Have public protocols refine SendableMetatype on Swift >= 6.2

Author: simonjbeaumont

Sources/NIOSSH/Connection State Machine/Operations/AcceptsUserAuthMessages.swift

@@ -14,7 +14,7 @@
 
 import NIOCore
 
-protocol AcceptsUserAuthMessages {
+protocol AcceptsUserAuthMessages: _NIOSSHSendableMetatype {
     var userAuthStateMachine: UserAuthenticationStateMachine { get set }
 
     var role: SSHConnectionRole { get }

Sources/NIOSSH/Key Exchange/EllipticCurveKeyExchange.swift

@@ -24,7 +24,7 @@ import Foundation
 
 /// This protocol defines a container used by the key exchange state machine to manage key exchange.
 /// This type erases the specific key exchanger.
-protocol EllipticCurveKeyExchangeProtocol {
+protocol EllipticCurveKeyExchangeProtocol: _NIOSSHSendableMetatype {
     init(ourRole: SSHConnectionRole, previousSessionIdentifier: ByteBuffer?)
 
     func initiateKeyExchangeClientSide(allocator: ByteBufferAllocator) -> SSHMessage.KeyExchangeECDHInitMessage

Sources/NIOSSH/TransportProtection/SSHTransportProtection.swift

@@ -44,7 +44,7 @@ import NIOCore
 /// Implementers of this protocol **must not** expose unauthenticated plaintext, except for the length field. This
 /// is required by the SSH protocol, and swift-nio-ssh does its best to treat the length field as fundamentally
 /// untrusted information.
-public protocol NIOSSHTransportProtection: AnyObject {
+public protocol NIOSSHTransportProtection: AnyObject, _NIOSSHSendableMetatype {
     /// The name of the cipher portion of this transport protection scheme as negotiated on the wire.
     static var cipherName: String { get }
 

Sources/NIOSSH/_NIOSSHSendableMetatype.swift

@@ -0,0 +1,19 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2019-2020 Apple Inc. and the SwiftNIO project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+#if compiler(>=6.2)
+public typealias _NIOSSHSendableMetatype = SendableMetatype
+#else
+public typealias _NIOSSHSendableMetatype = Any
+#endif