Option<T> parameters generated by a macro call are not recognized

[campbellcole]

I have a use case where I want users of my bot to be able to specify the default_member_permissions field for commands considered "admin only". I didn't want to reinvent the poise::command macro, so I wrote the following macro:

macro_rules! command {
    (
        $is_admin:literal;
        $(#[$attr:meta])*
        pub async fn $name:ident($($arg:ident: $arg_ty:ty),*) -> Result<$ret_ty:ty> $body:block
    ) => {
        pub fn command(config: & $crate::config::AppConfig) -> ::poise::Command<::std::sync::Arc<$crate::Data>, ::color_eyre::eyre::Report> {
            let mut cmd = $name();

            if $is_admin {
                cmd.default_member_permissions = *config.admin_permissions;
            }

            cmd
        }

        $(#[$attr])*
        #[::poise::command(slash_command)]
        async fn $name($($arg: $arg_ty),*) -> ::color_eyre::eyre::Result<$ret_ty> $body
    };
}

However, when invoking this macro with any function arguments that are Option<T>, the poise::command macro no longer recognizes Option and considers Option<T> as a distinct type.

For example:

use poise::serenity_prelude::User;

use crate::Context;

super::command! {
    true;
    pub async fn poc(ctx: Context<'_>, example: Option<User>) -> Result<()> {
        println!("demo user = {:?}", example);

        Ok(())
    }
}

produces the following compile error:

error[E0599]: the method `create` exists for reference `&&PhantomData<Option<User>>`, but its trait bounds were not satisfied
   --> src/command/poc.rs:5:1
    |
5   | / super::command! {
6   | |     true;
7   | |     pub async fn poc(ctx: Context<'_>, example: Option<User>) -> Result<()> {
8   | |         println!("demo user = {:?}", example);
...   |
11  | |     }
12  | | }
    | |_^ method cannot be called on `&&PhantomData<Option<User>>` due to unsatisfied trait bounds
    |
   ::: /nix/store/yv81f5ak2ywr02nryl52mpngii3sc06z-rust-default-1.84.0-nightly-2024-10-28/lib/rustlib/src/rust/library/core/src/option.rs:571:1
    |
571 |   pub enum Option<T> {
    |   ------------------ doesn't satisfy `_: ArgumentConvert`, `_: FromStr` or `_: SlashArgument`
    |
   ::: /nix/store/yv81f5ak2ywr02nryl52mpngii3sc06z-rust-default-1.84.0-nightly-2024-10-28/lib/rustlib/src/rust/library/core/src/marker.rs:753:1
    |
753 |   pub struct PhantomData<T: ?Sized>;
    |   --------------------------------- doesn't satisfy `_: SlashArgumentHack<Option<User>>`
    |
    = note: the following trait bounds were not satisfied:
            `std::option::Option<poise::serenity_prelude::User>: poise::SlashArgument`
            which is required by `&std::marker::PhantomData<std::option::Option<poise::serenity_prelude::User>>: poise::SlashArgumentHack<std::option::Option<poise::serenity_prelude::User>>`
            `std::option::Option<poise::serenity_prelude::User>: poise::serenity_prelude::ArgumentConvert`
            which is required by `std::marker::PhantomData<std::option::Option<poise::serenity_prelude::User>>: poise::SlashArgumentHack<std::option::Option<poise::serenity_prelude::User>>`
            `std::option::Option<poise::serenity_prelude::User>: std::str::FromStr`
            which is required by `std::marker::PhantomData<std::option::Option<poise::serenity_prelude::User>>: poise::SlashArgumentHack<std::option::Option<poise::serenity_prelude::User>>`
    = note: this error originates in the macro `poise::create_slash_argument` which comes from the expansion of the macro `super::command` (in Nightly builds, run with -Z macro-backtrace for more info)

I poked around in the expanded code using cargo-expand, and saw that the argument type is being set to Option<T> instead of T, and required is being set to true instead of false.

I read through the code that parses the type and I can't figure out why this might be happening. I suspect this is actually a bug in Rust or syn whereby the macro_rules invocation is removing the distinction between generic and simple types but I feel it's right to post it here first and move elsewhere once it's scope has been determined.

Thank you