Development Process

We use issues for asking questions (open one here!) and tracking bugs and unimplemented features, and pull requests (PRs) for tracking and reviewing code submissions. We triage new issues at each of our bi-weekly Wasmtime meetings.

Before submitting a PR

Consider opening an issue to talk about it. PRs without corresponding issues are appropriate for fairly narrow technical matters, not for fixes to user-facing bugs or for feature implementations, especially when those features might have multiple implementation strategies that usefully could be discussed. Changes that will significantly affect stakeholders should first be proposed in an RFC.

Our issue templates might help you through the process.

When submitting PRs

• Please answer the questions in the pull request template. They are the minimum information we need to know in order to understand your changes.

• Write clear commit messages that start with a one-line summary of the change (and if it's difficult to summarize in one line, consider splitting the change into multiple PRs), optionally followed by additional context. Good things to mention include which areas of the code are affected, which features are affected, and anything that reviewers might want to pay special attention to.

• If there is code which needs explanation, prefer to put the explanation in a comment in the code, or in documentation, rather than in the commit message. Commit messages should explain why the new version is better than the old.

• Please include new test cases that cover your changes, if you can. If you're not sure how to do that, we'll help you during our review process.

• For pull requests that fix existing issues, use issue keywords. Note that not all pull requests need to have accompanying issues.

• When updating your pull request, please make sure to re-request review if the request has been cancelled.

Focused commits or squashing

We are not picky about how your git commits are structured. When we merge your PR, we will squash all of your commits into one, so it's okay if you add fixes in new commits.

We appreciate it if you can organize your work into separate commits which each make one focused change, because then we can more easily understand your changes during review. But we don't require this.

Once someone has reviewed your PR, it's easier for us if you don't rebase it when making further changes. Instead, at that point we prefer that you make new commits on top of the already-reviewed work.

That said rebasing (or merging from main) may still be required in situations such as:

• Your PR has a merge conflict with the main branch.

• CI on your PR is failing for unrelated reasons and a fix was applied to main which needs to be picked up on your branch.

• Other miscellaneous technical reasons may cause us to ask for a rebase.

If you need help rebasing or merging, please ask!

Review and merge

Anyone may submit a pull request, and anyone may comment on or review others' pull requests. However, one approval from a maintainer is required before a PR can be merged. Maintainers must also create PRs and get review from another maintainer for every change, including minor work items such as version bumps, removing warnings, etc.

PR approvals may come with comments about additional minor changes that are requested. Contributors and maintainers alike should address these comments, if any, and then the PR is ready for merge. Wasmtime uses a merge queue to ensure that all tests pass before pushing to main. Note that the merge queue will run more tests than is run on PRs by default.

Contributors should expect Wasmtime maintainers to add the PR to the merge queue for them. If a PR hasn't been added, and it's approved with all comments addressed, feel free to leave a comment to notify maintainers that it's ready. Maintainers can add their own PRs to the merge queue. When approving a PR maintainers may also add the PR to the merge queue at that time if there are no remaining comments.

Note that if CI is failing on a PR then GitHub will automatically block adding a PR to the merge queue. PR authors will need to resolve PR CI before it can be added to the merge queue. If the merge queue CI fails then the PR will be removed from the merge queue and GitHub will leave a marker on the timeline and send a notification to the PR author. PR authors are expected to review CI logs and fix any failures in the PR itself. When ready maintainers can re-add their own PR for minor fixes and contributors can leave a comment saying that the PR is ready to be re-added to the queue.

To run full CI on the PR before the merge queue, include the string prtest:full in any commit in the PR. That can help debug CI failures without going through the merge queue if necessary.