Auto merge of #39572 - jseyfried:fix_inert_attributes, r=nrc

macros: fix inert attributes from `proc_macro_derives` with `#![feature(proc_macro)]`

This PR refactors collection of `proc_macro_derive` invocations to fix #39347.

After this PR, the input to a `#[proc_macro_derive]` function no longer sees `#[derive]`s on the underlying item. For example, consider:
```rust
extern crate my_derives;
use my_derives::{Trait, Trait2};

#[derive(Copy, Clone)]
#[derive(Trait)]
#[derive(Trait2)]
struct S;
```

Today, the input to the `Trait` derive is `#[derive(Copy, Clone, Trait2)] struct S;`, and the input to the `Trait2` derive is `#[derive(Copy, Clone)] struct S;`. More generally, a `proc_macro_derive` sees all builtin derives, as well as all `proc_macro_derive`s listed *after* the one being invoked.

After this PR, both `Trait` and `Trait2` will see `struct S;`.
This is a [breaking-change], but I believe it is highly unlikely to cause breakage in practice.

r? @nrc

0 files changed, 0 insertions, 0 deletions