---
type: reference, dev
stage: none
group: Development
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
---

# Style guides

## Editor/IDE styling standardization

We use [EditorConfig](https://editorconfig.org/) to automatically apply certain styling
standards before files are saved locally. Most editors/IDEs will honor the `.editorconfig`
settings automatically by default. If your editor/IDE does not automatically support `.editorconfig`,
we suggest investigating to see if a plugin exists. For instance here is the
[plugin for vim](https://github.com/editorconfig/editorconfig-vim).

## Pre-push static analysis with Lefthook

[Lefthook](https://github.com/Arkweid/lefthook) is a Git hooks manager that allows
custom logic to be executed prior to Git committing or pushing. GitLab comes with
Lefthook configuration (`lefthook.yml`), but it must be installed.

We have a `lefthook.yml` checked in but it is ignored until Lefthook is installed.

### Uninstall Overcommit

We were using Overcommit prior to Lefthook, so you may want to uninstall it first with `overcommit --uninstall`.

### Install Lefthook

1. Install the `lefthook` Ruby gem:

   ```shell
   bundle install
   ```

1. Install Lefthook managed Git hooks:

   ```shell
   bundle exec lefthook install
   ```

1. Test Lefthook is working by running the Lefthook `prepare-commit-msg` Git hook:

   ```shell
   bundle exec lefthook run prepare-commit-msg
   ```

This should return a fully qualified path command with no other output.

### Lefthook configuration

The current Lefthook configuration can be found in [`lefthook.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lefthook.yml).

Before you push your changes, Lefthook automatically runs the following checks:

- Danger: Runs a subset of checks that `danger-review` runs on your merge requests.
- ES lint: Run `yarn run lint:eslint` checks (with the [`.eslintrc.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.eslintrc.yml) configuration) on the modified `*.{js,vue}` files. Tags: `frontend`, `style`.
- HAML lint: Run `bundle exec haml-lint` checks (with the [`.haml-lint.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.haml-lint.yml) configuration) on the modified `*.html.haml` files. Tags: `view`, `haml`, `style`.
- Markdown lint: Run `yarn markdownlint` checks on the modified `*.md` files. Tags: `documentation`, `style`.
- SCSS lint: Run `yarn lint:stylelint` checks (with the [`.stylelintrc`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.stylelintrc) configuration) on the modified `*.scss{,.css}` files. Tags: `stylesheet`, `css`, `style`.
- RuboCop: Run `bundle exec rubocop` checks (with the [`.rubocop.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.rubocop.yml) configuration) on the modified `*.rb` files. Tags: `backend`, `style`.
- Vale: Run `vale` checks (with the [`.vale.ini`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.vale.ini) configuration) on the modified `*.md` files. Tags: `documentation`, `style`.

In addition to the default configuration, you can define a [local configuration](https://github.com/Arkweid/lefthook/blob/master/docs/full_guide.md#local-config).

### Disable Lefthook temporarily

To disable Lefthook temporarily, you can set the `LEFTHOOK` environment variable to `0`. For instance:

```shell
LEFTHOOK=0 git push ...
```

### Run Lefthook hooks manually

To run the `pre-push` Git hook, run:

```shell
bundle exec lefthook run pre-push
```

For more information, check out [Lefthook documentation](https://github.com/Arkweid/lefthook/blob/master/docs/full_guide.md#run-githook-group-directly).

### Skip Lefthook checks per tag

To skip some checks based on tags when pushing, you can set the `LEFTHOOK_EXCLUDE` environment variable. For instance:

```shell
LEFTHOOK_EXCLUDE=frontend,documentation git push ...
```

For more information, check out [Lefthook documentation](https://github.com/Arkweid/lefthook/blob/master/docs/full_guide.md#skip-some-tags-on-the-fly).

## Ruby, Rails, RSpec

Our codebase style is defined and enforced by [RuboCop](https://github.com/rubocop-hq/rubocop).

You can check for any offenses locally with `bundle exec rubocop --parallel`.
On the CI, this is automatically checked by the `static-analysis` jobs.

