We'd love to accept your patches and contributions to zerocopy. There are just a few small guidelines you need to follow.
Once you've read the rest of this doc, check out our good-first-issue label for some good issues you can use to get your toes wet!
Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.
You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.
All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult GitHub Help for more information on using pull requests.
This section is inspired by Flutter's style guide, which contains many general principles that you should apply to all your programming work. Read it. The below calls out specific aspects that we feel are particularly important.
In non-library code, it's often advised to only implement features you need. After all, it's hard to correctly design code without a concrete use case to guide its design. Since zerocopy is a library, this advice is not as applicable; we want our API surface to be featureful and complete even if not every feature or method has a known use case. However, the observation that unused code is hard to design still holds.
Thus, when designing external-facing features, try to make use of them somehow. This could be by using them to implement other features, or it could be by writing prototype code which won't actually be checked in anywhere. If you're feeling ambitious, you could even add (and check in) a Cargo example that exercises the new feature.
You will occasionally encounter behavior that surprises you or seems wrong. It probably is! Invest the time to find the root cause - you will either learn something, or fix something, and both are worth your time. Do not work around behavior you don't understand.
Avoid duplicating code whenever possible. In cases where existing code is not exposed in a manner suitable to your needs, prefer to extract the necessary parts into a common dependency.
When writing comments, take a moment to consider the future reader of your comment. Ensure that your comments are complete sentences with proper grammar and punctuation. Note that adding more comments or more verbose comments is not always better; for example, avoid comments that repeat the code they're anchored on.
Documentation comments should be self-contained; in other words, do not assume that the reader is aware of documentation in adjacent files or on adjacent structures. Avoid documentation comments on types which describe instances of the type; for example, AddressSet is a set of client addresses. is a comment that describes a field of type AddressSet, but the type may be used to hold any kind of Address, not just a client's.
Phrase your comments to avoid references that might become stale; for example: do not mention a variable or type by name when possible (certain doc comments are necessary exceptions). Also avoid references to past or future versions of or past or future work surrounding the item being documented; explain things from first principles rather than making external references (including past revisions).
When writing TODOs:
TODO(#123):Much of the code in zerocopy has the property that, if it is buggy, those bugs may not cause user code to fail. This makes it extra important to write thorough tests, but it also makes it harder to write those tests correctly. Here are some guidelines on how to test code in zerocopy:
Commits should be arranged for ease of reading; that is, incidental changes such as code movement or formatting changes should be committed separately from actual code changes.
Commits should always be focused. For example, a commit could add a feature, fix a bug, or refactor code, but not a mixture.
Commits should be thoughtfully sized; avoid overly large or complex commits which can be logically separated, but also avoid overly separated commits that require code reviews to load multiple commits into their mental working memory in order to properly understand how the various pieces fit together.
Commit messages should be concise but self-contained (avoid relying on issue references as explanations for changes) and written such that they are helpful to people reading in the future (include rationale and any necessary context).
Avoid superfluous details or narrative.
Commit messages should consist of a brief subject line and a separate explanatory paragraph in accordance with the following:
If the code affects a particular subsystem, prefix the subject line with the name of that subsystem in square brackets, omitting any "zerocopy" prefix (that's implicit). For example, for a commit adding a feature to the zerocopy-derive crate:
[derive] Support AsBytes on types with parameters
The body may be omitted if the subject is self-explanatory; e.g. when fixing a typo. The git book contains a Commit Guidelines section with much of the same advice, and the list above is part of a blog post by Chris Beams.
Commit messages should make use of issue integration. Including an issue reference like #123 will cause the GitHub UI to link the text of that reference to the referenced issue, and will also make it so that the referenced issue back-links to the commit. Use "Closes", "Fixes", or "Resolves" on its own line to automatically close an issue when your commit is merged:
Closes #123 Fixes #123 Resolves #123
When using issue integration, don't omit necessary context that may also be included in the relevant issue (see "Commit messages should be concise but self-contained" above). Git history is more likely to be retained indefinitely than issue history (for example, if this repository is migrated away from GitHub at some point in the future).
Commit messages should never contain references to any of:
This project follows Google's Open Source Community Guidelines.