factor out common parts of the then/upon_ algorithms

include/nvexec/stream/then.cuh

@@ -176,7 +176,7 @@ namespace nv::execution::_strm
     {
       return exec::transform_completion_signatures(
         STDEXEC::get_completion_signatures<__copy_cvref_t<Self, Sender>, Env...>(),
-        STDEXEC::__transform_upon_completion<Fun, then_t>(),
+        STDEXEC::__upon::__transform_completion<Fun, then_t>(),
         {},
         {},
         _cuda_error_completion_t());

include/nvexec/stream/upon_error.cuh

@@ -178,7 +178,7 @@ namespace nv::execution::_strm
       return exec::transform_completion_signatures(
         STDEXEC::get_completion_signatures<__copy_cvref_t<Self, Sender>, Env...>(),
         {},
-        STDEXEC::__transform_upon_completion<Fun, upon_error_t>(),
+        STDEXEC::__upon::__transform_completion<Fun, upon_error_t>(),
         {},
         _cuda_error_completion_t());
     }

include/nvexec/stream/upon_stopped.cuh

@@ -167,7 +167,7 @@ namespace nv::execution::_strm
         STDEXEC::get_completion_signatures<__copy_cvref_t<Self, Sender>, Env...>(),
         {},
         {},
-        STDEXEC::__transform_upon_completion<Fun, STDEXEC::upon_stopped_t>(),
+        STDEXEC::__upon::__transform_completion<Fun, STDEXEC::upon_stopped_t>(),
         _cuda_error_completion_t());
     }
 

include/stdexec/__detail/__then.hpp

@@ -26,13 +26,13 @@ import stdexec;
 #  include "__execution_fwd.hpp"
 
 #  include "__basic_sender.hpp"
-#  include "__completion_signatures_of.hpp"
-#  include "__diagnostics.hpp"
 #  include "__meta.hpp"
 #  include "__queries.hpp"
 #  include "__sender_adaptor_closure.hpp"
+#  include "__sender_introspection.hpp"
 #  include "__senders.hpp"
 #  include "__transform_completion_signatures.hpp"
+#  include "__upon.hpp"
 
 #  include "__prologue.hpp"
 
@@ -43,7 +43,7 @@ namespace STDEXEC
   // [exec.then]
   namespace __then
   {
-    struct __then_impl : __sexpr_defaults
+    struct __impl : __sexpr_defaults
     {
       static constexpr auto __get_attrs =
         []<class _Child>(__ignore, __ignore, _Child const & __child) noexcept
@@ -58,29 +58,10 @@ namespace STDEXEC
         using __fn_t = __decay_t<__data_of<_Sender>>;
         return STDEXEC::__transform_completion_signatures(
           STDEXEC::get_completion_signatures<__child_of<_Sender>, _Env...>(),
-          __transform_upon_completion<__fn_t, then_t>());
+          __upon::__transform_completion<__fn_t, then_t>());
       }
 
-      struct __complete_fn
-      {
-        template <class _Tag, class _State, class... _Args>
-        STDEXEC_ATTRIBUTE(host, device)
-        constexpr void operator()(__ignore, _State& __state, _Tag, _Args&&... __args) const noexcept
-        {
-          if constexpr (__same_as<_Tag, set_value_t>)
-          {
-            STDEXEC::__set_value_from(static_cast<_State&&>(__state).__rcvr_,
-                                      static_cast<_State&&>(__state).__data_,
-                                      static_cast<_Args&&>(__args)...);
-          }
-          else
-          {
-            _Tag()(static_cast<_State&&>(__state).__rcvr_, static_cast<_Args&&>(__args)...);
-          }
-        }
-      };
-
-      static constexpr auto __complete = __complete_fn{};
+      static constexpr auto __complete = __upon::__complete<set_value_t>;
     };
   }  // namespace __then
 
@@ -225,7 +206,7 @@ namespace STDEXEC
   };
 
   template <>
-  struct __sexpr_impl<then_t> : __then::__then_impl
+  struct __sexpr_impl<then_t> : __then::__impl
   {};
 
   template <class _Fun, class _Sender>

include/stdexec/__detail/__transform_completion_signatures.hpp

@@ -408,29 +408,6 @@ namespace STDEXEC
     }
   };
 
