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Add CMake module to detect std::filesystem availability
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Carles Fernandez
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cmake/Modules/FindFILESYSTEM.cmake
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256
cmake/Modules/FindFILESYSTEM.cmake
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# Copyright (C) 2019 (see AUTHORS file for a list of contributors)
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#
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# This file is part of GNSS-SDR.
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#
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# GNSS-SDR is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# GNSS-SDR is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with GNSS-SDR. If not, see <https://www.gnu.org/licenses/>.
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# Original Source: https://github.com/vector-of-bool/CMakeCM
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# Modified by C. Fernandez-Prades.
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#[=======================================================================[.rst:
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FindFILESYSTEM
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##############
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This module supports the C++17 standard library's filesystem utilities. Use the
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:imp-target:`std::filesystem` imported target to
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Options
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*******
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The ``COMPONENTS`` argument to this module supports the following values:
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.. find-component:: Experimental
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:name: fs.Experimental
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Allows the module to find the "experimental" Filesystem TS version of the
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Filesystem library. This is the library that should be used with the
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``std::experimental::filesystem`` namespace.
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.. find-component:: Final
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:name: fs.Final
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Finds the final C++17 standard version of the filesystem library.
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If no components are provided, behaves as if the
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:find-component:`fs.Final` component was specified.
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If both :find-component:`fs.Experimental` and :find-component:`fs.Final` are
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provided, first looks for ``Final``, and falls back to ``Experimental`` in case
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of failure. If ``Final`` is found, :imp-target:`std::filesystem` and all
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:ref:`variables <fs.variables>` will refer to the ``Final`` version.
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Imported Targets
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****************
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.. imp-target:: std::filesystem
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The ``std::filesystem`` imported target is defined when any requested
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version of the C++ filesystem library has been found, whether it is
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*Experimental* or *Final*.
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If no version of the filesystem library is available, this target will not
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be defined.
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.. note::
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This target has ``cxx_std_17`` as an ``INTERFACE``
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:ref:`compile language standard feature <req-lang-standards>`. Linking
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to this target will automatically enable C++17 if no later standard
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version is already required on the linking target.
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.. _fs.variables:
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Variables
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*********
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.. variable:: CXX_FILESYSTEM_IS_EXPERIMENTAL
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Set to ``TRUE`` when the :find-component:`fs.Experimental` version of C++
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filesystem library was found, otherwise ``FALSE``.
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.. variable:: CXX_FILESYSTEM_HAVE_FS
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Set to ``TRUE`` when a filesystem header was found.
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.. variable:: CXX_FILESYSTEM_HEADER
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Set to either ``filesystem`` or ``experimental/filesystem`` depending on
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whether :find-component:`fs.Final` or :find-component:`fs.Experimental` was
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found.
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.. variable:: CXX_FILESYSTEM_NAMESPACE
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Set to either ``std::filesystem`` or ``std::experimental::filesystem``
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depending on whether :find-component:`fs.Final` or
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:find-component:`fs.Experimental` was found.
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Examples
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********
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Using `find_package(FILESYSTEM)` with no component arguments:
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.. code-block:: cmake
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find_package(FILESYSTEM REQUIRED)
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add_executable(my-program main.cpp)
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target_link_libraries(my-program PRIVATE std::filesystem)
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#]=======================================================================]
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if(TARGET std::filesystem)
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# This module has already been processed. Don't do it again.
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return()
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endif()
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include(CMakePushCheckState)
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include(CheckIncludeFileCXX)
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include(CheckCXXSourceCompiles)
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cmake_push_check_state()
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set(CMAKE_REQUIRED_QUIET ${FILESYSTEM_FIND_QUIETLY})
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# All of our tests require C++17 or later
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set(OLD_CMAKE_CXX_STANDARD ${CMAKE_CXX_STANDARD})
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set(CMAKE_CXX_STANDARD 17)
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if((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER "9.0.0"))
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set(CMAKE_REQUIRED_FLAGS "-std=c++17")
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endif()
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if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") AND NOT (CMAKE_CXX_COMPILER_VERSION VERSION_LESS "8.99"))
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set(CMAKE_REQUIRED_FLAGS "-std=c++17")
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endif()
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# Normalize and check the component list we were given
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set(want_components ${FILESYSTEM_FIND_COMPONENTS})
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if(FILESYSTEM_FIND_COMPONENTS STREQUAL "")
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set(want_components Final)
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endif()
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# Warn on any unrecognized components
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set(extra_components ${want_components})
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list(REMOVE_ITEM extra_components Final Experimental)
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foreach(component IN LISTS extra_components)
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message(WARNING "Extraneous find_package component for FILESYSTEM: ${component}")
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endforeach()
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# Detect which of Experimental and Final we should look for
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set(find_experimental TRUE)
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set(find_final TRUE)
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if(NOT "Final" IN_LIST want_components)
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set(find_final FALSE)
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endif()
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if(NOT "Experimental" IN_LIST want_components)
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set(find_experimental FALSE)
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endif()
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if(find_final)
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check_include_file_cxx("filesystem" _CXX_FILESYSTEM_HAVE_HEADER)
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mark_as_advanced(_CXX_FILESYSTEM_HAVE_HEADER)
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if(_CXX_FILESYSTEM_HAVE_HEADER)
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# We found the non-experimental header. Don't bother looking for the
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# experimental one.
