WordCamp SF 2011: Debugging in WordPress

Debugging in WordPressWordCamp San Francisco 2011August 13, 2011

Andrew NacinCore Developer of WordPressTech Ninja at Audrey Capitalnacin@wordpress.org@nacin on Twitter

var_dump( $data ); die( ); // fin.

“I love suppressing errormessages!” — no one, ever.

So lets start withWP_DEBUGdeﬁne( WP_DEBUG, true );

What WP_DEBUG does:— Sets the error reporting level toinclude PHP notices— Bypasses some error suppression— Triggers notices for deprecatedusage (more on that later)

You can change its output:// A default of true forces on display_errors.define( WP_DEBUG_DISPLAY, true );// Setting it to false will let PHP (php.ini) decide.define( WP_DEBUG_DISPLAY, false );// So, if your php.ini has display_errors on, youll also need to turn it off:ini_set( display_errors, 0 );

Likely being simplified in 3.3:// A default of true forces on display_errors.define( WP_DEBUG_DISPLAY, true );// False forces off display_errors.define( WP_DEBUG_DISPLAY, false );// Null will let PHP (php.ini) decide.define( WP_DEBUG_DISPLAY, null );

You can specify an error log:// wp-content/debug.logdeﬁne( WP_DEBUG_LOG, true );// New in 3.3! (Likely.)deﬁne( WP_DEBUG_LOG, /tmp/php-errors );// Follow ticket #18391, created last night.

Debug admin CSS & JS withSCRIPT_DEBUGdeﬁne( SCRIPT_DEBUG, true );

SCRIPT_DEBUG preventsminiﬁcation and concatenation ofcore scripts and styles.load-scripts.php?c=1&load=global,wp-admin,ms…versus global.dev.css, wp-admin.dev.css, ms.dev.css

SCRIPT_DEBUG is good for:— Finding bugs in your admin screens— Studying the admin theme— Contributing to core

Debug queries withSAVEQUERIESdeﬁne( SAVEQUERIES, true );

SAVEQUERIES stores query data in$wpdb->queries.(OMG BBQ:This is NOT for production.)

Query: SELECT * FROM wp_usersWHERE user_login = nacinBacktrace: WP->init,wp_get_current_user,get_currentuserinfo,wp_validate_auth_cookie,get_user_byExecution time: 0.4ms

On using these in production:WP_DEBUG— Dont display errors— Dont log to wp-content/error.logSCRIPT_DEBUG— Bad idea.SAVEQUERIES— Barry will hunt you down.

Plugins

Your new best friend:The Debug BarIt’s like Firebug for your WordPress.

Debug Bar ConsoleA Firebug-like console forPHP and MySQL (really)

Whats stopping you frombuilding your own DebugBar extension?Nothing.

Log Deprecated Notices— Logs the usage of deprecated ﬁles,functions, and function arguments.— Pinpoints where the deprecatedfunctionality is being used.— NEVER use in production.

Theme Check— Test your theme for the latestWordPress standards and practices.— Required for the theme directory.

Common functions whendebugging— error_log and var_export / print_r— var_dump and sometimes die— debug_backtrace

Tracking it down

Step 1Disable pluginsSwitch to default theme

What might be left behind?Cron, Rewrites,Roles/Capabilities

Drop-ins— advanced-cache.php— db.php— object-cache.php— mu-plugins

Whats going on?Query vars set properly?Main query SQL look right?Rewrite rule matched?

Funny redirect?Conﬁrm its canonical.remove_action( template_redirect, redirect_canonical );

Testing multisite?I leave this in my conﬁg:// deﬁne( MULTISITE, true );

Dig into the codebase.Your friends are phpxref, grep.Learn the stack.Learn what things call what.

Some common traps

Step 1Is your code even running?(Spell the hook right?)die( wtf ); or error_log( )

White screen on thefrontend, no errors?Appearance > Themes

User interface doesnt work?Check the browsers JS consolefor an error, usually a conﬂict.

Internal server errors?Inﬁnite redirects. Check:— home and siteurl— then .htaccess— then canonical

Widgets got moved around?Do the sidebars have IDs?Otherwise, its the order in whichregister_sidebar() is called.

Lots of pages? Slow site?My next Q: Whats yourpermalink structure?No longer an issue in 3.3!

Weird Bug #1Somewhere deep in style.css:“Template: home.php”Miscalculated as a multisite bug:activated on single site beforestyle.css had the headers.

Weird Bug #2The admin looked weird

Weird Bug #2The admin looked weirdTrigger: Upgrade from 2.5 to 3.1

Weird Bug #2The admin looked weirdTrigger: Upgrade from 2.5 to 3.1Problem: No MySQL ALTERpermissions

Weird Bug #3Some bbPress rewritesfailed after activation

Weird Bug #3Some bbPress rewritesfailed after activationProblem: Custom post typerewrites arent registered onactivation

// Say you have:add_action( generate_rewrite_rules, function( $wp_rewrite ) { … } );// And:register_activation_hook( __FILE__, function() { ﬂush_rewrite_rules( );} );// But! This wont work for CPTs. Try this:add_action( init, my_register_post_types );register_activation_hook( __FILE__, function( ) { my_register_post_types( ); ﬂush_rewrite_rules( );} );

Local Development

/etc/hosts127.0.0.1 andrewnacin.comConﬁgure virtual hostsInstall local WordPress

Replace links with anoutput buﬀer fordevelopment or stagingenvironments

// Run this on development or staging.// A development wp-config.php or local-config.php is fine.ob_start( nacin_dev_urls );function nacin_dev_urls( $buffer ) { $live = http://andrewnacin.com; $dev = http://dev.andrewnacin.com; return str_replace( $live, $dev, $buffer );}

URLs are more portablewhen theyre absolute.Really.*The serialized stuﬀ is lame though.

Start of a conversationXdebug (backtraces, proﬁling)KCacheGrind (visualization)Using an IDEUnit testing

And ﬁnally, remember:Friends dont let friendsdevelop withoutWP_DEBUG.

Thanks! Questions?@nacin

http://www.ilovecolors.com.ar	471
http://planetwordpress.planetozh.com	274
http://feeds.feedburner.com	81
http://twitter.com	16
https://twitter.com	12
http://localhost	10
http://pushkarcreations.com	10
http://lanyrd.com	7
http://us-w1.rockmelt.com	5
http://mundo-powerpoints.blogspot.com	5
http://www.onlydoo.com	4
https://si0.twimg.com	4
http://a0.twimg.com	3
http://wpspeciali.st	3
http://nuevospowerpoints.blogspot.com	2
http://127.0.0.1:8795	2
http://www.zhuaxia.com	2
http://www.twylah.com	2
http://planetewordpress.planetozh.com	1
http://feedproxy.google.com	1

WordCamp SF 2011: Debugging in WordPress

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