Add missing 'Sendable' conformance

Motivation:

Sendable conformance was missing in a handful of places which generates
warnings in newer toolchains.

Modifications:

- Make client calls Sendable
- Client call wrappers should require Sendable types (this was
  implicitly enfored by calls requiring request and response types to be
  Sendable). This also requires the async sequence of requests to be
  Sendable for calls where requests are streamed which required a
  codegen change.
- Make the various gRPC async sequence types conditionally Sendable

Result:

Fewer warnings

Sources/Examples/Echo/Model/echo.grpc.swift

@@ -316,7 +316,7 @@ extension Echo_EchoAsyncClientProtocol {
   public func collect<RequestStream>(
     _ requests: RequestStream,
     callOptions: CallOptions? = nil
-  ) async throws -> Echo_EchoResponse where RequestStream: AsyncSequence, RequestStream.Element == Echo_EchoRequest {
+  ) async throws -> Echo_EchoResponse where RequestStream: AsyncSequence & Sendable, RequestStream.Element == Echo_EchoRequest {
     return try await self.performAsyncClientStreamingCall(
       path: Echo_EchoClientMetadata.Methods.collect.path,
       requests: requests,
@@ -340,7 +340,7 @@ extension Echo_EchoAsyncClientProtocol {
   public func update<RequestStream>(
     _ requests: RequestStream,
     callOptions: CallOptions? = nil
-  ) -> GRPCAsyncResponseStream<Echo_EchoResponse> where RequestStream: AsyncSequence, RequestStream.Element == Echo_EchoRequest {
+  ) -> GRPCAsyncResponseStream<Echo_EchoResponse> where RequestStream: AsyncSequence & Sendable, RequestStream.Element == Echo_EchoRequest {
     return self.performAsyncBidirectionalStreamingCall(
       path: Echo_EchoClientMetadata.Methods.update.path,
       requests: requests,

Sources/Examples/RouteGuide/Model/route_guide.grpc.swift

@@ -335,7 +335,7 @@ extension Routeguide_RouteGuideAsyncClientProtocol {
   public func recordRoute<RequestStream>(
     _ requests: RequestStream,
     callOptions: CallOptions? = nil
-  ) async throws -> Routeguide_RouteSummary where RequestStream: AsyncSequence, RequestStream.Element == Routeguide_Point {
+  ) async throws -> Routeguide_RouteSummary where RequestStream: AsyncSequence & Sendable, RequestStream.Element == Routeguide_Point {
     return try await self.performAsyncClientStreamingCall(
       path: Routeguide_RouteGuideClientMetadata.Methods.recordRoute.path,
       requests: requests,
@@ -359,7 +359,7 @@ extension Routeguide_RouteGuideAsyncClientProtocol {
   public func routeChat<RequestStream>(
     _ requests: RequestStream,
     callOptions: CallOptions? = nil
-  ) -> GRPCAsyncResponseStream<Routeguide_RouteNote> where RequestStream: AsyncSequence, RequestStream.Element == Routeguide_RouteNote {
+  ) -> GRPCAsyncResponseStream<Routeguide_RouteNote> where RequestStream: AsyncSequence & Sendable, RequestStream.Element == Routeguide_RouteNote {
     return self.performAsyncBidirectionalStreamingCall(
       path: Routeguide_RouteGuideClientMetadata.Methods.routeChat.path,
       requests: requests,

Sources/GRPC/AsyncAwaitSupport/AsyncWriter.swift

@@ -57,7 +57,7 @@ internal final actor AsyncWriter<Delegate: AsyncWriterDelegate>: Sendable {
   typealias PendingEnd = _Pending<End>
 
   @usableFromInline
-  internal enum _CompletionState {
+  internal enum _CompletionState: Sendable {
     /// Finish hasn't been called yet. May move to `pending` or `completed`.
     case incomplete
     /// Finish has been called but the writer is paused. May move to `completed`.

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncBidirectionalStreamingCall.swift

@@ -19,7 +19,7 @@ import NIOHPACK
 
 /// Async-await variant of BidirectionalStreamingCall.
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
-public struct GRPCAsyncBidirectionalStreamingCall<Request: Sendable, Response: Sendable> {
+public struct GRPCAsyncBidirectionalStreamingCall<Request: Sendable, Response: Sendable>: Sendable {
   private let call: Call<Request, Response>
   private let responseParts: StreamingResponseParts<Response>
   private let responseSource: PassthroughMessageSource<Response, Error>

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncClientStreamingCall.swift

@@ -19,7 +19,7 @@ import NIOHPACK
 
 /// Async-await variant of `ClientStreamingCall`.
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
-public struct GRPCAsyncClientStreamingCall<Request: Sendable, Response: Sendable> {
+public struct GRPCAsyncClientStreamingCall<Request: Sendable, Response: Sendable>: Sendable {
   private let call: Call<Request, Response>
   private let responseParts: UnaryResponseParts<Response>
 

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncRequestStream.swift

@@ -52,4 +52,9 @@ public struct GRPCAsyncRequestStream<Element: Sendable>: AsyncSequence {
   }
 }
 
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension GRPCAsyncRequestStream: Sendable where Element: Sendable {}
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension GRPCAsyncRequestStream.Iterator: Sendable where Element: Sendable {}
+
 #endif

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncRequestStreamWriter.swift

@@ -31,7 +31,7 @@
 /// try await stream.finish()
 /// ```
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
-public struct GRPCAsyncRequestStreamWriter<Request: Sendable> {
+public struct GRPCAsyncRequestStreamWriter<Request: Sendable>: Sendable {
   @usableFromInline
   internal let asyncWriter: AsyncWriter<Delegate<Request>>
 

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncResponseStream.swift

@@ -49,4 +49,9 @@ public struct GRPCAsyncResponseStream<Element>: AsyncSequence {
   }
 }
 
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension GRPCAsyncResponseStream: Sendable where Element: Sendable {}
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension GRPCAsyncResponseStream.Iterator: Sendable where Element: Sendable {}
+
 #endif

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncResponseStreamWriter.swift

@@ -18,7 +18,7 @@
 
 /// Writer for server-streaming RPC handlers to provide responses.
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
-public struct GRPCAsyncResponseStreamWriter<Response: Sendable> {
+public struct GRPCAsyncResponseStreamWriter<Response: Sendable>: Sendable {
   @usableFromInline
   internal typealias Element = (Response, Compression)
 

Sources/GRPC/AsyncAwaitSupport/GRPCAsyncUnaryCall.swift

@@ -22,7 +22,7 @@ import NIOHPACK
 /// Note: while this object is a `struct`, its implementation delegates to `Call`. It therefore
 /// has reference semantics.
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
-public struct GRPCAsyncUnaryCall<Request: Sendable, Response: Sendable> {
+public struct GRPCAsyncUnaryCall<Request: Sendable, Response: Sendable>: Sendable {
   private let call: Call<Request, Response>
   private let responseParts: UnaryResponseParts<Response>