src/test/run-pass/enum-clike-ffi-as-int.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 /*!
  12  * C-like enums have to be represented as LLVM ints, not wrapped in a
  13  * struct, because it's important for the FFI that they interoperate
  14  * with C integers/enums, and the ABI can treat structs differently.
  15  * For example, on i686-linux-gnu, a struct return value is passed by
  16  * storing to a hidden out parameter, whereas an integer would be
  17  * returned in a register.
  18  *
  19  * This test just checks that the ABIs for the enum and the plain
  20  * integer are compatible, rather than actually calling C code.
  21  * The unused parameter to `foo` is to increase the likelihood of
  22  * crashing if something goes wrong here.
  23  */
  24
  25 #[repr(u32)]
  26 enum Foo {
  27   A = 0,
  28   B = 23
  29 }
  30
  31 #[inline(never)]
  32 extern "C" fn foo(_x: uint) -> Foo { Foo::B }
  33
  34 pub fn main() {
  35   unsafe {
  36     let f: extern "C" fn(uint) -> u32 = ::std::mem::transmute(foo);
  37     assert_eq!(f(0xDEADBEEF), Foo::B as u32);
  38   }
  39 }