make MsgHdr and MsgHdrMut repr(transparent) to allow legally obtaining libc::msghdr from those types

Author: nerodono

CHANGELOG.md

@@ -1,3 +1,10 @@
+# Unreleased
+
+## Non-breaking changes
+
+* Added `repr(transparent)` attribute to `MsgHdr` and `MsgHdrMut` to allow legally transmuting those types into corresponding libc equivalent
+  (https://github.com/rust-lang/socket2/pull/635).
+
 # 0.6.1
 
 ## Added

src/lib.rs

@@ -562,6 +562,7 @@ impl TcpKeepalive {
 /// This wraps `msghdr` on Unix and `WSAMSG` on Windows. Also see [`MsgHdrMut`]
 /// for the variant used by `recvmsg(2)`.
 #[cfg(not(target_os = "redox"))]
+#[repr(transparent)]
 pub struct MsgHdr<'addr, 'bufs, 'control> {
     inner: sys::msghdr,
     #[allow(clippy::type_complexity)]
@@ -630,6 +631,7 @@ impl<'name, 'bufs, 'control> fmt::Debug for MsgHdr<'name, 'bufs, 'control> {
 /// This wraps `msghdr` on Unix and `WSAMSG` on Windows. Also see [`MsgHdr`] for
 /// the variant used by `sendmsg(2)`.
 #[cfg(not(target_os = "redox"))]
+#[repr(transparent)]
 pub struct MsgHdrMut<'addr, 'bufs, 'control> {
     inner: sys::msghdr,
     #[allow(clippy::type_complexity)]