fix usage of `autodiff` macro with inner functions
This PR adds additional handling into the expansion step of the `std::autodiff` macro (in `compiler/rustc_builtin_macros/src/autodiff.rs`), which allows the macro to be applied to inner functions.
```rust
#![feature(autodiff)]
use std::autodiff::autodiff;
fn main() {
#[autodiff(d_inner, Forward, Dual, DualOnly)]
fn inner(x: f32) -> f32 {
x * x
}
}
```
Previously, the compiler didn't allow this due to only handling `Annotatable::Item` and `Annotatable::AssocItem` and missing the handling of `Annotatable::Stmt`. This resulted in the rather generic error
```
error: autodiff must be applied to function
--> src/main.rs:6:5
|
6 | / fn inner(x: f32) -> f32 {
7 | | x * x
8 | | }
| |_____^
error: could not compile `enzyme-test` (bin "enzyme-test") due to 1 previous error
```
This issue was originally reported [here](https://github.com/EnzymeAD/rust/issues/184).
Quick question: would it make sense to add a ui test to ensure there is no regression on this?
This is my first contribution, so I'm extra grateful for any piece of feedback!! :D
r? `@oli-obk`
Tracking issue for autodiff: #124509
5a43d92382