Utility: add test for CORRADE_CONSTEXPR14

v2: test if CORRADE_CONSTEXPR is empty
v3: add an #if 0 to test whether SFINAE works

src/Corrade/Utility/Test/CMakeLists.txt

@@ -215,6 +215,14 @@ if(NOT CMAKE_CXX_FLAGS MATCHES "-std=")
             PROPERTIES CORRADE_CXX_STANDARD 17)
     endif()
 
+    if((CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0") OR
+       (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "3.4") OR
+       (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0.1") OR
+       (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "19.10"))
+        corrade_add_test(UtilityMacrosCpp14Test MacrosCpp14Test.cpp)
+        set_target_properties(UtilityMacrosCpp14Test PROPERTIES CORRADE_CXX_STANDARD 14)
+   endif()
+
     # Copied verbatim from src/Corrade/Test/CMakeLists.txt, please keep in sync
     if((CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "8.0") OR
        (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "6.0") OR

src/Corrade/Utility/Test/MacrosCpp14Test.cpp

@@ -0,0 +1,71 @@
+/*
+    This file is part of Corrade.
+
+    Copyright © 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
+                2017, 2018, 2019, 2020, 2021, 2022
+              Vladimír Vondruš <[email protected]>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#include "Corrade/TestSuite/Tester.h"
+#include "Corrade/Utility/Macros.h"
+
+namespace Corrade { namespace Utility { namespace Test { namespace {
+
+#if 0
+#undef CORRADE_CONSTEXPR14
+#define CORRADE_CONSTEXPR14
+#endif
+
+struct MacrosCpp14Test: TestSuite::Tester {
+    explicit MacrosCpp14Test();
+    void constexpr14();
+    static CORRADE_CONSTEXPR14 int sumInAStupidWay(int number);
+};
+
+MacrosCpp14Test::MacrosCpp14Test() {
+    addTests({&MacrosCpp14Test::constexpr14});
+}
+
+CORRADE_CONSTEXPR14 int MacrosCpp14Test::sumInAStupidWay(int number) {
+    int sum = 0;
+    for(int i = 0; i != number; ++i)
+        sum += i;
+    return sum;
+}
+
+template<int> struct sfinae : std::true_type{};
+template<class T> sfinae<(T::sumInAStupidWay(0), 0)> check(int);
+template<class> std::false_type check(...);
+template<class T> struct hasRelaxedConstexpr : decltype(check<T>(0)){};
+
+void MacrosCpp14Test::constexpr14() {
+    if (hasRelaxedConstexpr<MacrosCpp14Test>() == false)
+        CORRADE_SKIP("CORRADE_CONSTEXPR14 not available on this compiler.");
+    else {
+        CORRADE_CONSTEXPR14 int sum = sumInAStupidWay(17);
+        CORRADE_COMPARE(sum, 136);
+    }
+}
+
+
+}}}}
+
+CORRADE_TEST_MAIN(Corrade::Utility::Test::MacrosCpp14Test)