godot-cpp/cmake/windows.cmake

#[=======================================================================[.rst:
Windows
-------
This file contains functions for options and configuration for targeting the
Windows platform

Because this file is included into the top level CMakelists.txt before the
project directive, it means that

* ``CMAKE_CURRENT_SOURCE_DIR`` is the location of godot-cpp's CMakeLists.txt
* ``CMAKE_SOURCE_DIR`` is the location where any prior ``project(...)``
    directive was

MSVC Runtime Selection
----------------------

There are two main ways to set the msvc runtime library;
Using ``target_compile_options()`` to add the flags
or using the ``CMAKE_MSVC_RUNTIME_LIBRARY`` property_ abstraction, introduced
in CMake version 3.15 with the policy CMP0091_ to remove the flags from
``CMAKE_<LANG>_FLAGS_<CONFIG>``.

Default: ``CMAKE_MSVC_RUNTIME_LIBRARY="MultiThreaded$<$<CONFIG:Debug>:Debug>DLL"``

This initializes each target's ``MSVC_RUNTIME_LIBRARY`` property at the time of
target creation.

it is stated in the msvc_ documentation that: "All modules passed to a given
invocation of the linker must have been compiled with the same runtime library
compiler option (/MD, /MT, /LD)."

This creates a conundrum for us, the ``CMAKE_MSVC_RUNTIME_LIBRARY`` needs to be
correct at the time the target is created, but we have no control over the
consumers CMake scripts, and the per-target ``MSVC_RUNTIME_LIBRARY`` property
is not transient.

It has been raised that not using ``CMAKE_MSVC_RUNTIME_LIBRARY`` can also cause
issues_ when a dependency( independent to godot-cpp ) that doesn't set any
runtime flags, which relies purely on the ``CMAKE_MSVC_RUNTIME_LIBRARY``
variable will very likely not have the correct msvc runtime flags set.

So we'll set ``CMAKE_MSVC_RUNTIME_LIBRARY`` as CACHE STRING so that it will be
available for consumer target definitions, but also be able to be overridden if
needed.

Additionally we message consumers notifying them and pointing to this
documentation.

.. _CMP0091:https://cmake.org/cmake/help/latest/policy/CMP0091.html
.. _property:https://cmake.org/cmake/help/latest/variable/CMAKE_MSVC_RUNTIME_LIBRARY.html
.. https://discourse.cmake.org/t/mt-staticrelease-doesnt-match-value-md-dynamicrelease/5428/4
.. _msvc: https://learn.microsoft.com/en-us/cpp/build/reference/md-mt-ld-use-run-time-library
.. _issues: https://github.com/godotengine/godot-cpp/issues/1699

]=======================================================================]
function( windows_options )
    option( GODOT_USE_STATIC_CPP "Link MinGW/MSVC C++ runtime libraries statically" ON )
    option( GODOT_DEBUG_CRT "Compile with MSVC's debug CRT (/MDd)" OFF )

    message( STATUS "If not already cached, setting CMAKE_MSVC_RUNTIME_LIBRARY.\n"
            "\tFor more information please read godot-cpp/cmake/windows.cmake")

    set( CMAKE_MSVC_RUNTIME_LIBRARY
            "MultiThreaded$<IF:$<BOOL:${GODOT_DEBUG_CRT}>,DebugDLL,$<$<NOT:$<BOOL:${GODOT_USE_STATIC_CPP}>>:DLL>>"
            CACHE STRING "Select the MSVC runtime library for use by compilers targeting the MSVC ABI.")
endfunction()


#[===========================[ Target Generation ]===========================]
function( windows_generate )
    set( STATIC_CPP "$<BOOL:${GODOT_USE_STATIC_CPP}>")

    set_target_properties( ${TARGET_NAME}
            PROPERTIES
            PDB_OUTPUT_DIRECTORY "$<1:${CMAKE_SOURCE_DIR}/bin>"
    )

    target_compile_definitions( ${TARGET_NAME}
        PUBLIC
            WINDOWS_ENABLED
            $<${IS_MSVC}:
                TYPED_METHOD_BIND
                NOMINMAX
            >
    )

    target_link_options( ${TARGET_NAME}
            PUBLIC

            $<${NOT_MSVC}:
                -Wl,--no-undefined
                $<${STATIC_CPP}:
                    -static
                    -static-libgcc
                    -static-libstdc++
                >
            >

            $<${IS_CLANG}:-lstdc++>
    )

    common_compiler_flags()
endfunction()