Auto merge of #53910 - IsaacWoods:unify_cvoid, r=SimonSapin

Move std::os::raw::c_void into libcore and re-export in libstd

Implements the first part of [RFC 2521](rust-lang/rfcs#2521).

cc #53856

src/libcore/ffi.rs

@@ -0,0 +1,42 @@
+#![stable(feature = "", since = "1.30.0")]
+
+#![allow(non_camel_case_types)]
+
+//! Utilities related to FFI bindings.
+
+use ::fmt;
+
+/// Equivalent to C's `void` type when used as a [pointer].
+///
+/// In essence, `*const c_void` is equivalent to C's `const void*`
+/// and `*mut c_void` is equivalent to C's `void*`. That said, this is
+/// *not* the same as C's `void` return type, which is Rust's `()` type.
+///
+/// Ideally, this type would be equivalent to [`!`], but currently it may
+/// be more ideal to use `c_void` for FFI purposes.
+///
+/// [`!`]: ../../std/primitive.never.html
+/// [pointer]: ../../std/primitive.pointer.html
+// NB: For LLVM to recognize the void pointer type and by extension
+//     functions like malloc(), we need to have it represented as i8* in
+//     LLVM bitcode. The enum used here ensures this and prevents misuse
+//     of the "raw" type by only having private variants.. We need two
+//     variants, because the compiler complains about the repr attribute
+//     otherwise.
+#[repr(u8)]
+#[stable(feature = "raw_os", since = "1.1.0")]
+pub enum c_void {
+    #[unstable(feature = "c_void_variant", reason = "should not have to exist",
+               issue = "0")]
+    #[doc(hidden)] __variant1,
+    #[unstable(feature = "c_void_variant", reason = "should not have to exist",
+               issue = "0")]
+    #[doc(hidden)] __variant2,
+}
+
+#[stable(feature = "std_debug", since = "1.16.0")]
+impl fmt::Debug for c_void {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("c_void")
+    }
+}

src/libcore/lib.rs

@@ -202,6 +202,7 @@ pub mod iter;
 pub mod option;
 pub mod raw;
 pub mod result;
+pub mod ffi;
 
 pub mod slice;
 pub mod str;

src/libstd/ffi/mod.rs

@@ -171,5 +171,8 @@ pub use self::c_str::{FromBytesWithNulError};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::os_str::{OsString, OsStr};
 
+#[stable(feature = "raw_os", since = "1.1.0")]
+pub use core::ffi::c_void;
+
 mod c_str;
 mod os_str;

src/libstd/os/raw/mod.rs

@@ -18,8 +18,6 @@
 
 #![stable(feature = "raw_os", since = "1.1.0")]
 
-use fmt;
-
 #[doc(include = "os/raw/char.md")]
 #[cfg(any(all(target_os = "linux", any(target_arch = "aarch64",
                                        target_arch = "arm",
@@ -83,40 +81,9 @@ use fmt;
 #[doc(include = "os/raw/double.md")]
 #[stable(feature = "raw_os", since = "1.1.0")] pub type c_double = f64;
 
-/// Equivalent to C's `void` type when used as a [pointer].
-///
-/// In essence, `*const c_void` is equivalent to C's `const void*`
-/// and `*mut c_void` is equivalent to C's `void*`. That said, this is
-/// *not* the same as C's `void` return type, which is Rust's `()` type.
-///
-/// Ideally, this type would be equivalent to [`!`], but currently it may
-/// be more ideal to use `c_void` for FFI purposes.
-///
-/// [`!`]: ../../primitive.never.html
-/// [pointer]: ../../primitive.pointer.html
-// NB: For LLVM to recognize the void pointer type and by extension
-//     functions like malloc(), we need to have it represented as i8* in
-//     LLVM bitcode. The enum used here ensures this and prevents misuse
-//     of the "raw" type by only having private variants.. We need two
-//     variants, because the compiler complains about the repr attribute
-//     otherwise.
-#[repr(u8)]
 #[stable(feature = "raw_os", since = "1.1.0")]
-pub enum c_void {
-    #[unstable(feature = "c_void_variant", reason = "should not have to exist",
-               issue = "0")]
-    #[doc(hidden)] __variant1,
-    #[unstable(feature = "c_void_variant", reason = "should not have to exist",
-               issue = "0")]
-    #[doc(hidden)] __variant2,
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl fmt::Debug for c_void {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.pad("c_void")
-    }
-}
+#[doc(no_inline)]
+pub use core::ffi::c_void;
 
 #[cfg(test)]
 #[allow(unused_imports)]