Rust

Build

There are four GN target templates that should be used for Rust projects:

rustc_library defines a library and optionally a unit test target. The library can be depended on by other targets.
rustc_binary defines an executable and optionally a unit test target.
rustc_test defines a test-only target.
rustc_macro defines a procedural macro target.

The examples/rust directory has some examples of Rust packages that use these targets, as do the Rust FIDL examples.

Cargo.toml

Fuchsia Rust targets are not built with cargo. That said, you can generate Cargo.toml files for use with external tooling. This functionality is not guaranteed to work.

Autogenerated documentation

Once you have a Cargo.toml for your target you can generate and browse HTML documentation for your target and its dependencies by running:

fx rustdoc path/from/fuchsia/root/to/target:label --open

Tests

You can run unit tests on connected devices using fx, with the fx test {package name} command. See Testing Rust code for information on adding and running tests.

Procedural macros

Procedural macro targets are executed on the host at compile time. Therefore, they cannot depend on other crates that are only available on device, e.g. zircon.

Negative tests, e.g. asserting that a macro fails to compile with a specific error, are currently not supported.

Warnings and errors

By default our build configuration makes all Rust warnings into errors. This requirement can be onerous during development, and on your local machine you may wish to see warnings as warnings and let CQ enforce the hard boundary.

The deny_warnings GN arg allows you to control this behavior in your development environment. Setting deny_warnings = false in fx args or adding --args=deny_warnings=false to your fx set will allow you to develop locally without being blocked by warnings. You can add the argument to local/args.gn in your checkout so that it will be applied to all builds without needing to type it in your terminal each time.

Style

We don't currently have a style guide for Rust, but you should run fx rustfmt or fx format-code before submitting. We mostly use the rustfmt defaults, but have a couple custom settings.

Rust Idiomatic Usage Review

If you're new to Rust or would like someone to review your changes to validate that your usage of Rust is idiomatic, add "Fuchsia Rust Reviewers" as a reviewer to your CL in Gerrit and a reviewer will be assigned.

Email tq-rust-reviewers@google.com with any issues.

Communication channels

Public discussion happens on the rust-users@fuchsia.dev mailing list.