If I have the following Rust struct:

#[repr(C)]
pub struct MyStruct {
    value1: i32,
    pub value2: i32
}

It would be very useful for the generated struct to reflect the field's visibility:

struct MyStruct {
private:
    int32_t value1;
public:
    int32_t value2;
};

My main motivation for this is to create exported structs where all fields are private. An example is a pointer wrapper: If I allocate a pointer for an opaque struct with Box and then return the raw pointer, there's nothing stopping the caller from modifying it before passing it back for destruction. If instead I make a struct to wrap it, and give it private fields, all the caller can do is copy the struct around and pass it back unchanged.

A change like this would enable APIs that were more type-safe and more in the spirit of Rust.

An alternate, lower-tech approach would be an annotation to just unconditionally mark all fields private. I imagine most use-cases will want all-private or all-public fields, so an annotation to set them all private might be a smarter solution, and save field-specific visibility for a use case that needs it.

What do you think? Is there interest in this? If so I'd be happy to tackle it.