FP no_mangle_with_rust_abi, suggestion does not apply

[matthiaskrgr]

Summary

.

Lint Name

no_mangle_with_rust_abi

Reproducer

I tried this code:

// compile-flags: -C no-prepopulate-passes -Copt-level=0

#![crate_type = "lib"]
#![feature(const_eval_select)]
#![feature(core_intrinsics)]

use std::intrinsics::const_eval_select;

const fn foo(_: i32) -> i32 { 1 }

#[no_mangle]
pub fn hi(n: i32) -> i32 { n }

#[no_mangle]
pub unsafe fn hey() {
    // CHECK: call i32 @hi(i32
    const_eval_select((42,), foo, hi);
}

pub fn main() {}

I saw this happen:
cargo clippy --fix --allow-dirty -- -Aclippy::all -Wclippy::no-mangle-with-rust-abi

The suggestion does not compile when applied:

warning: failed to automatically apply fixes suggested by rustc to crate `clippyfix`

after fixes were automatically applied the compiler reported errors within these files:

  * src/main.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0277]: expected a `std::ops::FnOnce<(i32,)>` closure, found `extern "C" fn(i32) -> i32 {hi}`
    --> src/main.rs:17:35
     |
17   |     const_eval_select((42,), foo, hi);
     |     -----------------             ^^ expected an `FnOnce<(i32,)>` closure, found `extern "C" fn(i32) -> i32 {hi}`
     |     |
     |     required by a bound introduced by this call
     |
     = help: the trait `std::ops::FnOnce<(i32,)>` is not implemented for fn item `extern "C" fn(i32) -> i32 {hi}`
note: required by a bound in `std::intrinsics::const_eval_select`
    --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/intrinsics.rs:2182:12
     |
2182 |         G: FnOnce<ARG, Output = RET>,
     |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
Original diagnostics will follow.

warning: attribute #[no_mangle] set on a Rust ABI function
  --> src/main.rs:12:1
   |
12 | pub fn hi(n: i32) -> i32 { n }
   | ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `pub extern "C" fn hi(n: i32) -> i32`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#no_mangle_with_rust_abi
   = note: requested on the command line with `-W clippy::no-mangle-with-rust-abi`

warning: attribute #[no_mangle] set on a Rust ABI function
  --> src/main.rs:15:1
   |
15 | pub unsafe fn hey() {
   | ^^^^^^^^^^^^^^^^^^^ help: try: `pub unsafe extern "C" fn hey()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#no_mangle_with_rust_abi

Version

rustc 1.69.0-nightly (d962ea578 2023-02-26)
binary: rustc
commit-hash: d962ea57899d64dc8a57040142c6b498a57c8064
commit-date: 2023-02-26
host: x86_64-unknown-linux-gnu
release: 1.69.0-nightly
LLVM version: 15.0.7

Additional Labels

No response

[matthiaskrgr]

no_mangle on main() also introduces some interesting suggestion which does not compile 😅

warning: attribute #[no_mangle] set on a Rust ABI function
  --> src/main.rs:11:1
   |
11 | pub fn main() {
   | ^^^^^^^^^^^^^ help: try: `pub extern "C" fn main()`
   |

[matthiaskrgr]

^

#![crate_type = "cdylib"]

#[link(wasm_import_module = "test")]
extern "C" {
    fn log(message_data: u32, message_size: u32);
}

#[no_mangle]
pub fn main() {
    let message = "Hello, world!";
    unsafe {
        log(message.as_ptr() as u32, message.len() as u32);
    }
}

cc @nindalf