• Start Date: 2018-06-28
  • RFC PR: (leave this empty)
  • Tracking Issue: (leave this empty)


Adopt a simplified version of the Rust RFC process to the Rust and WebAssembly domain working group. The RFC process will provide a single place to decide on substantial changes and additions across the ecosystem for all stakeholders.


There are some decisions which have broad impact across the Rust and WebAssembly ecosystem, and therefore have many stakeholders who deserve to have a say in the decision and provide feedback on proposals and designs. Right now, these decisions tend to be made in whatever local repository pull request or issue tracker. This makes it difficult for stakeholders to stay on top of these decisions, because they need to watch many different places. For a repository owner or team, it is also difficult to determine whether the ecosystem is in favor of a feature or not.

After adopting this RFC process, stakeholders should have an easier time staying on top of substantial changes and features within the ecosystem. Additionally, the maintainers of a particular repository within the Rust and WebAssembly ecosystem should feel confident that they've solicited feedback from everyone involved after going through an RFC, and won't get angry bug reports from users who felt that they were not consulted. Everyone should have shared confidence in the direction that the ecosystem evolves in.

Detailed Explanation

Right now, governance for repositories within the rustwasm organization follow these rules describing policy for merging pull requests:

Unless otherwise noted, each rustwasm/* repository has the following general policies:

  • All pull requests must be reviewed and approved of by at least one relevant team member or repository collaborator before merging.

  • Larger, more nuanced decisions about design, architecture, breaking changes, trade offs, etc are made by the relevant team and/or repository collaborators consensus. In other words, decisions on things that aren't straightforward improvements to or bug fixes for things that already exist in the project.

This policy categorizes pull requests as either "larger, more nuanced ..." changes or not (we will use "substantial" from now on). When a change is not substantial, it requires only a single team member approve of it. When a change is larger and more substantial, then the relevant team comes to consensus on how to proceed.

This RFC intends to further sub-categorize substantial changes into those that affect only maintenance of the repository itself, and are therefore only substantial internally to the maintainers, versus those substantial changes that have an impact on external users and the larger Rust and WebAssembly community. For internally substantial changes, we do not intend to change the current policy at all. For substantial changes that have external impact, we will adopt a lightweight version of Rust's RFC process.

When does a change need an RFC?

You need to follow the RFC process if you intend to make externally substantial changes to any repository within the rustwasm organization, or the RFC process itself. What constitutes a "substantial" change is evolving based on community norms and varies depending on what part of the ecosystem you are proposing to change, but may include the following:

  • The removal of or breaking changes to public APIs in widespread use.
  • Public API additions that extend the public API in new ways (i.e. more than "we implement SomeTrait for ThisThing, so also implement SomeTrait for RelatedThing").

Some changes do not require an RFC:

  • Rephrasing, reorganizing, refactoring, or otherwise "changing shape does not change meaning".
  • Additions that strictly improve objective, numerical quality criteria (warning removal, speedup, better platform coverage, more parallelism, trap more errors, etc.)
  • Additions only likely to be noticed by other maintainers, and remain invisible to users.

If you submit a pull request to implement a new feature without going through the RFC process, it may be closed with a polite request to submit an RFC first.

The RFC process step by step

  • Fork the RFC repository.
  • Copy 000-template.md to text/000-my-feature.md (where "my-feature" is descriptive. Don't assign an RFC number yet).
  • 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.
  • 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.
  • Each new RFC pull request will be triaged in the next Rust and WebAssembly domain working group meeting and assigned to one or more of the @rustwasm/* teams.
  • 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 assignee in particular to get help identifying stakeholders and obstacles.
  • The team(s) will discuss the RFC pull request, as much as possible in the comment thread of the pull request itself. Offline discussion will be summarized on the pull request comment thread.
  • 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.
  • At some point, a member of the subteam will propose a "motion for final comment period" (FCP), along with a disposition for the RFC (merge, close, or postpone).
    • This step is taken when enough of the tradeoffs have been discussed that the team(s) are in a position to make a decision. That does not require consensus amongst all participants in the RFC thread (which may be 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 team(s). 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 should be 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 team(s) must sign off; this is often the point at which many team members first review the RFC in full depth.
  • The FCP lasts seven calendar days. It is also advertised widely, e.g. in an issue of "This Week in Rust and WebAssembly" on the Rust and WebAssembly blog. This way all stakeholders have a chance to lodge any final objections before a decision is reached.
  • 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.

From RFC to implementation

Once an RFC is merged it becomes "active" then authors may implement it and submit the feature as a pull request to the relevant repositories. Being "active" 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.

Furthermore, the fact that a given RFC has been accepted and is "active" implies nothing about what priority is assigned to its implementation, nor does it imply anything about whether a 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.

Modifications to "active" 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 at the time of the next major release.

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.

Rationale and Alternatives

The design space for decision making is very large, from democratic to autocratic and more.

Forking and simplifying Rust's RFC process is practical. Rather than designing a decision making process from scratch, we take an existing one that works well and tailor it to our needs. Many Rust and WebAssembly stakeholders are already familiar with it.

The main differences from the Rust RFC process are:

  • FCP lasts seven calendar days rather than ten. This reflects our desire for a lighter-weight process that moves more quickly than Rust's RFC process.
  • The RFC template is shorter and merges together into single sections what were distinct sections in the Rust RFC template. Again, this reflects our desire for a lighter-weight process where we do not need to go into quite as much painstaking detail as Rust RFCs sometimes do (perhaps excluding this RFC).

The phases of RFC development and post-RFC implementation are largely the same as the Rust RFC process. We found that the motivations for nearly every phase of Rust's RFC process are equally motivating for the Rust and WebAssembly domain. We expected to simplify phases a lot, for example, we initially considered removing FCP and going straight to signing off on accepting an RFC or not. However, FCP exists as a way to (1) allow stakeholders to voice any final concerns that hadn't been brought up yet, and (2) help enforce the "no new rationale" rule. Both points apply equally well to the Rust and WebAssembly domain working group and ecosystem as they apply to Rust itself.

We can also avoid adopting an RFC process, and move more quickly by allowing each repository's team or owner to be dictators of their corner of the ecosystem. However, this will result in valuable feedback, opinions, and insight not getting voiced, and narrow decisions being made.

Unresolved Questions

  • Will we use @rfcbot? If we can, we probably should, but this can be decided separately from whether to accept this RFC.

  • How to best advertise new RFCs and FCP? Should we make "This Week in Rust and WebAssembly" actually be weekly rather than every other week? The interaction between FCP length and frequency of TWiRaWA posting seems important.