implement Send and Sync for raw connection handle on Windows

crates/prettytty/src/conn.rs

@@ -81,9 +81,9 @@ pub struct Connection {
     connection: RawConnection,
 }
 
-fn _assert_connection_is_sync_send() {
-    fn is_sync_send<T: Sync + Send>() {}
-    is_sync_send::<Connection>();
+fn _assert_connection_is_send_sync() {
+    fn is_send_sync<T: Send + Sync>() {}
+    is_send_sync::<Connection>();
 }
 
 impl Connection {

crates/prettytty/src/sys/windows.rs

@@ -43,6 +43,13 @@ impl RawConnectionHandle {
     }
 }
 
+// SAFETY: Windows HANDLE is defined as a *mut c_void but most instances are
+// thread-safe. In fact, Rust's standard library [implements `Send` and
+// `Sync`](https://github.com/rust-lang/rust/blob/8e37e151835d96d6a7415e93e6876561485a3354/library/std/src/os/windows/io/handle.rs#L111),
+// for wrapped handles, too. Also, access to raw input is gated by a mutex.
+impl Send for RawConnectionHandle {}
+impl Sync for RawConnectionHandle {}
+
 /// A connection to a terminal device.
 #[derive(Debug)]
 pub(crate) struct RawConnection {