PSR Logger not working for Magento 2

Question

I'm trying to log some info in the existing Magento 2 module just to check if the code is running or not. Following files have been modified to log info.

Magento\Checkout\Block\Cart\Item\Renderer.php

<?php
/**
 * Copyright © 2016 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Checkout\Block\Cart\Item;
.
.
.
.
use Psr\Log\LoggerInterface;
.
.
.
protected $_logger;

 public function __construct(
        \Magento\Framework\View\Element\Template\Context $context,
        .
        .
        LoggerInterface $logger,
        array $data = []
    ) {
        .
        .
        .
        $this->logger = $logger;
        parent::__construct($context, $data);
        .
        .
        .

    }
.
.
.
public function getProductOptions()
    {
        /* @var $helper \Magento\Catalog\Helper\Product\Configuration */
        $helper = $this->_productConfig;
        $this->_logger->debug('Product Options');
        return $helper->getCustomOptions($this->getItem());
    }

I'm getting following error.

Exception #0 (Exception): Recoverable Error: Argument 10 passed to Magento\Checkout\Block\Cart\Item\Renderer::__construct() must implement interface Psr\Log\LoggerInterface, array given, called in /Applications/MAMP/htdocs/magentoce21/vendor/magento/module-bundle/Block/Checkout/Cart/Item/Renderer.php on line 65 and defined in /Applications/MAMP/htdocs/magentoce21/vendor/magento/module-checkout/Block/Cart/Item/Renderer.php on line 120

Answer 1

You should refresh generation files. Try to remove the var/generation directory content, like:

rm -rf var/generation/*

from the magento root directory.

Additional info: you can use logger from the parent class, without declaring new logger, becouse it already exists in the _logger parameter.

Update: It is possible that error is coming from the some other block which extends your block, but still uses a standard set of arguments in the __construct method when it try to call the parent __construct method.

I think this block located here:

vendor/magento/module-bundle/Block/Checkout/Cart/Item/Renderer.php

class Renderer extends \Magento\Checkout\Block\Cart\Item\Renderer // here is your block

.....

/**
 * @param \Magento\Framework\View\Element\Template\Context $context
 * @param \Magento\Catalog\Helper\Product\Configuration $productConfig
 * @param \Magento\Checkout\Model\Session $checkoutSession
 * @param \Magento\Catalog\Block\Product\ImageBuilder|\Magento\Catalog\Helper\Image $imageBuilder
 * @param \Magento\Framework\Url\Helper\Data $urlHelper
 * @param \Magento\Framework\Message\ManagerInterface $messageManager
 * @param PriceCurrencyInterface $priceCurrency
 * @param \Magento\Framework\Module\Manager $moduleManager
 * @param InterpretationStrategyInterface $messageInterpretationStrategy
 * @param Configuration $bundleProductConfiguration
 * @param array $data
 * @SuppressWarnings(PHPMD.ExcessiveParameterList)
 */
public function __construct(
    \Magento\Framework\View\Element\Template\Context $context,
    \Magento\Catalog\Helper\Product\Configuration $productConfig,
    \Magento\Checkout\Model\Session $checkoutSession,
    \Magento\Catalog\Block\Product\ImageBuilder $imageBuilder,
    \Magento\Framework\Url\Helper\Data $urlHelper,
    \Magento\Framework\Message\ManagerInterface $messageManager,
    PriceCurrencyInterface $priceCurrency,
    \Magento\Framework\Module\Manager $moduleManager,
    InterpretationStrategyInterface $messageInterpretationStrategy,
    Configuration $bundleProductConfiguration,
    array $data = []
) {
    $this->_bundleProductConfiguration = $bundleProductConfiguration;
    parent::__construct(
        $context,
        $productConfig,
        $checkoutSession,
        $imageBuilder,
        $urlHelper,
        $messageManager,
        $priceCurrency,
        $moduleManager,
        $messageInterpretationStrategy,
        $data // 10 is data-array , this should be your logger and next you should add the $data (11 argument)
    );
    $this->_isScopePrivate = true;
}

Answer 2

See below example of print log

protected $logger;
public function __construct(\Psr\Log\LoggerInterface $logger)
{
    $this->logger = $logger;
}

You use debug, exception, system for psr logger for example

$this->logger->info($message);
$this->logger->debug($message);