Generated core bindings use types beyond MSRV

[declanvk]

Input C/C++ Header

In /tmp/bindgen-msrv/vendor/header.h:

typedef unsigned char  mp_sign;

Bindgen Invocation

bindgen::Builder::default()
    .header("/tmp/bindgen-msrv/vendor/header.h")
    .use_core()
    .generate()
    .unwrap()

Actual Results

In /tmp/bindgen-msrv/target/debug/build/bindgen-msrv-76670de3f461768b/out/bindings.rs:

/* automatically generated by rust-bindgen 0.61.0 */

pub type mp_sign = ::core::ffi::c_uchar;

and while running cargo +1.57.0 build:

error[E0412]: cannot find type `c_uchar` in module `core::ffi`
 --> /private/tmp/bindgen-msrv/target/debug/build/bindgen-msrv-7c473a0810493086/out/bindings.rs:3:33
  |
3 | pub type mp_sign = ::core::ffi::c_uchar;
  |                                 ^^^^^^^ not found in `core::ffi`
  |
help: consider importing this type alias
  |
3 | use std::os::raw::c_uchar;
  |

core::ffi::c_uchar was introduced in Rust version 1.64.0.

Expected Results

Should compile without errors.

[declanvk]

I'm not actually sure if the MSRV is supposed to be 1) the minimum version of Rust that can build bindgen OR 2) the minimum version of Rust that can build the generated bindings.

[declanvk]

Seems related to #2277

[declanvk]

Ah I see the Builder::rust_target controls which version of rust the bindings support, I should just enable that.

This is probably not an issue then? Maybe just improving the MSRV statement to include some references to rust_target or mentioning that MSRV only covers building bindgen, not the generated bindings.

[pvdrz]

If you set the rust target to anything below 1.64.0, bindgen will use std::os::raw instead as expected.

The MSRV is the minimum version that can be used to compile bindgen. However, bindgen itself can produce code for targets below the current MSRV. Maybe we should clarify this in the readme.

[pvdrz]

Fixed via: d86db07

Thanks for the report and please feel free to reopen if you think this is not an adequate solution