Nightly regression: panic::set_hook() signature incompatible if used with core::panic::PanicInfo

[Manishearth]

Code

I tried this code:

#![no_std]

// Yes, this is `no_std` + `extern crate std`, which happens a lot in
// crates that are `cfg(not(something), no_std)`

extern crate std;
extern crate alloc;
use alloc::boxed::Box;

fn main() {
    
    std::panic::set_hook(Box::new(panic_handler));
}

fn panic_handler(info: &core::panic::PanicInfo) {

}

playground

I expected to see this happen: It compiles just fine

Instead, this happened: I get the following error:

error[E0631]: type mismatch in function arguments
  --> src/main.rs:9:26
   |
9  |     std::panic::set_hook(Box::new(panic_handler));
   |                          ^^^^^^^^^^^^^^^^^^^^^^^ expected due to this
...
12 | fn panic_handler(info: &core::panic::PanicInfo) {
   | ----------------------------------------------- found signature defined here
   |
   = note: expected function signature `for<'a, 'b> fn(&'a PanicHookInfo<'b>) -> _`
              found function signature `fn(&PanicInfo<'_>) -> _`
   = note: required for the cast from `Box<for<'a, 'b> fn(&'a PanicInfo<'b>) {panic_handler}>` to `Box<(dyn for<'a, 'b> Fn(&'a PanicHookInfo<'b>) + Send + Sync + 'static)>`

On nightly PanicInfo is a type alias for PanicHookInfo, however the alias only exists in the std crate. If you reference PanicInfo from core, that is now a different type that does not unify with PanicHookInfo.

It is relatively common in crates that support no_std to always use the lowest possible crate to reference for any reexported type, which is why our code was referencing core::panic even though this particular snippet of code needs std to work overall.

Version it worked on

It most recently worked on: Rust 1.79, Rust 1.80-beta3

Version with regression

rustc --version --verbose:

1.81.0-nightly (2024-06-19 d8a38b00024cd7156dea)

[asquared31415]

It doesn't even need to be a no_std crate, simply using use core::panic::PanicInfo; and using that PanicInfo in the panic hook signature reproduces this error.

[bjorn3]

#115974 was merged under the assumption that std crates are unlikely to use core::panic::PanicInfo instead of std::panic::PanicInfo when referring to the type of the panic hook argument. It is expected that core::panic::PanicInfo for the panic hook doesn't work after that PR.

[Manishearth]

Nice catch!

[asquared31415]

#115974 was merged under the assumption that std crates are unlikely to use core::panic::PanicInfo instead of std::panic::PanicInfo when referring to the type of the panic hook argument. It is expected that core::panic::PanicInfo for the panic hook doesn't work after that PR.

rust-analyzer has a setting for "prefer core over std for imports" that myself and i assume many others use, in all projects (also at this point I use core when possible by habit). If it's assumed that users should be using the std version when std is available, at the least the error should provide a fix that changes the import, and rust-analyzer should know how to exclude some imports from its setting.

[apiraino]

Closing since regression is mentioned in the release notes