transmutes_expressible_as_ptr_casts suggests invalid cast

[matthiaskrgr]

Summary

.

Lint Name

transmutes_expressible_as_ptr_casts

Reproducer

I tried this code:

#[derive(PartialEq, Debug)]
struct p {
  x: isize,
  y: isize,
}

fn p(x: isize, y: isize) -> p {
    p {
        x: x,
        y: y
    }
}

fn test_class() {
  let q = p(1, 2);
  let mut r = p(1, 2);

  unsafe {
  println!("q = {:x}, r = {:x}",
         (::std::mem::transmute::<*const p, usize>(&q)),
         (::std::mem::transmute::<*const p, usize>(&r)));
  }
}

pub fn main() {
    test_class();
}

I saw this happen:

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

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:
warning: type `p` should have an upper camel case name
 --> src/main.rs:2:8
  |
2 | struct p {
  |        ^ help: convert the identifier to upper camel case: `P`
  |
  = note: `#[warn(non_camel_case_types)]` on by default

error[E0606]: casting `&p` as `usize` is invalid
  --> src/main.rs:20:10
   |
20 |          &q as usize,
   |          ^^^^^^^^^^^
   |
   = help: cast through a raw pointer first

error[E0606]: casting `&p` as `usize` is invalid
  --> src/main.rs:21:10
   |
21 |          &r as usize);
   |          ^^^^^^^^^^^
   |
   = help: cast through a raw pointer first

error: aborting due to 2 previous errors; 1 warning emitted

For more information about this error, try `rustc --explain E0606`.
Original diagnostics will follow.

warning: type `p` should have an upper camel case name
 --> src/main.rs:2:8
  |
2 | struct p {
  |        ^ help: convert the identifier to upper camel case: `P`
  |
  = note: `#[warn(non_camel_case_types)]` on by default

warning: variable does not need to be mutable
  --> src/main.rs:16:7
   |
16 |   let mut r = p(1, 2);
   |       ----^
   |       |
   |       help: remove this `mut`
   |
   = note: `#[warn(unused_mut)]` on by default

warning: transmute from `*const p` to `usize` which could be expressed as a pointer cast instead
  --> src/main.rs:20:10
   |
20 |          (::std::mem::transmute::<*const p, usize>(&q)),
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&q as usize`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#transmutes_expressible_as_ptr_casts
   = note: requested on the command line with `-W clippy::transmutes-expressible-as-ptr-casts`

warning: transmute from `*const p` to `usize` which could be expressed as a pointer cast instead
  --> src/main.rs:21:10
   |
21 |          (::std::mem::transmute::<*const p, usize>(&r)));
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&r as usize`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#transmutes_expressible_as_ptr_casts

warning: `clpy` (bin "clpy") generated 4 warnings (run `cargo fix --bin "clpy"` to apply 3 suggestion

Version

rustc 1.67.0-nightly (c5d82ed7a 2022-11-19)
binary: rustc
commit-hash: c5d82ed7a4ad94a538bb87e5016e7d5ce0bd434b
commit-date: 2022-11-19
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly

Additional Labels

No response