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December 13, 2019 15:49

Nix RFCs (Request For Comments)

Many changes, including bug fixes and documentation improvements can be implemented and reviewed via the normal GitHub pull request workflow.

Some changes though are "substantial", and we ask that these be put through a bit of a design process and produce a consensus among the Nix community.

When this process is followed

This process is followed when one intends to make "substantial" changes to the Nix ecosystem. What constitutes a "substantial" change is evolving based on community norms, but may include the following.

  • Any semantic or syntactic change to the language that is not a bug fix
  • Removing language features
  • Big restructuring of Nixpkgs
  • Expansions to the scope of Nixpkgs (new arch, major subprojects, ...)
  • Introduction of new interfaces or functions

Certain changes do not require an RFC:

  • Adding, updating and removing packages in Nixpkgs
  • Fixing security updates and bugs that don't break interfaces

Pull requests that contain any of the aforementioned 'substantial' changes may be closed if there is no RFC connected to the proposed changes.


RFC Steering Committee

A team of people defined by RFC 36 and stays consistent until the team members are changed via a follow-up RFC. This committee is responsible for forming an RFC Shepherd team from the available nominations on each RFC. This team also names the leader of the Shepherd team. This has to happen within 1 week after the PR has been opened. Until then the Steering Committee is responsible for guiding the discussion. In case of the Shepherding Team not doing its work the Steering Committee shall encourage them or step in and assign new Shepherds. They also are in charge of merging accepted and rejected RFCs. Generally by these expectations they should find time to meet once a week for about an hour.

They have no special responsibility with regard to the content of an RFC, they can weigh in on them, the same as any other community member, but are only in charge of:

  • selecting the Shepherds unanimously
  • supervising that the Shepherds are carrying out their work
  • committing the final RFC
Shepherd Team

A team of 3-4 community members defined unanimously by the RFC Steering Committee, responsible for accepting or rejecting a specific RFC. This team is created per RFC from community members nominated in the discussion on that RFC.

This team should be people who are very familiar with the main components touched by the RFC. The author cannot be part of the Shepherd Team. In addition, at most half of the Shepherd Team can be part of the RFC Steering Committee.

The responsibility of the team is to guide the discussion as long as it is constructive, new points are brought up and the RFC is iterated on and from time to time summarise the current state of discussion. If this is the case no longer, then the Shepherd Team shall step in with a motion for FCP.

Shepherd Leader

The person in charge of the RFC process for a specific RFC, and responsible for ensuring the process is followed in a timely fashion. The Shepherd Leader has no special responsibility with regard to moving an undecided Shepherd Team to a certain decision.

Final Comment Period (FCP)

A period of ten calendar days, which will be called by the Shepherd Team after the RFC has received ample discussion and enough of the tradeoffs have been discussed. The Shepherd Team will propose to either accept or reject the RFC after the FCP.

Process from Creation to Merge

In short, to get a major change included in Nix or Nixpkgs, one must first get the RFC merged into the RFC repository as a markdown file under the rfcs directory. At that point the RFC is accepted and may be implemented with the goal of eventual inclusion into Nix or Nixpkgs.

