Cmake refactor

[Borwe]

Just some small refactoring:

1. Use add_compile_definitions instead of add_definitions
2. Shorten the code for checking c++17
3. Use FetchContent_MakeAvailable to make code simpler/shorter.

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This change is 

[codecov[bot]]

Codecov Report

Merging #1574 (8b7e932) into master (e1e9e09) will decrease coverage by 0.07%. The diff coverage is n/a.

:exclamation: Current head 8b7e932 differs from pull request most recent head 2cf01e3. Consider uploading reports for the commit 2cf01e3 to get more accurate results

@@            Coverage Diff             @@
##           master    #1574      +/-   ##
==========================================
- Coverage   96.32%   96.25%   -0.08%     
==========================================
  Files          90       90              
  Lines        7841     7906      +65     
  Branches      164      164              
==========================================
+ Hits         7553     7610      +57     
- Misses        235      244       +9     
+ Partials       53       52       -1     

[Borwe]

---

cpp/CMakeLists.txt, line 153 at r1 (raw file):

Previously, bstaletic (Boris Staletic) wrote…

This loses the compiler version checks. I'd love to be able to do it like this, but... std::filesystem arrived late. GCC 7 does have support for C++17, but is lacking std::filesystem. Same goes for Clang 6 and MSVC 1910.

Wait, I thaught that was the whole point of the dance try_compile @ cpp/ycm/CMakeLists.txt with :

# Check if we need to add -lstdc++fs or -lc++fs or nothing
file( WRITE ${CMAKE_CURRENT_BINARY_DIR}/main.cpp "#include <filesystem>\nint main( int argc, char ** argv ) {\n  std::filesystem::path p( argv[ 0 ] );\n  return p.string().length();\n}" )
try_compile( STD_FS_NO_LIB_NEEDED ${CMAKE_CURRENT_BINARY_DIR}
             SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
             CXX_STANDARD 17
             CXX_STANDARD_REQUIRED TRUE
             CXX_EXTENSIONS ${NEEDS_EXTENSIONS} )
try_compile( STD_FS_NEEDS_STDCXXFS ${CMAKE_CURRENT_BINARY_DIR}
             SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
             CXX_STANDARD 17
             CXX_STANDARD_REQUIRED TRUE
             CXX_EXTENSIONS ${NEEDS_EXTENSIONS}
             LINK_LIBRARIES stdc++fs )
try_compile( STD_FS_NEEDS_CXXFS ${CMAKE_CURRENT_BINARY_DIR}
             SOURCES ${CMAKE_CURRENT_BINARY_DIR}/main.cpp
             CXX_STANDARD 17
             CXX_STANDARD_REQUIRED TRUE
             CXX_EXTENSIONS ${NEEDS_EXTENSIONS}
             LINK_LIBRARIES c++fs )
file( REMOVE ${CMAKE_CURRENT_BINARY_DIR}/main.cpp )

if( ${STD_FS_NEEDS_STDCXXFS} )
  set( STD_FS_LIB stdc++fs )
elseif( ${STD_FS_NEEDS_CXXFS} )
  set( STD_FS_LIB c++fs )
elseif( ${STD_FS_NO_LIB_NEEDED} )
  set( STD_FS_LIB "" )
else()
  message( FATAL_ERROR "Unknown compiler - C++17 filesystem library missing" )
endif()

[puremourning]

@MergifyIO rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[puremourning]

@mergifyio rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[puremourning]

Seems abandoned, and I'm not sure that the risk of this warrants the benefit we get from it.