From affc47d86bcf7cd0035dd52a07180deed6fefc86 Mon Sep 17 00:00:00 2001
From: John Biddiscombe <biddisco@cscs.ch>
Date: Mon, 11 Nov 2024 16:25:56 +0100
Subject: [PATCH] Allow move only objects to be used (and kept alive) in
 transform_mpi

Add test for move only transform_mpi
---
 .../include/pika/async_mpi/transform_mpi.hpp          | 10 +++++++---
 .../async_mpi/tests/unit/algorithm_transform_mpi.cpp  | 11 +++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/libs/pika/async_mpi/include/pika/async_mpi/transform_mpi.hpp b/libs/pika/async_mpi/include/pika/async_mpi/transform_mpi.hpp
index fcea93afb..1c02b0fd8 100644
--- a/libs/pika/async_mpi/include/pika/async_mpi/transform_mpi.hpp
+++ b/libs/pika/async_mpi/include/pika/async_mpi/transform_mpi.hpp
@@ -20,6 +20,7 @@
 #include <pika/execution/algorithms/detail/partial_algorithm.hpp>
 #include <pika/execution/algorithms/just.hpp>
 #include <pika/execution/algorithms/let_value.hpp>
+#include <pika/execution/algorithms/unpack.hpp>
 #include <pika/execution_base/any_sender.hpp>
 #include <pika/execution_base/receiver.hpp>
 #include <pika/execution_base/sender.hpp>
@@ -52,6 +53,7 @@ namespace pika::mpi::experimental {
             using pika::execution::experimental::just;
             using pika::execution::experimental::let_value;
             using pika::execution::experimental::unique_any_sender;
+            using pika::execution::experimental::unpack;
 
             // get mpi completion mode settings
             auto mode = get_completion_mode();
@@ -79,8 +81,9 @@ namespace pika::mpi::experimental {
             if (requests_inline)
             {
                 return std::forward<Sender>(sender) |
-                    let_value([=, f = std::forward<F>(f)](auto&... args) mutable {
-                        auto snd0 = just(args...);
+                    let_value([=, f = std::forward<F>(f)](auto&&... args) mutable {
+                        std::tuple<decltype(args)&...> ts{args...};
+                        auto snd0 = just(ts) | ex::unpack();
                         return dispatch_mpi_sender<decltype(snd0), F>{
                                    std::move(snd0), std::move(f)} |
                             let_value(completion_snd);
@@ -90,7 +93,8 @@ namespace pika::mpi::experimental {
             {
                 return std::forward<Sender>(sender) | continues_on(mpi_pool_scheduler(p)) |
                     let_value([=, f = std::forward<F>(f)](auto&... args) mutable {
-                        auto snd0 = just(args...);
+                        std::tuple<decltype(args)&...> ts{args...};
+                        auto snd0 = just(ts) | ex::unpack();
                         return dispatch_mpi_sender<decltype(snd0), F>{
                                    std::move(snd0), std::move(f)} |
                             let_value(completion_snd);
diff --git a/libs/pika/async_mpi/tests/unit/algorithm_transform_mpi.cpp b/libs/pika/async_mpi/tests/unit/algorithm_transform_mpi.cpp
index 3b030dbaf..c79684f39 100644
--- a/libs/pika/async_mpi/tests/unit/algorithm_transform_mpi.cpp
+++ b/libs/pika/async_mpi/tests/unit/algorithm_transform_mpi.cpp
@@ -212,6 +212,17 @@ int pika_main()
                 tt::sync_wait(PIKA_MOVE(s));
             }
 
+            {
+                auto s = ex::just(custom_type_non_default_constructible_non_copyable{42}, datatype,
+                             0, comm) |
+                    ex::drop_operation_state() |
+                    mpi::transform_mpi([](auto& data, MPI_Datatype datatype, int i, MPI_Comm comm,
+                                           MPI_Request* request) {
+                        MPI_Ibcast(&data, 1, datatype, i, comm, request);
+                    });
+                tt::sync_wait(PIKA_MOVE(s));
+            }
+
             // transform_mpi should be able to handle reference types (by copying
             // them to the operation state)
             {