Re-export core::ffi::c_void if supported

Author: IsaacWoods

Cargo.lock

@@ -12,6 +12,7 @@ description = """
 A library for types and bindings to native C functions often found in libc or
 other common platform libraries.
 """
+build = "build.rs"
 
 [badges]
 travis-ci = { repository = "rust-lang/libc" }
@@ -24,3 +25,6 @@ align = []
 
 [workspace]
 members = ["libc-test"]
+
+[build-dependencies]
+rustc_version = "0.2"

Cargo.toml

@@ -0,0 +1,15 @@
+extern crate rustc_version;
+
+fn main() {
+    /*
+     * If `core::ffi::c_void` exists, libc can just re-export it. Otherwise, it must define an
+     * incompatible type to retain backwards-compatibility.
+     */
+    let core_has_cvoid = {
+        let version = rustc_version::version().expect("Could not get rustc version");
+        (version.major > 1) || (version.major == 1 && version.minor >= 31)
+    };
+    if core_has_cvoid {
+        println!("cargo:rustc-cfg=core_cvoid");
+    }
+}

build.rs

@@ -108,7 +108,10 @@ cfg_if! {
         // On the Switch, we only define some useful universal types for
         // convenience. Those can be found in the switch.rs file.
     } else {
+        #[cfg(core_cvoid)]
+        pub use core::ffi::c_void;
 
+        #[cfg(not(core_cvoid))]
         // Use repr(u8) as LLVM expects `void*` to be the same as `i8*` to help enable
         // more optimization opportunities around it recognizing things like
         // malloc/free.

src/lib.rs

@@ -1,5 +1,9 @@
 //! Switch C type definitions
 
+#[cfg(core_cvoid)]
+pub use core::ffi::c_void;
+
+#[cfg(not(core_cvoid))]
 // Use repr(u8) as LLVM expects `void*` to be the same as `i8*` to help enable
 // more optimization opportunities around it recognizing things like
 // malloc/free.