  ( $name:ident, [ $( $(#[$doc:meta])* $var:ident$(($inner:ty))? => $exec:expr, ) *] ) => {
     #[derive(Debug, PartialEq, structopt::StructOpt)]
     pub enum $name {
       $(
-        $var($inner),
+        $(#[$doc])*
+        $var$(($inner))?,
       )*
     }
 
@@ -41,7 +50,7 @@ macro_rules! Command {
       ) -> crate::Result<()> {
         match self {
           $(
-            $name::$var(args) => $exec(ctx, args),
+            $name::$var$((tr!(args, $inner)))? => $exec(ctx $(,tr!(args, $inner))?),
           )*
         }
       }
-- 
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