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

We strongly recommend installing Lefthook to automatically check for static analysis offenses before pushing your changes.

To install lefthook, run the following in your GitLab source directory:

# 1. Make sure to uninstall Overcommit first
overcommit --uninstall

# If using rbenv, at this point you may need to do: rbenv rehash

# 2. Install lefthook...

## With Homebrew (macOS)
brew install Arkweid/lefthook/lefthook

## Or with Go
go get

## Or with Rubygems
gem install lefthook

### You may need to run the following if you're using rbenv
rbenv rehash

# 3. Install the Git hooks
lefthook install -f

Before you push your changes, Lefthook then automatically run Danger checks, and other checks for changed files. This saves you time as you don't have to wait for the same errors to be detected by CI/CD.

Lefthook relies on a pre-push hook to prevent commits that violate its ruleset. To override this behavior, pass the environment variable LEFTHOOK=0. That is, LEFTHOOK=0 git push.

You can also:

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.

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.

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.

When creating a new cop that could be applied to multiple applications, we encourage you to add it to our GitLab Styles gem.

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.

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.

bundle exec rubocop --auto-gen-config --auto-gen-only-exclude --exclude-limit=10000

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.

Database migrations

See the dedicated Database Migrations Style Guide.


See the dedicated JS Style Guide.


See the dedicated SCSS Style Guide.


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.


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


See the dedicated Documentation Style Guide.


See the dedicated Python Development Guidelines.


Code should be written in US English.

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