The bad, the ugly and Query Monitor

The right way to debug in WordPress

Daniele Scasciafratte / @Mte90Net

Daniele Scasciafratte

• Co Founder/CTO Codeat
• Italian Linux Society council member
• Mozillian
• WordPress Core Contributor/Developer
• Podcast 🇮🇹 Daniele.tech - Opinioni in open source
• Old school developer

Art of debugging

“While the meaning of the verb to debug is to remove errors, in reality it is more about seeing step by step execution of a program. As well as examining it against some specification of how program should behave. A programmer who has no access to high quality debugger is like a shortsighted person. He can function but he can miss some dangerous things in the environment very easily. ”

Joe's (Joe Armstrong) Law of Debugging

“All errors will be plus/minus three statements of the place you last changed the program”

First of all

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_DISPLAY', false );
define( 'WP_DEBUG_LOG', true );
define( 'SCRIPT_DEBUG', true );
# If you need Jetpack
define( 'JETPACK_DEV_DEBUG', true );
define( 'JETPACK_STAGING_MODE', true );
# If you need Freemius
define( 'WP_FS__SKIP_EMAIL_ACTIVATION', true);
define( 'WP_FS__DEV_MODE', true );

3 phases of debugging

DOH

3 phases of debugging

Understand the taste

3 phases of debugging

Release the hot patch

The real 3 phases

• Replicate the bug
• Isolate and understand the bug
• Do the magic killer patch

In this talk we will focus on phase 2

User (classic) case

• User open a form: "Riscuotere la taglia"
• User input some data: "Nome: El gringo"
• User get output: "Taglia incassata, 200 Wapuu $"
• Data should be sanitized: "Non si lava da mesi"
• Data should be parsed: "Scappato con un buco nel muro"

Let's inspect the data

The Bad way

echo $var;

print_r( $var );

var_dump( $var );

var_dump( $var ); die();

The ugly way

Custom Error log path in WP 5.2

define( 'WP_DEBUG_LOG', 'path/to/log/file' );

Print what you want in the log of your web server

error_log( print_r( $var, true ) );

The ugly old school way

function vvv-debug(){
    log="/var/www/VVV/www/$1/htdocs/wp-content/debug.log"
    if [ ! -f $log ]; then
        log="/var/www/VVV/www/$1/public_html/wp-content/debug.log"
    fi
    
    if [ -f $log ]; then
        actualsize=$(du -k $log | cut -f 1)
        if [ $actualsize -ge 300 ]; then
            rm $log;
        fi
        echo "" > $log
        multitail -cS php -m 600 $log;
    else
        echo "Log not found"
    fi
}
# Open the log in a terminal of a specific site in VVV
$ vvv-debug demo

The ugly old school way

(
    [error] => Notice
    [file] => /home/domain/wp-content/plugins/lifterlms/vendor/ericmann/wp-session-manager/includes/class-wp-session.php
    [line] => 77
    [context] => Array
        (
            [cookie] => cxxxxxxxxxxx
            [cookie_crumbs] => Array
                (
                    [0] => cxxxxxxxxxxx
                )

        )

    [url] => https://domain/author/daniele/feed/
    [filter] => plugins_loaded
    [path] => /home/domain/wp-content/plugins/lifterlms/vendor/ericmann/wp-session-manager/includes/class-wp-session.php
    [message] => Notice (8): Undefined offset: 1 in [/home/domain/wp-content/plugins/lifterlms/vendor/ericmann/wp-session-manager/includes/class-wp-session.php, line 77]
)

Drop-in mu-plugin by Me (Query monitor supported).

The Query Monitor way

The spaghetti western way of Blow your mind.

In your wp-config.php

define( 'QM_HIDE_SELF', true );
define( 'QM_HIDE_CORE_HOOKS', true );

Integrate in your plugin

Create a custom alternative panel for log stuff inside Query Monitor
Add a timer method that use the Query Monitor internals
Add a method to print in the internal log panel of Query Monitor

$debug = new WPBP_Debug( __( 'Name of the panel', 'your-textdomain' ) );
$debug->log( __( 'Plugin Loaded', 'your-textdomain' ) );
$debug->qm_log( __( 'Error inside the log panel of Query Monitor', 'your-textdomain' ), 'error' );
$debug->qm_timer( 'profile_that_callback', function () { echo 'I need to be profiled!'; } );

https://github.com/WPBP/Debug

Other useful features

• Silencing Errors from Certain Plugins and Themes
• Clickable Stack Traces and Function Names
• Profiling and Logging
• New Features in Query Monitor 3.3
• Debugging WordPress Template Part Loading
• Supports all the Debug Bar plugins natively

Companions

xDebug

Airplane Mode

User Switching

Wp Crontrol

Debug Bar Rewrite Rules

WooFakePay

JSM's Show Post Meta

WP-CLI Profile command

wp profile stage --all
+--------------------------+----------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+
| hook                     | callback_count | time    | query_time | query_count | cache_ratio | cache_hits | cache_misses | request_time | request_count |
+--------------------------+----------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+      |
| plugins_loaded:before    |                | 0.2855s | 0.0041s    | 19          | 83.95%      | 136        | 26           | 0s           | 0             |
| plugins_loaded           | 34             | 0.2442s | 0.0009s    | 3           | 98.31%      | 116        | 2            | 0s           | 0             |
| setup_theme:before       |                | 0.0005s | 0s         | 0           | 100%        | 4          | 0            | 0s           | 0             |
| setup_theme              | 1              | 0s      | 0s         | 0           |             | 0          | 0            | 0s           | 0             |
+--------------------------+----------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+
| total (31)               | 242            | 1.4571s | 0.0284s    | 78          | 90.8%       | 3323       | 84           | 0s           | 0             |
+--------------------------+----------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+
wp profile hook --all --spotlight --url=https://yourdomain.com
+----------------------------------------------+-----------------------------------------------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+
| callback                                     | location                                            | time    | query_time | query_count | cache_ratio | cache_hits | cache_misses | request_time | request_count |
+----------------------------------------------+-----------------------------------------------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+
| wpseo_init()                                 | wordpress-seo/wp-seo-main.php:252                   | 0.0136s | 0s         | 0           | 100%        | 34         | 0            | 0s           | 0             |
| wp_enqueue_scripts()                         | wp-includes/script-loader.php:1294                  | 0.015s  | 0s         | 0           | 100%        | 348        | 0            | 0s           | 0             |
| wp_trim_excerpt()                            | wp-includes/formatting.php:3289                     | 0.0186s | 0s         | 0           | 100%        | 16         | 0            | 0s           | 0             |
+----------------------------------------------+-----------------------------------------------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+
| total (7)                                    |                                                     | 0.0927s | 0.0006s    | 6           | 100%        | 1054       | 0            | 0s           | 0             |
+----------------------------------------------+-----------------------------------------------------+---------+------------+-------------+-------------+------------+--------------+--------------+---------------+

Debug Toolkit

https://wordpress.org/plugins/debug-toolkit/

WP Query Console

Fluent Query Logger

Query Monitor plugin

WordPress Performance Profiler - Open Source Fork

THE END

- http://mte90.tech/Talk-WP-Debug