Can't use raw pointers

[Michael-F-Bryan]

I'm guessing this is just a case of things not being implemented yet, but what is required to let C functions return raw pointers?

For example this code

use std::os::raw::c_char;

#[cxx::bridge]
mod ffi {
    extern "C" {
        include!("vendor/bzip2/bzlib.h");

        fn BZ2_bzlibVersion() -> *const c_char;
    }
}

Fails to compile with

   Compiling cxx-experiment v0.1.0 (/home/michael/Documents/cxx-experiment)
error: unsupported type
 --> src/lib.rs:8:34
  |
8 |         fn BZ2_bzlibVersion() -> *const c_char;
  |                                  ^^^^^^^^^^^^^

warning: unused import: `std::os::raw::c_char`
 --> src/lib.rs:1:5
  |
1 | use std::os::raw::c_char;
  |     ^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error: aborting due to previous error
error: could not compile `cxx-experiment`.
To learn more, run the command again with --verbose.

[dtolnay]

So far I am not decided on supporting raw pointers, but currently leaning against. I'd like to see if we can instead specialize toward interfaces that are structured to make it possible to always decide "is this code correct" without looking at the other language.

So in the context of your use case in https://github.com/Michael-F-Bryan/cxx-experiment/blob/1695c0f0d74f045ebfd0565a4d33d9b3222ccb03/src/lib.rs maybe something like one of these options:

#[cxx::bridge]
mod ffi {
    extern "C" {
        fn bzlib_version_equals(expected: &str) -> bool;
    }
}

// c++
bool bzlib_version_equals(RustStr expected) {
  auto actual = BZ2_bzlibVersion();
  return strncmp(actual, expected.data(), expected.size()) == 0
      && actual[expected.size()] == '\0';
}

// rust
assert!(ffi::bzlib_version_equals("1.0.8, 13-Jul-2019"));

#[cxx::bridge]
mod ffi {
    extern "C" {
        fn bzlib_version() -> String;
    }
}

// c++
RustString bzlib_version() {
  return RustString(BZ2_bzlibVersion());
}