ElementalContentControllerExtension should 404 instead of 500 error when elements are not found

[kinglozzer]

ElementalContentControllerExtension::handleElement() has a bunch of places which call user_error(), resulting in a 500 internal server error when users visit a URL for an element which doesn’t exist (or previously existed, but has been removed). This can be caused by bots scanning sites, or legitimate users visiting URLs that have since been removed.

silverstripe-elemental/src/Extensions/ElementalContentControllerExtension.php

Lines 18 to 49 in f626840

	public function handleElement()
	{
	$id = $this->owner->getRequest()->param('ID');
	if (!$id) {
	user_error('No element ID supplied', E_USER_ERROR);
	return false;
	}
	/** @var SiteTree $elementOwner */
	$elementOwner = $this->owner->data();
	$elementalAreaRelations = $this->owner->getElementalRelations();
	if (!$elementalAreaRelations) {
	user_error(get_class($this->owner) . ' has no ElementalArea relationships', E_USER_ERROR);
	return false;
	}
	foreach ($elementalAreaRelations as $elementalAreaRelation) {
	$element = $elementOwner->$elementalAreaRelation()->Elements()
	->filter('ID', $id)
	->First();
	if ($element) {
	return $element->getController();
	}
	}
	user_error('Element $id not found for this page', E_USER_ERROR);
	return false;
	}

For example, if you visit a URL like http://mysite.test/home/element/12345/action you’ll get a server error when that may simply be a URL that no longer exists.

These should be replaced with 404 responses, though we could keep the more descriptive error messages for dev mode.