fixed a few coroutine related issues (#113)

* fixed a few coroutine related issues

* fixed formatting issues

* reverted te chnage checking the result from unhandled_stopped().

Author: dietmarkuehl

include/beman/execution26/detail/product_type.hpp

@@ -7,6 +7,8 @@
 #include <memory>
 #include <cstddef>
 
+#include <beman/execution26/detail/suppress_push.hpp>
+
 // ----------------------------------------------------------------------------
 
 namespace beman::execution26::detail {
@@ -126,4 +128,6 @@ struct tuple_element<I, T> {
 
 // ----------------------------------------------------------------------------
 
+#include <beman/execution26/detail/suppress_pop.hpp>
+
 #endif

include/beman/execution26/detail/single_sender_value_type.hpp

@@ -27,6 +27,8 @@ struct single_sender_value_type_helper<Sender, Env> {
 
 template <typename Sender, typename Env>
     requires ::std::same_as<::std::variant<::std::tuple<>>,
+                            ::beman::execution26::value_types_of_t<Sender, Env, ::std::tuple, ::std::variant>> ||
+             ::std::same_as<::std::variant<>,
                             ::beman::execution26::value_types_of_t<Sender, Env, ::std::tuple, ::std::variant>>
 struct single_sender_value_type_helper<Sender, Env> {
     using type = void;

tests/beman/execution26/execution-syn.test.cpp

@@ -225,18 +225,18 @@ auto test_single_sender_value_type() -> void {
                                test_detail::single_sender_value_type<multi_type_sender, test_std::empty_env>>);
     test_single_sender_value_type<true>(single_type_sender{}, test_std::empty_env{});
     test_single_sender_value_type<true>(single_type_sender{}, test_env{});
-    test_single_sender_value_type<false>(single_type_sender{}, no_value_env{});
+    test_single_sender_value_type<true>(single_type_sender{}, no_value_env{});
     test_single_sender_value_type<false>(multi_single_sender{}, test_std::empty_env{});
-    test_single_sender_value_type<false>(no_value_sender{}, test_std::empty_env{});
+    test_single_sender_value_type<true>(no_value_sender{}, test_std::empty_env{});
 }
 
 auto test_single_sender() -> void {
     static_assert(test_detail::single_sender<single_type_sender, test_std::empty_env>);
-    static_assert(not test_detail::single_sender<single_type_sender, no_value_env>);
+    static_assert(test_detail::single_sender<single_type_sender, no_value_env>);
     static_assert(test_detail::single_sender<void_sender, test_std::empty_env>);
     static_assert(not test_detail::single_sender<multi_single_sender, test_std::empty_env>);
     static_assert(test_detail::single_sender<multi_type_sender, test_std::empty_env>);
-    static_assert(not test_detail::single_sender<no_value_sender, test_std::empty_env>);
+    static_assert(test_detail::single_sender<no_value_sender, test_std::empty_env>);
 }
 
 struct connect_sender {