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Evolution and governance

Overview​

Carbon's evolution process uses proposals to evaluate and approve significant changes to the project or language. This process is designed to:

  • Ensure these kinds of changes can receive feedback from the entire community.
  • Resolve questions and decide direction efficiently.
  • Create a clear log of rationale for why the project and language have evolved in particular directions.

When there are questions, concerns, or issues with a proposal that need to be resolved, Carbon uses its governance system of Carbon leads to decide how to move forward. Leads are fundamentally responsible for encouraging Carbon's ongoing and healthy evolution and so also take on the critical steps of the evolution process for proposals.

Proposals​

These are primarily structured as GitHub pull requests that use a somewhat more formal document structure and process to ensure changes to the project or language are well explained, justified, and reviewed by the community.

Life of a proposal​

  • Proposals consist of a PR (pull request) in GitHub that adds a document to the proposals/ directory following the template.

  • Proposal PRs start out in draft mode. When proposal PRs are ready, click on "Ready for review", and change the Proposals project column to "RFC". The project column should be available as a dropdown under "Projects" on the PR.

    • This will result in a Carbon lead being assigned to review the PR.

    • This also signifies an RFC (request for comment) from the entire community.

  • Contributors are encouraged to react with a thumbs-up to proposal PRs if they are generally interested and supportive of the high level direction based on title and summary. Similarly, other reactions are encouraged to help surface contributor's sentiment.

  • We use GitHub issues to discuss and track blocking issues with proposals, such as open questions or alternative approaches that may need further consideration. These are assigned to carbon-leads to decide.

  • A Carbon lead will be assigned to a proposal PR. They are responsible for the basic review (or delegating that) as well as ultimately approving the PR.

  • The assigned lead should ensure that there is a reasonable degree of consensus among the contributors outside of the identified blocking issues. Contributors should have a reasonable chance to raise concerns, and where needed they should become blocking issues. Community consensus isn't intended to be perfect though, and is ultimately a judgement call by the lead. When things are missed or mistakes are made here, we should just revert or fix-forward as usual.

  • Once a reasonable degree of community consensus is reached and the assigned lead finishes code review, the lead should approve the PR. Any outstanding high-level concerns should be handled with blocking issues.

  • Optionally, the assigned lead can file a blocking issue for a one week final comment period when they approve. This is rarely needed, and only when it is both useful and important for the proposal to give extra time for community comments.

  • The leads are responsible for resolving any blocking issues for a proposal PR, including the one week comment period where resolving it indicates comments arrived which require the proposal to undergo further review.

  • The proposal PR can be merged once the assigned lead approves, all blocking issues have been decided, and any related decisions are incorporated.

  • If the leads choose to defer or reject the proposal, the reviewing lead should explain why and close the PR.

Proposal roles​

It is also useful to see what the process looks like for different roles within the community. These perspectives are also the most critical to keep simple and easily understood.

Proposal authors​

For proposal authors, this should feel like a code review, with some broken out issues for longer discussion:

  • Create a proposal document and draft PR following the template.

  • When ready, click on "Ready for review" in GitHub, and change the Proposals project column to "RFC". The project column should be available as a dropdown under "Projects" on the PR.

    • This will result in the PR being assigned to an individual for review.

    • This will also send the proposal as a broad RFC to the community.

    • While setting the "RFC" project column will also add the "RFC" label, the reverse is not true. Unfortunately, this is currently a limit of GitHub automation. Similarly, Adding the "RFC" project column currently does not set "Ready for review".

  • Address comments where you can and they make sense.

  • If you don't see an obvious way to address comments, that's OK.

    • It's great to engage a bit with the commenter to clarify their comment or why you don't see an obvious way to address it, just like you would in code review.

    • If the commenter feels this is important, they can move it to a blocking issue for a longer discussion and resolution from the leads.

    • You don't need to try to resolve everything yourself.

  • Incorporate any changes needed based on the resolution of blocking issues. Once the leads have provided a resolution, it's important to make progress with that direction.

  • When you both have approval from the assigned lead and the last blocking issue is addressed, merge!