-  STDEXEC_MODULE_EXPORT_AUTHORING
-  template <class _Fun, class AlgoTag>
-  struct __transform_upon_completion
-  {
-    template <class... _Args>
-    constexpr auto operator()() const
-    {
-      if constexpr (__nothrow_invocable<_Fun, _Args...>)
-      {
-        return completion_signatures<__single_value_sig_t<__invoke_result_t<_Fun, _Args...>>>();
-      }
-      else if constexpr (__invocable<_Fun, _Args...>)
-      {
-        return completion_signatures<__single_value_sig_t<__invoke_result_t<_Fun, _Args...>>,
-                                     set_error_t(std::exception_ptr)>();
-      }
-      else
-      {
-        return STDEXEC::__throw_compile_time_error(__callable_error_t<AlgoTag, _Fun, _Args...>());
-      }
-    }
-  };
-
   //! @brief Transforms completion signatures using provided transformation
   //! functions.
   //!

include/stdexec/__detail/__upon.hpp

@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2021-2024 NVIDIA Corporation
+ *
+ * Licensed under the Apache License Version 2.0 with LLVM Exceptions
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *   https://llvm.org/LICENSE.txt
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include "__config.hpp"
+
+#if STDEXEC_USE_MODULES() && !defined(STDEXEC_IN_MODULE_PURVIEW)
+
+import stdexec;
+
+#else
+
+#  include "__execution_fwd.hpp"
+
+#  include "../functional.hpp"
+#  include "__completion_signatures.hpp"
+#  include "__concepts.hpp"
+#  include "__diagnostics.hpp"
+#  include "__meta.hpp"
+#  include "__partition_completion_signatures.hpp"
+#  include "__receivers.hpp"
+
+#  if !STDEXEC_USE_MODULES()
+#    include <exception>
+#  endif
+
+#  include "__prologue.hpp"
+
+// NOLINTNEXTLINE(bugprone-std-namespace-modification, modernize-concat-nested-namespaces)
+namespace STDEXEC
+{
+  //////////////////////////////////////////////////////////////////////////////
+  // Helpers for [exec.then]
+  namespace __upon
+  {
+    template <class _SetTag>
+    static constexpr auto __complete =
+      []<class _Tag, class _State, class... _Args>(__ignore,
+                                                   _State& __state,
+                                                   _Tag,
+                                                   _Args&&... __args) noexcept -> void
+    {
+      if constexpr (__same_as<_Tag, _SetTag>)
+      {
+        STDEXEC::__set_value_from(static_cast<_State&&>(__state).__rcvr_,
+                                  static_cast<_State&&>(__state).__data_,
+                                  static_cast<_Args&&>(__args)...);
+      }
+      else
+      {
+        _Tag()(static_cast<_State&&>(__state).__rcvr_, static_cast<_Args&&>(__args)...);
+      }
+    };
+
+    STDEXEC_MODULE_EXPORT_AUTHORING
+    template <class _Fun, class AlgoTag>
+    struct __transform_completion
+    {
+      template <class... _Args>
+      constexpr auto operator()() const
+      {
+        if constexpr (__nothrow_invocable<_Fun, _Args...>)
+        {
+          return completion_signatures<__single_value_sig_t<__invoke_result_t<_Fun, _Args...>>>();
+        }
+        else if constexpr (__invocable<_Fun, _Args...>)
+        {
+          return completion_signatures<__single_value_sig_t<__invoke_result_t<_Fun, _Args...>>,
+                                       set_error_t(std::exception_ptr)>();
+        }
+        else
+        {
+          return STDEXEC::__throw_compile_time_error(__callable_error_t<AlgoTag, _Fun, _Args...>());
+        }
+      }
+    };
+  }  // namespace __upon
+}  // namespace STDEXEC
+
+#  include "__epilogue.hpp"
+#endif  // !STDEXEC_USE_MODULES() || defined(STDEXEC_IN_MODULE_PURVIEW)

include/stdexec/__detail/__upon_error.hpp

@@ -26,13 +26,13 @@ import stdexec;
 #  include "__execution_fwd.hpp"
 
 #  include "__basic_sender.hpp"
-#  include "__completion_signatures_of.hpp"
-#  include "__diagnostics.hpp"
 #  include "__meta.hpp"
 #  include "__queries.hpp"
 #  include "__sender_adaptor_closure.hpp"
-#  include "__senders.hpp"  // IWYU pragma: keep for __well_formed_sender
+#  include "__sender_introspection.hpp"
+#  include "__senders.hpp"
 #  include "__transform_completion_signatures.hpp"
+#  include "__upon.hpp"
 
