Compile issue on F41

[warthog9]

Building wheels for collected packages: pyluwen
  Building wheel for pyluwen (pyproject.toml) ... error
  error: subprocess-exited-with-error
  
  × Building wheel for pyluwen (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [48 lines of output]
      Running `maturin pep517 build-wheel -i /home/jhawley/git/luwen/crates/pyluwen/venv/bin/python3 --compatibility off`
      🔗 Found pyo3 bindings
      🐍 Found CPython 3.13 at /home/jhawley/git/luwen/crates/pyluwen/venv/bin/python3
      📡 Using build options features from pyproject.toml
         Compiling pyo3-build-config v0.19.2
         Compiling luwen-if v0.6.5 (/home/jhawley/git/luwen/crates/luwen-if)
         Compiling luwen-core v0.2.0 (/home/jhawley/git/luwen/crates/luwen-core)
         Compiling bytemuck_derive v1.9.3
         Compiling ttkmd-if v0.2.2 (/home/jhawley/git/luwen/crates/ttkmd-if)
      error[E0658]: use of unstable library feature 'pointer_byte_offsets'
         --> crates/ttkmd-if/src/lib.rs:724:30
          |
      724 | ...                   .byte_add(offset as usize),
          |                        ^^^^^^^^
          |
          = note: see issue #96283 <https://github.com/rust-lang/rust/issues/96283> for more information
      
      error[E0658]: use of unstable library feature 'pointer_byte_offsets'
         --> crates/ttkmd-if/src/lib.rs:766:30
          |
      766 | ...                   .byte_add(offset as usize),
          |                        ^^^^^^^^
          |
          = note: see issue #96283 <https://github.com/rust-lang/rust/issues/96283> for more information
      
      error[E0658]: use of unstable library feature 'pointer_byte_offsets'
         --> crates/ttkmd-if/src/lib.rs:802:26
          |
      802 |                         .byte_add(offset as usize) as usize
          |                          ^^^^^^^^
          |
          = note: see issue #96283 <https://github.com/rust-lang/rust/issues/96283> for more information
      
      error[E0658]: use of unstable library feature 'pointer_byte_offsets'
         --> crates/ttkmd-if/src/lib.rs:829:26
          |
      829 |                         .byte_add(offset as usize) as usize
          |                          ^^^^^^^^
          |
          = note: see issue #96283 <https://github.com/rust-lang/rust/issues/96283> for more information
      
      For more information about this error, try `rustc --explain E0658`.
      error: could not compile `ttkmd-if` (lib) due to 4 previous errors
      warning: build failed, waiting for other jobs to finish...
      💥 maturin failed
        Caused by: Failed to build a native library through cargo
        Caused by: Cargo build finished with "exit status: 101": `env -u CARGO PYO3_ENVIRONMENT_SIGNATURE="cpython-3.13-64bit" PYO3_PYTHON="/home/jhawley/git/luwen/crates/pyluwen/venv/bin/python3" PYTHON_SYS_EXECUTABLE="/home/jhawley/git/luwen/crates/pyluwen/venv/bin/python3" "cargo" "rustc" "--features" "pyo3/extension-module" "--message-format" "json-render-diagnostics" "--manifest-path" "/home/jhawley/git/luwen/crates/pyluwen/Cargo.toml" "--release" "--lib"`
      Error: command ['maturin', 'pep517', 'build-wheel', '-i', '/home/jhawley/git/luwen/crates/pyluwen/venv/bin/python3', '--compatibility', 'off'] returned non-zero exit status 1
      [end of output]

rustc: 1.73.0
python 3.13.3

[olofj]

Hm, I thought we used rustup to get a newer toolchain? 1.73.0 is fairly old by now.

[kaplanz]

Issue is caused by use of the (then) unstable feature, pointer_byte_offsets, which was stabilized in Rust v1.75.0 (released: 28 December 2023, see here).

As this is an almost 2+ year old version of Rust, I propose we set an MSRV of v1.75.0, which feels pretty reasonable given:

1. Fedora 41 (via DNF) provides the latest version of Rust (v1.90.0 when this was written).
2. Ubuntu 22.04 (mentioned in Add missing checksums in Cargo.lock #108 as a version we may wish to support, via APT) defaults to v1.75.0, the exact version we need for this issue.
3. Rust is typically installed and managed using rustup, which makes it trivial to install any version of the Rust toolchain. Edit: This isn't necessarily a valid justification, as downstream users may not necessarily be able to use rustup. For this reason, let's prefer to use platform provided instances of the Rust toolchain.

@warthog9 How do you feel about implementing an MSRV policy?