    • If you end up making significant changes when incorporating resolved issues after the approval from the assigned lead, circle back for a fresh approval before merging, just like you would with code review.

Community​

  • We use the Proposals dashboard to track proposals that are in RFC.

    • Anyone that is interested can participate once a proposal is ready for review and in RFC.

    • It's OK to only comment when particularly interested in a proposal, or when asked by one of the leads to help ensure thorough review. Not everyone needs to participate heavily in every RFC.

    • PRs that are in "draft" status in GitHub are considered works-in-progress. Check with the author before spending time reviewing these, and generally avoid distracting the author with comments unless they ask for them. The proposal may be actively undergoing edits.

  • Read the proposal and leave comments to try to help make the proposal an improvement for Carbon.

    • Note that progress and improvement are more important than perfection here!

  • Try to make comments on proposals constructive. Suggest how the proposal could be better if at all possible.

  • If there is an open question or a critical blocking issue that needs to get resolved, move it to its own issue that the PR depends on, and focus the discussion there.

    • The issue should focus on surfacing the important aspects of the tradeoff represented by the issue or open question, not on advocacy.

Active contributors​

Everyone actively contributing to the evolution of Carbon should try to regularly:

  • Give a thumbs-up or other reaction on any interesting PRs out for RFC to help surface the community's sentiment around the high level idea or direction. Don't worry about "approving" or the detailed text of the proposal here.

  • If interested and time permitting, dive into some RFCs and provide community feedback.

Carbon leads​

Carbon leads are responsible for making decisions rapidly and ensuring proposal PRs land:

  • Rapidly resolve all blocking issues raised across any proposals.

  • When assigned a specific proposal PR:

    • Make sure it gets both constructive general comments and good code review.

    • Ideally, you should directly participate in the code review, but it's fine to ask others to help. However, ultimately you have to review and approve the PR.

    • Escalate any blocking issues without a resolution that are slowing down the proposal to the other leads.

    • Evaluate whether the community has had a reasonable chance to raise concerns and there is sufficient consensus to move forward given the decisions on the blocking issues. This doesn't need to be perfect though. Here too, we prioritize progress over perfection. We can revert or fix-forward mistakes whenever necessary, especially for low-risk changes. In rare cases, an extended final comment period can be used when warranted for a proposal.

    • Once ready, approve and help the author merge the proposal.

When to write a proposal​

Any substantive change to Carbon -- whether the language, project, infrastructure, or otherwise -- should be done through an evolution proposal. The meaning of "substantive" is subjective, but will generally include:

  • Any semantic or syntactic language change that isn't fixing a bug.
  • Major changes to project infrastructure, including additions and removals.
  • Rolling back an accepted proposal, even if never executed.

Changes which generally will not require a proposal are:

  • Fixing typos or bugs that don't change the meaning or intent.
  • Rephrasing or refactoring documentation for easier reading.
  • Minor infrastructure updates, improvements, setting changes, tweaks.

If you're not sure whether to write a proposal, please err on the side of writing a proposal. A team can always ask for a change to be made directly if they believe it doesn't need review. Conversely, a reviewer might also ask that a pull request instead go through the full evolution process.

Proposal PRs​

A proposal PR should use the proposal label, have a descriptive title, and easily understood initial summary comment. Authors and leads are encouraged to edit both as necessary to ensure they give the best high-level understanding of the proposal possible.

A proposal PR will include a "P-numbered" proposal document, proposals/pNNNN.md, where NNNN is the pull request number. This file should be based on the proposal template file.

When writing a proposal, try to keep it brief and focused to maximize the community's engagement in it. Beyond the above structure, try to use Inverted Pyramid or BLUF writing style to help readers rapidly skim the material.

What goes in the proposal document​

The purpose of the proposal document is to present the case for deciding to adopt the proposal. Any information that feeds into making that decision, and that should not be maintained as part of our living design documentation, belongs in the proposal document. This includes background material to introduce the problem, comparisons to any alternative designs that were considered and any other current proposals in the same area, records of informal polls taken to determine community preferences, and rationale for the decision based on the project's goals.

