WP/WC Hooks

debug-wp-rewrite.php

<?php

function debug_wp_rewrite_dump(&$wp) {
	echo '<pre>';
	global $wp_rewrite;

	echo '<h2>rewrite rules</h2>';
	echo var_export($wp_rewrite->wp_rewrite_rules(), true);

	echo '<h2>permalink structure</h2>';
	echo var_export($wp_rewrite->permalink_structure, true);

	echo '<h2>page permastruct</h2>';
	echo var_export($wp_rewrite->get_page_permastruct(), true);

	echo '<h2>matched rule and query</h2>';
	echo var_export($wp->matched_rule, true);

	echo '<h2>matched query</h2>';
	echo var_export($wp->matched_query, true);

	echo '<h2>request</h2>';
	echo var_export($wp->request, true);

	global $wp_the_query;
	echo '<h2>the query</h2>';
	echo var_export($wp_the_query, true);
	echo '</pre>';
}

add_action('parse_request', 'debug_wp_rewrite_dump');

wc_get_logger.php

<?php

$logger = wc_get_logger();
$logger_context = ['source' => 'f4t'];
$logger->debug(wc_print_r(['key' => 'value'], true), $logger_context);

wp_mail_failed_log.php

<?php

add_action('wp_mail_failed', 'f4t_mail_error_log', 10, 1);
function f4t_mail_error_log($wp_error) {
	$fn = WP_CONTENT_DIR . DS . 'mail.log'; // say you've got a mail.log file in your wp-content dir
	$fp = fopen($fn, 'a');
	fputs($fp, date('[Y-m-d H:i:s] ') . 'Mailer error: ' . $wp_error->get_error_message() ."\n");
	fclose($fp);
}