How to use the tool include-what-you-use together with CMake to detect unused headers?

Question

The tool include-what-you-use can be used to detect unneeded headers. I am using CMake for my C++ software project. How can I instruct CMake to run include-what-you-use automatically on the source files of my software project?

Answer 1

CMake 3.3 introduced the new target property CXX_INCLUDE_WHAT_YOU_USE that can be set to the path of the program include-what-you-use. For instance this CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR) add_executable(hello main.cc)  find_program(iwyu_path NAMES include-what-you-use iwyu REQUIRED)  # If using CGAL<3.18, you remove REQUIRED and use # if(NOT iwyu_path) #   message(FATAL_ERROR "Could not find the program include-what-you-use") # endif()  set_property(TARGET hello PROPERTY CXX_INCLUDE_WHAT_YOU_USE ${iwyu_path}) 

is able to build the file main.cc

#include <iostream> #include <vector>  int main() {   std::cout << "Hello World!" << std::endl;   return 0; } 

and at the same time have include-what-you-use give out a warning that the included header vector is not needed.

user@ubuntu:/tmp$ ls ~/hello CMakeLists.txt  main.cc user@ubuntu:/tmp$ mkdir /tmp/build user@ubuntu:/tmp$ cd /tmp/build user@ubuntu:/tmp/build$ ~/cmake-3.3.0-rc2-Linux-x86_64/bin/cmake ~/hello -- The C compiler identification is GNU 4.9.2 -- The CXX compiler identification is GNU 4.9.2 -- Check for working C compiler: /usr/bin/cc -- Check for working C compiler: /usr/bin/cc -- works -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Detecting C compile features -- Detecting C compile features - done -- Check for working CXX compiler: /usr/bin/c++ -- Check for working CXX compiler: /usr/bin/c++ -- works -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Detecting CXX compile features -- Detecting CXX compile features - done -- Configuring done -- Generating done -- Build files have been written to: /tmp/build user@ubuntu:/tmp/build$ make Scanning dependencies of target hello [ 50%] Building CXX object CMakeFiles/hello.dir/main.cc.o Warning: include-what-you-use reported diagnostics:  /home/user/hello/main.cc should add these lines:  /home/user/hello/main.cc should remove these lines: - #include <vector>  // lines 2-2  The full include-list for /home/user/hello/main.cc: #include <iostream>  // for operator<<, basic_ostream, cout, endl, ostream ---  [100%] Linking CXX executable hello [100%] Built target hello user@ubuntu:/tmp/build$ ./hello  Hello World! user@ubuntu:/tmp/build$ 

If you want to pass custom options to include-what-you-use, like for instance --mapping_file you can do it via

set(iwyu_path_and_options     ${iwyu_path}     -Xiwyu     --mapping_file=${my_mapping})  set_property(TARGET hello     PROPERTY CXX_INCLUDE_WHAT_YOU_USE ${iwyu_path_and_options})