fix: fix build on MacOS when FindFileSystem fails

Author: aminya

cmake/FindFilesystem.cmake

@@ -248,5 +248,5 @@ 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 a simple program using std::filesystem\nYou need to update your C++ compiler to use this library")
+    message(STATUS "Could not run a simple program using std::filesystem\nYou might need to update your C++ compiler to use this library")
 endif()

source/matplot/CMakeLists.txt

@@ -102,7 +102,7 @@ target_include_directories(matplot
            $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 
 # Dependencies
-if(NOT MINGW)
+if(TARGET std::filesystem AND NOT MINGW)
 target_link_libraries_system(matplot
   PRIVATE cimg nodesoup std::filesystem)
 else()

test/generate_examples/CMakeLists.txt

@@ -1,8 +1,8 @@
 if(NOT MINGW)
-find_package(Filesystem REQUIRED)
+  find_package(Filesystem REQUIRED)
 endif()
 add_executable(generate_examples main.cpp)
-if(NOT MINGW)
-target_link_libraries(generate_examples std::filesystem)
+if(TARGET std::filesystem)
+  target_link_libraries(generate_examples std::filesystem)
 endif()
-target_compile_features(generate_examples PRIVATE cxx_std_17)
+target_compile_features(generate_examples PRIVATE cxx_std_17)