Fixing tests

Author: VioletGiraffe

tests/test-app/extra_type_traits_tests.cpp

@@ -28,7 +28,9 @@ TEST_CASE("is_equal_comparable", "[extra_type_traits]") {
 	static_assert (is_equal_comparable_v<comparable, comparable>);
 	static_assert (!is_equal_comparable_v<non_comparable, non_comparable>);
 	static_assert (is_equal_comparable_v<comparable, int>);
-#if __cplusplus > 201703L && (!defined __GNUC__ || __GNUC__ >= 10)
+// C++20 rewritten candidates make 'int == comparable' valid via comparable::operator==(int). Clang defines
+// __GNUC__ as 4 yet supports this, so gate it in explicitly, alongside GCC>=10 and MSVC (which defines neither).
+#if __cplusplus > 201703L && (defined __clang__ || !defined __GNUC__ || __GNUC__ >= 10)
 	static_assert (is_equal_comparable_v<int, comparable>);
 #else
 	static_assert (!is_equal_comparable_v<int, comparable>);

utility/constexpr_algorithms.hpp

@@ -12,7 +12,10 @@ namespace detail {
 		{
 			if constexpr (std::is_same_v<bool, decltype(f.template operator()<First>())>)
 			{
-				constexpr bool proceed = f.template operator()<First>();
+				// 'f' is a function parameter, not a constant expression: calling it here is non-portable (Apple
+				// Clang rejects f.operator()<First>() in this constexpr context). A captureless closure is
+				// default-constructible in C++20, so a fresh value-initialized one gives a genuine constant.
+				constexpr bool proceed = decltype(f){}.template operator()<First>();
 				if constexpr (proceed)
 					consteval_for_T<T, First + 1, Last>(f);
 			}