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Contributing to Catch

Contents
Branches
Directory structure
Testing your changes
Documenting your code
Code constructs to watch out for

So you want to contribute something to Catch? That's great! Whether it's a bug fix, a new feature, support for additional compilers - or just a fix to the documentation - all contributions are very welcome and very much appreciated. Of course so are bug reports and other comments and questions.

If you are contributing to the code base there are a few simple guidelines to keep in mind. This also includes notes to help you find your way around. As this is liable to drift out of date please raise an issue or, better still, a pull request for this file, if you notice that.

Branches

Ongoing development is currently on master. At some point an integration branch will be set-up and PRs should target that - but for now it's all against master. You may see feature branches come and go from time to time, too.

Directory structure

Users of Catch primarily use the single header version. Maintainers should work with the full source (which is still, primarily, in headers). This can be found in the include folder. There are a set of test files, currently under projects/SelfTest. The test app can be built via CMake from the CMakeLists.txt file in the root, or you can generate project files for Visual Studio, XCode, and others (instructions in the projects folder). If you have access to CLion, it can work with the CMake file directly.

As well as the runtime test files you'll also see a SurrogateCpps directory under projects/SelfTest. This contains a set of .cpp files that each #include a single header. While these files are not essential to compilation they help to keep the implementation headers self-contained. At time of writing this set is not complete but has reasonable coverage. If you add additional headers please try to remember to add a surrogate cpp for it.

The other directories are scripts which contains a set of python scripts to help in testing Catch as well as generating the single include, and docs, which contains the documentation as a set of markdown files.

When submitting a pull request please do not include changes to the single include, or to the version number file as these are managed by the scripts!

Testing your changes

Obviously all changes to Catch's code should be tested. If you added new functionality, you should add tests covering and showcasing it. Even if you have only made changes to Catch internals (i.e. you implemented some performance improvements), you should still test your changes.

This means 2 things

Compiling Catch's SelfTest project:

$ cd Catch2
$ cmake -Bdebug-build -H. -DCMAKE_BUILD_TYPE=Debug
$ cmake --build debug-build

because code that does not compile is evidently incorrect. Obviously, you are not expected to have access to all the compilers and platforms supported by Catch2, but you should at least smoke test your changes on your platform. Our CI pipeline will check your PR against most of the supported platforms, but it takes an hour to finish -- compiling locally takes just a few minutes.

Running the tests via CTest:

$ cd debug-build
$ ctest -j 2 --output-on-failure

Note: When running your tests with multi-configuration generators like Visual Studio, you might get errors "Test not available without configuration." You then have to pick one configuration (e.g. -C Debug) in the ctest call.

If you added new tests, approval tests are very likely to fail. If they do not, it means that your changes weren't run as part of them. This might be intentional, but usually is not.

The approval tests compare current output of the SelfTest binary in various configurations against known good outputs. The reason it fails is, usually, that you've added new tests but have not yet approved the changes they introduce. This is done with the scripts/approve.py script, but before you do so, you need to check that the introduced changes are indeed intentional.

Documenting your code

If you have added new feature to Catch2, it needs documentation, so that other people can use it as well. This section collects some technical information that you will need for updating Catch2's documentation, and possibly some generic advise as well.

First, the technicalities:

We introduced version tags to the documentation, which show users in which version a specific feature was introduced. This means that newly written documentation should be tagged with a placeholder, that will be replaced with the actual version upon release. There are 2 styles of placeholders used through the documentation, you should pick one that fits your text better (if in doubt, take a look at the existing version tags for other features).
- > [Introduced](link-to-issue-or-PR) in Catch X.Y.Z - this placeholder is usually used after a section heading
- > X (Y and Z) was [introduced](link-to-issue-or-PR) in Catch X.Y.Z
- this placeholder is used when you need to tag a subpart of something, e.g. list
Crosslinks to different pages should target the top anchor, like this [link to contributing](contributing.md#top).
If you have introduced a new document, there is a simple template you should use. It provides you with the top anchor mentioned above, and also with a backlink to the top of the documentation:

<a id="top"></a>
# Cool feature

Text that explains how to use the cool feature.


---

[Home](Readme.md#top)

For pages with more than 4 subheadings, we provide a table of contents (ToC) at the top of the page. Because GitHub markdown does not support automatic generation of ToC, it has to be handled semi-manually. Thus, if you've added a new subheading to some page, you should add it to the ToC. This can be done either manually, or by running the updateDocumentToC.py script in the scripts/ folder.

Now, for the generic tips:

Usage examples are good
Don't be afraid to introduce new pages
Try to be reasonably consistent with the surrounding documentation

Code constructs to watch out for

This section is a (sadly incomplete) listing of various constructs that are problematic and are not always caught by our CI infrastructure.

If you are throwing an exception, it should be done via CATCH_ERROR or CATCH_RUNTIME_ERROR in catch_enforce.h. These macros will handle the differences between compilation with or without exceptions for you. However, some platforms (IAR) also have problems with exceptions-related functions, such as std::current_exceptions. We do not have IAR in our CI, but luckily there should not be too many reasons to use these. However, if you do, they should be kept behind a CATCH_CONFIG_DISABLE_EXCEPTIONS macro.

Unqualified usage of functions from C's stdlib

If you are using a function from C's stdlib, please include the header as <cfoo> and call the function qualified. The common knowledge that there is no difference is wrong, QNX and VxWorks won't compile if you include the header as <cfoo> and call the function unqualified.

This documentation will always be in-progress as new information comes up, but we are trying to keep it as up to date as possible.

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