transmute_int_to_non_zero does not work in const context

--force-warn clippy::transmute_int_to_non_zero

this code:

// check-pass

// Some constants that *are* valid

use std::mem;
use std::ptr::NonNull;
use std::num::{NonZeroU8, NonZeroUsize};

const NON_NULL_PTR1: NonNull<u8> = unsafe { mem::transmute(1usize) };
const NON_NULL_PTR2: NonNull<u8> = unsafe { mem::transmute(&0) };

const NON_NULL_U8: NonZeroU8 = unsafe { mem::transmute(1u8) };
const NON_NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(1usize) };

const UNIT: () = ();

fn main() {}

caused the following diagnostics:

    Checking _177158189332677763 v0.1.0 (/tmp/icemaker_global_tempdir.gPgWiqot4T9Z/icemaker_clippyfix_tempdir.XzfiozsNr9XH/_177158189332677763)
warning: transmute from a `u8` to a `NonZero<u8>`
  --> src/main.rs:12:41
   |
12 | const NON_NULL_U8: NonZeroU8 = unsafe { mem::transmute(1u8) };
   |                                         ^^^^^^^^^^^^^^^^^^^ help: consider using: `NonZero::new_unchecked(1u8)`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#transmute_int_to_non_zero
   = note: requested on the command line with `--force-warn clippy::transmute-int-to-non-zero`

warning: transmute from a `usize` to a `NonZero<usize>`
  --> src/main.rs:13:47
   |
13 | const NON_NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(1usize) };
   |                                               ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `NonZero::new_unchecked(1usize)`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#transmute_int_to_non_zero

warning: `_177158189332677763` (bin "_177158189332677763") generated 2 warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.15s

However after applying these diagnostics, the resulting code:

// check-pass

// Some constants that *are* valid

use std::num::NonZero;
use std::mem;
use std::ptr::NonNull;
use std::num::{NonZeroU8, NonZeroUsize};

const NON_NULL_PTR1: NonNull<u8> = unsafe { mem::transmute(1usize) };
const NON_NULL_PTR2: NonNull<u8> = unsafe { mem::transmute(&0) };

const NON_NULL_U8: NonZeroU8 = unsafe { NonZero::new_unchecked(1u8) };
const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1usize) };

const UNIT: () = ();

fn main() {}

no longer compiled:

    Checking _177158189332677763 v0.1.0 (/tmp/icemaker_global_tempdir.gPgWiqot4T9Z/icemaker_clippyfix_tempdir.XzfiozsNr9XH/_177158189332677763)
warning: failed to automatically apply fixes suggested by rustc to crate `_177158189332677763`

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-clippy/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[E0658]: cannot call conditionally-const method `<std::num::NonZero<u8> as std::convert::Into<std::num::NonZero<usize>>>::into` in constants
  --> src/main.rs:14:77
   |
14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1u8).into() };
   |                                                                             ^^^^^^
   |
   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
   = note: see issue #143874 <https://github.com/rust-lang/rust/issues/143874> for more information
   = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
   = note: this compiler was built on 2026-03-07; consider upgrading it if it is out of date

error: `std::convert::Into` is not yet stable as a const trait
  --> src/main.rs:14:47
   |
14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1u8).into() };
   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
help: add `#![feature(const_convert)]` to the crate attributes to enable
   |
 5 + #![feature(const_convert)]
   |

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0658`.
Original diagnostics will follow.

error[E0308]: mismatched types
   --> src/main.rs:14:72
    |
 14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1usize) };
    |                                               ------------------------ ^^^^^^ expected `u8`, found `usize`
    |                                               |
    |                                               arguments to this function are incorrect
    |
note: associated function defined here
   --> /home/gh-matthiaskrgr/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/num/nonzero.rs:418:25
    |
418 |     pub const unsafe fn new_unchecked(n: T) -> Self {
    |                         ^^^^^^^^^^^^^
help: change the type of the numeric literal from `usize` to `u8`
    |
 14 - const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1usize) };
 14 + const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1u8) };
    |

error[E0308]: mismatched types
  --> src/main.rs:14:47
   |
14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1usize) };
   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `NonZero<usize>`, found `NonZero<u8>`
   |
   = note: expected struct `std::num::NonZero<usize>`
              found struct `std::num::NonZero<u8>`
help: call `Into::into` on this expression to convert `std::num::NonZero<u8>` into `std::num::NonZero<usize>`
   |
14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1usize).into() };
   |                                                                               +++++++

For more information about this error, try `rustc --explain E0308`.
error: could not compile `_177158189332677763` (bin "_177158189332677763" test) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
warning: failed to automatically apply fixes suggested by rustc to crate `_177158189332677763`

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-clippy/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[E0658]: cannot call conditionally-const method `<std::num::NonZero<u8> as std::convert::Into<std::num::NonZero<usize>>>::into` in constants
  --> src/main.rs:15:77
   |
15 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1u8).into() };
   |                                                                             ^^^^^^
   |
   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
   = note: see issue #143874 <https://github.com/rust-lang/rust/issues/143874> for more information
   = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
   = note: this compiler was built on 2026-03-07; consider upgrading it if it is out of date

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0658`.
Original diagnostics will follow.

error[E0658]: cannot call conditionally-const method `<std::num::NonZero<u8> as std::convert::Into<std::num::NonZero<usize>>>::into` in constants
  --> src/main.rs:14:77
   |
14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1u8).into() };
   |                                                                             ^^^^^^
   |
   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
   = note: see issue #143874 <https://github.com/rust-lang/rust/issues/143874> for more information
   = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
   = note: this compiler was built on 2026-03-07; consider upgrading it if it is out of date

error: `std::convert::Into` is not yet stable as a const trait
  --> src/main.rs:14:47
   |
14 | const NON_NULL_USIZE: NonZeroUsize = unsafe { NonZeroU8::new_unchecked(1u8).into() };
   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
help: add `#![feature(const_convert)]` to the crate attributes to enable
   |
 5 + #![feature(const_convert)]
   |

For more information about this error, try `rustc --explain E0658`.
error: could not compile `_177158189332677763` (bin "_177158189332677763") due to 2 previous errors

Version:

rustc 1.96.0-nightly (e3d66fe39 2026-03-07)
binary: rustc
commit-hash: e3d66fe39ae70380fa2365c008e2927479114844
commit-date: 2026-03-07
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

Start with the provided Rust const-context example and the transmute_int_to_non_zero lint entry point. Reproduce the diagnostic and suggested replacement, then verify that the resulting code preserves the original target types and compiles in a const context. Done when the suggestion is valid for both NonZeroU8 and NonZeroUsize cases.