Developer Tooling

Pre-commit hook

If you have all the relevant tools installed, you can have git automatically check the style of code and json by adding these commands to your git pre-commit hook (typically at .git/hooks/pre-commit):

git diff --cached --name-only -z HEAD | grep -z 'data/.*\.json' | \
    xargs -r -0 -L 1 ./tools/format/json_formatter.[ce]* || exit 1

make astyle-check || exit 1

More details below on how to make these work and other ways to invoke these tools.

Code style (astyle)

Automatic formatting of source code is performed by Artistic Style.

If you have both make and astyle installed then this can be done with:

make astyle

If you have only astyle then use:

astyle --options=.astylerc --recursive src/*.cpp,*.h tests/*.cpp,*.h

On Windows, there is an AStyle extension for Visual Studio 2019 with an unmerged update for Visual Studio 2022.


  1. Install aforementioned extension to Visual Studio IDE.

  2. Go to Tools - Options - AStyle Formatter - General.

  3. Import on Export/Import tab using Import button:


  1. After import is successful you can see imported rules on C/C++ tab:


  1. Close Options menu, open file to be astyled and use Format Document (Astyle) or Format Selection (Astyle) commands from Edit - Advanced menu.


Note: You can also configure keybindings for aforementioned commands in Tools - Options - Environment - Keybindings menu:


JSON style

See the JSON style guide.


In addition to the usual means of creating a tags file via e.g. ctags, we provide tools/json_tools/ to augment a tags file with locations of definitions taken from CDDA’s JSON data. is designed to safely update a tags file containing source code tags, so if you want both types of tags in your tags file then you can run ctags -R . && tools/json_tools/ Alternatively, there is a rule in the Makefile to do this for you; just run make ctags or make etags.


Cataclysm has a clang-tidy configuration file and if you have clang-tidy available you can run it to perform static analysis of the codebase. We test with clang-tidy from LLVM 12.0.0 with CI, so for the most consistent results, you might want to use that version.

To run it, you have a few options.

  • clang-tidy ships with a wrapper script

  • Use CMake’s built-in support by adding -DCMAKE_CXX_CLANG_TIDY=clang-tidy or similar, pointing it to your chosen clang-tidy version.

  • To run clang-tidy directly try something like

    grep '"file": "' build/compile_commands.json | \
      sed "s+.*$PWD/++;s+\"$++" | \
      egrep '.' | \
      xargs -P 9 -n 1 clang-tidy -quiet

    To focus on a subset of files add their names into the egrep regex in the middle of the command-line.

Custom clang-tidy plugin

We have written our own clang-tidy checks in a custom plugin. Unfortunately, clang-tidy as distributed by LLVM doesn’t support plugins, so making this work requires some extra steps.

Extreme tl;dr for Ubuntu Focal (including WSL)

The following set of commands should take you from zero to running clang-tidy equivalent to the CI job. This will lint all sources in a random order.

sudo apt install build-essential cmake clang-12 libclang-12-dev llvm-12 llvm-12-dev llvm-12-tools pip
sudo pip install compiledb lit
test -f /usr/bin/python || sudo ln -s /usr/bin/python3 /usr/bin/python
# The following command invokes clang-tidy exactly like CI does
COMPILER=clang++-12 CLANG=clang++-12 CMAKE=1 CATA_CLANG_TIDY=plugin TILES=1 LOCALIZE=0 ./build-scripts/

Ubuntu Focal

If you are on Ubuntu Focal then you might be able to get it working the same way our CI does. Add the LLVM 12 Focal source listed here to your sources.list, install the needed packages (clang-12 libclang-12-dev llvm-12-dev llvm-12-tools), and build Cataclysm with CMake, adding -DCATA_CLANG_TIDY_PLUGIN=ON.

Other Linux distributions

On other distributions you will probably need to build clang-tidy yourself.

