Feature flags are useful to hide or show features before they are completed or ready for release to allow a developer to test a feature without disrupting the codebase.

Feature Levels in Djblets

djblets/djblets/features/level.py

This file has the different options for a feature level (docs). The current feature levels available are:

• Unavailable: feature is completely unavailable, feature checkers will not be consulted
• Experimental: a feature checker must enable this feature
• Beta: a feature checker must enable this feature
• Stable: this feature will always be enabled

Adding a New Feature Flag in ReviewBoard

reviewboard/reviewboard/reviews/features.py

This file contains many of the feature flags for ReviewBoard. Here is an example of what a feature flag definition could look like:

class MyFeature(Feature):
    """A description about what this feature will do."""

    feature_id = 'reviews.my_feature'
    name = _('My Feature Name')
    level = FeatureLevel.FEATURE_LEVEL
    summary = _('A summary of my feature.')

my_feature = MyFeature()

The feature_id is how it will be identified in the code.

The level corresponds to the Feature Levels in Djblets.

/reviewboard/settings.py

Add

ENABLED_FEATURES = {
    'reviews.FEATURE_FLAG_NAME': True
}

to the bottom of this file.

FEATURE_FLAG_NAME is the feature_id of the feature identified in the features.py file. For example, reviews.my_feature.

Using Feature Flags

The feature flags can be used as is in Django templates and .py files.

To use the feature flags in Javascript files, add this to the corresponding Django template:

RB.EnabledFeatures = {
	VARIABLE_NAME: {% if_feature_enabled 'FEATURE_FLAG_NAME' %}true{% else %}false{% endif_feature_enabled %},
};

FEATURE_FLAG_NAME is the ID in the features.py file.

This feature flag can now be accessed in the Javascript file with RB.EnabledFeatures.VARIABLE_NAME.