Deprecation: #104789 - Fluid variables true, false, null

See forge#104789

Description

Fluid standalone will add proper language syntax for booleans and null with Fluid v4, which will be used in TYPO3 v13. Thus, user-defined variables named true, false and null are no longer allowed.

Impact

Assigning variables with name true, false or null will throw an exception in Fluid v4. In preparation of this change, Fluid v2.15 logs a deprecation level error message if any of these variable names are used.

Affected installations

Instances with Fluid templates using true, false or null as user-defined variable names. This should rarely happen, as it would involve using $view->assign('true', $someVar).

Migration

Template code using these variables should be adjusted to use different variable names. In Fluid v4, the variables will contain their matching PHP counterparts.