How to add the option `llvm-config --cxxflags --ldflags --libs` in CMake? - cmake

Question

Does anyone know how to add the option `llvm-config --cxxflags --ldflags --libs` into CMake? The tricky part for me is the backtick `.
I need to config my CMake files to obtain a compilation command like:
g++ test.cpp -lclangBasic -I/usr/lib/llvm-6.0/include
-Wall `llvm-config --cxxflags --ldflags --libs`
I tried to use the following options, but they don't work:
add_compile_options(`llvm-config --cxxflags --ldflags --libs`)
# or
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} `llvm-config --cxxflags --ldflags --libs`")
Thank you in advance.
===============
Update 1.
Using the output from `llvm-config --cxxflags --ldflags --libs`, I can compile successfully with the following command:
g++ test.cpp -lclangBasic -I/usr/lib/llvm-6.0/include
-Wall -I/usr/lib/llvm-6.0/include -L/usr/lib/llvm-6.0/lib -lLLVM-6.0
I can pass -I/usr/lib/llvm-6.0/include by using include_directories(usr/lib/llvm-6.0/include).
But still, I don't know how to pass the part -L/usr/lib/llvm-6.0/lib -lLLVM-6.0 to CMake. Using link_directories and target_link_libraries like the following doesn't work for me:
link_directories(/usr/lib/llvm-6.0/lib)
target_link_libraries(test PUBLIC "LLVM-6.0")
Does anyone know to make them work in CMake?
===============
Update 2.
I have to add the following code into the file CMakeLists.txt to make CMake work.
add_library(LLVM-6.0 SHARED IMPORTED) # or STATIC instead of SHARED
set_target_properties(LLVM-6.0 PROPERTIES
IMPORTED_LOCATION "/usr/lib/llvm-6.0/lib/libLLVM-6.0.so"
INTERFACE_INCLUDE_DIRECTORIES "/usr/lib/llvm-6.0/include"
)
add_library(clangBasic SHARED IMPORTED) # or STATIC instead of SHARED
set_target_properties(clangBasic PROPERTIES
IMPORTED_LOCATION "/usr/lib/llvm-6.0/lib/libclangBasic.a"
INTERFACE_INCLUDE_DIRECTORIES "/usr/lib/llvm-6.0/include"
)
target_link_libraries(solidity PUBLIC "LLVM-6.0;clangBasic")
However, this looks manually, and I'm still looking for better solutions...

Answer 1

LLVM/Clang use CMake and provide a config module, so any project trying to use LLVM/Clang just need a find_package(Clang...) to bring the exported targets into a scope (and don't need to use any external tools (like llvm-config or pkg-config blah-blah)). Meaning that after Clang has found, you can use target_link_libraries(blah Clang::clangBasic ...) and no need to do any "manual import" or whatever ppl suggest in the comments...
As a quick check one may use the following command:
$ cmake --find-package -DNAME=Clang -DCOMPILER_ID=GNU -DLANGUAGE=CXX -DMODE=EXIST
Clang found.
$ cmake --find-package -DNAME=Clang -DCOMPILER_ID=GNU -DLANGUAGE=CXX -DMODE=COMPILE
-I/usr/lib/llvm-6.0/include
I used Clang 6.0 installed from the deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-6.0 main repo.