 #  include "__prologue.hpp"
 
@@ -43,7 +43,7 @@ namespace STDEXEC
   // [exec.then]
   namespace __upon_error
   {
-    struct __upon_error_impl : __sexpr_defaults
+    struct __impl : __sexpr_defaults
     {
       static constexpr auto __get_attrs =
         []<class _Child>(__ignore, __ignore, _Child const & __child) noexcept
@@ -59,26 +59,10 @@ namespace STDEXEC
         return STDEXEC::__transform_completion_signatures(
           STDEXEC::get_completion_signatures<__child_of<_Sender>, _Env...>(),
           {},
-          __transform_upon_completion<__fn_t, upon_error_t>());
+          __upon::__transform_completion<__fn_t, upon_error_t>());
       }
 
-      static constexpr auto __complete =
-        []<class _Tag, class _State, class... _Args>(__ignore,
-                                                     _State& __state,
-                                                     _Tag,
-                                                     _Args&&... __args) noexcept -> void
-      {
-        if constexpr (__same_as<_Tag, set_error_t>)
-        {
-          STDEXEC::__set_value_from(static_cast<_State&&>(__state).__rcvr_,
-                                    static_cast<_State&&>(__state).__data_,
-                                    static_cast<_Args&&>(__args)...);
-        }
-        else
-        {
-          _Tag()(static_cast<_State&&>(__state).__rcvr_, static_cast<_Args&&>(__args)...);
-        }
-      };
+      static constexpr auto __complete = __upon::__complete<set_error_t>;
     };
   }  // namespace __upon_error
 
@@ -225,7 +209,7 @@ namespace STDEXEC
   };
 
   template <>
-  struct __sexpr_impl<upon_error_t> : __upon_error::__upon_error_impl
+  struct __sexpr_impl<upon_error_t> : __upon_error::__impl
   {};
 
   template <class _Fun, class _Sender>

include/stdexec/__detail/__upon_stopped.hpp

@@ -26,11 +26,11 @@ import stdexec;
 #  include "__execution_fwd.hpp"
 
 #  include "__basic_sender.hpp"
-#  include "__completion_signatures_of.hpp"
-#  include "__meta.hpp"
 #  include "__sender_adaptor_closure.hpp"
-#  include "__senders.hpp"  // IWYU pragma: keep for __well_formed_sender
+#  include "__sender_introspection.hpp"
+#  include "__senders.hpp"
 #  include "__transform_completion_signatures.hpp"
+#  include "__upon.hpp"
 
 #  include "__prologue.hpp"
 
@@ -41,7 +41,7 @@ namespace STDEXEC
   // [exec.then]
   namespace __upon_stopped
   {
-    struct __upon_stopped_impl : __sexpr_defaults
+    struct __impl : __sexpr_defaults
     {
       template <class _Sender, class... _Env>
       static consteval auto __get_completion_signatures()
@@ -52,27 +52,10 @@ namespace STDEXEC
           STDEXEC::get_completion_signatures<__child_of<_Sender>, _Env...>(),
           {},
           {},
-          __always{__set_value_from_t<__fn_t>()},
-          __eptr_completion_unless_t<__mbool<__nothrow_callable<__fn_t>>>());
+          __upon::__transform_completion<__fn_t, upon_stopped_t>());
       }
 
-      static constexpr auto __complete =
-        []<class _Tag, class _State, class... _Args>(__ignore,
-                                                     _State& __state,
-                                                     _Tag,
-                                                     _Args&&... __args) noexcept -> void
-      {
-        if constexpr (__same_as<_Tag, set_stopped_t>)
-        {
-          STDEXEC::__set_value_from(static_cast<_State&&>(__state).__rcvr_,
-                                    static_cast<_State&&>(__state).__data_,
-                                    static_cast<_Args&&>(__args)...);
-        }
-        else
-        {
-          _Tag()(static_cast<_State&&>(__state).__rcvr_, static_cast<_Args&&>(__args)...);
-        }
-      };
+      static constexpr auto __complete = __upon::__complete<set_stopped_t>;
     };
   }  // namespace __upon_stopped
 
@@ -215,7 +198,7 @@ namespace STDEXEC
   };
 
   template <>
-  struct __sexpr_impl<upon_stopped_t> : __upon_stopped::__upon_stopped_impl
+  struct __sexpr_impl<upon_stopped_t> : __upon_stopped::__impl
   {};
 
   template <class _Fun, class _Sender>