add tests verifying issue 252 is resolved

tests/beman/execution/CMakeLists.txt

@@ -89,6 +89,7 @@ list(
     issue-144.test
     issue-174.test
     issue-186.test
+    issue-252.test
     issue-313.test
     meta-combine.test
     meta-contains.test

tests/beman/execution/issue-252.test.cpp

@@ -0,0 +1,44 @@
+// tests/beman/execution/issue-252.test.cpp                          -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <test/execution.hpp>
+#ifdef BEMAN_HAS_MODULES
+import beman.execution;
+#else
+#include <beman/execution.hpp>
+#endif
+
+namespace ex = beman::execution;
+
+namespace {
+struct non_decomposable_sender {
+    using sender_concept = ex::sender_tag;
+
+    template <typename...>
+    static consteval auto get_completion_signatures() -> ex::completion_signatures<ex::set_value_t()> {
+        return {};
+    }
+
+    non_decomposable_sender(int, int) {}
+};
+
+struct decomposable_sender {
+    using sender_concept      = ex::sender_tag;
+    using is_basic_sender_tag = void;
+
+    struct tag {};
+    tag tag_value;
+    int data;
+};
+} // namespace
+
+TEST(issue252) {
+    static_assert(ex::sender<non_decomposable_sender>);
+    static_assert(std::same_as<ex::completion_signatures<ex::set_value_t()>,
+                               decltype(ex::get_completion_signatures<non_decomposable_sender, ex::env<>>())>);
+
+    static_assert(std::same_as<void, ex::tag_of_t<non_decomposable_sender>>);
+    static_assert(std::same_as<decomposable_sender::tag, ex::tag_of_t<decomposable_sender>>);
+
+    (void)ex::get_completion_signatures<non_decomposable_sender, ex::env<>>();
+}