compiler: Forward attributes to eii-expanded macros
Since https://github.com/rust-lang/rust/pull/150592 is quite complicated to reason about I figured it would be good to split it up in smaller pieces that are easier to digest. Here is the attribute fix in isolation.
## The Problem
With this eii in **library/std/src/io/mod.rs**:
```rs
/// Foo
#[eii(on_broken_pipe)]
#[unstable(feature = "on_broken_pipe", issue = "150588")]
pub fn on_broken_pipe() -> OnBrokenPipe {
OnBrokenPipe::BackwardsCompatible
}
```
you currently get this compilation error:
```
error: attribute macro has missing stability attribute
--> library/std/src/io/mod.rs:2269:1
|
2269 | #[eii(on_broken_pipe)]
| ^^^^^^^^^^^^^^^^^^^^--
| |
| in this attribute macro expansion
|
::: library/core/src/macros/mod.rs:1899:5
|
1899 | pub macro eii($item:item) {
| ------------- in this expansion of `#[eii]`
```
because with ` MAGIC_EXTRA_RUSTFLAGS=-Zunpretty=expanded ./x build library/std` we can see that a pub item in the expanded code is indeed missing that attribute:
```rs
const _: () =
{
#[on_broken_pipe]
fn on_broken_pipe() -> OnBrokenPipe {
OnBrokenPipe::BackwardsCompatible
}
};
unsafe extern "Rust" {
/// Foo
#[unstable(feature = "on_broken_pipe", issue = "150588")]
#[rustc_eii_extern_item]
pub safe fn on_broken_pipe()
-> OnBrokenPipe;
}
#[rustc_builtin_macro(eii_shared_macro)]
#[eii_extern_target(on_broken_pipe)]
pub macro on_broken_pipe { () => {} }
```
## The Solution
With the fix, that error goes away because we get this expanded code instead:
```rs
const _: () =
{
#[on_broken_pipe]
fn on_broken_pipe() -> OnBrokenPipe {
OnBrokenPipe::BackwardsCompatible
}
};
unsafe extern "Rust" {
/// Foo
#[unstable(feature = "on_broken_pipe", issue = "150588")]
#[rustc_eii_extern_item]
pub safe fn on_broken_pipe()
-> OnBrokenPipe;
}
/// Foo
#[unstable(feature = "on_broken_pipe", issue = "150588")]
#[rustc_builtin_macro(eii_shared_macro)]
#[eii_extern_target(on_broken_pipe)]
pub macro on_broken_pipe { () => {} }
```
Note that we also need to forward the docs, otherwise get get (fatal) warnings like these:
```
warning: missing documentation for an attribute macro
--> library/std/src/io/mod.rs:2269:1
```
r? @jdonszelmann
Tracking issues:
- https://github.com/rust-lang/rust/issues/125418
- https://github.com/rust-lang/rust/issues/150588
### What about a test?
https://github.com/rust-lang/rust/pull/150591 will prevent regressions once it lands since it does not build without this fix. I think it is overkill to add a temporary eii to std before that.
1987b15908