zig/.github/CONTRIBUTING.md

Contributing

Start a Project Using Zig

One of the best ways you can contribute to Zig is to start using it for a personal project. Here are some great examples:

• TM35-Metronome - tools for modifying and randomizing Pokémon games
• River - a dynamic tiling wayland compositor

More examples can be found on the Community Projects Wiki.

Without fail, these projects lead to discovering bugs and helping flesh out use cases, which lead to further design iterations of Zig. Importantly, each issue found this way comes with real world motivations, so it is easy to explain your reasoning behind proposals and feature requests.

Ideally, such a project will help you to learn new skills and add something to your personal portfolio at the same time.

Spread the Word

Another way to contribute is to write about Zig, or speak about Zig at a conference, or do either of those things for your project which uses Zig. Here are some examples:

• Iterative Replacement of C with Zig
• The Right Tool for the Right Job: Redis Modules & Zig
• Writing a small ray tracer in Rust and Zig

Zig is a brand new language, with no advertising budget. Word of mouth is the only way people find out about the project, and the more people hear about it, the more people will use it, and the better chance we have to take over the world.

Finding Contributor Friendly Issues

Please note that issues labeled Proposal but do not also have the Accepted label are still under consideration, and efforts to implement such a proposal have a high risk of being wasted. If you are interested in a proposal which is still under consideration, please express your interest in the issue tracker, providing extra insights and considerations that others have not yet expressed. The most highly regarded argument in such a discussion is a real world use case.

The issue label Contributor Friendly exists to help you find issues that are limited in scope and/or knowledge of Zig internals.

Editing Source Code

First, build the Stage 1 compiler as described in Building Zig From Source.

Zig locates lib files relative to executable path by searching up the filesystem tree for a sub-path of lib/zig/std/std.zig or lib/std/std.zig. Typically the former is an install and the latter a git working tree which contains the build directory.

During development it is not necessary to perform installs when modifying stage1 or userland sources and in fact it is faster and simpler to run, test and debug from a git working tree.

• make is typically sufficient to build zig during development iterations.
• make install performs a build and install.
• msbuild -p:Configuration=Release INSTALL.vcxproj on Windows performs a build and install. To avoid install, pass cmake option -DZIG_NO_LIB=ON.

To test changes, do the following from the build directory:

1. Run make (on POSIX) or msbuild -p:Configuration=Release INSTALL.vcxproj (on Windows).
2. $BUILD_DIR/zig build test (on POSIX) or $BUILD_DIR/Release\zig.exe build test (on Windows).

That runs the whole test suite, which does a lot of extra testing that you likely won't always need, and can take upwards of 1 hour. This is what the CI server runs when you make a pull request. (Note: actually it runs a few more tests; keep reading.)

To save time, you can add the --help option to the zig build command and see what options are available. One of the most helpful ones is -Dskip-release. Adding this option to the command in step 2 above will take the time down from around 2 hours to about 6 minutes, and this is a good enough amount of testing before making a pull request.

Another example is choosing a different set of things to test. For example, test-std instead of test will only run the standard library tests, and not the other ones. Combining this suggestion with the previous one, you could do this:

$BUILD_DIR/bin/zig build test-std -Dskip-release (on POSIX) or $BUILD_DIR/Release\zig.exe build test-std -Dskip-release (on Windows).

This will run only the standard library tests, in debug mode only, for all targets (it will cross-compile the tests for non-native targets but not run them).

When making changes to the compiler source code, the most helpful test step to run is test-behavior. When editing documentation it is docs. You can find this information and more in the --help menu.

Testing Changes to std lib

To quickly test a change to a file in the standard library, you can run zig test and specify a custom lib directory with the follow command-line argument.

./build/zig test lib/std/fmt.zig --zig-lib-dir lib --main-pkg-path lib/std

Testing Non-Native Architectures with QEMU

The Linux CI server additionally has qemu installed and sets -fqemu. This provides test coverage for, e.g. aarch64 even on x86_64 machines. It's recommended for Linux users to install qemu and enable this testing option when editing the standard library or anything related to a non-native architecture.

glibc

Testing foreign architectures with dynamically linked glibc is one step trickier. This requires enabling --glibc-runtimes /path/to/glibc/multi/install/glibcs. This path is obtained by building glibc for multiple architectures. This process for me took an entire day to complete and takes up 65 GiB on my hard drive. The CI server does not provide this test coverage. Instructions for producing this path can be found on the wiki. Just the part with build-many-glibcs.py.

It's understood that most contributors will not have these tests enabled.

Testing Windows from a Linux Machine with Wine

When developing on Linux, another option is available to you: -fwine. This will enable running behavior tests and std lib tests with Wine. It's recommended for Linux users to install Wine and enable this testing option when editing the standard library or anything Windows-related.

Testing WebAssembly using wasmtime

If you have wasmtime installed, take advantage of the -fwasmtime flag which will enable running WASI behavior tests and std lib tests. It's recommended for all users to install wasmtime and enable this testing option when editing the standard library and especially anything WebAssembly-related.

Improving Translate-C

Please read the Editing Source Code section as a prerequisite to this one.

translate-c is a feature provided by Zig that converts C source code into Zig source code. It powers the zig translate-c command as well as @cImport, allowing Zig code to not only take advantage of function prototypes defined in .h files, but also static inline functions written in C, and even some macros.

This feature works by using libclang API to parse and semantically analyze C/C++ files, and then based on the provided AST and type information, generating Zig AST, and finally using the mechanisms of zig fmt to render the Zig AST to a file.

The relevant tests for this feature are:

• test/run_translated_c.zig - each test case is C code with a main function. The C code is translated into Zig code, compiled, and run, and tests that the expected output is the same, and that the program exits cleanly. This kind of test coverage is preferred, when possible, because it makes sure that the resulting Zig code is actually viable.

• test/stage1/behavior/translate_c_macros.zig - each test case consists of a Zig test which checks that the relevant macros in test/stage1/behavior/translate_c_macros.h. have the correct values. Macros have to be tested separately since they are expanded by Clang in run_translated_c tests.

• test/translate_c.zig - each test case is C code, with a list of expected strings which must be found in the resulting Zig code. This kind of test is more precise in what it measures, but does not provide test coverage of whether the resulting Zig code is valid.

This feature is self-hosted, even though Zig is not fully self-hosted yet. In the Zig source repo, we maintain a C API on top of Clang's C++ API:

• src/zig_clang.h - the C API that we maintain on top of Clang's C++ API. This file does not include any Clang's C++ headers. Instead, C types and C enums are defined here.

• src/zig_clang.cpp - a lightweight wrapper that fulfills the C API on top of the C++ API. It takes advantage of static_assert to make sure we get compile errors when Clang's C++ API changes. This one file necessarily does include Clang's C++ headers, which makes it the slowest-to-compile source file in all of Zig's codebase.

• src/clang.zig - the Zig equivalent of src/zig_clang.h. This is a manually maintained list of types and functions that are ABI-compatible with the Clang C API we maintain. In theory this could be generated by running translate-c on src/zig_clang.h, but that would introduce a dependency cycle, since we are using this file to implement translate-c.

Finally, the actual source code for the translate-c feature is src/translate_c.zig. This code uses the Clang C API exposed by src/clang.zig, and produces Zig AST.

The steps for contributing to translate-c look like this:

1. Identify a test case you want to improve. Add it as a run-translated-c test case (usually preferable), or as a translate-c test case.

2. Edit src/translate_c.zig to improve the behavior.

3. Run the relevant tests: ./zig build test-run-translated-c test-translate-c