Macro generics::parse

macro_rules! parse {
    (
        $callback:path { $($callback_args:tt)* } < $($token:tt)*
    ) => { ... };
    (
        $callback:path { $($callback_args:tt)* } $($token:tt)*
    ) => { ... };
}

Parses (optional) generics and (optional) subsequent where clause.

This macro accepts an input in the following form:

$callback_macro { $($callback_macro_args)* }
$(
    < $generics >
    $( $tokens_between_generics_and_where_clause )*
    $(
        where $where_clause
    )?
)?
$(
    $( ; | { $($body)* } )
    $($remaining_tokens)*
)?

and expands into

$callback_macro! {
    $( $callback_macro_args )*
    [ $( < $generics > )? ]
    [ $( < $generics_without_constraints > )? ]
    [ $( where $where_clause )? ]
    $($( $tokens_between_generics_and_where_clause )*)?
    $(
        $( ; | { $($body)* } )
        $($remaining_tokens)*
    )?
}

Examples

pub trait TheTrait { }

#[doc(hidden)]
pub use generics::parse as generics_parse;
#[doc(hidden)]
pub use std::compile_error as std_compile_error;

#[macro_export]
macro_rules! impl_the_trait {
    (
        $name:ident $($token:tt)*
    ) => {
        $crate::generics_parse! {
            $crate::impl_the_trait {
                @impl $name
            }
            $($token)*
        }
    };
    (
        @impl $name:ident [$($g:tt)*] [$($r:tt)*] [$($w:tt)*]
    ) => {
        impl $($g)* $crate::TheTrait for $name $($r)* $($w)* { }
    };
    (
        @impl $name:ident [$($g:tt)*] [$($r:tt)*] [$($w:tt)*] $($token:tt)+ 
    ) => {
        $crate::std_compile_error!(
            "invalid input, allowed input is '$name $( < $generics > $(where $where_clause)? )?'"
        );
    };
}