Tidy

Tidy is the Rust project's custom internal linter and a crucial part of our testing and continuous integration (CI) infrastructure. It is designed to enforce a consistent style and formatting across the entire codebase, but its role extends beyond simple linting. Tidy also helps with infrastructure, policy, and documentation, ensuring the project remains organized, functional, and... tidy.

This document will cover how to use tidy, the specific checks tidy performs, and using tidy directives to manage its behavior. By understanding and utilizing tidy, you can help us maintain the high standards of the Rust project.

Tidy Checks

Style and Code Quality

These lints focus on enforcing consistent formatting, style, and general code health.

• alphabetical: Checks that lists are sorted alphabetically
• style: Check to enforce various stylistic guidelines on the Rust codebase.
• filenames: Check to prevent invalid characters in file names.
• pal: Check to enforce rules about platform-specific code in std.
• target_policy: Check for target tier policy compliance.
• error_codes: Check to ensure error codes are properly documented and tested.

Infrastructure

These checks focus on the integrity of the project's dependencies, internal tools, and documentation.

• bins: Prevent stray binaries from being checked into the source tree.

• fluent_alphabetical / fluent_period / fluent_used: Various checks related to Fluent for localization and natural language translation.

• deps / extdeps: Check for valid licenses and sources for external dependencies.

• gcc_submodule: Check that the src/gcc submodule version is valid.

• triagebot: Check to ensure paths mentioned in triagebot.toml exist in the project.

• x_version: Validates the current version of the x tool.

• edition / features: Check for a valid Rust edition and proper ordering of unstable features.

• rustdoc_css_themes / rustdoc_templates: Verify that Rust documentation templates and themes are correct.

• unstable_book: Synchronizes the unstable book with unstable features.

Testing

These checks ensure that tests are correctly structured, cleaned up, and free of common errors.

• tests_placement / unit_tests: Verify that tests are located in the correct directories and are not using improper attributes.
• known_bug / unknown_revision: Ensure that test directives and annotations are used correctly.
• debug_artifacts / mir_opt_tests: Prevent unnecessary artifacts and stale files in test directories.
• tests_revision_unpaired_stdout_stderr / ui_tests: Check for unpaired or stray test output files.
• target_specific_tests: Check to ensure that all target specific tests (those that require a --target flag) also require the pre-requisite LLVM components to run.
• rustdoc_gui_tests: Checks that rustdoc gui tests start with a small description
• rustdoc_json: Verify that FORMAT_VERSION is in sync with rust-json-types.

Using Tidy

Tidy is used in a number of different ways.

• Every time ./x test is used tidy will run automatically.

• On every pull request, tidy will run automatically during CI checks.

• Optionally, with the use of git-hooks, tidy can run locally on every push. This can be setup with ./x setup. See the rustc-dev-guide for more information.

You can run tidy manually with:

./x test tidy

To first run the relevant formatter and then run tidy you can add --bless.

./x test tidy --bless

Extra Checks

extra_checks are optional checks primarily focused on other file types and programming languages.

Example usage:

./x test tidy --extra-checks=py,cpp,js,spellcheck

All options for --extra-checks:

• cpp, cpp:fmt
• py, py:lint, py:fmt
• js, js:lint, js:fmt, js:typecheck
• shell, shell:lint
• spellcheck

Default values for tidy's extra-checks can be set in bootstrap.toml. For example, build.tidy-extra-checks = "js,py".

Any argument without a suffix (eg. py or js) will include all possible checks. For example, --extra-checks=js is the same as extra-checks=js:lint,js:fmt,js:typecheck.

Any argument can be prefixed with auto: to only run if relevant files are modified (eg. --extra-checks=auto:py).

A specific configuration file or folder can be passed to tidy after a double dash (--extra-checks=py -- foo.py)

Tidy Directives

Tidy directives are special comments that help tidy operate.

Tidy directives can be used in the following types of comments:

• //
• #
• /* {...} */
• <!-- {...} -->

You might find yourself needing to ignore a specific tidy style check and can do so with:

• ignore-tidy-cr

• ignore-tidy-undocumented-unsafe

• ignore-tidy-tab

• ignore-tidy-linelength

• ignore-tidy-filelength

• ignore-tidy-end-whitespace

• ignore-tidy-trailing-newlines

• ignore-tidy-leading-newlines

• ignore-tidy-copyright

• ignore-tidy-dbg

• ignore-tidy-odd-backticks

• ignore-tidy-todo

Some checks, like alphabetical, require a tidy directive to use:

// tidy-alphabetical-start
fn aaa() {}
fn eee() {}
fn z() {}
// tidy-alphabetical-end

Test Specific Directives

target-specific-tests can be ignored with // ignore-tidy-target-specific-tests

Tidy's unknown_revision check can be suppressed by adding the revision name to //@ unused-revision-names:{revision} or with //@ unused-revision-names:*.