CMake: Added dynamic verification of C++14 support

Flag-based check sometimes fails to properly identify does compiler supports C++14 or not.

Author: Wohlstand

CMakeLists.txt

@@ -25,8 +25,23 @@ else()
     endif()
 endif()
 
+function(CheckCPP14Build OUTVAR)
+    set(CMAKE_CXX_STANDARD 14)
+    try_compile(${OUTVAR}
+        ${CMAKE_CURRENT_BINARY_DIR}/cmake-checks
+        ${CMAKE_CURRENT_SOURCE_DIR}/cmake/checks/cpp14.cpp
+        CMAKE_FLAGS -DCMAKE_CXX_FLAGS=${FLAG_CPP14}
+    )
+endfunction()
+
 if(COMPILER_SUPPORTS_CXX14)
-    message("== Your C++ compiler supports C++14, YMFM emulator will be ENABLED")
+    CheckCPP14Build(COMPILER_BUILDS_CXX14)
+    if(COMPILER_BUILDS_CXX14)
+        message("== Your C++ compiler supports C++14, YMFM emulator will be ENABLED")
+    else()
+        message("== Your C++ compiler can't build C++14, YMFM emulator will be DISABLED")
+        set(COMPILER_SUPPORTS_CXX14 FALSE)
+    endif()
 else()
     message("== Your C++ compiler does NOT supports C++14, YMFM emulator will be DISABLED")
 endif()

cmake/checks/cpp14.cpp

@@ -0,0 +1,49 @@
+// A test program to verify C++ compiler for C++14 support
+// Based on The Javatar's example: https://stackoverflow.com/questions/30940504/simplest-c-example-to-verify-my-compiler-is-c14-compliant
+
+#include <iostream>
+#include <tuple>
+#include <cstdint>
+#include <assert.h>
+#include <functional>
+
+class TestClass
+{
+public:
+    static constexpr int test_constant = 42;
+
+    static constexpr int  test_funk(uint32_t chnum)
+    {
+        assert(chnum >= 42);
+        return chnum;
+    }
+};
+
+auto f() // this function returns multiple values
+{
+    int x = 5;
+    return std::make_tuple(x, 7); // not "return {x,7};" because the corresponding
+                                  // tuple constructor is explicit (LWG 2051)
+}
+
+int main()
+{
+    // heterogeneous tuple construction
+    int n = 1;
+    TestClass tc;
+    auto t = std::make_tuple(10, "Test", 3.14, std::ref(n), n);
+    n = 7;
+    std::cout << "The value of t is "  << "("
+              << std::get<0>(t) << ", " << std::get<1>(t) << ", "
+              << std::get<2>(t) << ", " << std::get<3>(t) << ", "
+              << std::get<4>(t) << ")\n";
+
+    int q = tc.test_funk(40);
+
+    // function returning multiple values
+    int a, b;
+    std::tie(a, b) = f();
+    std::cout << a << " " << b << "\n";
+
+    return 0;
+}