error[E0308]: mismatched types
  --> tests/ui-nightly/transmute-mut-src-not-a-reference.rs:17:53
   |
17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
   |                                      ---------------^^^^^^-
   |                                      |              |
   |                                      |              expected `&mut _`, found `usize`
   |                                      expected due to this
   |
   = note: expected mutable reference `&mut _`
                           found type `usize`
help: consider mutably borrowing here
   |
17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(&mut 0usize);
   |                                                     ++++

warning: this function depends on never type fallback being `()`
  --> tests/ui-nightly/transmute-mut-src-not-a-reference.rs:17:1
   |
17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
   = help: specify the types explicitly
note: in edition 2024, the requirement `!: FromBytes` will fail
  --> tests/ui-nightly/transmute-mut-src-not-a-reference.rs:17:38
   |
17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
   |                                      ^^^^^^^^^^^^^^^^^^^^^^
   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default
   = note: this warning originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `()` annotations to avoid fallback changes
  --> src/macros.rs
   |
   |         let e: &mut () = $e;
   |                     ~~

warning: never type fallback affects this call to an `unsafe` function
  --> tests/ui-nightly/transmute-mut-src-not-a-reference.rs:17:38
   |
17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
   |                                      ^^^^^^^^^^^^^^^^^^^^^^
   |
   = warning: this will change its meaning in a future release!
   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
   = help: specify the type explicitly
   = note: `#[warn(never_type_fallback_flowing_into_unsafe)]` on by default
   = note: this warning originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)