Non-inline modules are not stable

[TheButlah]

I tried to use this as follows:

use dynpath::dynpath;
#[dynpath("OUT_DIR")]
mod generated;

But I got:

error[E0658]: non-inline modules in proc macro input are unstable
  --> client/serialize/rust/src/lib.rs:20:1
   |
20 | mod generated;
   | ^^^^^^^^^^^^^^
   |
   = note: see issue #54727 <https://github.com/rust-lang/rust/issues/54727> for more information
   = help: add `#![feature(proc_macro_hygiene)]` to the crate attributes to enable