Improve detection of std::uncaught_exceptions support

The problem was that Catch2 did not reliably include `<exception>`
before it checked for the feature test macro for
`std::uncaught_exceptions`. To avoid overhead of including
`<exception>` everywhere, the configuration check was split out
into a separate header.

Closes #2021

src/CMakeLists.txt

@@ -50,6 +50,7 @@ set(INTERNAL_HEADERS
     ${SOURCES_DIR}/internal/catch_common.hpp
     ${SOURCES_DIR}/internal/catch_compiler_capabilities.hpp
     ${SOURCES_DIR}/catch_config.hpp
+    ${SOURCES_DIR}/internal/catch_config_uncaught_exceptions.hpp
     ${SOURCES_DIR}/internal/catch_console_colour.hpp
     ${SOURCES_DIR}/internal/catch_context.hpp
     ${SOURCES_DIR}/internal/catch_debug_console.hpp

src/catch2/catch_all.hpp

@@ -51,6 +51,7 @@
 #include <catch2/internal/catch_commandline.hpp>
 #include <catch2/internal/catch_common.hpp>
 #include <catch2/internal/catch_compiler_capabilities.hpp>
+#include <catch2/internal/catch_config_uncaught_exceptions.hpp>
 #include <catch2/internal/catch_console_colour.hpp>
 #include <catch2/internal/catch_console_width.hpp>
 #include <catch2/internal/catch_container_nonmembers.hpp>

src/catch2/internal/catch_combined_tu.cpp

@@ -76,13 +76,15 @@ namespace Catch {
 
 #include <catch2/internal/catch_compiler_capabilities.hpp>
 #include <catch2/internal/catch_uncaught_exceptions.hpp>
+#include <catch2/internal/catch_config_uncaught_exceptions.hpp>
+
 #include <exception>
 
 namespace Catch {
     bool uncaught_exceptions() {
 #if defined(CATCH_CONFIG_DISABLE_EXCEPTIONS)
         return false;
-#elif defined(CATCH_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS) || (defined(__cpp_lib_uncaught_exceptions) && !defined(CATCH_CONFIG_NO_CPP17_UNCAUGHT_EXCEPTIONS))
+#elif defined(CATCH_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS)
         return std::uncaught_exceptions() > 0;
 #else
         return std::uncaught_exception();

src/catch2/internal/catch_config_uncaught_exceptions.hpp

@@ -0,0 +1,44 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE_1_0.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+/** \file
+ * Wrapper for UNCAUGHT_EXCEPTIONS configuration option
+ *
+ * For some functionality, Catch2 requires to know whether there is
+ * an active exception. Because `std::uncaught_exception` is deprecated
+ * in C++17, we want to use `std::uncaught_exceptions` if possible.
+ */
+
+#ifndef CATCH_CONFIG_UNCAUGHT_EXCEPTIONS_HPP
+#define CATCH_CONFIG_UNCAUGHT_EXCEPTIONS_HPP
+
+#if defined(_MSC_VER)
+#  if _MSC_VER >= 1900 // Visual Studio 2015 or newer
+#    define CATCH_INTERNAL_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS
+#  endif
+#endif
+
+
+#include <exception>
+
+#if defined(__cpp_lib_uncaught_exceptions) \
+    && !defined(CATCH_INTERNAL_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS)
+
+#  define CATCH_INTERNAL_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS
+#endif // __cpp_lib_uncaught_exceptions
+
+
+#if defined(CATCH_INTERNAL_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS) \
+    && !defined(CATCH_CONFIG_NO_CPP17_UNCAUGHT_EXCEPTIONS) \
+    && !defined(CATCH_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS)
+
+#  define CATCH_CONFIG_CPP17_UNCAUGHT_EXCEPTIONS
+#endif
+
+
+#endif // CATCH_CONFIG_UNCAUGHT_EXCEPTIONS_HPP