build.rs

extern crate bindgen;

use std::env;
use std::path::{Path, PathBuf};

fn main() {
    println!("cargo:rustc-link-search=framework=/System/Library/Frameworks/");
    println!("cargo:rustc-link-lib=framework=OpenCL");

    let headers = env::var("CARGO_MANIFEST_DIR").unwrap() + "/opencl22/CL/";
    let headers = Path::new(&headers);

    let bindings = bindgen::Builder::default()
        .link_framework("OpenCL")
        // .clang_arg("-framework OpenCL")

        .header(headers.join("opencl.h").to_string_lossy())
        .generate()
        .expect("Unable to generate bindings");

    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
    bindings
        .write_to_file(out_path.join("bindings.rs"))
        .expect("Couldn't write bindings!");
}

output-of-cargo.txt

   Compiling opencl-sys v0.1.0 (file:///.../linen/opencl-sys)
error: failed to run custom build command for `opencl-sys v0.1.0 (file:///.../linen/opencl-sys)`
process didn't exit successfully: `.../linen/target/debug/build/opencl-sys-39388fb3de4cc39f/build-script-build` (exit code: 101)
--- stdout
cargo:rustc-link-search=framework=/System/Library/Frameworks/
cargo:rustc-link-lib=framework=OpenCL

--- stderr
.../linen/opencl-sys/opencl22/CL/opencl.h:40:10: fatal error: 'OpenCL/cl.h' file not found
.../linen/opencl-sys/opencl22/CL/opencl.h:40:10: fatal error: 'OpenCL/cl.h' file not found, err: true
thread 'main' panicked at 'Unable to generate bindings: ()', libcore/result.rs:916:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

test.c

// compile me with: clang -framework OpenCL -o test test.c

#include <stdio.h>
#include <stdlib.h>
// #include <OpenCL/opencl.h>
#include "opencl22/CL/opencl.h"

int main(int argc, char* const argv[]) {
    cl_uint num_devices, i;
    clGetDeviceIDs(NULL, CL_DEVICE_TYPE_ALL, 0, NULL, &num_devices);

    cl_device_id* devices = calloc(sizeof(cl_device_id), num_devices);
    clGetDeviceIDs(NULL, CL_DEVICE_TYPE_ALL, num_devices, devices, NULL);

    char buf[128];
    for (i = 0; i < num_devices; i++) {
        clGetDeviceInfo(devices[i], CL_DEVICE_NAME, 128, buf, NULL);
        fprintf(stdout, "Device %s supports ", buf);

        clGetDeviceInfo(devices[i], CL_DEVICE_VERSION, 128, buf, NULL);
        fprintf(stdout, "%s\n", buf);
    }

    free(devices);
}