Document features deployed behind feature flags

GitLab uses feature flags to roll out the deployment of its own features.

When the state of a feature flag changes, the developer who made the change must update the documentation.

When to document features behind a feature flag

Every feature introduced to the codebase, even if it's behind a disabled feature flag, must be documented. For more information, see the discussion that led to this decision. Experiment or Beta features are usually behind a feature flag, and must also be documented. For more information, see Document Experiment or Beta features.

When the feature is implemented in multiple merge requests, discuss the plan with your technical writer.

You can create a documentation issue and delay the documentation if the feature:

• Is far-reaching (makes changes across many areas of GitLab), like navigation changes.
• Includes many MRs.
• Affects more than a few documentation pages.
• Is not fully functional if the feature flag is enabled for testing.

The PM, EM, and writer should make sure the documentation work is assigned and scheduled.

Every feature flag in the codebase is in the documentation, even when the feature is not fully functional or otherwise documented.

How to add feature flag documentation

When you document feature flags, you must:

• Add version history text.
• Add a note at the start of the topic.

Add version history text

When the state of a flag changes (for example, disabled by default to enabled by default), add the change to the version history.

Possible version history entries are:

> - [Introduced](issue-link) in GitLab X.X [with a flag](../../administration/feature_flags.md) named `flag_name`. Disabled by default.
> - [Enabled on GitLab.com](issue-link) in GitLab X.X.
> - [Enabled on GitLab.com](issue-link) in GitLab X.X. Available to GitLab.com administrators only.
> - [Enabled on self-managed](issue-link) in GitLab X.X.
> - [Generally available](issue-link) in GitLab X.Y. Feature flag `flag_name` removed.

Use a note to describe the state of the feature flag

Information about feature flags should be in a FLAG note at the start of the topic (just below the version history).

The note has three parts, and follows this structure:

FLAG:
<Self-managed GitLab availability information.>
<GitLab.com availability information.>
<This feature is not ready for production use.>

A FLAG note renders on the GitLab documentation site as:

FLAG: On self-managed GitLab, by default this feature is not available. To make it available, ask an administrator to enable the feature flag named example_flag. On GitLab.com, this feature is not available. This feature is not ready for production use.

Self-managed GitLab availability information

GitLab.com availability information

Optional information

If needed, you can add this sentence:

The feature is not ready for production use.

Feature flag documentation examples

The following examples show the progression of a feature flag.

> Introduced in GitLab 13.7 [with a flag](../../administration/feature_flags.md) named `forti_token_cloud`. Disabled by default.

FLAG:
On self-managed GitLab, by default this feature is not available. To make it available,
ask an administrator to [enable the feature flag](../administration/feature_flags.md) named `forti_token_cloud`.
The feature is not ready for production use.

When the feature is enabled in production, you can update the version history:

> - Introduced in GitLab 13.7 [with a flag](../../administration/feature_flags.md) named `forti_token_cloud`. Disabled by default.
> - [Enabled on self-managed](https://gitlab.com/issue/etc) GitLab 13.8.

FLAG:
On self-managed GitLab, by default this feature is available. To hide the feature per user,
ask an administrator to [disable the feature flag](../administration/feature_flags.md) named `forti_token_cloud`.

And, when the feature is done and fully available to all users:

> - Introduced in GitLab 13.7 [with a flag](../../administration/feature_flags.md) named `forti_token_cloud`. Disabled by default.
> - [Enabled on self-managed](https://gitlab.com/issue/etc) in GitLab 13.8.
> - [Enabled on GitLab.com](https://gitlab.com/issue/etc) in GitLab 13.9.
> - [Generally available](issue-link) in GitLab 14.0. Feature flag `forti_token_cloud` removed.

Simplify long version history

The version history can get long, but you can sometimes simplify or remove entries.

Combine entries if they happened in the same release:

• Before:

  > - [Introduced](issue-link) in GitLab 14.2 [with a flag](../../administration/feature_flags.md) named `ci_include_rules`. Disabled by default.
  > - [Enabled on GitLab.com](issue-link) in GitLab 14.3.
  > - [Enabled on self-managed](issue-link) in GitLab 14.3.

• After:

  > - [Introduced](issue-link) in GitLab 14.2 [with a flag](../../administration/feature_flags.md) named `ci_include_rules`. Disabled by default.
  > - [Enabled on GitLab.com and self-managed](issue-link) in GitLab 14.3.

Remove Enabled on GitLab.com entries when the feature is enabled by default for both GitLab.com and self-managed:

• Before:

  > - [Introduced](issue-link) in GitLab 15.6 [with a flag](../../administration/feature_flags.md) named `ci_hooks_pre_get_sources_script`. Disabled by default.
  > - [Enabled on GitLab.com](issue-link) in GitLab 15.9.
  > - [Generally available](issue-link) in GitLab 15.10. Feature flag `ci_hooks_pre_get_sources_script` removed.

• After:

  > - [Introduced](issue-link) in GitLab 15.6 [with a flag](../../administration/feature_flags.md) named `ci_hooks_pre_get_sources_script`. Disabled by default.
  > - [Generally available](issue-link) in GitLab 15.10. Feature flag `ci_hooks_pre_get_sources_script` removed.