Get rid of MantidKernel/System.h

[peterfpeterson]

Describe the outcome that is desired.

Remove System.h since it is created in the generate files called DllConfig.h by way of GenerateMantidExporteHeader.cmake

Describe any solutions you are considering

This can be done in stages, but each removal from System.h will invalidate almost the entire build tree. Consider that when planning out the work.

• Move the #pragma warning(disable: commands from L33, 37, and 42 to exist as compiler flags in WindowsSetup.cmake. When doing the move, consider whether the flags are still necessary.
• Remove all hand-written DllConfig.h from the source tree and change those sub-packages to use the generated one. At the time of this writing,there are 13.
• DO SECOND Remove direct #include "MantidKernel/System.h" from everything. Some sub-packages predate the existence of DllConfig.h being created and should use that instead. There are currently 503 files that directly include MantidKernel/System.h.
• The macros for exporting symbols on L34-55 is generated already by GenerateMantidExportHeader.cmake and can be removed
• The macros for deprecating symbols on L70-77 is generated already by GenerateMantidExportHeader.cmake and can be removed
• The macro for UNUSED_ARG on L63-65 is generated already by GenerateMantidExportHeader.cmake and can be removed. Add a comment/link in the generated DllConfig.h that one should consider maybe_unused instead.
• Remove the includes for cstddef and cstdint. If this generates an excess of changes, move the includes into GENERATE_EXTERN clause of GenerateMantidExportHeader.cmake
• DO LAST Remove MantidKernel/System.h and update GenerateMantidExportHeader.cmake to not include it.

NOTE ABOUT UNUSED_ARG

This is the main reason why tests include MantidKernel/System.h. Either change them to use the sub-package specific DllConfig.h or change to maybe_unused

[peterfpeterson]

From a small test, removing cstddef from MantidKernel/System.h can be done without much work.

[peterfpeterson]

For reference, the generated MantidKernel/DllConfig.h for windows is

#ifndef MANTID_KERNEL_DLL_H
#define MANTID_KERNEL_DLL_H

#ifdef MANTID_KERNEL_STATIC_DEFINE
#  define MANTID_KERNEL_DLL
#  define MANTID_KERNEL_NO_EXPORT
#else
#  ifndef MANTID_KERNEL_DLL
#    ifdef Kernel_EXPORTS
        /* We are building this library */
#      define MANTID_KERNEL_DLL __declspec(dllexport)
#    else
        /* We are using this library */
#      define MANTID_KERNEL_DLL __declspec(dllimport)
#    endif
#  endif

#  ifndef MANTID_KERNEL_NO_EXPORT
#    define MANTID_KERNEL_NO_EXPORT 
#  endif
#endif

#ifndef MANTID_KERNEL_DEPRECATED
#  define MANTID_KERNEL_DEPRECATED __declspec(deprecated)
#endif

#ifndef MANTID_KERNEL_DEPRECATED_EXPORT
#  define MANTID_KERNEL_DEPRECATED_EXPORT MANTID_KERNEL_DLL MANTID_KERNEL_DEPRECATED
#endif

#ifndef MANTID_KERNEL_DEPRECATED_NO_EXPORT
#  define MANTID_KERNEL_DEPRECATED_NO_EXPORT MANTID_KERNEL_NO_EXPORT MANTID_KERNEL_DEPRECATED
#endif

/* NOLINTNEXTLINE(readability-avoid-unconditional-preprocessor-if) */
#if 0 /* DEFINE_NO_DEPRECATED */
#  ifndef MANTID_KERNEL_NO_DEPRECATED
#    define MANTID_KERNEL_NO_DEPRECATED
#  endif
#endif


#ifdef _WIN32
    // 'identifier' : class 'type' needs to have dll-interface to be used by clients
    // of class 'type2'
    // Things from the std library give these warnings and we can't do anything
    // about them.
    #pragma warning(disable : 4251)
    // Given that we are compiling everything with msvc under Windows and
    // linking all with the same runtime we can disable the warning about
    // inheriting from a non-exported interface, e.g. std::runtime_error */
    #pragma warning(disable : 4275)
    // Warning C4373: previous versions of the compiler did not override when
    // parameters only differed by const/volatile qualifiers
    // This is basically saying that it now follows the C++ standard and doesn't
    // seem useful
    #pragma warning(disable : 4373)
#endif

#ifndef UNUSED_ARG
    #define UNUSED_ARG(x) (void) x;
#endif

#ifndef KERNEL_DEPRECATED
    #define KERNEL_DEPRECATED(func) MANTID_KERNEL_DEPRECATED func
#endif

// Use extern keyword in client code to suppress class template instantiation
#include "MantidKernel/System.h"

#ifdef Kernel_EXPORTS
#define EXTERN_MANTID_KERNEL
#else
#define EXTERN_MANTID_KERNEL EXTERN_IMPORT
#endif /* Kernel_EXPORTS*/
 
#endif /* MANTID_KERNEL_DLL_H */

[martyngigg]

Just a note.

The Windows #pragma warning in System.h should be able to move to compiler flags in WindowsSetup such as /wd4251. https://learn.microsoft.com/en-us/cpp/build/reference/compiler-option-warning-level?view=msvc-170 for reference.