Style guides

Editor/IDE styling standardization

We use EditorConfig 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.

Pre-push static analysis with Lefthook

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

Install the lefthook Ruby gem:
```
bundle install
```
Install Lefthook managed Git hooks:
```
bundle exec lefthook install
```
Test Lefthook is working by running the Lefthook prepare-commit-msg Git hook:
```
bundle exec lefthook run prepare-commit-msg
```

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

Lefthook configuration

Lefthook is configured with a combination of:

Project configuration in lefthook.yml.
Any local configuration.

Disable Lefthook temporarily

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

LEFTHOOK=0 git push ...

Run Lefthook hooks manually

To run the pre-push Git hook, run:

bundle exec lefthook run pre-push

For more information, check out Lefthook documentation.

Skip Lefthook checks per tag

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

LEFTHOOK_EXCLUDE=frontend,documentation git push ...

As an alternative, you can create lefthook-local.yml with this structure:

pre-push:
  exclude_tags:
    - frontend
    - documentation

For more information, check out Lefthook documentation.

Skip or enable a specific Lefthook check

To skip or enable a check based on its name when pushing, you can add skip: true or skip: false to the lefthook-local.yml section for that hook. For instance, you might want to enable the gettext check to detect issues with locale/gitlab.pot:

pre-push:
  commands:
    gettext:
      skip: false

For more information, check out Lefthook documentation Skipping commands section.

Ruby, Rails, RSpec

Our codebase style is defined and enforced by 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.

In addition, you can integrate RuboCop into supported IDEs using the Solargraph gem.

For RuboCop rules that we have not taken a decision on yet, we follow the Ruby Style Guide, Rails Style Guide, and 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, and ideally we should enable all RuboCop rules to avoid style-related discussions/nitpicking/back-and-forth in reviews. There are some styles that commonly come up in reviews that are not enforced, the GitLab Ruby style guide includes a non-exhaustive list of these topics.

Additionally, we have a dedicated newlines style guide, as well as dedicated test-specific style guides and best practices.

Creating new RuboCop cops

Typically it is better for the linting rules to be enforced programmatically as it reduces the aforementioned bike-shedding.

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

We maintain Cops across several Ruby code bases, and not all of them are specific to the GitLab application. When creating a new cop that could be applied to multiple applications, we encourage you to add it to our GitLab Styles gem. If the Cop targets rules that only apply to the main GitLab application, it should be added to GitLab instead.

RuboCop node pattern

When creating node patterns to match Ruby's AST, you can use scripts/rubocop-parse to display the AST of a Ruby expression, in order to help you create the matcher. See also !97024.

Resolving RuboCop exceptions

When the number of RuboCop exceptions exceed the default exclude-limit of 15, we may want to resolve exceptions over multiple commits. To minimize confusion, we should track our progress through the exception list.

The preferred way to generate the initial list or a list for specific RuboCop rules is to run the Rake task rubocop:todo:generate:

# Initial list
bundle exec rake rubocop:todo:generate

# List for specific RuboCop rules
bundle exec rake 'rubocop:todo:generate[Gitlab/NamespacedClass,Lint/Syntax]'

This Rake task creates or updates the exception list in .rubocop_todo/. For example, the configuration for the RuboCop rule Gitlab/NamespacedClass is located in .rubocop_todo/gitlab/namespaced_class.yml.

Make sure to commit any changes in .rubocop_todo/ after running the Rake task.

Reveal existing RuboCop exceptions

To reveal existing RuboCop exceptions in the code that have been excluded via .rubocop_todo.yml and .rubocop_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: Define permanent Excludes in .rubocop.yml instead of .rubocop_todo/**/*.yml.

Database migrations

See the dedicated Database Migrations Style Guide.

JavaScript

See the dedicated JS Style Guide.

SCSS

See the dedicated SCSS Style Guide.

Go

See the dedicated Go standards and style guidelines.

Shell commands (Ruby)

See the dedicated Guidelines for shell commands in the GitLab codebase.

Shell scripting

See the dedicated Shell scripting standards and style guidelines.

Markdown

We're following Ciro Santilli's Markdown Style Guide.

Documentation

See the dedicated Documentation Style Guide.

Guidelines for good practices

Introduced in GitLab 13.2 as GitLab Development documentation.

Good practice examples demonstrate encouraged ways of writing code while comparing with examples of practices to avoid. These examples are labeled as Bad or Good. In GitLab development guidelines, when presenting the cases, it's recommended to follow a first-bad-then-good strategy. First demonstrate the Bad practice (how things could be done, which is often still working code), and then how things should be done better, using a Good example. This is typically an improved example of the same code.

Consider the following guidelines when offering examples:

First, offer the Bad example, and then the Good one.
When only one bad case and one good case is given, use the same code block.
When more than one bad case or one good case is offered, use separated code blocks for each. With many examples being presented, a clear separation helps the reader to go directly to the good part. Consider offering an explanation (for example, a comment, or a link to a resource) on why something is bad practice.
Better and best cases can be considered part of the good cases' code block. In the same code block, precede each with comments: # Better and # Best.

Although the bad-then-good approach is acceptable for the GitLab development guidelines, do not use it for user documentation. For user documentation, use Do and Don't. For examples, see the Pajamas Design System.

Python

See the dedicated Python Development Guidelines.

Misc

Code should be written in US English.