Bump minimum Swift version to 6.0 (#216)

## Motivation

Now that Swift 6.2 has been released, we should drop support for 5.10,
in line with our three version support window.

## Modifications

- Bump minimum tools version in package manifest
- Update README with minimum Swift version for each version range
- Remove compiler settings in package manifest that are subsumed by
Swift 6 language mode
- Add `public typealias _NIOSSHSendableMetatype`, which resolves to
`Swift.SendableMetatype` for Swift >= 6.2, and `Any` on < 6.2
- Have public protocols refine `SendableMetatype` on Swift >= 6.2, using
`_NIOSSHSendableMetatype`

## Result

Package now requires Swift >= 6.0.

---------

Co-authored-by: Cory Benfield <[email protected]>

Author: simonjbeaumont

.github/workflows/pull_request.yml

@@ -17,12 +17,11 @@ jobs:
         name: Unit tests
         uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
         with:
-            linux_5_10_arguments_override: "--explicit-target-dependency-import-check error"
-            linux_6_0_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
-            linux_6_1_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
-            linux_6_2_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
-            linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error"
-            linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error"
+            linux_6_0_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable -Xswiftc -warnings-as-errors"
+            linux_6_1_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable -Xswiftc -warnings-as-errors"
+            linux_6_2_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable -Xswiftc -warnings-as-errors"
+            linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
+            linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
 
     benchmarks:
         name: Benchmarks

Benchmarks/Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.10
+// swift-tools-version:6.0
 
 import PackageDescription
 

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.10
+// swift-tools-version:6.0
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the SwiftNIO open source project
@@ -17,21 +17,13 @@ import PackageDescription
 
 let strictConcurrencyDevelopment = false
 
-let strictConcurrencySettings: [SwiftSetting] = {
-    var initialSettings: [SwiftSetting] = []
-    initialSettings.append(contentsOf: [
-        .enableUpcomingFeature("StrictConcurrency"),
-        .enableUpcomingFeature("InferSendableFromCaptures"),
-    ])
+var swiftSettings: [SwiftSetting] = []
 
-    if strictConcurrencyDevelopment {
-        // -warnings-as-errors here is a workaround so that IDE-based development can
-        // get tripped up on -require-explicit-sendable.
-        initialSettings.append(.unsafeFlags(["-Xfrontend", "-require-explicit-sendable", "-warnings-as-errors"]))
-    }
-
-    return initialSettings
-}()
+if strictConcurrencyDevelopment {
+    // -warnings-as-errors here is a workaround so that IDE-based development can
+    // get tripped up on -require-explicit-sendable.
+    swiftSettings.append(.unsafeFlags(["-Xfrontend", "-require-explicit-sendable", "-warnings-as-errors"]))
+}
 
 let package = Package(
     name: "swift-nio-ssh",
@@ -59,7 +51,7 @@ let package = Package(
                 .product(name: "Crypto", package: "swift-crypto"),
                 .product(name: "Atomics", package: "swift-atomics"),
             ],
-            swiftSettings: strictConcurrencySettings
+            swiftSettings: swiftSettings
         ),
         .executableTarget(
             name: "NIOSSHClient",
@@ -69,7 +61,7 @@ let package = Package(
                 .product(name: "NIOPosix", package: "swift-nio"),
                 .product(name: "NIOConcurrencyHelpers", package: "swift-nio"),
             ],
-            swiftSettings: strictConcurrencySettings
+            swiftSettings: swiftSettings
         ),
         .executableTarget(
             name: "NIOSSHServer",
@@ -80,7 +72,7 @@ let package = Package(
                 .product(name: "NIOFoundationCompat", package: "swift-nio"),
                 .product(name: "Crypto", package: "swift-crypto"),
             ],
-            swiftSettings: strictConcurrencySettings
+            swiftSettings: swiftSettings
         ),
         .executableTarget(
             name: "NIOSSHPerformanceTester",
@@ -90,7 +82,7 @@ let package = Package(
                 .product(name: "NIOEmbedded", package: "swift-nio"),
                 .product(name: "Crypto", package: "swift-crypto"),
             ],
-            swiftSettings: strictConcurrencySettings
+            swiftSettings: swiftSettings
         ),
         .testTarget(
             name: "NIOSSHTests",
@@ -100,7 +92,7 @@ let package = Package(
                 .product(name: "NIOEmbedded", package: "swift-nio"),
                 .product(name: "NIOFoundationCompat", package: "swift-nio"),
             ],
-            swiftSettings: strictConcurrencySettings
+            swiftSettings: swiftSettings
         ),
     ]
 )

README.md

@@ -21,7 +21,8 @@ SwiftNIO SSH        | Minimum Swift Version
 `0.6.2  ..< 0.9.0`  | 5.6
 `0.9.0  ..< 0.9.2`  | 5.8
 `0.9.2  ..< 0.10.0` | 5.9
-`0.10.0 ...`        | 5.10
+`0.10.0 ... 0.12.0` | 5.10
+`0.12.0 ...`        | 6.0
 
 ## What does SwiftNIO SSH support?
 

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/Constants.swift

@@ -15,7 +15,8 @@
 public enum Constants: Sendable {
     static let version = "SSH-2.0-SwiftNIOSSH_1.0"
 
-    public static let bundledTransportProtectionSchemes: [NIOSSHTransportProtection.Type] = [
-        AES256GCMOpenSSHTransportProtection.self, AES128GCMOpenSSHTransportProtection.self,
-    ]
+    public static let bundledTransportProtectionSchemes: [(NIOSSHTransportProtection & _NIOSSHSendableMetatype).Type] =
+        [
+            AES256GCMOpenSSHTransportProtection.self, AES128GCMOpenSSHTransportProtection.self,
+        ]
 }

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/AESGCM.swift

@@ -162,7 +162,7 @@ extension AESGCMTransportProtection: NIOSSHTransportProtection {
 /// algorithm, and instead by ignoring the result of the MAC negotiation.
 ///
 /// This algorithm does not encrypt the length field, instead encoding it as associated data.
-final class AES128GCMOpenSSHTransportProtection: AESGCMTransportProtection {
+final class AES128GCMOpenSSHTransportProtection: AESGCMTransportProtection, _NIOSSHSendableMetatype {
     override static var cipherName: String {
         "[email protected]"
     }
@@ -182,7 +182,7 @@ final class AES128GCMOpenSSHTransportProtection: AESGCMTransportProtection {
 /// algorithm, and instead by ignoring the result of the MAC negotiation.
 ///
 /// This algorithm does not encrypt the length field, instead encoding it as associated data.
-final class AES256GCMOpenSSHTransportProtection: AESGCMTransportProtection {
+final class AES256GCMOpenSSHTransportProtection: AESGCMTransportProtection, _NIOSSHSendableMetatype {
     override static var cipherName: String {
         "[email protected]"
     }

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