Externalize derive macro implementation

[vic1707]

Hi,
I'm currently trying to make a crate built on top of serde to try to implement a relatively naive idea for struture versioning regarding #1137 as a POC (and hopefully a suitable solution).

For ease of use (both as the developper and user of the crate) I'd like my crate to be able to benefit from serde's derive implementation that is thankfully in a separate function that could be exported.

This would allow my crate (and other ones of the same kind) to be 100% compatible with all of serde derive's attribute and features by manually running the derive function and modifying the AST with quote and syn.

This would allow crate developers to inject their features direclty on the Serialize or Deserialize implementation outputed by serde_derive, kinda like what I'm doing:

--- usage.expanded.initial.rs	2024-06-28 23:42:09
+++ usage.expanded.modified.rs	2024-06-28 23:42:09
@@ -4,7 +4,7 @@
 use std::prelude::rust_2021::*;
 #[macro_use]
 extern crate std;
-use serde_derive::Deserialize;
+use my_serde::Deserialize;
 struct Foo {
     name: String,
     age: u8,
@@ -24,6 +24,11 @@
         where
             __D: _serde::Deserializer<'de>,
         {
+            'my_serde: {
+                {
+                    ::std::io::_print(format_args!("HI!!!\n"));
+                };
+            }
             #[allow(non_camel_case_types)]
             #[doc(hidden)]
             enum __Field {

original file being:

/* Clippy config */
#![allow(dead_code)]
/* Dependencies */
use serde_derive::Deserialize;

#[derive(Deserialize)]
struct Foo {
    name: String,
    age: u8,
    #[serde(default)]
    place_holder: String,
}

fn main() {}

This is, I think, kinda related to #2021.

To do so I pretty much replicated the serde_derive_internals situation.

If this change is ok to you (if its not I can simply use my fork for the time being), I'd like to have your opinion on how you want me to fix the current clippy issues (the lib file currently being the same as for serde_derive_internals)
Simply add a bunch of #[allow()] on the lib.rs, try my best to fix every one of them, alternative ?

Notes

English isn't my primary language, I'm sorry if I made mistakes, if anything sounds bad or if I'm hard to understand 😓.

[vic1707]

Just released my code for versioning here if you want to take a look at what this PR allows ^^
https://github.com/vic1707/serde-versioning

btw, if you have time, I'd love to hear your opinion the project