[Concurrency/Runtime] Implement function/continuation type generation for AsyncSignature

`AsyncFunctionTypeImpl` has its `type` defaulted to `TaskContinuationFunction`
which is incorrect because it has to append arguments, result type and account
for throws bit.

These changes expand `AsyncSignature` with `ContinuationType` and expand `FunctionType`
to include all of the appropriate information.

include/swift/ABI/Executor.h

@@ -149,6 +149,8 @@ template <class AsyncSignature>
 class AsyncFunctionPointer;
 template <class AsyncSignature>
 struct AsyncFunctionTypeImpl;
+template <class AsyncSignature>
+struct AsyncContinuationTypeImpl;
 
 /// The abstract signature for an asynchronous function.
 template <class Sig, bool HasErrorResult>
@@ -163,6 +165,7 @@ struct AsyncSignature<DirectResultTy(ArgTys...), HasErrorResult> {
 
   using FunctionPointer = AsyncFunctionPointer<AsyncSignature>;
   using FunctionType = typename AsyncFunctionTypeImpl<AsyncSignature>::type;
+  using ContinuationType = typename AsyncContinuationTypeImpl<AsyncSignature>::type;
 };
 
 /// A signature for a thin async function that takes no arguments
@@ -175,30 +178,58 @@ using ThinNullaryAsyncSignature =
 using ThickNullaryAsyncSignature =
   AsyncSignature<void(HeapObject*), false>;
 
-/// A class which can be used to statically query whether a type
-/// is a specialization of AsyncSignature.
-template <class T>
-struct IsAsyncSignature {
-  static const bool value = false;
-};
+template <class Signature>
+struct AsyncFunctionTypeImpl;
+
 template <class DirectResultTy, class... ArgTys, bool HasErrorResult>
-struct IsAsyncSignature<AsyncSignature<DirectResultTy(ArgTys...),
-                                       HasErrorResult>> {
-  static const bool value = true;
+struct AsyncFunctionTypeImpl<
+    AsyncSignature<DirectResultTy(ArgTys...), HasErrorResult>> {
+
+  using type = SWIFT_CC(swiftasync) void(SWIFT_ASYNC_CONTEXT AsyncContext *,
+                                         ArgTys...);
 };
 
 template <class Signature>
-struct AsyncFunctionTypeImpl {
-  static_assert(IsAsyncSignature<Signature>::value,
-                "template argument is not an AsyncSignature");
+struct AsyncContinuationTypeImpl;
 
-  // TODO: expand and include the arguments in the parameters.
-  using type = TaskContinuationFunction;
+template <class DirectResultTy, class... ArgTys>
+struct AsyncContinuationTypeImpl<
+  AsyncSignature<DirectResultTy(ArgTys...), /*throws=*/true>> {
+
+  using type = SWIFT_CC(swiftasync) void(SWIFT_ASYNC_CONTEXT AsyncContext *,
+                                         DirectResultTy,
+                                         SWIFT_CONTEXT void *);
+};
+
+template <class DirectResultTy, class... ArgTys>
+struct AsyncContinuationTypeImpl<
+  AsyncSignature<DirectResultTy(ArgTys...), /*throws=*/false>> {
+
+  using type = SWIFT_CC(swiftasync) void(SWIFT_ASYNC_CONTEXT AsyncContext *,
+                                         DirectResultTy);
+};
+
+template <class... ArgTys>
+struct AsyncContinuationTypeImpl<
+  AsyncSignature<void(ArgTys...), /*throws=*/true>> {
+
+  using type = SWIFT_CC(swiftasync) void(SWIFT_ASYNC_CONTEXT AsyncContext *,
+                                         SWIFT_CONTEXT void *);
+};
+
+template <class... ArgTys>
+struct AsyncContinuationTypeImpl<
+  AsyncSignature<void(ArgTys...), /*throws=*/false>> {
+
+  using type = SWIFT_CC(swiftasync) void(SWIFT_ASYNC_CONTEXT AsyncContext *);
 };
 
 template <class Fn>
 using AsyncFunctionType = typename AsyncFunctionTypeImpl<Fn>::type;
 
+template <class Fn>
+using AsyncContinuationType = typename AsyncContinuationTypeImpl<Fn>::type;
+
 /// A "function pointer" for an async function.
 ///
 /// Eventually, this will always be signed with the data key

include/swift/Runtime/Concurrency.h

@@ -71,7 +71,7 @@ AsyncTaskAndContext swift_task_create_common(
     size_t taskCreateFlags,
     TaskOptionRecord *options,
     const Metadata *futureResultType,
-    FutureAsyncSignature::FunctionType *function, void *closureContext,
+    TaskContinuationFunction *function, void *closureContext,
     size_t initialContextSize);
 
 /// Allocate memory in a task.

stdlib/public/CompatibilityOverride/CompatibilityOverrideConcurrency.def

@@ -97,7 +97,7 @@ OVERRIDE_TASK(task_create_common, AsyncTaskAndContext,
               (size_t taskCreateFlags,
                TaskOptionRecord *options,
                const Metadata *futureResultType,
-               FutureAsyncSignature::FunctionType *function,
+               TaskContinuationFunction *function,
                void *closureContext,
                size_t initialContextSize),
               (taskCreateFlags, options, futureResultType, function,

stdlib/public/Concurrency/Task.cpp

@@ -432,7 +432,7 @@ static AsyncTaskAndContext swift_task_create_commonImpl(
     size_t rawTaskCreateFlags,
     TaskOptionRecord *options,
     const Metadata *futureResultType,
-    FutureAsyncSignature::FunctionType *function, void *closureContext,
+    TaskContinuationFunction *function, void *closureContext,
     size_t initialContextSize) {
   TaskCreateFlags taskCreateFlags(rawTaskCreateFlags);
 
@@ -745,7 +745,8 @@ AsyncTaskAndContext swift::swift_task_create(
     >(closureEntry, closureContext);
 
   return swift_task_create_common(
-      taskCreateFlags, options, futureResultType, taskEntry, closureContext,
+      taskCreateFlags, options, futureResultType,
+      reinterpret_cast<TaskContinuationFunction *>(taskEntry), closureContext,
       initialContextSize);
 }