How can I do a var_dump in Symfony?

I need to see $_POST['criteria']. I want to use var_dump to do it, but I don't how to incorporate that into a Symfony Controller.

Here's the code:

public function saveAction($id, Request $request){
		$data = $_POST['challenge'];

		// validate fields
		foreach(['campName', 'campPointConv', 'campHierarchy', 'campParticUnits', 'campStartDate', 'campEndDate'] as $requiredField){
			if(!Util::valid($requiredField, $data)){
				$this->addNotice('You are missing required fields', 'error');
				return $this->redirectToRoute('admin_gamification_challenges_edit', ['id'=>$id]);
			}
		}

		if(!empty($data['campAutoSync'])){
			foreach(['campAutoSyncHrId', 'campAutoSyncPoints', 'campAutoSyncUnits'] as $requiredField){
				if(!Util::valid($requiredField, $data)){
					$this->addNotice('You are missing required auto sync fields', 'error');
					return $this->redirectToRoute('admin_gamification_challenges_edit', ['id'=>$id]);
				}
			}

			if(!is_numeric($data['campAutoSyncPoints']) || !is_numeric($data['campAutoSyncUnits'])){
				$this->addNotice('Auto sync points and units must be numbers', 'error');
				return $this->redirectToRoute('admin_gamification_challenges_edit', ['id'=>$id]);
			}
		}
		
		//here you're looking to make sure that if the "BETWEEN" clause was used for any of the rules, that the values inputted are, in fact, integers

		$isNew = (empty($id) || $id == 'new')?true:false;

		// save
		$resp = $this->get('gamification.challenges')->saveChallenge($id, $data, $this->user->cpScope);

		if(!$resp){
			$this->addNotice('There was an error saving this challenge.', 'error');
			return $this->redirectToRoute('admin_gamification_challenges');
		}

		$id = $resp['id'];

		$criteria = (isset($_POST['criteria']) && !empty($_POST['criteria']))?$this->_assembleCriteria($_POST['criteria']):['and'=>[], 'or'=>[]];
		$rule = ['ruleName'=>'Rule: '.$data['campName'], 'ruleDesc'=>$_POST['ruleDesc'], 'ruleStatus'=>'Active', 'ruleCriteria'=>$criteria];
		$ruleID = (isset($_POST['ruleID']) && !empty($_POST['ruleID']))?$_POST['ruleID']:'new';
		$resp_rule = $this->get('gamification.rules')->saveRule($ruleID, $rule, $id, $this->user->cpID, true);

		$this->get('gamification.challenges')->saveParticLimits($_POST['partic_limits'], $id);

		if(isset($_POST['lrnID'])){
			$this->get('learning.learning')->saveChallengeAssignment($_POST['lrnID'], $id);
		}

        if($isNew){
            $employers = $this->get('gamification.campaigns')->getPopulationEmployers($data['campHierarchy'], $this->user->cpID);
            $userPushTokens = $this->get('push_notifications')->getUserTokensFromEmpScope(array_keys($employers), $this->user->cpScope);
            if(!empty($userPushTokens)){
                $notificationData = $this->get('push_notifications')->getNotificationContent('GamificationNewChallenge');
                $this->get('push_notifications')->sendNotification($userPushTokens, ['title'=>$notificationData['title'], 'message'=>sprintf($notificationData['message'], $data['campName']), 'screen'=>'Gamification', 'params'=>['campID'=>$id]]);
            }
        }


		$this->addNotice('Your challenge was successfully saved', 'success');

		return $this->redirectToRoute('admin_gamification_challenges');
	}

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At one point, I tried to eliminate the "return $this->redirectToRoute('admin_gamification_challenges');" and do a "var_dump," but I got an error that said Symfony requires a "return" of some sort, but...

...how can I do a var_dump and see what the "_POST[criteria] array looks like?

Thanks!