Make EventLoopFuture/Promise conditionally Sendable

and `.get()` only available if `Value` is `Sendable`.
Also fix warnings because of that change.

Sources/NIOAsyncAwaitDemo/AsyncChannelIO.swift

@@ -17,7 +17,7 @@ import NIOHTTP1
 
 #if canImport(_Concurrency) && compiler(>=5.5.2)
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
-struct AsyncChannelIO<Request, Response> {
+struct AsyncChannelIO<Request: Sendable, Response: Sendable> {
     let channel: Channel
 
     init(_ channel: Channel) {

Sources/NIOAsyncAwaitDemo/main.swift

@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 import NIOCore
 import NIOPosix
-import NIOHTTP1
+@preconcurrency import NIOHTTP1
 import Dispatch
 
 #if canImport(_Concurrency) && compiler(>=5.5.2)

Sources/NIOCore/AsyncAwaitSupport+OldXcodes.swift

@@ -14,7 +14,7 @@
 
 #if compiler(>=5.5) && !compiler(>=5.5.2) && canImport(_Concurrency) 
 
-extension EventLoopFuture {
+extension EventLoopFuture where Value: Sendable {
     /// Get the value/error from an `EventLoopFuture` in an `async` context.
     ///
     /// This function can be used to bridge an `EventLoopFuture` into the `async` world. Ie. if you're in an `async`

Sources/NIOCore/AsyncAwaitSupport.swift

@@ -14,7 +14,7 @@
 
 #if compiler(>=5.5.2) && canImport(_Concurrency)
 
-extension EventLoopFuture {
+extension EventLoopFuture where Value: Sendable {
     /// Get the value/error from an `EventLoopFuture` in an `async` context.
     ///
     /// This function can be used to bridge an `EventLoopFuture` into the `async` world. Ie. if you're in an `async`
@@ -98,7 +98,7 @@ extension Channel {
     /// Get the value of `option` for this `Channel`.
     @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
     @inlinable
-    public func getOption<Option: ChannelOption>(_ option: Option) async throws -> Option.Value {
+    public func getOption<Option: ChannelOption>(_ option: Option) async throws -> Option.Value where Option.Value: Sendable {
         return try await self.getOption(option).get()
     }
 }
@@ -187,20 +187,20 @@ extension ChannelPipeline {
     @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
     @available(*, deprecated, message: "ChannelHandlerContext is not Sendable and it is therefore not safe to be used outside of its EventLoop")
     public func context(handler: ChannelHandler) async throws -> ChannelHandlerContext {
-        return try await self.context(handler: handler).get()
+        return try await self.context(handler: handler).map(UncheckedSendable.init(_:)).get().value
     }
 
     @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
     @available(*, deprecated, message: "ChannelHandlerContext is not Sendable and it is therefore not safe to be used outside of its EventLoop")
     public func context(name: String) async throws -> ChannelHandlerContext {
-        return try await self.context(name: name).get()
+        return try await self.context(name: name).map(UncheckedSendable.init(_:)).get().value
     }
 
     @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
     @available(*, deprecated, message: "ChannelHandlerContext is not Sendable and it is therefore not safe to be used outside of its EventLoop")
     @inlinable
     public func context<Handler: ChannelHandler>(handlerType: Handler.Type) async throws -> ChannelHandlerContext {
-        return try await self.context(handlerType: handlerType).get()
+        return try await self.context(handlerType: handlerType).map(UncheckedSendable.init(_:)).get().value
     }
 
     @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)

Sources/NIOCore/EventLoopFuture.swift

@@ -1569,14 +1569,13 @@ public struct _NIOEventLoopFutureIdentifier: Hashable {
     }
 }
 
-// EventLoopPromise is a reference type, but by its very nature is Sendable.
-extension EventLoopPromise: NIOSendable { }
-
 #if swift(>=5.5) && canImport(_Concurrency)
+// EventLoopPromise is a reference type, but by its very nature is Sendable.
+extension EventLoopPromise: @unchecked Sendable where Value: Sendable { }
 
 // EventLoopFuture is a reference type, but it is Sendable. However, we enforce
 // that by way of the guarantees of the EventLoop protocol, so the compiler cannot
 // check it.
-extension EventLoopFuture: @unchecked NIOSendable { }
+extension EventLoopFuture: @unchecked Sendable where Value: Sendable { }
 
 #endif

Sources/NIOCore/NIOSendable.swift

@@ -23,3 +23,15 @@ public typealias NIOSendable = Any
 #else
 public protocol NIOPreconcurrencySendable {}
 #endif
+
+#if swift(>=5.5) && canImport(_Concurrency)
+@usableFromInline
+internal struct UncheckedSendable<Value>: @unchecked Sendable {
+    @usableFromInline
+    var value: Value
+    @inlinable
+    init(_ value: Value) {
+        self.value = value
+    }
+}
+#endif