experimental code to compute completions during constant evaluation

include/exec/detail/basic_sequence.hpp

@@ -127,6 +127,6 @@ namespace STDEXEC::__detail
   extern decltype(_DescriptorFn()) __desc_of_v<exec::__seqexpr<_DescriptorFn>>;
 
   template <auto _DescriptorFn>
-  extern __declfn_t<__minvoke<decltype(_DescriptorFn()), __q<exec::__basic_sequence_sender_t>>>
+  extern __mtype<__minvoke<decltype(_DescriptorFn()), __q<exec::__basic_sequence_sender_t>>>
     __demangle_v<exec::__seqexpr<_DescriptorFn>>;
 }  // namespace STDEXEC::__detail

include/exec/repeat_until.hpp

@@ -275,8 +275,8 @@ namespace experimental::execution
         using __eptr_completion_t        = set_error_t(std::exception_ptr);
         constexpr auto __eptr_completion = (__eptr_completion_t *) nullptr;
 
-        STDEXEC_COMPLSIGS_LET(
-          __sigs,
+        STDEXEC_TRY_LET(
+          auto __sigs,
           exec::transform_completion_signatures(get_completion_signatures<__child_t, _Env...>(),
                                                 __transform_values<__child_t>,
                                                 __transform_errors))

include/exec/static_thread_pool.hpp

@@ -45,7 +45,6 @@
 #include "sequence/iterate.hpp"
 #include "sequence_senders.hpp"
 
-#include <algorithm>
 #include <compare>
 #include <condition_variable>
 #include <cstdint>

include/nvexec/nvtx.cuh

@@ -196,7 +196,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <nvexec::_strm::nvtx::kind Kind, class Sender>
-  extern __declfn_t<nvexec::_strm::nvtx::nvtx_sender<Kind, __demangle_t<Sender>>>
+  extern __mtype<nvexec::_strm::nvtx::nvtx_sender<Kind, __demangle_t<Sender>>>
     __demangle_v<nvexec::_strm::nvtx::nvtx_sender<Kind, Sender>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/algorithm_base.cuh

@@ -145,7 +145,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class InitT, class Fun, class DerivedSender>
-  extern __declfn_t<nvexec::_strm::__algo_range_init_fun::
-                      sender<__demangle_t<Sender>, InitT, Fun, __demangle_t<DerivedSender>>>
+  extern __mtype<nvexec::_strm::__algo_range_init_fun::
+                   sender<__demangle_t<Sender>, InitT, Fun, __demangle_t<DerivedSender>>>
     __demangle_v<nvexec::_strm::__algo_range_init_fun::sender<Sender, InitT, Fun, DerivedSender>>;
 }  // namespace STDEXEC::__detail

include/nvexec/stream/bulk.cuh

@@ -440,12 +440,11 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Shape, class Fun>
-  inline constexpr __declfn_t<nvexec::_strm::bulk_sender<__demangle_t<Sender>, Shape, Fun>>
+  inline constexpr __mtype<nvexec::_strm::bulk_sender<__demangle_t<Sender>, Shape, Fun>>
     __demangle_v<nvexec::_strm::bulk_sender<Sender, Shape, Fun>>{};
 
   template <class Sender, class Shape, class Fun>
-  inline constexpr __declfn_t<
-    nvexec::_strm::multi_gpu_bulk_sender<__demangle_t<Sender>, Shape, Fun>>
+  inline constexpr __mtype<nvexec::_strm::multi_gpu_bulk_sender<__demangle_t<Sender>, Shape, Fun>>
     __demangle_v<nvexec::_strm::multi_gpu_bulk_sender<Sender, Shape, Fun>>{};
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/continues_on.cuh

@@ -284,7 +284,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Scheduler, class Sender>
-  extern __declfn_t<nvexec::_strm::continues_on_sender<Scheduler, __demangle_t<Sender>>>
+  extern __mtype<nvexec::_strm::continues_on_sender<Scheduler, __demangle_t<Sender>>>
     __demangle_v<nvexec::_strm::continues_on_sender<Scheduler, Sender>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/ensure_started.cuh

@@ -430,7 +430,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender>
-  extern __declfn_t<nvexec::_strm::ensure_started_sender<__demangle_t<Sender>>>
+  extern __mtype<nvexec::_strm::ensure_started_sender<__demangle_t<Sender>>>
     __demangle_v<nvexec::_strm::ensure_started_sender<Sender>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/launch.cuh

@@ -204,7 +204,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Fun>
-  extern __declfn_t<nvexec::_strm::launch_sender<__demangle_t<Sender>, Fun>>
+  extern __mtype<nvexec::_strm::launch_sender<__demangle_t<Sender>, Fun>>
     __demangle_v<nvexec::_strm::launch_sender<Sender, Fun>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/let_xxx.cuh

