Add an option to override the representation of enums

In https://github.com/nbigaouette/onnxruntime-rs I use bindgen in onnxruntime-sys/build.rs to generate bindings on different platforms (macos, linux, windows).

The original C header file is https://github.com/microsoft/onnxruntime/blob/v1.5.2/include/onnxruntime/core/session/onnxruntime_c_api.h (which is quite large).

This header contains a couple of enums, for example OrtLoggingLevel that gets wrapper as u32: https://docs.rs/onnxruntime-sys/0.0.9/onnxruntime_sys/type.OrtLoggingLevel.html

But on Windows, I get i32s for them (docs.rs doesn't contain windows values, yet).

Because of this I have trouble creating an API that can work both on Windows an other platforms.

Input C/C++ Header

wrapper.h

#include "onnxruntime_c_api.h"

onnxruntime_c_api.h

typedef enum OrtLoggingLevel {
  ORT_LOGGING_LEVEL_VERBOSE,
  ORT_LOGGING_LEVEL_INFO,
  ORT_LOGGING_LEVEL_WARNING,
  ORT_LOGGING_LEVEL_ERROR,
  ORT_LOGGING_LEVEL_FATAL,
} OrtLoggingLevel;

Bindgen Invocation

On macOS:

$ bindgen onnxruntime-sys/wrapper.h --whitelist-type OrtLoggingLevel -- -I target/debug/build/onnxruntime-sys-4dd6b75a91cb40e3/out/onnxruntime/onnxruntime-osx-x64-1.5.2/include

On Windows:

$ bindgen onnxruntime-sys/wrapper.h --whitelist-type OrtLoggingLevel -- -I C:\cargo_target\debug\b
uild\onnxruntime-sys-6a0af3699f92fd5c\out\onnxruntime\onnxruntime-win-x64-1.5.2\include

Actual Results

On macOS:

/* automatically generated by rust-bindgen 0.55.1 */

pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_VERBOSE: OrtLoggingLevel = 0;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_INFO: OrtLoggingLevel = 1;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_WARNING: OrtLoggingLevel = 2;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_ERROR: OrtLoggingLevel = 3;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_FATAL: OrtLoggingLevel = 4;
pub type OrtLoggingLevel = ::std::os::raw::c_uint;

On Windows:

/* automatically generated by rust-bindgen 0.55.1 */

pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_VERBOSE: OrtLoggingLevel = 0;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_INFO: OrtLoggingLevel = 1;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_WARNING: OrtLoggingLevel = 2;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_ERROR: OrtLoggingLevel = 3;
pub const OrtLoggingLevel_ORT_LOGGING_LEVEL_FATAL: OrtLoggingLevel = 4;
pub type OrtLoggingLevel = ::std::os::raw::c_int;

Using --rustified-enum="*" I get:

❯ bindgen onnxruntime-sys/wrapper.h --rustified-enum="*" --whitelist-type OrtLoggingLevel -- -I target/debug/build/onnxruntime-sys-4dd6b75a91cb40e3/out/onnxruntime/onnxruntime-osx-x64-1.5.2/include
/* automatically generated by rust-bindgen 0.55.1 */

#[repr(u32)]
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum OrtLoggingLevel {
    ORT_LOGGING_LEVEL_VERBOSE = 0,
    ORT_LOGGING_LEVEL_INFO = 1,
    ORT_LOGGING_LEVEL_WARNING = 2,
    ORT_LOGGING_LEVEL_ERROR = 3,
    ORT_LOGGING_LEVEL_FATAL = 4,
}

PS Microsoft.PowerShell.Core\FileSystem::\\VBOXSVR\onnxruntime> bindgen onnxruntime-sys/wrapper.h --rustified-enum="*" --whitelist-type OrtLoggingLevel -- -I C:
\cargo_target\debug\build\onnxruntime-sys-6a0af3699f92fd5c\out\onnxruntime\onnxruntime-win-x64-1.5.2\include
/* automatically generated by rust-bindgen 0.55.1 */

#[repr(i32)]
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum OrtLoggingLevel {
    ORT_LOGGING_LEVEL_VERBOSE = 0,
    ORT_LOGGING_LEVEL_INFO = 1,
    ORT_LOGGING_LEVEL_WARNING = 2,
    ORT_LOGGING_LEVEL_ERROR = 3,
    ORT_LOGGING_LEVEL_FATAL = 4,
}

Expected Results

Note how macOS gives me a std::os::raw::c_uint and Windows gives me a std::os::raw::c_int (or #[repr(u32)] vs #[repr(i32)]) for the enum representation.

Why does bindgen generates different code on macOS/Linux and Windows? Can I tell bindgen to use std::os::raw::c_int everywhere? Or i64, or whatever else?

Thank you!

Start by reproducing the bindgen invocation with wrapper.h and the OrtLoggingLevel declaration on macOS or Windows. Compare the generated c_uint/c_int and u32/i32 representations, then trace how bindgen chooses the enum representation. Done means an explicit option can select a consistent representation across platforms for this case.