Using the_widget on a widget that has not been registered results in an undefined index notice.

[SeBsZ]

First of all, this may be by design to notify the developer that they've probably made a mistake.

However, I'd like to suggest a small check that prevents this notice.

In Wordpress 4.8.1 wp-includes\widgets.php on line 1039 (or the second line inside the the_widget() function) there is:

$widget_obj = $wp_widget_factory->widgets[$widget];
if ( ! ( $widget_obj instanceof WP_Widget ) ) {
  return;
}

This means that calling the_widget with a $widget name that has not been registered, instantly results in an undefined index notice.

A simple check would solve this:

if ( ! ( isset($wp_widget_factory->widgets[$widget]) ) ) {
  return;
}

$widget_obj = $wp_widget_factory->widgets[$widget];
if ( ! ( $widget_obj instanceof WP_Widget ) ) {
  return;
}

Apologies if this is not a bug but by design.

[obenland]

Introduced in [11317].

Would you want to write a patch for that?

[SeBsZ]

Sure. This is my first patch here, let's hope I did it correctly.

[mrasharirfan]

Cleaned up the patch according to WP Coding Standards.

[mrasharirfan]

Hi @obenland and @SeBsZ

I have tested the patch. And it is working fine.

Also, I have cleaned up the code according to WP Coding Standards given here: ​https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/

Cheers!

[SeBsZ]

Great, glad to have helped.

BTW, you cleaned up my code (added some spaces), however the line of code below mine does not use spaces inside the square brackets yet. Might need to clean that up as well? I actually copied that part for my patch.

[mrasharirfan]

Here you go. Cleaned up the line below as well.

[westonruter]

To me it seems having a notice/warning is better than failing silently. If you have a theme/plugin that is calling the_widget() then you should know when it fails.

The other option would be to return a WP_Error on failure, and true on success.

[obenland]

Agreed, I was about to suggest adding a _doing_it_wrong() call here to tell developers that widgets need to be registered first

[SeBsZ]

I also agree, hence the reason my very first line in this ticket was:

First of all, this may be by design to notify the developer that they've probably made a mistake.

The reason I came across these notifications is my plugin was correctly registering and using, but another plugin (Yoast SEO) uses this call in certain situations:

<?php
remove_all_actions( 'widgets_init' );

Which led to my widgets not being registered when I tried to use them and that's how I first encountered the undefined index notice. I'm only saying this to explain that sometimes this isn't a mistake by a developer per se, but could be because of another plugin's incorrect behavior.

I do agree a _doing_it_wrong() is better than failing silently, so at least a developer will know something is wrong.

[obenland]

In 41327:

Widgets: Add nudge for registered widgets

Informs developers that widgets need to be registered before they can be
displayed through the_widget(). Previously it would fail with an ambiguous
undefined index notice.

Props SeBsZ, mrasharirfan.
Fixes #41743.

[ramiy]

@obenland,

The text can be more informative. We can explain how to register widgets. It is done in other messages for developers.

Just replace:

_doing_it_wrong( __FUNCTION__, __( 'Widgets need to be registered before they can be displayed.' ), '4.9.0' );

With:

/* translators: %s: register_widget() */
_doing_it_wrong( __FUNCTION__, sprintf( __( 'Widgets need to be registered using %s, before they can be displayed.' ), '<code>register_widget()</code>' ), '4.9.0' );

[SergeyBiryukov]

Reopening to address comment:12.

[ramiy]

Use informative message in _doing_it_wrong() function

[ramiy]

@obenland, @SergeyBiryukov

You can use the attached patch and close this ticket.

[obenland]

In 41340:

Widgets: Improve _doing_it_wrong message.

Adds more context to help sending developers on the path to success.

Props ramiy.
Fixes 41743.