Draft: Resolve "New feature: data staging API"

# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying

# file Copyright.txt or https://cmake.org/licensing for details.

#[=======================================================================[.rst:

FindFilesystem

##############

This module supports the C++17 standard library's filesystem utilities. Use the

:imp-target:`std::filesystem` imported target to

Options

*******

The ``COMPONENTS`` argument to this module supports the following values:

.. find-component:: Experimental

    :name: fs.Experimental

    Allows the module to find the "experimental" Filesystem TS version of the

    Filesystem library. This is the library that should be used with the

    ``std::experimental::filesystem`` namespace.

.. find-component:: Final

    :name: fs.Final

    Finds the final C++17 standard version of the filesystem library.

If no components are provided, behaves as if the

:find-component:`fs.Final` component was specified.

If both :find-component:`fs.Experimental` and :find-component:`fs.Final` are

provided, first looks for ``Final``, and falls back to ``Experimental`` in case

of failure. If ``Final`` is found, :imp-target:`std::filesystem` and all

:ref:`variables <fs.variables>` will refer to the ``Final`` version.

Imported Targets

****************

.. imp-target:: std::filesystem

    The ``std::filesystem`` imported target is defined when any requested

    version of the C++ filesystem library has been found, whether it is

    *Experimental* or *Final*.

    If no version of the filesystem library is available, this target will not

    be defined.

    .. note::

        This target has ``cxx_std_17`` as an ``INTERFACE``

        :ref:`compile language standard feature <req-lang-standards>`. Linking

        to this target will automatically enable C++17 if no later standard

        version is already required on the linking target.

.. _fs.variables:

Variables

*********

.. variable:: CXX_FILESYSTEM_IS_EXPERIMENTAL

    Set to ``TRUE`` when the :find-component:`fs.Experimental` version of C++

    filesystem library was found, otherwise ``FALSE``.

.. variable:: CXX_FILESYSTEM_HAVE_FS

    Set to ``TRUE`` when a filesystem header was found.

.. variable:: CXX_FILESYSTEM_HEADER

    Set to either ``filesystem`` or ``experimental/filesystem`` depending on

    whether :find-component:`fs.Final` or :find-component:`fs.Experimental` was

    found.

.. variable:: CXX_FILESYSTEM_NAMESPACE

    Set to either ``std::filesystem`` or ``std::experimental::filesystem``

    depending on whether :find-component:`fs.Final` or

    :find-component:`fs.Experimental` was found.

Examples

********

Using `find_package(Filesystem)` with no component arguments:

.. code-block:: cmake

    find_package(Filesystem REQUIRED)

    add_executable(my-program main.cpp)

    target_link_libraries(my-program PRIVATE std::filesystem)

#]=======================================================================]

if(TARGET std::filesystem)

    # This module has already been processed. Don't do it again.

    return()

endif()

cmake_minimum_required(VERSION 3.10)

include(CMakePushCheckState)

include(CheckIncludeFileCXX)

# If we're not cross-compiling, try to run test executables.

# Otherwise, assume that compile + link is a sufficient check.

if(CMAKE_CROSSCOMPILING)

    include(CheckCXXSourceCompiles)

    macro(_cmcm_check_cxx_source code var)

        check_cxx_source_compiles("${code}" ${var})

    endmacro()

else()

    include(CheckCXXSourceRuns)

    macro(_cmcm_check_cxx_source code var)

        check_cxx_source_runs("${code}" ${var})

    endmacro()

endif()

cmake_push_check_state()

set(CMAKE_REQUIRED_QUIET ${Filesystem_FIND_QUIETLY})

# All of our tests required C++17 or later

set(CMAKE_CXX_STANDARD 17)

# Normalize and check the component list we were given

set(want_components ${Filesystem_FIND_COMPONENTS})

if(Filesystem_FIND_COMPONENTS STREQUAL "")

    set(want_components Final)

endif()

# Warn on any unrecognized components

set(extra_components ${want_components})

list(REMOVE_ITEM extra_components Final Experimental)

foreach(component IN LISTS extra_components)

    message(WARNING "Extraneous find_package component for Filesystem: ${component}")

endforeach()

# Detect which of Experimental and Final we should look for

set(find_experimental TRUE)

set(find_final TRUE)

if(NOT "Final" IN_LIST want_components)

    set(find_final FALSE)

endif()

if(NOT "Experimental" IN_LIST want_components)

    set(find_experimental FALSE)

endif()

if(find_final)

    check_include_file_cxx("filesystem" _CXX_FILESYSTEM_HAVE_HEADER)

    mark_as_advanced(_CXX_FILESYSTEM_HAVE_HEADER)

    if(_CXX_FILESYSTEM_HAVE_HEADER)