For RuboCop rules that we have not taken a decision on yet, we follow the
[Ruby Style Guide](https://github.com/rubocop-hq/ruby-style-guide),
[Rails Style Guide](https://github.com/rubocop-hq/rails-style-guide), and
[RSpec Style Guide](https://github.com/rubocop-hq/rspec-style-guide) as general
guidelines to write idiomatic Ruby/Rails/RSpec, but reviewers/maintainers should
be tolerant and not too pedantic about style.

Similarly, some RuboCop rules are currently disabled, and for those,
reviewers/maintainers must not ask authors to use one style or the other, as both
are accepted. This isn't an ideal situation since this leaves space for
[bike-shedding](https://en.wiktionary.org/wiki/bikeshedding), and ideally we
should enable all RuboCop rules to avoid style-related
discussions/nitpicking/back-and-forth in reviews.

Additionally, we have a dedicated
[newlines style guide](../newlines_styleguide.md), as well as dedicated
[test-specific style guides and best practices](../testing_guide/index.md).

### Creating new RuboCop cops

Typically it is better for the linting rules to be enforced programmatically as it
reduces the aforementioned [bike-shedding](https://en.wiktionary.org/wiki/bikeshedding).

To that end, we encourage creation of new RuboCop rules in the codebase.

When creating a new cop that could be applied to multiple applications, we encourage you
to add it to our [GitLab Styles](https://gitlab.com/gitlab-org/gitlab-styles) gem.

### Resolving RuboCop exceptions

When the number of RuboCop exceptions exceed the default [`exclude-limit` of 15](https://docs.rubocop.org/rubocop/1.2/usage/basic_usage.html#command-line-flags),
we may want to resolve exceptions over multiple commits. To minimize confusion,
we should track our progress through the exception list.

When auto-generating the `.rubocop_todo.yml` exception list for a particular Cop,
and more than 15 files are affected, we should add the exception list to
a different file, `.rubocop_manual_todo.yml`.

This ensures that our list isn't mistakenly removed by another auto generation of
the `.rubocop_todo.yml`. This also allows us greater visibility into the exceptions
which are currently being resolved.

One way to generate the initial list is to run the `todo` auto generation,
with `exclude limit` set to a high number.

```shell
bundle exec rubocop --auto-gen-config --auto-gen-only-exclude --exclude-limit=100000
```

You can then move the list from the freshly generated `.rubocop_todo.yml` for the Cop being actively
resolved and place it in the `.rubocop_manual_todo.yml`. In this scenario, do not commit auto generated
changes to the `.rubocop_todo.yml` as an `exclude limit` that is higher than 15 will make the
`.rubocop_todo.yml` hard to parse.

### Reveal existing RuboCop exceptions

To reveal existing RuboCop exceptions in the code that have been excluded via `.rubocop_todo.yml` and
`.rubocop_manual_todo.yml`, set the environment variable `REVEAL_RUBOCOP_TODO` to `1`.

This allows you to reveal existing RuboCop exceptions during your daily work cycle and fix them along the way.

NOTE:
Permanent `Exclude`s should be defined in `.rubocop.yml` instead of `.rubocop_manual_todo.yml`.

## Database migrations

See the dedicated [Database Migrations Style Guide](../migration_style_guide.md).

## JavaScript

See the dedicated [JS Style Guide](../fe_guide/style/javascript.md).

## SCSS

See the dedicated [SCSS Style Guide](../fe_guide/style/scss.md).

## Go

See the dedicated [Go standards and style guidelines](../go_guide/index.md).

## Shell commands (Ruby)

See the dedicated [Guidelines for shell commands in the GitLab codebase](../shell_commands.md).

## Shell scripting

See the dedicated [Shell scripting standards and style guidelines](../shell_scripting_guide/index.md).

## Markdown

<!-- vale gitlab.Spelling = NO -->

We're following [Ciro Santilli's Markdown Style Guide](https://cirosantilli.com/markdown-style-guide/).

<!-- vale gitlab.Spelling = YES -->

## Documentation

See the dedicated [Documentation Style Guide](../documentation/styleguide/index.md).

## Python

See the dedicated [Python Development Guidelines](../python_guide/index.md).

## Misc

Code should be written in [US English](https://en.wikipedia.org/wiki/American_English).

---

[Return to Contributing documentation](index.md)
