tokio-xmpp: Error out when both tls-native and tls-rust features are enabled

If the user enables the tls-rust feature and forgets to disable
default-features (which includes tls-native), tell them and bail out.

The code was made to work anyway when both are enabled, and here it
defaults to tls-native. It does seem better to have one explicitely
choose one though hence the compile_error! message.

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

tokio-xmpp/src/starttls.rs

@@ -1,6 +1,6 @@
 use futures::{sink::SinkExt, stream::StreamExt};
 
-#[cfg(feature = "tls-rust")]
+#[cfg(all(feature = "tls-rust", not(feature = "tls-native")))]
 use {
     std::convert::TryFrom,
     std::sync::Arc,
@@ -37,7 +37,7 @@ async fn get_tls_stream<S: AsyncRead + AsyncWrite + Unpin>(
     Ok(tls_stream)
 }
 
-#[cfg(feature = "tls-rust")]
+#[cfg(all(feature = "tls-rust", not(feature = "tls-native")))]
 async fn get_tls_stream<S: AsyncRead + AsyncWrite + Unpin>(
     xmpp_stream: XMPPStream<S>,
 ) -> Result<TlsStream<S>, Error> {