The proposal PR can contain related changes to the Carbon project, such as updates to the design documentation. Those changes form part of the proposal, and need not be additionally described in the proposal document beyond a mention in the "Proposal" section that such changes exist. For example:

## Proposal

See the proposed changes to the design documents.

Readers of proposals are expected to consult the PR or the git commit that merged the PR in order to understand the proposed changes.

The author of a proposal is not required to include changes to the design documentation as part of a proposal, and it may in some cases be preferable to decouple the proposal process from updating the design. When accepted, the proposal would then be implemented through a series of future PRs to the rest of the project, and the proposal document should describe what is being proposed in enough detail to validate that those future PRs properly implement the proposed direction.

Open questions​

Feel free to factor out open questions in a proposal to issues that you assign to the leads to resolve. You can even do this before sending the proposal for review. Even after it's resolved, an open question issue can be reopened if new information comes up during the RFC.

When opening issues, add them to the "Issues for leads" project under "Questions". Carbon leads use this to locate and prioritize the issue for resolution.

Review and RFC on proposal PRs​

When a proposal PR is assigned to the carbon-leads GitHub group, one of them will be assigned the PR. They are responsible for helping land that proposal, or explaining why the project won't move forward in that direction. The assigned lead is also ultimately responsible for the code review on the PR. Proposals sent for review are also sent as an RFC to the entire community.

All active Carbon contributors are strongly encouraged to regularly skim the title and summary comment of proposals under RFC that are interesting to them. They should use GitHub reactions, including at least a thumbs-up, to show their interest and enthusiasm about the proposal, and help encourage the author. Writing proposals is extremely hard work, and we need to clearly show both interest in the proposed direction of Carbon and appreciation for the work put into the proposal. This is not about approving the proposal, or any of its details. It is completely fine and coherent to both give a thumbs-up to a proposal and provide a serious, blocking issue that needs to be resolved.

Anyone in the community is welcome to participate in the RFC in detail if interested. However, not everyone needs to participate in every RFC. If a proposal is already getting actively and thoroughly reviewed, feel free to focus your time on other proposals with fewer commenters. Even if there are issues or problems discovered later, we can always fix them with follow-up proposals.

Both code review and high-level design comments are welcome. If an open question comes up or a high-level blocking issue is uncovered, feel free to move it to its own GitHub issue and assign it to the leads to resolve. That issue is also a good place to focus discussion on that specific topic rather than the main PR.

The assigned lead should approve proposals once the following criteria are met:

  • It looks good from a code review perspective.

  • At least three thumbs-up reactions showing general community interest.

  • The community has had a sufficient opportunity to review the proposed change, given its scope and complexity.

  • Any remaining blocking issues are reasonably likely to resolve in a way that allows the proposal to move forward. It is fine if some are not fully decided, but a lead shouldn't approve a proposal that's unlikely to move forward.

The last two criteria are fundamentally judgement calls for the lead to make, and we don't try to formulate a rigid or fixed bar for them. If resolving the blocking issues requires significant changes, the author should also get a fresh approval from the assigned lead after those changes, just like they would with code review.

The assigned lead may also request a final comment period for the community when approving. This signals to the community that the proposal is likely to be merged once the blocking issues are resolved, and any remaining concerns need to be surfaced. The goal is to help uncover concerns that were hidden until it was clear that the proposal is likely to move forward. However, requesting a final comment period is not the default; the assigned lead should only do this when there is some reason to expect further community comment is especially important to solicit. Common cases to consider are contentious, complex, or dramatic changes to the language or project. Ultimately, whether this is important is a judgement call for the lead. This will be modeled by filing a blocking issue that resolves in one week when approving. This issue will also explain the motivation for requesting a final comment period.

Blocking issues​

We use blocking GitHub issues to track open questions or other discussions that the leads are asked to resolve. Any time a blocking issue is filed, that issue forms both the primary discussion thread and where the leads signal how it is resolved. We use issues both to track that there is a specific resolution expected and that there may be dependencies.

