Generated bitfield code triggers clippy ptr_offset_of_cast lint

[bonzini]

This is an example of the output from clippy.

warning: use of `offset` with a `usize` casted to an `isize`
  --> /builds/bonzini/qemu/rust/target/debug/build/qemu_api-35cb647f4db404b8/out/bindings.inc.rs:39:21
   |
39 |         let byte = *(core::ptr::addr_of!((*this).storage) as *const u8).offset(byte_index as isize);
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(core::ptr::addr_of!((*this).storage) as *const u8).add(byte_index)`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_offset_with_cast 
   = note: `#[warn(clippy::ptr_offset_with_cast)]` on by default
warning: use of `offset` with a `usize` casted to an `isize`
  --> /builds/bonzini/qemu/rust/target/debug/build/qemu_api-35cb647f4db404b8/out/bindings.inc.rs:68:13
   |
68 |             (core::ptr::addr_of_mut!((*this).storage) as *mut u8).offset(byte_index as isize);
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(core::ptr::addr_of_mut!((*this).storage) as *mut u8).add(byte_index)`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_offset_with_cast

The lint is enabled by default at "warn" level.

[bonzini]

Seems to be new in 0.71.0? Could be related to commit 3300618.

[pvdrz]

3300618 was added because bindgen was generating code with addr_of regardless of the Rust target version. That commit only gates this feature behind Rust 1.51.

However, the fix is pretty straightforward as it only requires these two lines with add(byte_index):

rust-bindgen/bindgen/codegen/bitfield_unit_raw_ref_macros.rs

Line 47 in 1cd618e

.offset(byte_index as isize);

rust-bindgen/bindgen/codegen/bitfield_unit_raw_ref_macros.rs

Line 84 in 1cd618e

.offset(byte_index as isize);