Include What You Use

Include-what-you-use is a promising little tool for cleaning up a codebase. It didn’t end up working for the use I had for it, but it still could be useful. Here is a quick guideline on installing it on macOS.

Install to a brew llvm install

First, install the latest LLVM suite using brew (brew install llvm). You’ll want to activate this install; I use LMod (the files here). Pay attention to what version you end up getting.

Next, you’ll follow the guidelines on a out-of-source install. Basically, that amounts to:

mkdir IWYU
git clone
cd include-what-you-use
git checkout clang_5.0 # Or whatever you got with brew
cd ..
mkdir build
cd build
cmake ../include-what-you-use -DCMAKE_INSTALL_PREFIX=$(brew --prefix llvm) -DIWYU_LLVM_ROOT_PATH=$(brew --prefix llvm)
make install

(If you are using fish instead of bash, remove the $)


Then, to use in another CMake project:

cmake .. -DCMAKE_CXX_INCLUDE_WHAT_YOU_USE=$(which include-what-you-use)
make 2> iwyu.out -n --nosafe_headers --comments < iwyu.ou

(remove the -n to actually make the changes)

That’s all there is to it! It, unfortunately, broke the software I was trying to clean up, but the idea is great.

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