        # We found the non-experimental header. Don't bother looking for the

        # experimental one.

        set(find_experimental FALSE)

    endif()

else()

    set(_CXX_FILESYSTEM_HAVE_HEADER FALSE)

endif()

if(find_experimental)

    check_include_file_cxx("experimental/filesystem" _CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER)

    mark_as_advanced(_CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER)

else()

    set(_CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER FALSE)

endif()

if(_CXX_FILESYSTEM_HAVE_HEADER)

    set(_have_fs TRUE)

    set(_fs_header filesystem)

    set(_fs_namespace std::filesystem)

    set(_is_experimental FALSE)

elseif(_CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER)

    set(_have_fs TRUE)

    set(_fs_header experimental/filesystem)

    set(_fs_namespace std::experimental::filesystem)

    set(_is_experimental TRUE)

else()

    set(_have_fs FALSE)

endif()

set(CXX_FILESYSTEM_HAVE_FS ${_have_fs} CACHE BOOL "TRUE if we have the C++ filesystem headers")

set(CXX_FILESYSTEM_HEADER ${_fs_header} CACHE STRING "The header that should be included to obtain the filesystem APIs")

set(CXX_FILESYSTEM_NAMESPACE ${_fs_namespace} CACHE STRING "The C++ namespace that contains the filesystem APIs")

set(CXX_FILESYSTEM_IS_EXPERIMENTAL ${_is_experimental} CACHE BOOL "TRUE if the C++ filesystem library is the experimental version")

set(_found FALSE)

if(CXX_FILESYSTEM_HAVE_FS)

    # We have some filesystem library available. Do link checks

    string(CONFIGURE [[

        #include <cstdlib>

        #include <@CXX_FILESYSTEM_HEADER@>

        int main() {

            auto cwd = @CXX_FILESYSTEM_NAMESPACE@::current_path();

            printf("%s", cwd.c_str());

            return EXIT_SUCCESS;

        }

    ]] code @ONLY)

    # Check a simple filesystem program without any linker flags

    _cmcm_check_cxx_source("${code}" CXX_FILESYSTEM_NO_LINK_NEEDED)

    set(can_link ${CXX_FILESYSTEM_NO_LINK_NEEDED})

    if(NOT CXX_FILESYSTEM_NO_LINK_NEEDED)

        set(prev_libraries ${CMAKE_REQUIRED_LIBRARIES})

        # Add the libstdc++ flag

        set(CMAKE_REQUIRED_LIBRARIES ${prev_libraries} -lstdc++fs)

        _cmcm_check_cxx_source("${code}" CXX_FILESYSTEM_STDCPPFS_NEEDED)

        set(can_link ${CXX_FILESYSTEM_STDCPPFS_NEEDED})

        if(NOT CXX_FILESYSTEM_STDCPPFS_NEEDED)

            # Try the libc++ flag

            set(CMAKE_REQUIRED_LIBRARIES ${prev_libraries} -lc++fs)

            _cmcm_check_cxx_source("${code}" CXX_FILESYSTEM_CPPFS_NEEDED)

            set(can_link ${CXX_FILESYSTEM_CPPFS_NEEDED})

        endif()

    endif()

    if(can_link)

        add_library(std::filesystem INTERFACE IMPORTED)

        set_property(TARGET std::filesystem APPEND PROPERTY INTERFACE_COMPILE_FEATURES cxx_std_17)

        set(_found TRUE)

        if(CXX_FILESYSTEM_NO_LINK_NEEDED)

            # Nothing to add...

        elseif(CXX_FILESYSTEM_STDCPPFS_NEEDED)

            set_property(TARGET std::filesystem APPEND PROPERTY INTERFACE_LINK_LIBRARIES -lstdc++fs)

        elseif(CXX_FILESYSTEM_CPPFS_NEEDED)

            set_property(TARGET std::filesystem APPEND PROPERTY INTERFACE_LINK_LIBRARIES -lc++fs)

        endif()

    endif()

endif()

cmake_pop_check_state()

set(Filesystem_FOUND ${_found} CACHE BOOL "TRUE if we can run a program using std::filesystem" FORCE)

if(Filesystem_FIND_REQUIRED AND NOT Filesystem_FOUND)

    message(FATAL_ERROR "Cannot run simple program using std::filesystem")

endif()

Subproject commit 0af45bfa667f7ff9c78167ef94d975bffbd879f0

Subproject commit 97820ed81aba9ef7c05891ce80c53a8533b78609