  1. Have a cool idea!
  2. Fill in the RFC. Put care into the details: RFCs that do not present convincing motivation, demonstrate understanding of the impact of the design, or are disingenuous about the drawbacks or alternatives tend to be poorly-received. You might want to create a PR in your fork of the RFCs repository to help you flesh it out with a few supporters or chat/video conference with a few people involved in the topic of the RFC.
  3. In case your RFC is a technical proposal, you might want to prepare a prototype of your idea to firstly make yourself aware of potential pitfalls and also help reviewers understand the RFC. Code may be able to explain some issues in short.
  4. Submit a pull request. As a pull request the RFC will receive design feedback from the larger community, and the author should be prepared to revise it in response.
  5. For the nomination process for potential members of the RFC Shepherd Team, that is specific to each RFC, anyone interested can either nominate another person or themselves to be a potential member of the RFC Shepherd Team. This can already be done when submitting the PR.
  6. The RFC Steering Committee assigns a subset of the nominees to the RFC Shepherd Team and designates a leader for it. This has to be done unanimously.
  7. Build consensus and integrate feedback. RFCs that have broad support are much more likely to make progress than those that don't receive any comments. Feel free to reach out to the RFC Shepherd Team leader in particular to get help identifying stakeholders and obstacles.
  8. The RFC Shepherd Team will discuss the RFC pull request, as much as possible in the comment thread of the pull request itself. Discussion outside of the pull request, either offline or in a video conference, that might be preferable to get to a solution for complex issues, will be summarized on the pull request comment thread.
  9. RFCs rarely go through this process unchanged, especially as alternatives and drawbacks are shown. You can make edits, big and small, to the RFC to clarify or change the design, but make changes as new commits to the pull request, and leave a comment on the pull request explaining your changes. Specifically, do not squash or rebase commits after they are visible on the pull request.
  10. At some point, a member of the RFC Shepherd Team will propose a "motion for final comment period" (FCP), along with a disposition for the RFC (merge or close).
    • This step is taken when enough of the tradeoffs have been discussed that the RFC Shepherd Team is in a position to make a decision. That does not require consensus amongst all participants in the RFC thread (which is usually impossible). However, the argument supporting the disposition on the RFC needs to have already been clearly articulated, and there should not be a strong consensus against that position outside of the RFC Shepherd Team. RFC Shepherd Team members use their best judgment in taking this step, and the FCP itself ensures there is ample time and notification for stakeholders to push back if it is made prematurely.
    • For RFCs with lengthy discussion, the motion to FCP is usually preceded by a summary comment trying to lay out the current state of the discussion and major tradeoffs/points of disagreement.
    • Before actually entering FCP, all members of the RFC Shepherd Team must sign off the motion.
  11. The FCP lasts ten calendar days, so that it is open for at least 5 business days. It is also advertised widely, e.g. in NixOS Weekly and through Discourse announcements. This way all stakeholders have a chance to lodge any final objections before a decision is reached.
  12. In most cases, the FCP period is quiet, and the RFC is either merged or closed. However, sometimes substantial new arguments or ideas are raised, the FCP is canceled, and the RFC goes back into development mode.
  13. In case of acceptance, the RFC Steering Committee merges the PR. Otherwise the RFC's pull request is closed. If no consensus can be reached on the RFC but the idea in general is accepted, it gets closed, too. A note is added that is should be proposed again, when the circumstances, that are stopping the discussion to come to another decision, change.

RFC Process Review Process

The RFC life-cycle

Once an RFC is accepted the authors may implement it and submit the feature as a pull request to the Nix or Nixpkgs repo. Being accepted is not a rubber stamp, and in particular still does not mean the feature will ultimately be merged; it does mean that in principle all the major stakeholders have agreed to the feature and are amenable to merging it. In general though this means that the implementation will be merged as long as there are no substantial technical objections to the implementation.

Furthermore, the fact that a given RFC has been accepted implies nothing about what priority is assigned to its implementation, nor does it imply anything about whether a Nix/Nixpkgs developer has been assigned the task of implementing the feature. While it is not necessary that the author of the RFC also write the implementation, it is by far the most effective way to see an RFC through to completion: authors should not expect that other project developers will take on responsibility for implementing their accepted feature.

Minor modifications to accepted RFCs can be done in follow-up pull requests. We strive to write each RFC in a manner that it will reflect the final design of the feature; but the nature of the process means that we cannot expect every merged RFC to actually reflect what the end result will be after implementation.

In general, once accepted, RFCs should not be substantially changed. Only very minor changes should be submitted as amendments. More substantial changes should be new RFCs, with a note added to the original RFC. Exactly what counts as a "very minor change" is up to the RFC Shepherd Team of the RFC to be amended, to be decided in cooperation with the RFC Steering Committee.

Members of the RFC Steering Committee

The current members of the RFC Steering Committee can be seen at the NixOS/rfc-steering-committee repository.


All contributions are licensed by their respective authors under the CC-BY-SA 4.0 License.


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