enum_primitive::enum_from_primitive!

macro_rules! enum_from_primitive {
    (
        $( #[$enum_attr:meta] )*
        enum $name:ident {
            $( $( #[$variant_attr:meta] )* $variant:ident ),+ $( = $discriminator:expr, $( $( #[$variant_two_attr:meta] )* $variant_two:ident ),+ )*
        }
    ) => {
        $( #[$enum_attr] )*
        enum $name {
            $( $( #[$variant_attr] )* $variant ),+ $( = $discriminator, $( $( #[$variant_two_attr] )* $variant_two ),+ )*
        }
        enum_from_primitive_impl! { $name, $( $variant )+ $( $( $variant_two )+ )* }
    };

    (
        $( #[$enum_attr:meta] )*
        enum $name:ident {
            $( $( $( #[$variant_attr:meta] )* $variant:ident ),+ = $discriminator:expr ),*
        }
    ) => {
        $( #[$enum_attr] )*
        enum $name {
            $( $( $( #[$variant_attr] )* $variant ),+ = $discriminator ),*
        }
        enum_from_primitive_impl! { $name, $( $( $variant )+ )* }
    };

    (
        $( #[$enum_attr:meta] )*
        enum $name:ident {
            $( $( #[$variant_attr:meta] )* $variant:ident ),+ $( = $discriminator:expr, $( $( #[$variant_two_attr:meta] )* $variant_two:ident ),+ )*,
        }
    ) => {
        $( #[$enum_attr] )*
        enum $name {
            $( $( #[$variant_attr] )* $variant ),+ $( = $discriminator, $( $( #[$variant_two_attr] )* $variant_two ),+ )*,
        }
        enum_from_primitive_impl! { $name, $( $variant )+ $( $( $variant_two )+ )* }
    };

    (
        $( #[$enum_attr:meta] )*
        enum $name:ident {
            $( $( $( #[$variant_attr:meta] )* $variant:ident ),+ = $discriminator:expr ),+,
        }
    ) => {
        $( #[$enum_attr] )*
        enum $name {
            $( $( $( #[$variant_attr] )* $variant ),+ = $discriminator ),+,
        }
        enum_from_primitive_impl! { $name, $( $( $variant )+ )+ }
    };

    (
        $( #[$enum_attr:meta] )*
        pub enum $name:ident {
            $( $( #[$variant_attr:meta] )* $variant:ident ),+ $( = $discriminator:expr, $( $( #[$variant_two_attr:meta] )* $variant_two:ident ),+ )*
        }
    ) => {
        $( #[$enum_attr] )*
        pub enum $name {
            $( $( #[$variant_attr] )* $variant ),+ $( = $discriminator, $( $( #[$variant_two_attr] )* $variant_two ),+ )*
        }
        enum_from_primitive_impl! { $name, $( $variant )+ $( $( $variant_two )+ )* }
    };

    (
        $( #[$enum_attr:meta] )*
        pub enum $name:ident {
            $( $( $( #[$variant_attr:meta] )* $variant:ident ),+ = $discriminator:expr ),*
        }
    ) => {
        $( #[$enum_attr] )*
        pub enum $name {
            $( $( $( #[$variant_attr] )* $variant ),+ = $discriminator ),*
        }
        enum_from_primitive_impl! { $name, $( $( $variant )+ )* }
    };

    (
        $( #[$enum_attr:meta] )*
        pub enum $name:ident {
            $( $( #[$variant_attr:meta] )* $variant:ident ),+ $( = $discriminator:expr, $( $( #[$variant_two_attr:meta] )* $variant_two:ident ),+ )*,
        }
    ) => {
        $( #[$enum_attr] )*
        pub enum $name {
            $( $( #[$variant_attr] )* $variant ),+ $( = $discriminator, $( $( #[$variant_two_attr] )* $variant_two ),+ )*,
        }
        enum_from_primitive_impl! { $name, $( $variant )+ $( $( $variant_two )+ )* }
    };

    (
        $( #[$enum_attr:meta] )*
        pub enum $name:ident {
            $( $( $( #[$variant_attr:meta] )* $variant:ident ),+ = $discriminator:expr ),+,
        }
    ) => {
        $( #[$enum_attr] )*
        pub enum $name {
            $( $( $( #[$variant_attr] )* $variant ),+ = $discriminator ),+,
        }
        enum_from_primitive_impl! { $name, $( $( $variant )+ )+ }
    };
}

Wrap this macro around an enum declaration to get an automatically generated implementation of num::FromPrimitive.