wp-config-debug.php

<?php
/**
 * == About this Gist ==
 * 
 * Code to add to wp-config.php to enhance information available for debugging.
 * 
 * You would typically add this code below the database, language and salt settings
 * 
 * Oh.. and *do* make sure you change the path to the log file to a proper file path on your server (make sure it exists).
 * 
 * Set WP_DEBUG to false if you don't want errors displayed on the screen.
 * Independently of the WP_DEBUG setting, PHP errors, warnings and notices should now appear in your error.log file.
 * 
 * == DO == test whether it's all working by using the code at the end of the gist.
 * 
 * If error logging is not working, try:
 * - Check if the file was created at all, if not, upload an empty (text) file named error.log and try again.
 * - Fiddle around with the CHMOD settings for the error.log file to see what permissions are needed for your server setup.
 * - If you put the error.log outside of the web root: this will not work in all server setups. You may need to move the directory & file to be within the web root.
 */


/**
 * 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.
 */
define('WP_DEBUG', true);

/**
 * Turn on error logging and show errors on-screen if in debugging mode
 */
@error_reporting( E_ALL );
@ini_set('log_errors', true);
@ini_set('log_errors_max_len', '0');

/**
 * Change the path to one on your webserver, the directory does not have to be in the web root
 * Don't forget to CHMOD this dir+file and add an .htaccess file denying access to all
 * For an example .htaccess file, see https://gist.github.com/jrfnl/5953256
 */
@ini_set('error_log', '/path/to/writable/file/logs/error.log');

if ( WP_DEBUG !== true ) {
  @ini_set( 'display_errors', false ); // Don't show errors on screen
}
else {
	@ini_set( 'display_errors', true ); // Show errors on screen
	@ini_set( 'html_errors', true );
	@ini_set( 'docref_root', 'http://php.net/manual/' );
	@ini_set( 'docref_ext', '.php' );
	@ini_set( 'error_prepend_string', '<span style="color: #ff0000; background-color: transparent;">' );
	@ini_set( 'error_append_string', '</span>' );
}


/**
 * Adds a backtrace to PHP errors
 * 
 * Copied from: https://gist.github.com/625769
 * Forked from: http://stackoverflow.com/questions/1159216/how-can-i-get-php-to-produce-a-backtrace-upon-errors/1159235#1159235
 * Adjusted by jrfnl
 */
function process_error_backtrace($errno, $errstr, $errfile, $errline) {
	if(!(error_reporting() & $errno))
		return;
	switch($errno) {
		case E_WARNING	    :
		case E_USER_WARNING :
		case E_STRICT	    :
		case E_NOTICE	    :
		case ( defined( 'E_DEPRECATED' ) ? E_DEPRECATED : 8192 )   :
		case E_USER_NOTICE  :
			$type = 'warning';
			$fatal = false;
			break;
		default			 :
			$type = 'fatal error';
			$fatal = true;
			break;
	}
	$trace = debug_backtrace();
	array_shift($trace);
	if(php_sapi_name() == 'cli' && ini_get('display_errors') ) {
		echo 'Backtrace from ' . $type . ' \'' . $errstr . '\' at ' . $errfile . ' ' . $errline . ':' . "\n";
		foreach($trace as $item)
			echo '  ' . (isset($item['file']) ? $item['file'] : '<unknown file>') . ' ' . (isset($item['line']) ? $item['line'] : '<unknown line>') . ' calling ' . $item['function'] . '()' . "\n";
			
		flush();
	} else if( ini_get('display_errors') ) {
		echo '<p class="error_backtrace">' . "\n";
		echo '  Backtrace from ' . $type . ' \'' . $errstr . '\' at ' . $errfile . ' ' . $errline . ':' . "\n";
		echo '  <ol>' . "\n";
		foreach($trace as $item)
			echo '	<li>' . (isset($item['file']) ? $item['file'] : '<unknown file>') . ' ' . (isset($item['line']) ? $item['line'] : '<unknown line>') . ' calling ' . $item['function'] . '()</li>' . "\n";
		echo '  </ol>' . "\n";
		echo '</p>' . "\n";

		flush();
	}
	if(ini_get('log_errors')) {
		$items = array();
		foreach($trace as $item)
			$items[] = (isset($item['file']) ? $item['file'] : '<unknown file>') . ' ' . (isset($item['line']) ? $item['line'] : '<unknown line>') . ' calling ' . $item['function'] . '()';
		$message = 'Backtrace from ' . $type . ' \'' . $errstr . '\' at ' . $errfile . ' ' . $errline . ': ' . join(' | ', $items);
		error_log($message);
	}

	if($fatal)
		exit(1);
}

set_error_handler('process_error_backtrace');

/**
 * Now test whether it all works by uncommenting the below line
 *
 * If all is well:
 * - With WP_DEBUG set to true: You should see a red error notice on your screen 
 * - Independently of the WP_DEBUG setting, the below 'error'-message should have been written to your log file. *Do* check whether it has been....
 */
//trigger_error( 'Testing 1..2..3.. Debugging code is working!', E_USER_NOTICE );