TYPO3 Core

If we follow the execution logic from https://github.com/TYPO3/TYPO3.CMS/blob/master/typo3/sysext/fluid/Classes/ViewHelpers/Form/CheckboxViewHelper.php#L91 to the end of the function it does look like some of the conditions might cause some weird results:

• $propertyValue is possibly not-null in quite a lot of cases
• $checked is overridden if $propertyValue is not-null in the final "elseif" without checking $checked !== null

It should be possible to fix this by changing the condition in https://github.com/TYPO3/TYPO3.CMS/blob/master/typo3/sysext/fluid/Classes/ViewHelpers/Form/CheckboxViewHelper.php#L110 to also check `$checked !== null` instead of just checking `$propertyValue !== null`.

Another possibility is that `$checked` defaults to `false` when the argument is not specified... I don't remember the Fluid logic exactly but we did optimise the way BooleanNode gets created and processed and somewhere during that it is possible we implemented casting of the default value (null) which then becomes `false` which causes the conditions in CheckboxViewHelper to fail (see links above). This should be fairly easy to confirm by debugging the `$checked` variable as soon as it is set (but not in a unit test which creates mock arguments, of course, which is why I haven't tested this - I've no setup, only unit tests currently).

The code generated by the Fluid compiler does not process correctly boolean attributes. Below are parts of the code generated by TYPO3 7.6.9, TYPO3 8.2.1 and TYPO3 8.3.1. In TYPO3 8.3.1, the checked attribute is a string instead of a boolean.

// TYPO3 7.6.9
// Rendering ViewHelper TYPO3\CMS\Fluid\ViewHelpers\Form\CheckboxViewHelper
$arguments4 = array();
$arguments4['name'] = 'myCheckbox';
$arguments4['value'] = '1';
// Rendering Boolean node
$arguments4['checked'] = TYPO3\CMS\Fluid\Core\Parser\SyntaxTree\BooleanNode::convertToBoolean('checked');

// TYPO3 8.2.1
// Rendering ViewHelper TYPO3\CMS\Fluid\ViewHelpers\Form\CheckboxViewHelper
$arguments6 = array();
$arguments6['name'] = 'myCheckbox';
$arguments6['value'] = 1;
// Rendering Boolean node
// Rendering Array
$array7 = array();
$array7['0'] = 'checked';

$expression8 = function($context) {return "checked";};
$arguments6['checked'] = TYPO3Fluid\Fluid\Core\Parser\SyntaxTree\BooleanNode::convertToBoolean(
                    $expression8(
                        TYPO3Fluid\Fluid\Core\Parser\SyntaxTree\BooleanNode::gatherContext($renderingContext, $array7)
                    ),
                    $renderingContext
                );

// TYPO3 8.3.1
// Rendering ViewHelper TYPO3\CMS\Fluid\ViewHelpers\Form\CheckboxViewHelper
$arguments6 = array();
$arguments6['name'] = 'myCheckbox';
$arguments6['value'] = 1;
$arguments6['checked'] = 'checked';

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/51375