Implement get_await_completion_adaptor (#226)

* Implement `get_await_completion_adaptor`

* Fix CI error

* Add a workaround about `has_completions` for clang 22

---------

Co-authored-by: Dietmar Kühl <dietmar.kuehl@me.com>

Author: Cra3z

include/beman/execution/detail/as_awaitable.hpp

@@ -9,17 +9,26 @@
 import std;
 #else
 #include <coroutine>
+#include <functional>
 #include <type_traits>
 #include <utility>
 #endif
 #ifdef BEMAN_HAS_MODULES
 import beman.execution.detail.awaitable_sender;
+import beman.execution.detail.get_await_completion_adaptor;
+import beman.execution.detail.get_env;
+import beman.execution.detail.query_with_default;
 import beman.execution.detail.is_awaitable;
+import beman.execution.detail.sender;
 import beman.execution.detail.sender_awaitable;
 import beman.execution.detail.unspecified_promise;
 #else
 #include <beman/execution/detail/awaitable_sender.hpp>
+#include <beman/execution/detail/get_await_completion_adaptor.hpp>
+#include <beman/execution/detail/get_env.hpp>
+#include <beman/execution/detail/query_with_default.hpp>
 #include <beman/execution/detail/is_awaitable.hpp>
+#include <beman/execution/detail/sender.hpp>
 #include <beman/execution/detail/sender_awaitable.hpp>
 #include <beman/execution/detail/unspecified_promise.hpp>
 #endif
@@ -40,12 +49,25 @@ struct as_awaitable_t {
                                                          Promise>,
                 "as_awaitable must return an awaitable");
             return ::std::forward<Expr>(expr).as_awaitable(promise);
-        } else if constexpr (::beman::execution::detail::
-                                 is_awaitable<Expr, ::beman::execution::detail::unspecified_promise> ||
-                             !::beman::execution::detail::awaitable_sender<Expr, Promise>) {
-            return ::std::forward<Expr>(expr);
+        } else if constexpr (::beman::execution::sender<Expr> &&
+                             !::beman::execution::detail::
+                                 is_awaitable<Expr, ::beman::execution::detail::unspecified_promise>) {
+            auto adaptor =
+                ::beman::execution::detail::query_with_default(::beman::execution::get_await_completion_adaptor,
+                                                               ::beman::execution::get_env(expr),
+                                                               ::std::identity{});
+            using sender_t = ::std::invoke_result_t<decltype(adaptor), Expr>;
+            if constexpr (::beman::execution::detail::awaitable_sender<sender_t, Promise>) {
+                return ::beman::execution::detail::sender_awaitable<sender_t, Promise>{
+                    adaptor(::std::forward<Expr>(expr)), promise};
+            } else if constexpr (::beman::execution::detail::awaitable_sender<Expr, Promise>) {
+                return ::beman::execution::detail::sender_awaitable<Expr, Promise>{::std::forward<Expr>(expr),
+                                                                                   promise};
+            } else {
+                return ::std::forward<Expr>(expr);
+            }
         } else {
-            return ::beman::execution::detail::sender_awaitable<Expr, Promise>{::std::forward<Expr>(expr), promise};
+            return ::std::forward<Expr>(expr);
         }
     }
 };

include/beman/execution/detail/get_await_completion_adaptor.hpp

@@ -0,0 +1,38 @@
+// include/beman/execution/detail/get_await_completion_adaptor.hpp      -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef INCLUDED_BEMAN_EXECUTION_DETAIL_GET_AWAIT_COMPLETION_ADAPTOR
+#define INCLUDED_BEMAN_EXECUTION_DETAIL_GET_AWAIT_COMPLETION_ADAPTOR
+
+#include <beman/execution/detail/common.hpp>
+#ifdef BEMAN_HAS_IMPORT_STD
+import std;
+#else
+#include <utility>
+#endif
+#ifdef BEMAN_HAS_MODULES
+import beman.execution.detail.forwarding_query;
+#else
+#include <beman/execution/detail/forwarding_query.hpp>
+#endif
+
+// ----------------------------------------------------------------------------
+
+namespace beman::execution {
+struct get_await_completion_adaptor_t {
+    template <typename Env>
+        requires requires(Env&& env, const get_await_completion_adaptor_t& g) {
+            { ::std::as_const(env).query(g) } noexcept;
+        }
+    auto operator()(Env&& env) const noexcept {
+        return ::std::as_const(env).query(*this);
+    }
+    static constexpr auto query(const ::beman::execution::forwarding_query_t&) noexcept -> bool { return true; }
+};
+
+inline constexpr get_await_completion_adaptor_t get_await_completion_adaptor{};
+} // namespace beman::execution
+
+// ----------------------------------------------------------------------------
+
+#endif // INCLUDED_BEMAN_EXECUTION_DETAIL_GET_AWAIT_COMPLETION_ADAPTOR

src/beman/execution/CMakeLists.txt

@@ -79,6 +79,7 @@ target_sources(
                 ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/fwd_env.hpp
                 ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/gather_signatures.hpp
                 ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/get_allocator.hpp
+                ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/get_await_completion_adaptor.hpp
                 ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/get_awaiter.hpp
                 ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/get_completion_scheduler.hpp
                 ${PROJECT_SOURCE_DIR}/include/beman/execution/detail/get_completion_signatures.hpp
@@ -259,6 +260,7 @@ if(BEMAN_USE_MODULES)
                     fwd_env.cppm
                     gather_signatures.cppm
                     get_allocator.cppm
+                    get_await_completion_adaptor.cppm
                     get_awaiter.cppm
                     get_completion_scheduler.cppm
                     get_completion_signatures.cppm

src/beman/execution/get_await_completion_adaptor.cppm

@@ -0,0 +1,12 @@
+module;
+// src/beman/execution/get_await_completion_adaptor.cppm                  -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/detail/get_await_completion_adaptor.hpp>
+
+export module beman.execution.detail.get_await_completion_adaptor;
+
+namespace beman::execution {
+export using beman::execution::get_await_completion_adaptor_t;
+export using beman::execution::get_await_completion_adaptor;
+} // namespace beman::execution