From 7140b857e15849db62d6970ad4ef6f182e270639 Mon Sep 17 00:00:00 2001
From: isidorostsa <tsa.isidoros@gmail.com>
Date: Mon, 10 Jun 2024 14:23:25 -0500
Subject: [PATCH] make mpi transform sender conform to p2300

---
 .../include/hpx/async_mpi/transform_mpi.hpp   | 66 +++++++++++++++++--
 .../hpx/execution_base/stdexec_forward.hpp    |  1 +
 2 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/libs/core/async_mpi/include/hpx/async_mpi/transform_mpi.hpp b/libs/core/async_mpi/include/hpx/async_mpi/transform_mpi.hpp
index 6264c273b778..1ee16a310755 100644
--- a/libs/core/async_mpi/include/hpx/async_mpi/transform_mpi.hpp
+++ b/libs/core/async_mpi/include/hpx/async_mpi/transform_mpi.hpp
@@ -146,12 +146,68 @@ namespace hpx { namespace mpi { namespace experimental {
         template <typename Sender, typename F>
         struct transform_mpi_sender
         {
-#ifdef HPX_HAVE_STDEXEC
-            using is_sender = void;
-#endif
             HPX_NO_UNIQUE_ADDRESS std::decay_t<Sender> s;
             HPX_NO_UNIQUE_ADDRESS std::decay_t<F> f;
 
+
+#ifdef HPX_HAVE_STDEXEC
+            using is_sender = void;
+
+            template <typename... Args>
+            struct invoke_function_transformation_helper
+            {
+                template <bool IsVoid, typename T>
+                struct set_value_void_checked
+                {
+                    using type = hpx::execution::experimental::set_value_t(T);
+                };
+
+                template <typename T>
+                struct set_value_void_checked<true, T>
+                {
+                    using type = hpx::execution::experimental::set_value_t();
+                };
+
+                static_assert(hpx::is_invocable_v<F, Args..., MPI_Request*>,
+                    "F not invocable with the value_types specified.");
+
+                using result_type =
+                    hpx::util::invoke_result_t<F, Args..., MPI_Request*>;
+                using set_value_result_type =
+                    typename set_value_void_checked<std::is_void_v<result_type>,
+                        result_type>::type;
+                using type =
+                    hpx::execution::experimental::completion_signatures<
+                        set_value_result_type>;
+            };
+
+            template <typename... Args>
+            using invoke_function_transformation =
+                invoke_function_transformation_helper<Args...>::type;
+
+            template <typename Err>
+            using default_set_error =
+                hpx::execution::experimental::completion_signatures<
+                    hpx::execution::experimental::set_error_t(Err)>;
+
+            using no_set_stopped_signature =
+                hpx::execution::experimental::completion_signatures<>;
+
+            // clang-format off
+            template <typename Env>
+            friend auto tag_invoke(
+                hpx::execution::experimental::get_completion_signatures_t,
+                transform_mpi_sender const&, Env const&)
+            -> hpx::execution::experimental::transform_completion_signatures_of<
+                Sender, Env,
+                hpx::execution::experimental::completion_signatures<
+                    hpx::execution::experimental::set_error_t(std::exception_ptr)
+                >,
+                invoke_function_transformation,
+                default_set_error,
+                no_set_stopped_signature
+            >{};
+#else
             template <typename Env>
             struct generate_completion_signatures
             {
@@ -192,7 +248,9 @@ namespace hpx { namespace mpi { namespace experimental {
             friend auto tag_invoke(
                 hpx::execution::experimental::get_completion_signatures_t,
                 transform_mpi_sender const&, Env)
-                -> generate_completion_signatures<Env>;
+            -> generate_completion_signatures<Env>;
+            // clang-format on
+#endif
 
             template <typename R>
             friend constexpr auto tag_invoke(
diff --git a/libs/core/execution_base/include/hpx/execution_base/stdexec_forward.hpp b/libs/core/execution_base/include/hpx/execution_base/stdexec_forward.hpp
index a596c756fe0d..314b0e9c298c 100644
--- a/libs/core/execution_base/include/hpx/execution_base/stdexec_forward.hpp
+++ b/libs/core/execution_base/include/hpx/execution_base/stdexec_forward.hpp
@@ -211,6 +211,7 @@ namespace hpx::execution::experimental {
 
     using stdexec::make_completion_signatures;
     using stdexec::transform_completion_signatures_of;
+    using stdexec::transform_completion_signatures;
 
     // Transform sender
     using stdexec::transform_env;