We add blocking issues to the "Issues for leads" project under "Blocking issues". Carbon leads use this to locate and prioritize the issue for resolution.

These issues can be created at any time and by any one. Issues can be created while the proposal is being drafted in order to help inform specific content that should go into the proposal. It is even fine to create an issue first, even before a proposal exists, as an open question about whether to produce a particular proposal, or what a proposal that is being planned should say. For issues which don't (yet) have a specific proposal PR associated with them, at some point the leads may ask that a proposal be created to help collect in a more cohesive place a written overview of the issue and related information, but this process need not be strictly or rigidly bound to having proposal text.

Avoid using issues for things that are just requests or suggestions on a proposal PR. If in doubt, start off with a simple comment on the PR and see if there is any disagreement -- everyone may already be aligned and agree. When a comment does seem worth turning into an issue, don't worry about that as the author or the commenter. Getting the leads to resolve disagreement isn't a bad thing for anyone involved. This should be seen as a friendly way to move the discussion out to its own forum where it'll get resolved, and focus the PR on improving the proposal and getting it ready to merge.

When an issue is created from a discussion on a PR, and after the discussion on the issue all the original parties come to a happy agreement, it's totally OK to close the issue and move back to the code review in the PR. Anyone who would prefer the leads to still chime in can re-open the issue and the leads will follow up, even if it's only to get confirmation that everyone did end up happy with the resolution. At the end of the day, while it's fine to resolve an issue that everyone actually ended up agreeing about (maybe once some confusion is addressed), ultimately the leads are responsible for resolving these issues and there is no pressure on anyone else to do so.

Discussion on blocking issues​

Discussion on these issues, especially contentious ones, should endeavor to focus on surfacing information and highlighting the nature of the tradeoff implied by the decisions available. This is in contrast to focusing on advocacy or persuasion. The goal of the issues shouldn't be to persuade or convince the leads to make a specific decision, but to give the leads the information they need to make the best decision for Carbon.

It's fine that some people have a specific belief of which decision would be best; however, framing their contributions to the discussion as surfacing the information that underpins that belief will make the discussion more constructive, welcoming, and effective. Overall, everyone should strive to focus on data-based arguments to the extent they can, minimizing their use of appeals to emotion or excessive rhetoric.

None of this should preclude gathering information like polls of opinion among groups, or signaling agreement. Where community members stand and how many agree with that stance on any issue is information, and useful to surface.

Governance structure​

Carbon leads​

Carbon leads are responsible for reviewing proposals and setting Carbon's roadmap and managing evolution. This team should broadly understand both the users of Carbon and the project itself in order to factor different needs, concerns, and pressures into a consensus decision-making process.

While leads may approve proposals individually, they should decide on issues raised to them using blocking consensus with a quorum of two.

Carbon's current leads are:

Subteams​

As Carbon grows, the leads may decide to form subteams that provide leadership for specific areas. These subteams are expected to largely organize in a similar fashion to the Carbon leads, with a more narrow focus and scope. Subteam decisions may be escalated to the Carbon leads.

Painter​

Whenever possible, we want Carbon to make syntax and other decisions based on understanding its users, data, and the underlying goals of the language. However, there will be times when those don't provide a clear cut rationale for any particular decision -- all of the options are fine/good and someone simply needs to choose which color to paint the bikeshed. The goal of the painter role is to have a simple way to quickly decide these points.

Leads and teams may defer a decision to the painter if there is a consensus that it is merely a bikeshed in need of paint. They may also open an issue to revisit the color with data and/or user studies of some kind. This allows progress to be unblocked while also ensuring we return to issues later and attempt to find more definite rationale.

The painter is a single person in order to keep decisions around taste or aesthetics reasonably consistent.

The current painter is:

Adding and removing governance members​

Any member of Carbon governance may step down or be replaced when they are no longer able to contribute effectively. The Carbon leads can nominate and decide on adding, removing, or replacing members using the usual evolution processes.

Acknowledgements​

Our governance and evolution process is influenced by the Rust, Swift, and C++ processes. Many thanks to these communities for providing a basis.