Debugging with WordPress - enable WP_DEBUG, with sample usage to investigate wc_get_template()

conditional-debug-code.php

<?php
// Only call error_log() when in debug mode.
if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
		error_log('WP_DEBUG is enabled');
}

debug-demo.php

<?php
/*
Plugin Name: Debug Demo
Plugin URI:  http://www.damiencarbery.com/2017/01/debugging-with-wordpress-and-being-secure/
Description: Demonstrate error_log().
Author: Damien Carbery
Version: 0.1
*/

add_action('wp_head', 'dc_debug_demo');

function dc_debug_demo() {
    global $post;

    // Add this to html as a comment.
    echo '<!-- Post type: ' . $post->post_type . '; Post name: ' . $post->post_name . ' -->';
    // Write to the wp-content/debug.log file.
    error_log('Post type: ' . $post->post_type . '; Post name: ' . $post->post_name);
}

debug-wc_get_template.log

[20-Jan-2017 13:35:57 UTC] wc_get_template: located:/var/www/web/wp-content/plugins/woocommerce/templates/notices/notice.php; template_name:notices/notice.php; template_path:; default_path:; args:array (
  'messages' => 
  array (
    0 => 'Have a coupon? <a href="#" class="showcoupon">Click here to enter your code</a>',
  ),
)

debug.log

[20-Jan-2017 12:56:53 UTC] Post type: post; Post name: hello-world
[20-Jan-2017 12:56:56 UTC] Post type: page; Post name: sample-page

htaccess

<Files debug.log>
 order deny,allow
 deny from all
 allow from 12.34.56.78
</Files>

wc-template-logging.php

<?php
/*
Plugin Name: Log Template Searches in WooCommerce
Plugin URI: http://www.damiencarbery.com
Description: Log calls to the WooCommerce template functions to help determine how to intercept the calls.
Author: Damien Carbery
Version: 0.1
*/

add_filter( 'wc_get_template', 'lts_get_template', 20, 5 );
function lts_get_template( $located, $template_name, $args, $template_path, $default_path ) {
    
    error_log( sprintf('wc_get_template: located:%s; template_name:%s; template_path:%s; default_path:%s; args:%s', $located, $template_name, $template_path, $default_path, var_export( $args, true ) ) );
    
    return $located;
}

wp-config.php

<?php
/**
 * For developers: WordPress debugging mode.
 *
 * Change this to true to enable the display of notices during development.
 * It is strongly recommended that plugin and theme developers use WP_DEBUG
 * in their development environments.
 */
if ($_SERVER['REMOTE_ADDR'] == '12.34.56.78') {  // Only enable for the specified IP address
    define('WP_DEBUG', true);
    define('WP_DEBUG_LOG', true);  // error_log() will write to wp-content/debug.log
    //define('WP_DEBUG_LOG', '/maybe/path/outside/htdocs/debug.log');  // You can specify a path for the log file.
    define('WP_DEBUG_DISPLAY', false);  // Write notices/warnings/errors to debug.log instead of the html
    @ini_set('display_errors', 0);
} else {
    define('WP_DEBUG', false);
}