Rust Fmt

rustfmt_aspect
rustfmt_test
rustfmt_toolchain

Overview

Rustfmt is a tool for formatting Rust code according to style guidelines. By default, Rustfmt uses a style which conforms to the Rust style guide that has been formalized through the style RFC process. A complete list of all configuration options can be found in the Rustfmt GitHub Pages.

Setup

Formatting your Rust targets' source code requires no setup outside of loading rules_rust in your workspace. Simply run bazel run @rules_rust//:rustfmt to format source code.

In addition to this formatter, a simple check can be performed using the rustfmt_aspect aspect by running

bazel build --aspects=@rules_rust//rust:defs.bzl%rustfmt_aspect --output_groups=rustfmt_checks

Add the following to a .bazelrc file to enable this check during the build phase.

build --aspects=@rules_rust//rust:defs.bzl%rustfmt_aspect
build --output_groups=+rustfmt_checks

It's recommended to only enable this aspect in your CI environment so formatting issues do not impact user's ability to rapidly iterate on changes.

The rustfmt_aspect also uses a --@rules_rust//:rustfmt.toml setting which determines the configuration file used by the formatter (@rules_rust//tools/rustfmt) and the aspect (rustfmt_aspect). This flag can be added to your .bazelrc file to ensure a consistent config file is used whenever rustfmt is run:

build --@rules_rust//:rustfmt.toml=//:rustfmt.toml

Tips

Any target which uses Bazel generated sources will cause the @rules_rust//tools/rustfmt tool to fail with failed to resolve mod `MOD` . To avoid failures, skip_children = true is recommended to be set in the workspace's rustfmt.toml file which allows rustfmt to run on these targets without failing.

rustfmt_test

rustfmt_test(name, targets)

A test rule for performing rustfmt --check on a set of targets

ATTRIBUTES

Name	Description	Type	Mandatory	Default
name	A unique name for this target.	Name	required
targets	Rust targets to run `rustfmt --check` on.	List of labels	optional	`[]`

rustfmt_toolchain

rustfmt_toolchain(name, rustc, rustc_lib, rustfmt)

A toolchain for rustfmt

ATTRIBUTES

Name	Description	Type	Mandatory	Default
name	A unique name for this target.	Name	required
rustc	The location of the `rustc` binary. Can be a direct source or a filegroup containing one item.	Label	optional	`None`
rustc_lib	The libraries used by rustc during compilation.	Label	optional	`None`
rustfmt	The location of the `rustfmt` binary. Can be a direct source or a filegroup containing one item.	Label	required

rustfmt_aspect

rustfmt_aspect(name)

This aspect is used to gather information about a crate for use in rustfmt and perform rustfmt checks

Output Groups:

rustfmt_checks: Executes rustfmt --check on the specified target.

The build setting @rules_rust//:rustfmt.toml is used to control the Rustfmt configuration settings used at runtime.

This aspect is executed on any target which provides the CrateInfo provider. However users may tag a target with no-rustfmt or no-format to have it skipped. Additionally, generated source files are also ignored by this aspect.

ASPECT ATTRIBUTES

ATTRIBUTES

Name	Description	Type	Mandatory	Default
name	A unique name for this target.	Name	required