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set(find_experimental FALSE)
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endif()
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else()
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set(_CXX_FILESYSTEM_HAVE_HEADER FALSE)
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endif()
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if(find_experimental)
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check_include_file_cxx("experimental/filesystem" _CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER)
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mark_as_advanced(_CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER)
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else()
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set(_CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER FALSE)
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endif()
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if(_CXX_FILESYSTEM_HAVE_HEADER)
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set(_have_fs TRUE)
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set(_fs_header filesystem)
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set(_fs_namespace std::filesystem)
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elseif(_CXX_FILESYSTEM_HAVE_EXPERIMENTAL_HEADER)
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set(_have_fs TRUE)
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set(_fs_header experimental/filesystem)
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set(_fs_namespace std::experimental::filesystem)
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else()
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set(_have_fs FALSE)
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endif()
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set(CXX_FILESYSTEM_HAVE_FS ${_have_fs} CACHE BOOL "TRUE if we have the C++ filesystem headers")
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set(CXX_FILESYSTEM_HEADER ${_fs_header} CACHE STRING "The header that should be included to obtain the filesystem APIs")
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set(CXX_FILESYSTEM_NAMESPACE ${_fs_namespace} CACHE STRING "The C++ namespace that contains the filesystem APIs")
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set(_found FALSE)
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if(CXX_FILESYSTEM_HAVE_FS)
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# We have some filesystem library available. Do link checks
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string(CONFIGURE [[
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#include <@CXX_FILESYSTEM_HEADER@>
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int main() {
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auto cwd = @CXX_FILESYSTEM_NAMESPACE@::current_path();
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return static_cast<int>(cwd.string().size());
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}
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]] code @ONLY)
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# Try to compile a simple filesystem program without any linker flags
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check_cxx_source_compiles("${code}" CXX_FILESYSTEM_NO_LINK_NEEDED)
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set(can_link ${CXX_FILESYSTEM_NO_LINK_NEEDED})
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if(NOT CXX_FILESYSTEM_NO_LINK_NEEDED)
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set(prev_libraries ${CMAKE_REQUIRED_LIBRARIES})
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set(CMAKE_REQUIRED_FLAGS "-std=c++17")
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# Add the libstdc++ flag
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set(CMAKE_REQUIRED_LIBRARIES ${prev_libraries} -lstdc++fs)
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check_cxx_source_compiles("${code}" CXX_FILESYSTEM_STDCPPFS_NEEDED)
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set(can_link ${CXX_FILESYSTEM_STDCPPFS_NEEDED})
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if(NOT CXX_FILESYSTEM_STDCPPFS_NEEDED)
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# Try the libc++ flag
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set(CMAKE_REQUIRED_LIBRARIES ${prev_libraries} -lc++fs)
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check_cxx_source_compiles("${code}" CXX_FILESYSTEM_CPPFS_NEEDED)
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set(can_link ${CXX_FILESYSTEM_CPPFS_NEEDED})
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endif()
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endif()
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if(can_link)
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add_library(std::filesystem INTERFACE IMPORTED)
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target_compile_features(std::filesystem INTERFACE cxx_std_17)
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set(_found TRUE)
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if(CXX_FILESYSTEM_NO_LINK_NEEDED)
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# Nothing to add...
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elseif(CXX_FILESYSTEM_STDCPPFS_NEEDED)
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target_link_libraries(std::filesystem INTERFACE -lstdc++fs)
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elseif(CXX_FILESYSTEM_CPPFS_NEEDED)
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target_link_libraries(std::filesystem INTERFACE -lc++fs)
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endif()
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endif()
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endif()
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if(NOT ${_found})
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set(CMAKE_CXX_STANDARD ${OLD_CMAKE_CXX_STANDARD})
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endif()
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cmake_pop_check_state()
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set(FILESYSTEM_FOUND ${_found} CACHE BOOL "TRUE if we can compile and link a program using std::filesystem" FORCE)
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if(FILESYSTEM_FIND_REQUIRED AND NOT FILESYSTEM_FOUND)
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message(FATAL_ERROR "Cannot compile a simple program using std::filesystem")
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endif()
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