clap::clap_app!

macro_rules! clap_app {
    (@app ($builder:expr)) => { $builder };
    (@app ($builder:expr) (@arg $name:ident: $($tail:tt)*) $($tt:tt)*) => {
        clap_app!{ @app
            ($builder.arg(clap_app!{ @arg ($crate::Arg::with_name(stringify!($name))) (-) $($tail)* }))
            $($tt)*
        }
    };
    (@app ($builder:expr) (@setting $setting:ident) $($tt:tt)*) => {
        clap_app!{ @app
            ($builder.setting($crate::AppSettings::$setting))
            $($tt)*
        }
    };
    // Treat the application builder as an argument to set it's attributes
    (@app ($builder:expr) (@attributes $($attr:tt)*) $($tt:tt)*) => {
        clap_app!{ @app (clap_app!{ @arg ($builder) $($attr)* }) $($tt)* }
    };
    (@app ($builder:expr) (@group $name:ident => $($tail:tt)*) $($tt:tt)*) => {
        clap_app!{ @app
            (clap_app!{ @group ($builder, $crate::ArgGroup::with_name(stringify!($name))) $($tail)* })
            $($tt)*
        }
    };
    // Handle subcommand creation
    (@app ($builder:expr) (@subcommand $name:ident => $($tail:tt)*) $($tt:tt)*) => {
        clap_app!{ @app
            ($builder.subcommand(
                clap_app!{ @app ($crate::SubCommand::with_name(stringify!($name))) $($tail)* }
            ))
            $($tt)*
        }
    };
    // Yaml like function calls - used for setting various meta directly against the app
    (@app ($builder:expr) ($ident:ident: $($v:expr),*) $($tt:tt)*) => {
        // clap_app!{ @app ($builder.$ident($($v),*)) $($tt)* }
        clap_app!{ @app
            ($builder.$ident($($v),*))
            $($tt)*
        }
    };

    // Add members to group and continue argument handling with the parent builder
    (@group ($builder:expr, $group:expr)) => { $builder.arg_group($group) };
    (@group ($builder:expr, $group:expr) (@attributes $($attr:tt)*) $($tt:tt)*) => {
        clap_app!{ @group ($builder, clap_app!{ @arg ($group) (-) $($attr)* }) $($tt)* }
    };
    (@group ($builder:expr, $group:expr) (@arg $name:ident: $($tail:tt)*) $($tt:tt)*) => {
        clap_app!{ @group
            (clap_app!{ @app ($builder) (@arg $name: $($tail)*) },
             $group.add(stringify!($name)))
            $($tt)*
        }
    };

    // No more tokens to munch
    (@arg ($arg:expr) $modes:tt) => { $arg };
    // Shorthand tokens influenced by the usage_string
    (@arg ($arg:expr) $modes:tt --$long:ident $($tail:tt)*) => {
        clap_app!{ @arg ($arg.long(stringify!($long))) $modes $($tail)* }
    };
    (@arg ($arg:expr) $modes:tt -$short:ident $($tail:tt)*) => {
        clap_app!{ @arg ($arg.short(stringify!($short))) $modes $($tail)* }
    };
    (@arg ($arg:expr) (-) <$var:ident> $($tail:tt)*) => {
        clap_app!{ @arg ($arg.value_name(stringify!($var))) (+) +takes_value +required $($tail)* }
    };
    (@arg ($arg:expr) (+) <$var:ident> $($tail:tt)*) => {
        clap_app!{ @arg ($arg.value_name(stringify!($var))) (+) $($tail)* }
    };
    (@arg ($arg:expr) (-) [$var:ident] $($tail:tt)*) => {
        clap_app!{ @arg ($arg.value_name(stringify!($var))) (+) +takes_value $($tail)* }
    };
    (@arg ($arg:expr) (+) [$var:ident] $($tail:tt)*) => {
        clap_app!{ @arg ($arg.value_name(stringify!($var))) (+) $($tail)* }
    };
    (@arg ($arg:expr) $modes:tt ... $($tail:tt)*) => {
        clap_app!{ @arg ($arg) $modes +multiple $($tail)* }
    };
    // Shorthand magic
    (@arg ($arg:expr) $modes:tt #{$n:expr, $m:expr} $($tail:tt)*) => {
        clap_app!{ @arg ($arg) $modes min_values($n) max_values($m) $($tail)* }
    };
    (@arg ($arg:expr) $modes:tt * $($tail:tt)*) => {
        clap_app!{ @arg ($arg) $modes +required $($tail)* }
    };
    // !foo -> .foo(false)
    (@arg ($arg:expr) $modes:tt !$ident $($tail:tt)*) => {
        clap_app!{ @arg ($arg.$ident(false)) $modes $($tail)* }
    };
    // foo -> .foo(true)
    (@arg ($arg:expr) $modes:tt +$ident:ident $($tail:tt)*) => {
        clap_app!{ @arg ($arg.$ident(true)) $modes $($tail)* }
    };
    // Validator
    (@arg ($arg:expr) $modes:tt {$fn_:expr} $($tail:tt)*) => {
        clap_app!{ @arg ($arg.validator($fn_)) $modes $($tail)* }
    };
    (@as_expr $expr:expr) => { $expr };
    // Help
    (@arg ($arg:expr) $modes:tt $desc:tt) => { $arg.help(clap_app!{ @as_expr $desc }) };
    // Handle functions that need to be called multiple times for each argument
    (@arg ($arg:expr) $modes:tt $ident:ident[$($target:ident)*] $($tail:tt)*) => {
        clap_app!{ @arg ($arg $( .$ident(stringify!($target)) )*) $modes $($tail)* }
    };
    // Inherit builder's functions
    (@arg ($arg:expr) $modes:tt $ident:ident($($expr:expr)*) $($tail:tt)*) => {
        clap_app!{ @arg ($arg.$ident($($expr)*)) $modes $($tail)* }
    };

    // Build a subcommand outside of an app.
    (@subcommand $name:ident => $($tail:tt)*) => {
        clap_app!{ @app ($crate::SubCommand::with_name(stringify!($name))) $($tail)* }
    };
    // Start the magic
    ($name:ident => $($tail:tt)*) => {{
        clap_app!{ @app ($crate::App::new(stringify!($name))) $($tail)*}
    }};
}

App, Arg, SubCommand and Group builder macro (Usage-string like input)