apply_filters_deprecated() should tell the caller location

[Cybr]

When calling this inside a plugin:

add_filter( 'contextual_help_list', function( $a ) { return $a; } );

We get:

• Deprecated: Hook contextual_help_list is deprecated since version 3.3.0! Use get_current_screen()->add_help_tab(), get_current_screen()->remove_help_tab() instead. in /www/public/wp-includes/functions.php on line 6033

This points directly to the trigger_error() call inside function wp_trigger_error(), which isn't useful in resolving the deprecation issue.

It'd be helpful to assert the location of the deprecated filter call.

[swissspidy]

Makes sense to me. I think the same should be done for similar functions. We got quite a few trac tickets and support requests in the forums because of these messages, as people think the error is coming from core rather than their plugin/theme.

Introduces a 'callers' property to WP_Hook and assigns it to filters utilized by plugins. This enhancement facilitates distinguishing those called by plugins from those invoked by the core.

Trac ticket: https://core.trac.wordpress.org/ticket/60212

Sorry, new contributor here, I messed up with the commits. I will make a new PR

Introduces a 'callers' property to WP_Hook and assigns it to filters utilized by plugins. This enhancement facilitates distinguishing those called by plugins from those invoked by the core.

Trac ticket: https://core.trac.wordpress.org/ticket/60212

The solution proposed adds a lot of processing every time a filter is added.

I recommend registering the location regardless of whether it's from a plugin --- fewer branches, more consistency.
Practically, only this line is necessary for add_filter() (I added the 'line' part, which I recommend incorporating in the deprecation message later):

$caller               = debug_backtrace()[1];
$this->callers[] = [ 
    'file' => $caller['file'], 
    'line' => $caller['line'],
];

Thanks for the feedback @sybrew I thought I want to only add it for plugins because I thought this would reduce the amount of memory that would be needed when we add the caller to every filter

Adding it to core files too would use about 0,5MB memory currently. I think we should test how the extra processing affects the performance with many plugins activated and then weigh which option is better.