`AddBounds::Fields` doesn't seem to care about the lifecycle

[823984418]

The following code

use proc_macro2::TokenStream;
use quote::quote;
use syn::parse_quote;
use synstructure::{decl_derive, AddBounds, Structure};

decl_derive!([GcTraget, attributes(unsafe_ignore_trace)] => derive_trace);

fn derive_trace(mut s: Structure<'_>) -> TokenStream {
    s.filter(|_| true);
    let body = s.each(|bi| quote!(::regc::GcTarget::trace(#bi, token);));
    s.add_impl_generic(parse_quote!('regc_lifetime));
    s.add_bounds(AddBounds::Fields);
    s.gen_impl(quote! {
        extern crate self as regc;
        gen impl<'regc_lifetime> ::regc::GcTarget<'regc_lifetime> for @Self {
            fn trace(&self, token: &mut ::regc::GcTraceToken<'regc_lifetime>) {
                match self {
                    #body
                }
            }
        }
    })
}

in

#[derive(GcTraget)]
struct A<'c, S> {
    x: GcRootThin<'c>,
    y: Option<S>,
}

generate

struct A<'c, S> {
    x: GcRootThin<'c>,
    y: Option<S>,
}
#[allow(non_upper_case_globals)]
const _DERIVE_regc_GcTarget_regc_lifetime_FOR_A: () = {
    extern crate self as regc;
    impl<'regc_lifetime, 'c, S> ::regc::GcTarget<'regc_lifetime> for A<'c, S>
    where
        Option<S>: ::regc::GcTarget<'regc_lifetime>,
    {
        fn trace(&self, token: &mut ::regc::GcTraceToken<'regc_lifetime>) {
            match self {
                A { x: ref __binding_0, y: ref __binding_1 } => {
                    {
                        ::regc::GcTarget::trace(__binding_0, token);
                    }
                    {
                        ::regc::GcTarget::trace(__binding_1, token);
                    }
                }
            }
        }
    }
};

Missing

GcRootThin<'c>: ...

This resulted in an implementation for any lifecycle, resulting in an error:

error: lifetime may not live long enough
   --> src\lib.rs:812:10
    |
812 | #[derive(GcTraget)]
    |          ^^^^^^^^
    |          |
    |          lifetime `'regc_lifetime` defined here
    |          argument requires that `'regc_lifetime` must outlive `'c`
813 | struct A<'c, S> {
    |          -- lifetime `'c` defined here
    |
    = help: consider adding the following bound: `'regc_lifetime: 'c`
    = note: requirement occurs because of a mutable reference to `GcTraceToken<'_>`
    = note: mutable references are invariant over their type parameter
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
    = note: this error originates in the derive macro `GcTraget` (in Nightly builds, run with -Z macro-backtrace for more info)

Error disappears after adding where GcRoot.

What I mean is, in add_trait_bounds In the implementation of boundaries', there seems to be a lack of consideration for the lifecycle,but they are also part of the type.