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Contributing

Table of contents

Overview

Thank you for your interest in contributing to Carbon! There are many ways to contribute, and we appreciate all of them. If you have questions, please feel free to ask on Discord #contributing-help channel or GitHub.

Everyone who contributes to Carbon is expected to:

We also encourage anyone interested in contributing to check out all the information here in our contributing guide, especially the guidelines and philosophy for contributions

Ways to contribute

Contributing to the language design

Comment on proposals

If you're looking for a quick way to contribute, commenting on proposals is a way to provide proposal authors with a breadth of feedback. The "leads questions" label has questions the community is looking for a decision on. The list of open proposals will have more mature proposals that are nearing a decision. For more about the difference, see the evolution process.

When giving feedback, please keep comments positive, constructive, and concise. Our goal is to use community discussion to improve proposals and assist authors.

Contribute design ideas to Carbon

If you have ideas for Carbon, we encourage you to discuss it with the community, and potentially prepare a proposal for it. Ultimately, any changes or improvements to Carbon will need to turn into a proposal and go through our evolution process.

If you do start working on a proposal, keep in mind that this requires a time investment to discuss the idea with the community, get it reviewed, and eventually implemented. A good starting point is to read through the evolution process. We encourage discussing the idea early, before even writing a proposal, and the process explains how to do that.

Contributing to the language implementation

Experiment with Carbon and report issues (no code)

You can experiment with the current implementation of the Carbon language using the online version of Carbon Explorer. The state of the design implementation for Explorer is documented on the "Are we explorer yet" wiki page.

If you uncover a bug or implementation problem, you can report an issue on GitHub.

Review and comment on Pull Requests (no code)

Helping with pull requests review is a good way to provide feedback, while getting a acquainted with the code base.

Implement Carbon's design

The implementation of the Carbon language design takes place in two distinct locations:

The Carbon Explorer is generally simpler to contribute to, while the toolchain implements the compiler and tools needed for the language. Some issues are also marked as "good first issues". These are intended to be a good place to start contributing.

To pick up a "good first issue", check to make sure there's no in-flight pull request on the issue, and then start working on it. We don't assign issues to new contributors because some people have different time constraints, and we want new contributors to feel welcome to pick the issue up when it may not be making progress. Even if someone else merges a fix before you, these issues should be a quick and helpful way to start learning how Carbon is built, building towards larger contributions.

Triage, analyze or address bugs

As Carbon's design and implementation take shape, we'll inevitably encounter plenty of bugs. Helping us triage, analyze, and address them is always a great way to get involved. See open issues on GitHub.

When triaging issues, we typically won't assign issues because we want to be confident that contributors who have an issue assigned to them are planning for the amount of time it will take, which requires familiarity. Contributors with write access are expected to have that familiarity and may assign issues to themselves.

How to become a contributor to Carbon

Contributor License Agreements (CLAs)

We'd love to accept your documentation, pull requests, and comments! Before we can accept them, we need you to cover some legal bases.

Please fill out either the individual or corporate CLA.

  • If you are an individual contributing to spec discussions or writing original source code and you're sure you own the intellectual property, then you'll need to sign an individual CLA.
  • If you work for a company that wants to allow you to contribute your work, then you'll need to sign a corporate CLA.

Follow either of the two links above to access the appropriate CLA and instructions for how to sign and return it. Once we receive it, we'll be able to accept your documents, comments and pull requests.

NOTE: Only original content from you and other people who have signed the CLA can be accepted as Carbon contributions: this covers GitHub (including both code and discussion), Google Docs, and Discord.

Future CLA plans

Initially, Carbon is bootstrapping using Google's CLA. We are planning to create an open source foundation and transfer all Carbon-related rights to it; our goal is for the foundation setup to be similar to other open source projects, such as LLVM or Kubernetes.

Collaboration systems

We use a few systems for collaboration which contributors should be aware of.

Before using these systems, everyone must sign the CLA. They are all governed by the Code of Conduct.

Getting access

Our collaboration systems are all viewable publicly, and most can be joined without particular requests. However, some require extra permissions, such as editing Google Docs, joining meetings, or some details of the proposal process.

When requesting any of the following access, please provide a reason for the access. All requests require a signed CLA.

If you simply want to chime in on GitHub or Discord, none of this is needed. If you're interested in joining meetings, ask for commenter access. If you're trying to write proposals, both types of contributor access will help.

Contribution tools

Please see our contribution tool documentation for information on setting up a git client for Carbon development, as well as helpful tooling that will ease the contribution process. For example, pre-commit is used to simplify code review.

Contribution guidelines and standards

All documents and pull requests must be consistent with the guidelines and follow the Carbon documentation and coding styles.

Guidelines and philosophy for contributions

  • For both documentation and code:

    • When the Carbon team accepts new documentation or features, to Carbon, by default they take on the maintenance burden. This means they'll weigh the benefit of each contribution against the cost of maintaining it.
    • The appropriate style is applied.
    • The license is present in all contributions.
    • Code review is used to improve the correctness, clarity, and consistency of all contributions.
      • Please avoid rebasing PRs after receiving comments; it can break viewing of the comments in files.

  • For documentation:

    • All documentation is written for clarity and readability. Beyond fixing spelling and grammar, this also means content is worded to be accessible to a broad audience.
    • Substantive changes to Carbon follow the evolution process. Pull requests are only sent after the documentation changes have been accepted by the reviewing team.
    • Typos or other minor fixes that don't change the meaning of a document do not need formal review, and are often handled directly as a pull request.