  • Expect this process to take about 80GB of disk space.
  • Check out the llvm project, release 12 branch, with e.g. git clone --branch release/12.x --depth 1 llvm-12.
  • Enter the newly cloned repo cd llvm-12.
  • Patch in plugin support for clang-tidy using this patch. curl | patch -p1
  • Configure LLVM using CMake, including the -DCMAKE_EXE_LINKER_FLAGS="-rdynamic" option. Some additional options below are simply to reduce the amount of stuff that gets built. These might nee to be adjusted to your situation (e.g. if you’re on another architecture then choose that target instead of X86).
    mkdir build
    cd build
    cmake \
      -DCMAKE_BUILD_TYPE=RelWithDebInfo \
      -DCMAKE_EXE_LINKER_FLAGS="-rdynamic" \
      -DLLVM_ENABLE_PROJECTS='clang;clang-tools-extra;compiler-rt' \
  • Build LLVM make -j$(nproc). This can take a long time (maybe 6 core-hours or more).
  • Add the build/bin directory to your path so that clang-tidy and FileCheck are found from there.

Then you can use your locally built clang-tidy to compile Cataclysm. You’ll need to use the CMake version of the Cataclysm build rather than the Makefile build. Add the following CMake options:


where $llvm_dir is the location of your LLVM source directory.

To run clang-tidy with this plugin enabled add the '-plugins=$build_dir/tools/clang-tidy-plugin/' option to your clang-tidy command line.

If you wish to run the tests for the custom clang-tidy plugin you will also need lit. This will be built as part of LLVM, or you can install it via pip or your local package manager if you prefer.

Then, assuming build is your Cataclysm build directory, you can run the tests with

lit -v build/tools/clang-tidy-plugin/test


Build LLVM

It is probably faster and easier to install WSL and follow the steps described above in Extreme tl;dr for Ubuntu Focal (including WSL).

To build LLVM natively on Windows, you’ll first need to get some tools installed.

  • Cmake
  • Python 3
  • MinGW-w64 (other compilers may or may not work. Clang itself does not seem to be building LLVM on Windows correctly.)
  • A shell environment

After the tools are installed, a patch still needs to be applied before building LLVM, since clang-tidy as distributed by LLVM doesn’t support plugins.

First, clone the LLVM repo from, for example, the official github repo. Checkout the release/12.x branch, since that’s what our patch was based on.

On Windows, in addition to applying plugin-support.patch mentioned in the previous section, you should also apply clang-tidy-scripts.patch so you can run the lit test with the custom clang-tidy executable and let clang-tidy apply suggestions automatically.

After the patch is applied, you can then build the LLVM code. Unfortunately, it seems that clang itself cannot correctly compile the LLVM code on Windows (gives some sort of relocation error). Luckily, MinGW-w64 can be used instead to compile the code.

The first step to build the code is to run CMake to generate the makefile. On the root dir of LLVM, run the following script (substitute values inside <> with the actual paths). Make sure CMake, python, and MinGW-w64 are on the path.

mkdir -p build
cd build
cmake \
    -DCMAKE_MAKE_PROGRAM="<mingw-w64-root>/bin/mingw32-make" \
    -G "MSYS Makefiles" \
    -DLLVM_ENABLE_PROJECTS='clang;clang-tools-extra' \

The next step is to call make to actually build clang-tidy as a library. When using MinGW-w64 to build, you should call mingw32-make instead. Also, because FileCheck is not shipped with Windows, you’ll also need to build it yourself using LLVM sources by adding the FileCheck target to the make command.

mkdir -p build
cd build
mingw32-make -j4 clang-tidy clangTidyMain FileCheck

Here clang-tidy is only added to trigger the building of several targets that are needed to build our custom clang-tidy executable later.

Build clang-tidy with custom checks

After building clang-tidy as a library from the LLVM source, the next step is to build clang-tidy as an executable, with the custom checks from the CDDA source.

In this step, the following tools are required.

  • Python 3
  • CMake
  • MinGW-w64
  • FileCheck (built from the LLVM source)
  • A shell environment

You also need to install yaml for python 3 to work. Download the .whl installer corresponding to your python version from here and execute the following command inside the <python3_root>/Scripts directory

pip install path/to/your/downloaded/file.whl

The next step is to run CMake to generate the compilation database. The compilation database contains compiler flags that clang-tidy uses to check the source files.

Make sure Python 3, CMake, MinGW-w64, and FileCheck are on the path. Note that two bin directories of MinGW-w64 should be on the path: <mingw-w64-root>/bin, and <mingw-w64-root>/x86_64-w64-mingw32/bin. FileCheck’s path is <llvm-source-root>/build/bin, if you built it with the instructions in the previous section.

Then add the following CMake options to generate the compilation database (substitute values inside <> with the actual paths) and build the CDDA source and the custom clang-tidy executable with mingw32-make. In this tutorial we run CMake and mingw32-make in the build subdirectory. Note that DCATA_CLANG_TIDY_EXECUTABLE is defined instead of DCATA_CLANG_TIDY_PLUGIN.

