config derive conflicts with some other derive macro attributes. Better error message / documentation

[luketpeterson]

This code doesn't compile:

#[config]
#[derive(Parser, Debug, Default)]
pub struct FrameworkConfig <AppArgsT>
    where AppArgsT: clap::Args + Clone + Sync + Send + std::fmt::Debug + Default + DeserializeOwned + Serialize
{
    #[command(flatten)]
    #[serde(skip)]
    pub app_args: AppArgsT,
}

But this does:

#[derive(Parser, Debug, Default)]
#[config]
pub struct FrameworkConfig <AppArgsT>
    where AppArgsT: clap::Args + Clone + Sync + Send + std::fmt::Debug + Default + DeserializeOwned + Serialize
{
    #[command(flatten)]
    #[serde(skip)]
    pub app_args: AppArgsT,
}

The issue is the way the config proc macro handles the clap field attributes. Basically the config proc macro need to run first.

I don't see an easy fix for this, given the #[config] macro fundamentally reimplements the type, rather than just deriving a trait implementation. Perhaps it can be documented or better error messages can be given though.

Thank you