Hi! my team is in the process of upgrading to 0.8 and I encountered a very minor issue, kinda similar to #561 but with a #[deprecated] struct field. Example:

use rkyv::{Archive, Deserialize, Serialize};

#[derive(Clone, Debug, Archive, Serialize, Deserialize)]
pub struct Foo {
    #[deprecated]
    pub bar: i32,
    pub baz: Option<i32>,
}

warning: use of deprecated field `Foo::bar`
 --> src/main.rs:3:24
  |
3 | #[derive(Clone, Debug, Archive, Serialize, Deserialize)]
  |                        ^^^^^^^
  |
  = note: `#[warn(deprecated)]` on by default
  = note: this warning originates in the macro `::core::mem::offset_of` which comes from the expansion of the derive macro `Archive` (in Nightly builds, run with -Z macro-backtrace for more info)

This can be worked around by moving the struct into a module, adding #![allow(deprecated)] and re-exporting it, but it would be nice if either

• the lint was not emitted in the first place
• or we could inject an attribute somewhere somehow (on the impl, or associated const, or somewhere else?)

I also noticed that the rustc docs state that #[automatically_derived] should be placed on impls and may have no effect in other positions.

When I looked at the expansion of #[derive(Archive)], it looks like the #[automatically_derived] is being placed on the derived structs, but not e.g. impl rkyv::Archive for Foo (which is where this lint is firing) nor impl Portable for ArchivedFoo. So maybe a simple fix is just to add #[automatically_derived] onto those impls?

Thanks for this really cool library!