@@ -344,7 +344,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Fun, class SetTag>
-  extern __declfn_t<nvexec::_strm::let_sender<__demangle_t<Sender>, Fun, SetTag>>
+  extern __mtype<nvexec::_strm::let_sender<__demangle_t<Sender>, Fun, SetTag>>
     __demangle_v<nvexec::_strm::let_sender<Sender, Fun, SetTag>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/reduce.cuh

@@ -165,7 +165,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Init, class Fun>
-  extern __declfn_t<nvexec::_strm::reduce_::sender<__demangle_t<Sender>, Init, Fun>>
+  extern __mtype<nvexec::_strm::reduce_::sender<__demangle_t<Sender>, Init, Fun>>
     __demangle_v<nvexec::_strm::reduce_::sender<Sender, Init, Fun>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/schedule_from.cuh

@@ -196,6 +196,6 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender>
-  extern __declfn_t<nvexec::_strm::schedule_from_sender<__demangle_t<Sender>>>
+  extern __mtype<nvexec::_strm::schedule_from_sender<__demangle_t<Sender>>>
     __demangle_v<nvexec::_strm::schedule_from_sender<Sender>>;
 }  // namespace STDEXEC::__detail

include/nvexec/stream/split.cuh

@@ -412,7 +412,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender>
-  extern __declfn_t<nvexec::_strm::split_sender<__demangle_t<Sender>>>
+  extern __mtype<nvexec::_strm::split_sender<__demangle_t<Sender>>>
     __demangle_v<nvexec::_strm::split_sender<Sender>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/then.cuh

@@ -228,7 +228,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Fun>
-  extern __declfn_t<nvexec::_strm::then_sender<__demangle_t<Sender>, Fun>>
+  extern __mtype<nvexec::_strm::then_sender<__demangle_t<Sender>, Fun>>
     __demangle_v<nvexec::_strm::then_sender<Sender, Fun>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/upon_error.cuh

@@ -216,7 +216,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Fun>
-  extern __declfn_t<nvexec::_strm::upon_error_sender<__demangle_t<Sender>, Fun>>
+  extern __mtype<nvexec::_strm::upon_error_sender<__demangle_t<Sender>, Fun>>
     __demangle_v<nvexec::_strm::upon_error_sender<Sender, Fun>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/upon_stopped.cuh

@@ -207,7 +207,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class Sender, class Fun>
-  extern __declfn_t<nvexec::_strm::upon_stopped_sender<__demangle_t<Sender>, Fun>>
+  extern __mtype<nvexec::_strm::upon_stopped_sender<__demangle_t<Sender>, Fun>>
     __demangle_v<nvexec::_strm::upon_stopped_sender<Sender, Fun>>;
 }  // namespace STDEXEC::__detail
 

include/nvexec/stream/when_all.cuh

@@ -576,7 +576,7 @@ namespace nvexec = nv::execution;
 namespace STDEXEC::__detail
 {
   template <class WhenAllTag, class Scheduler, class... Senders>
-  extern __declfn_t<nvexec::_strm::when_all_sender<WhenAllTag, Scheduler, __demangle_t<Senders>...>>
+  extern __mtype<nvexec::_strm::when_all_sender<WhenAllTag, Scheduler, __demangle_t<Senders>...>>
     __demangle_v<nvexec::_strm::when_all_sender<WhenAllTag, Scheduler, Senders...>>;
 }  // namespace STDEXEC::__detail
 

include/stdexec/__detail/__basic_sender.hpp

@@ -456,7 +456,7 @@ namespace STDEXEC
     using __basic_sender_t = __basic_sender<_Tag, _Data, __demangle_t<_Child>...>::type;
 
     template <auto _Descriptor>
-    extern __declfn_t<__minvoke<decltype(_Descriptor()), __q<__basic_sender_t>>>
+    extern __mtype<__minvoke<decltype(_Descriptor()), __q<__basic_sender_t>>>
       __demangle_v<__sexpr<_Descriptor>>;
   }  // namespace __detail
 }  // namespace STDEXEC

