Input C/C++ Header

#define MYCONST 2

Bindgen Invocation

$ bindgen input.h

Actual Results

/* automatically generated by rust-bindgen 0.59.1 */

pub const MYCONST: u32 = 2;

Expected Results

It would be better to generate something like

macro_rules! MYCONST { () => { 2 }; }

and to expect users to use MYCONST!() instead of MYCONST.

Reasoning

Constants using #define in a C header file do not have a type. They are inserted by the preprocessor as a literal where needed. Translating them to a Rust const with a type (u32, i32, or others) may lead to unexpected results. For example, i32 can be interchaged with std::os::raw::c_int on most platforms. But code that relies on that will not be portable. See discussion on Rust Users Forum "Interfacing C code with bindgen: #define and types".

Migration

Maybe it can be made possible to enable this new described behavior with an option that is not enabled by default; or the generated macro_rules!s could be created in addition to the consts (unless being switched off by an option).