Feature: #83429 - Feature Toggles

See Issue #83429

Description

In order to allow better support for alternative functionality while keeping old functionality, a new API for enabling installation-wide features - called "Feature Toggles" - has been added.

The new API checks against a system-wide option array within $TYPO3_CONF_VARS['SYS']['features'] which can be enabled system-wide. Both TYPO3 Core and Extensions can then provide alternative functionality for a certain feature.

Features are usually breaking changes for a minor version / sprint release, which site administrators can enable at their own risk, or stay fully compatible with third-party extensions by choosing not to enable them.

Examples for having features are: * Throw exceptions on certain occasions instead of just returning a string message as error message. * Disable obsolete functionality which might still be used, but slows down the system. * Enable alternative PageNotFound handling for an installation.

Impact

Features are documented for TYPO3 Core. For extension authors, the API can be used for any custom feature provided by an extension:

if (GeneralUtility::makeInstance(Features::class)->isFeatureEnabled('myFeatureName')) {
        // do custom processing
}