-DCATA_CHECK_CLANG_TIDY="<llvm-source-root>/clang-tools-extra/test/clang-tidy/ -clang-tidy=<cdda-source-root>/build/tools/clang-tidy-plugin/CataAnalyzer.exe"

Next, change the directory back to the source root and run tools/ with Python 3 to fix some errors in the compilation database. Then the compilation database should be usable by clang-tidy.

If you want to check if the custom checks are working correctly, run the following script.

python3 <llvm-source-root>/llvm/utils/lit/ -v build/tools/clang-tidy-plugin/test

Finally, use the following command to run clang-tidy with the custom checks. In the following command, the first line of “-extra-arg”s are used to tell clang-tidy to mimic g++ behavior, and the second line of “-extra-arg”s are used to tell clang-tidy to use clang’s x86intrin.h instead of g++’s, so as to avoid compiler errors.

python3 <llvm-source-root>/clang-tools-extra/clang-tidy/tool/ \
    -clang-tidy-binary=build/tools/clang-tidy-plugin/CataAnalyzer.exe \
    -p=build "\.cpp$" \
    -extra-arg=-target -extra-arg=x86_64-pc-windows-gnu -extra-arg=-pthread -extra-arg=-DSDL_DISABLE_ANALYZE_MACROS \
    -extra-arg=-isystem -extra-arg=<llvm-source-root>/clang/lib/Headers

You can also add -fix-errors to apply fixes reported by the checks or -checks="-*,xxx,yyy" to specify the checks you would like to run.


include-what-you-use (IWYU) is a project intended to optimize includes. It will calculate the required headers and add and remove includes as appropriate.

Running IWYU on this codebase revealed some issues. You will need a version of IWYU where the following PR has been merged (which has not yet happened at time of writing, but with luck might make it into the clang-10 release of IWYU):


Once you have IWYU built, build the codebase using CMake, with CMAKE_EXPORT_COMPILE_COMMANDS=ON on to create a compilation database (Look for compile_commands.json in the build dir to see whether that worked).

Then run: -p $CMAKE_BUILD_DIR/compile_commands.json -- -Xiwyu --mapping_file=$PWD/tools/iwyu/cata.imp | --nosafe_headers --reorder

IWYU will sometimes add C-style library headers which clang-tidy doesn’t like, so you might need to run clang-tidy (as described above) and then re-run IWYU a second time.

There are mapping files in tools/iwyu intended to help IWYU pick the right headers. Mostly they should be fairly obvious, but the SDL mappings might warrant further explanation. We want to force most SDL includes to go via sdl_wrappers.h, because that handles the platform-dependence issues (the include paths are different on Windows). There are a couple of exceptions (SDL_version.h and SDL_mixer.h). The former is because main.cpp can’t include all SDL headers, because they #define WinMain. All the mappings in sdl.imp are designed to make this happen.

We have to use IWYU pragmas in some situations. Some of the reasons are:

  • IWYU has a concept of associated headers, where each cpp file can have some number of such headers. The cpp file is expected to define the things declared in those headers. In Cata, the mapping between headers and cpp files is not nearly so simple, so there are files with multiple associated headers, and files with none. Headers that are not the associated header of any cpp file will not get their includes updated, which could lead to broken builds, so ideally all headers would be associated to some cpp file. You can use the following command to get a list of headers which are not currently associated to any cpp file (requires GNU sed):
diff <(ls src/*.h | sed 's!.*/!!') <(for i in src/*.cpp; do echo $i; sed -n '/^#include/{p; :loop n; p; /^$/q; b loop}' $i; done | grep 'e "' | grep -o '"[^"]*"' | sort -u | tr -d '"')
  • Due to a clang bug, uses in template arguments to explicit instantiations are not counted, which leads to some need for IWYU pragma: keep.

  • Due to these missing features of IWYU, it does not count uses in template arguments to return types, which leads to other requirements for IWYU pragma: keep.

  • IWYU seems to have particular trouble with types used in maps and cata::optional (NOTE: cata::optional replaced with std::optional around the C++17 migration). Have not looked into this in detail, but again worked around it with pragmas.

Python and pyvips on Windows

They are needed to work with and some other tileset infrastructure scripts. See