  • For code:

    • New features should have a documented design that has been approved through the evolution process. This includes modifications to preexisting designs.
    • Bug fixes and mechanical improvements don't need this.
    • All new features include unit tests, as they help to (a) document and validate concrete usage of the feature and its edge cases, and (b) guard against future breaking changes to lower the maintenance cost.
    • Bug fixes also generally include unit tests, because the presence of bugs usually indicates insufficient test coverage.
    • Unit tests must pass with the changes.
    • If some tests fail for unrelated reasons, we wait until they're fixed. It helps to contribute a fix!
    • Code changes should be made with API compatibility and evolvability in mind.
    • Keep in mind that code contribution guidelines are incomplete while we start work on Carbon, and may change later.

How to say things

  • Treat others with respect.
  • Recognize that other points of view are valid, and most decisions are about choosing the best set of trade-offs or closest alignment with Carbon's goals since there usually isn't a single best answer. It is important to frame feedback and discussion about someone else's proposal under the assumption that they too have deep experience in the area but may have come to a different conclusion.
  • Be clear when something is an opinion by using "I" or "me":
    • Not as helpful: "foo is objectively better word to use"
    • More helpful: "I find bar confusing since it has this alternate meaning, I think foo is clearer."
  • It can be helpful to define your terms.

When trying to make a point, please employ these strategies to make your argument effective and helpful:

  • Focus should be on explaining the basis by which others can come to a conclusion. Generally this means connecting a potential solution to the use cases it helps with.
  • Be specific and concrete, using examples to demonstrate the benefits and disadvantages of the different options
    • Minimally helpful: "I like <X>", "Carbon should have feature <Y>"
    • More helpful: "I think Carbon should have feature <Z>, it would mean <this example> would be written <like this> instead of <like that>." (Assuming the reader will think the example is representative of an important class of use cases.)
    • Very helpful: "If we go with approach <X>, it helps with problem <P> in <this example> of use case <A>. It doesn't help with use case <B>, but that can be better solved by <Y>, as can be seen in <other example>."
    • Very helpful: "Yes <X> gives a nice answer in that case, but it has a problem / I don't see how it applies in <this other situation>."
  • Explain the reasoning by which you can come to your conclusion

If someone questions or argues with your point, try to directly address the points being made. Try not to step backwards or switch to a more general or more meta level as that can seem like you're evading the question.

Make your point concisely
  • Asking questions is OK: Asking questions about a particular discussion is almost always OK. If you're worried the questions might be more about background and might be long enough to get distracting, you can always ask them in some of our dedicated spaces like #language-questions on Discord.
  • Favor new and relevant information: When sharing ideas and opinions in community discussions, it is important to do so in a way that both adds new information in some way/shape/form, makes sure that information is relevant to the discussion, and avoids repetition. This means reviewing what you write before posting a larger response, and editing it down to just the points you want to make that have not already been made, and any new arguments supporting those points.
  • Be inclusive by staying concise: We need to be mindful that writing many paragraphs of extra text is going to exclude people. Some people can be excluded from consuming the conversation, either because a wall of text is too intimidating to read, or they don't have the time or bandwidth to wade through the extra text to find the new information being conveyed. It can also drown out other contributors
  • Prefer upvote to repetition: One person saying "I don't like this feature" is useful, and that same message with 100 upvotes is extremely useful, but 100 people writing separate messages saying "I don't like this feature" is not. Emoji reactions are available in both Discord and GitHub and should be used for this purpose in both.

It is also okay to do things like ask a question to get clarification about what someone has said or to solicit opinions about various options. Just be respectful, and don't drown out other discussion.

Style

Google Docs and Markdown

Changes to Carbon documentation follow the Google developer documentation style guide.

Markdown files should additionally use Prettier for formatting, which we automate with pre-commit.

Other style points to be aware of are:

  • Whereas the Google developer documentation style guide says to use an em dash (text—text), we are using a double-hyphen with surrounding spaces (text -- text). We are doing this because we frequently read Markdown with fixed-width fonts where em dashes are not clearly visible.
  • Prefer the term "developers" when talking about people who would write Carbon code. We expect the Carbon's community to include people who think of themselves using many titles, including software developers, software engineers, systems engineers, reliability engineers, data scientists, computer scientists, programmers, and coders. We're using "developers" to succinctly cover the variety of titles.

Other files

If you're not sure what style to use, please ask on Discord or GitHub.

License

A license is required at the top of all documents and files.

Google Docs

Google Docs all use this template. It puts the license at the top of every page if printed.

Markdown

Markdown files always have at the top:

# DOC TITLE

<!--
Part of the Carbon Language project, under the Apache License v2.0 with LLVM
Exceptions. See /LICENSE for license information.
SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-->

For example, see the top of CONTRIBUTING.md's raw content.

Other files

Every file type uses a variation on the same license text ("Apache-2.0 WITH LLVM-exception") with similar formatting. If you're not sure what text to use, please ask on Discord or GitHub.

Workflow

Carbon repositories all follow a common pull-request workflow for landing changes. It is a trunk-based development model that emphasizes small, incremental changes and preserves a simple linear history.

Acknowledgements

Carbon's Contributing guidelines are based on TensorFlow and Flutter guidelines. Many thanks to these communities for their help in providing a basis.