Add 'widget_display_callback' filter to the_widget()

[MarcGuay]

When a widget is output through a registered sidebar it passes through the 'widget_display_callback' filter (see 'display_callback' in 'wp-includes/widgets.php', allowing for short-circuiting. This is not the case when 'the_widget' is called, however. This patch simply adds the same feature to that function.

The reason I came across this is because I am using the ​Display Widgets plugin to hide widgets under certain circumstances. It hooks into 'widget_display_callback', runs some logic, and returns false if it should not appear. Using 'the_widget' in a template file, I noticed that the widget still appeared.

It seems logical to me that any time a widget is displayed, it should go through this filter.

[welcher]

Thanks for the ticket and welcome!

This seems like a good idea to me - my only hesitation would be backwards compat. Getting some unit tests on this to confirm that the patch doesn't break anything would go a long way.

The 2nd $widget_obj in the patch doesn't match the doc block as well.

[MarcGuay]

Patch updated for 4.4 and changed $this to $widget_obj in the docblock.

[donmhico]

Refreshed the patch and added unit test.

[SergeyBiryukov]

In 45798:

Widgets: Allow for short-circuiting widget output in the_widget() using the widget_display_callback filter, for consistency with output via a registered sidebar.

Props MarcGuay, donmhico.
Fixes #34226.