include/stdexec/__detail/__completion_info.hpp

@@ -0,0 +1,159 @@
+/*
+ * Copyright (c) 2026 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 "__execution_fwd.hpp"
+
+// IWYU pragma: begin_keep
+#include "__completion_behavior.hpp"
+#include "__completion_signatures.hpp"
+#include "__meta.hpp"
+#include "__static_vector.hpp"
+#include "__typeinfo.hpp"
+
+#include "../functional.hpp"
+
+#include <algorithm>
+#include <array>
+#include <compare>
+#include <span>
+#include <vector>
+// IWYU pragma: end_keep
+
+namespace STDEXEC
+{
+  template <class _Sig>
+  constexpr _Sig *__signature = nullptr;
+
+  struct __completion_info
+  {
+    using __behavior_t = __completion_behavior::__behavior;
+
+    STDEXEC::__disposition __disposition = __invalid_disposition;
+    __type_index           __signature   = __mtypeid<void>;
+    __type_index           __domain      = __mtypeid<void>;
+    __behavior_t           __behavior    = __completion_behavior::__unknown;
+
+    __completion_info() = default;
+
+    template <__completion_tag _Tag, class... _Args>
+    constexpr __completion_info(_Tag (*)(_Args...),
+                                __type_index __domain   = __mtypeid<void>,
+                                __behavior_t __behavior = __completion_behavior::__unknown) noexcept
+      : __disposition(_Tag::__disposition)
+      , __signature(__mtypeid<_Tag(_Args...)>)
+      , __domain(__domain)
+      , __behavior(__behavior)
+    {}
+
+    template <class _Sender, class... _Env>
+    constexpr auto __populate() noexcept -> __completion_info &
+    {
+      switch (__disposition)
+      {
+      case __disposition::__value:
+        __domain   = __mtypeid<__completion_domain_t<set_value_t, env_of_t<_Sender>, _Env...>>;
+        __behavior = STDEXEC::__get_completion_behavior<set_value_t, _Sender, _Env...>();
+        break;
+      case __disposition::__error:
+        __domain   = __mtypeid<__completion_domain_t<set_error_t, env_of_t<_Sender>, _Env...>>;
+        __behavior = STDEXEC::__get_completion_behavior<set_error_t, _Sender, _Env...>();
+        break;
+      case __disposition::__stopped:
+        __domain   = __mtypeid<__completion_domain_t<set_stopped_t, env_of_t<_Sender>, _Env...>>;
+        __behavior = STDEXEC::__get_completion_behavior<set_stopped_t, _Sender, _Env...>();
+        break;
+      }
+      return *this;
+    }
+
+    [[nodiscard]]
+    constexpr auto
+    operator<=>(__completion_info const &) const noexcept -> std::strong_ordering = default;
+  };
+
+  namespace __cmplsigs
+  {
+    template <auto _GetComplInfo>
+    constexpr auto __completion_info_from_v = []() noexcept
+    {
+      STDEXEC_TRY_LET(auto __cmpl_info, _GetComplInfo())
+      {
+        constexpr auto __size = _GetComplInfo().size();
+        auto           __arr  = __static_vector<__completion_info, __size>();
+        std::ranges::sort(__cmpl_info);
+        auto const __end = std::ranges::unique_copy(__cmpl_info, __arr.begin()).out;
+        __arr.resize(__end - __arr.begin());
+        return __arr;
+      }
+    }();
+
+    template <class _GetComplInfo>
+    consteval auto __completion_info_from(_GetComplInfo) noexcept -> auto const &
+    {
+      return __completion_info_from_v<(_GetComplInfo())>;
+    }
+
+    template <auto _GetComplInfo>
+    constexpr auto __completion_sigs_from_v = []() noexcept
+    {
+      STDEXEC_TRY_LET(constexpr auto __completions, __completion_info_from_v<_GetComplInfo>)
+      {
+        auto __signatures = __static_vector<__type_index, __completions.size()>();
+        __signatures.resize(__completions.size());
+        std::ranges::transform(__completions,
+                               __signatures.begin(),
+                               &__completion_info::__signature);
+        auto const __end = std::ranges::unique(__signatures).begin();
+        __signatures.resize(__end - __signatures.begin());
+        return __signatures;
+      }
+    }();
+
+    template <class _GetComplInfo>
+    consteval auto __completion_sigs_from(_GetComplInfo) noexcept
+    {
+      STDEXEC_TRY_LET(constexpr auto __sigs, __completion_sigs_from_v<(_GetComplInfo())>)
+      {
+        constexpr auto __fn = [=]<std::size_t... _Is>(__indices<_Is...>)
+        {
+          return completion_signatures<__mtypeof<__sigs[_Is]>...>();
+        };
+        return __fn(__make_indices<__sigs.size()>());
+      }
+    }
+
+    template <class... _Sigs>
+    [[nodiscard]]
+    consteval auto __to_array(completion_signatures<_Sigs...>) noexcept
+    {
+      using __array_t = __static_vector<__completion_info, sizeof...(_Sigs)>;
+      auto __compls   = __array_t{__completion_info(__signature<_Sigs>)...};
+      std::ranges::sort(__compls);
+      return __compls;
+    }
+
+    template <class _Ty>
+    constexpr auto __append_range(std::vector<_Ty> &__dst, std::span<_Ty const> __src)
+    {
+  #if __cpp_lib_containers_ranges >= 202202L
+      __dst.append_range(__src);
+  #else
+      __dst.insert(__dst.end(), __src.begin(), __src.end());
+  #endif
+    }
+  }  // namespace __cmplsigs
+}  // namespace STDEXEC