Contributing to Inko

Before you continue reading this document, please familiarise yourself with our Code of Conduct. All contributors are expected to adhere to this code of conduct.

Creating issues

Reporting bugs

Bugs should be reported at the appropriate issue tracker. For example, bugs for Inko itself should be reported in the project inko-lang/inko, while bugs specific to Inko's version manager should be reported in the project inko-lang/ivm. Here are a few of our projects:

ProjectDescriptionIssue tracker
inko-lang/inkoThe main project for Inko
inko-lang/ivmInko's version manager
inko-lang/inko.vimVim integration for Inko
inko-lang/websiteThe Inko website

For an up to date list, take a look at the inko-lang GitHub group.

Before reporting a bug, please make sure an issue doesn't already exist for the bug. To find all reported bugs, filter the list of issues using the bug label. Duplicate issues may be closed without warning. If you found an existing issue, please don't reply with comments such as "Me too!" and "+1". Instead, click on the thumbs up Emoji displayed when viewing the issue.

If no issue exists for the bug, please create a new issue. When reporting an issue, please use the "bug" issue template. You can find this template in the "Description" dropdown.

When selected, the issue description will be filled in with the template. Please fill in all the necessary fields and sections. The more information you provide, the easier it will be for maintainers to help you out.

Feature requests

Before creating an issue to request a new feature, make sure no issue already exists. Features use the label feature. Similar to existing bug reports, please use the thumbs up Emoji if you'd like to see the feature implemented; instead of replying with comments such as "+1".

If no issue exists, you can create one using the "feature" issue template. When requesting a new feature, please fill in all the sections of the issue template. Also please include examples of how your feature would be used, details about how other languages implement the feature (if applicable), and so on.

Submitting changes

Before submitting code changes, please note that we only accept merge requests for issues labelled as "Accepting contributions".

To submit changes to Inko, you'll need a local Git clone of the repository. If you want to contribute to inko-lang/inko, you need to build Inko from source.

Rust code

Rust code is formatted using rustfmt, and clippy is used for additional linting. You can install both using rustup as follows:

rustup component add rustfmt clippy

For rustfmt we recommend setting up your editor so it automatically formats your code. If this isn't possible, you can run it manually like so:

rustfmt --emit files */src/ */src/

Clippy can be run using the command cargo clippy. Unit tests are run using the cargo test command.

Inko code

For contributing changes to Inko source code, please follow the Inko style guide. We don't have any tools yet to enforce the style guide, so this is done manually during code review.

Standard library tests

Unit tests for Inko are located in std/test and are named test_X.inko, where X is the module to test. For example, the tests for std.string are located in std/test/std/test_string.inko. Test modules are structured as follows:

import std.test.Tests

fn pub tests(t: mut Tests) {
  t.test('Test name') fn (t) {
    t.equal(foo, bar)

To run the stdlib tests:

  1. Enter the std directory cd std

2. Run the tests using cargo run -p inko --release -- test

Compiler diagnostic tests

The test suite also contains tests for the compiler. These tests are structured differently, and are meant to test the diagnostics the compiler produces based on the input it's provided. We write such tests in Inko instead of Rust, as writing them in Rust requires a lot of boilerplate for every test. These diagnostic tests are located in std/test/diagnostics. The test files can be anything as long as they don't start with test_, for example:

$ ls std/test/diagnostics/
duplicate_class.inko  duplicate_method.inko  duplicate_trait.inko ...

The contents of these files can be anything. If a directory with the same name as the test (minus the extension) exists, it's automatically added to the include path. This allows you to import files specific to the test, without cluttering the diagnostics directory.

Assertions are defined by adding comments at the end of the file using this format:


When running inko test, these lines are parsed into a list of expected diagnostics, which is then compared to the list of diagnostics produced by running inko check with the test file (e.g. duplicate_method.inko) as its input. An example of such a test is the following:

fn a {}
fn a {}

# duplicate_method.inko:2:1 error(duplicate-symbol): the symbol 'a' is already defined

Writing diagnostic tests is simple:

  1. Create the file in std/test/diagnostics/NAME.inko, where NAME is the name of the test (e.g. duplicate_class or undefined_local_variable)
  2. If you need additional files, place them in std/test/diagnostics/NAME/, you can then import these files as usual
  3. Run inko check on the NAME.inko file to get a list of diagnostics
  4. Copy these to the end of the file as shown in the example above
  5. Make sure the paths of the diagnostics are relative to std/test/diagnostics
  6. Run inko test to run all tests or inko test diagnostics to run all diagnostics tests, and make sure they all pass. You can run a specific diagnostics test using inko test NAME diagnostics (e.g. inko test duplicate_method diagnostics)

Shell scripts

Some parts of our continuous integration setup depend on some shell scripts. These scripts are checked using shellcheck. Lines are wrapped at 80 characters per line.


Documentation is written in Markdown. For the manual we use Vale to enforce a consistent style. We recommend setting up your editor so it automatically checks Markdown using Vale. If this isn't possible, you can run Vale manually like so:

vale docs

For English, we use British English instead of American English.

Writing commit messages

Writing a good commit message is important. Code and tests help explain what is implemented and how it works. Commit messages help explain the thought process that went into these changes, who is involved in the work, what work may be related, and more. This information is invaluable to maintainers, for example when debugging a bug introduced some time in the past.

Commit messages follow these rules:

  1. The first line is the subject, and must not be longer than 50 characters.
  2. The second line is empty.
  3. The third and following lines make up the commit body. These lines must not be longer than 72 characters.

The second and all following lines can be left out if the subject is explanatory enough.

The first line of a commit message is used when updating a project's changelog.

Here is an example of a good commit message:

Lint commits using gitlint

This adds a CI job called `lint:gitlint` that lints commits using
gitlint ( In addition, we
include three custom linters to help enforce good commit message
practises. For example, commit bodies may not be longer than 72
characters _unless_ they exceed this limit due to a URL.

Another example can be seen in commit b64323.

When writing commit messages, please refrain from including tags like "feat:", "bug:", and others recommended by projects such as Conventional Commits. Such information is not helpful when looking at commits, and is better suited for issues and merge requests. Keeping the above rules in mind, it also reduces the amount of space available per line; the subject in particular.

These rules are enforced using gitlint, which runs as part of our continuous integration setup. If needed, you can run gitlint manually like so:


To run gitlint for the last 10 commits:

gitlint --commits 'HEAD~10..HEAD'

For more details about writing commit messages, take a look at this article.

Changelog entries

The changelog is generated from Git commits. To include a commit in the changelog, add the Changelog trailer to the end of the commit. This trailer can be set to the following values:

  • added: for new features
  • fixed: for bug fixes
  • changed: for something that changed but isn't necessarily a bug fix
  • other: for any other kind of change
  • performance: improvements to the performance of Inko

For example:

This is the subject of a commit

This is the body of the commit message, providing more details about the

Changelog: fixed