Fix main llvm 22 (#229)

* Fix Clang C++20 modules AST serialization bug with lambdas

Clang fails to deserialize the unevaluated generic lambda used in the
`has_completions` concept when building as a C++20 module. Extracted the
lambda into a namespace-scope `constexpr` variable template to bypass
the AST serialization crash.

Extracting it to a constexpr variable caused another set of bugs
with MSVC. therefore, lambda completely replaced with SFINAE style
'struct has_completions_impl'

* Relax template template parameter matching for Clang 22

Clang 22 rejects passing the constrained template `wrap` to an
unconstrained template template parameter (related to LLVM #182671).
Relaxed `wrap` and `bad` to use `template <typename S>` in
`exec-scope-concepts.test.cpp` to resolve the constraint violation.

Author: ecoezen

include/beman/execution/detail/has_completions.hpp

@@ -5,6 +5,12 @@
 #define INCLUDED_BEMAN_EXECUTION_DETAIL_HAS_COMPLETIONS
 
 #include <beman/execution/detail/common.hpp>
+
+#ifdef BEMAN_HAS_IMPORT_STD
+import std;
+#else
+#include <type_traits>
+#endif
 #ifdef BEMAN_HAS_MODULES
 import beman.execution.detail.completion_signatures;
 import beman.execution.detail.valid_completion_for;
@@ -16,11 +22,16 @@ import beman.execution.detail.valid_completion_for;
 // ----------------------------------------------------------------------------
 
 namespace beman::execution::detail {
+
 template <typename Receiver, typename Completions>
-concept has_completions = requires(Completions* completions) {
-    []<::beman::execution::detail::valid_completion_for<Receiver>... Signatures>(
-        ::beman::execution::completion_signatures<Signatures...>*) {}(completions);
-};
+struct has_completions_impl : std::false_type {};
+
+template <typename Receiver, ::beman::execution::detail::valid_completion_for<Receiver>... Signatures>
+struct has_completions_impl<Receiver, ::beman::execution::completion_signatures<Signatures...>> : std::true_type {};
+
+template <typename Receiver, typename Completions>
+concept has_completions = has_completions_impl<Receiver, Completions>::value;
+
 } // namespace beman::execution::detail
 
 // ----------------------------------------------------------------------------

tests/beman/execution/exec-scope-concepts.test.cpp

@@ -32,7 +32,7 @@ static_assert(not std::copyable<non_copyable>);
 
 struct empty {};
 
-template <test_std::sender S>
+template <typename S>
 struct wrap {
     using sender_concept = test_std::sender_t;
     std::remove_cvref_t<S> sndr;