On 2025-07-17 at 22:46:56, Taylor Blau wrote: > On Thu, Jul 17, 2025 at 08:32:21PM +0000, Ezekiel Newren via GitGitGadget wrote: > > From: Ezekiel Newren <ezekielnewren@xxxxxxxxx> > > > > A few commits ago, we added definitions for Rust primitive types, > > to facilitate interoperability between C and Rust. Switch a > > few variables to use these types. Which, for now, will > > require adding some casts. > > Hmm, interesting. I am not super familiar with how people typically > handle interoperability between C and Rust, but having to change types > on the C side to make it work with Rust is a bit surprising to me. > > I would have expected that the Rust side would have declared its types > using libc::c_int, libc::size_t, and so on. I think I have a vague > preference towards putting the burden of casting on the Rust side, but, > again, I am not super familiar with how transitions like these are > typically approached. Rust normally handles byte strings as slices or vectors of u8 (that is, C's uint8_t). C handles them as char, which may or may not be unsigned, as we all know, which leads to some "entertaining" problems from time to time. Also, in general, Rust doesn't offer generic system-specific types, such as `long`, except for C FFI. This is actually a strong benefit, since it means we're not inclined to write `unsigned long` and then wonder why things are broken on Windows: instead, we write either `usize` (the equivalent of `size_t`) or `u64` (for things like file sizes). This is much more ingrained than it is in Go, which has a tendency to use `int` (Rust's `isize`) a lot and much less often specific types. If we're going to move this code entirely into Rust, then it makes sense to cast temporarily, and I'm fine doing that in C, since it's C that has the weird system-dependent behaviour (arbitrary decisions on the signedness of char). That actually allows us to have more confidence in the safety and maintainability of the Rust code since it is less system dependent and leave the suspect pieces in C. It may also, interestingly enough, also allow us to easily get rid of the weird 2 GB limit on diffs due to the unpleasant dependency on `int` in the xdiff code, which I would absolutely love to see. However, I'm not dead set against casting in Rust if that's what everyone else wants instead. -- brian m. carlson (they/them) Toronto, Ontario, CA
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