# Contributing

## Intro

This article goes into detail about multiple areas of interest to contributors, which includes
reviewers, developers, and integrators who each share an interest in guiding crosvm's direction.

## Bug Reports

We use the Chromium issue tracker. Please use
[`OS>Systems>Containers`](https://bugs.chromium.org/p/chromium/issues/list?q=component:OS%3ESystems%3EContainers)
component.

## Philosophy

The following is high level guidance for producing contributions to crosvm.

- Prefer mechanism to policy.
- Use existing protocols when they are adequate, such as virtio.
- Prefer security over code re-use and speed of development.
- Only the version of Rust in use by the Chrome OS toolchain is supported. This is ordinarily the
  stable version of Rust, but can be behind a version for a few weeks.
- Avoid distribution specific code.

## Style guidelines

To format all code, crosvm defers to rustfmt. In addition, the code adheres to the following rules:

The `use` statements for each module should be grouped in this order

1. `std`
1. third-party crates
1. chrome os crates
1. crosvm crates
1. `crate`

crosvm uses the [remain](https://github.com/dtolnay/remain) crate to keep error enums sorted, along
with the `#[sorted]` attribute to keep their corresponding match statements in the same order.

## Contributing Code

### Prerequisites

You need to set up a user account with [gerrit](https://chromium-review.googlesource.com/). Once
logged in, you can obtain
[HTTP Credentials](https://chromium-review.googlesource.com/settings/#HTTPCredentials) to set up git
to upload changes.

Once set up, run `./tools/cl` to install the gerrit commit message hook. This will insert a unique
"Change-Id" into all commit messages so gerrit can identify changes.

### Contributor License Agreement

Contributions to this project must be accompanied by a Contributor License Agreement (CLA). 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.

### Uploading changes

To make changes to crosvm, start your work on a new branch tracking `origin/main`.

```bash
git checkout --branch myfeature --track origin/main
```

After making the necessary changes, and testing them via
[Presubmit Checks](https://crosvm.dev/book/building_crosvm.html#presubmit-checks), you can commit
and upload them:

```bash
git commit
./tools/cl upload
```

If you need to revise your change, you can amend the existing commit and upload again:

```bash
git commit --amend
./tools/cl upload
```

This will create a new version of the same change in gerrit.

> Note: We don't accept any pull requests on the [GitHub mirror].

### Getting Reviews

All submissions needs to be reviewed by one of the [crosvm owners]. Use the gerrit UI to request a
review. If you are uncertain about the correct person to review, reach out to the team via
[chat](https://matrix.to/#/#crosvm:matrix.org) or
[email list](https://groups.google.com/a/chromium.org/g/crosvm-dev).

### Submitting code

Crosvm uses a Commit Queue, which will run pre-submit testing on all changes before merging them
into crosvm.

Once one of the [crosvm owners] has voted "Code-Review+2" on your change, you can use the "Submit to
CQ" button, which will trigger the test process.

Gerrit will show any test failures. Refer to
[Building Crosvm](https://crosvm.dev/book/building_crosvm.html) for information on how to run the
same tests locally.

When all tests pass, your change is merged into `origin/main`.

## Contributing to the documentation

[The book of crosvm] is build with [mdBook]. Each markdown files must follow
[Google Markdown style guide].

To render the book locally, you need to install mdbook and [mdbook-mermaid], which should be
installed when you run `./tools/install-deps`script. Or you can use the `tools/dev_container`
environment.

```sh
cd docs/book/
mdbook build
```

Output is found at `docs/book/book/html/`.

> Note: If you make a certain size of changes, it's recommended to reinstall mdbook manually with
> `cargo install mdbook`, as `./tools/install-deps` only installs a binary with some convenient
> features disabled. For example, the full version of mdbook allows you to edit files while checking
> rendered results.

[crosvm owners]: https://chromium.googlesource.com/crosvm/crosvm/+/HEAD/OWNERS
[github mirror]: https://github.com/google/crosvm
[google markdown style guide]: https://github.com/google/styleguide/blob/gh-pages/docguide/style.md
[mdbook]: https://rust-lang.github.io/mdBook/
[mdbook-mermaid]: https://github.com/badboy/mdbook-mermaid
[the book of crosvm]: https://crosvm.dev/book/