WordPress at a glance
filter is not described

pre_trash_post filter-hook . WP 4.9.0

Filters whether a post trashing should take place.

Usage

add_filter( 'pre_trash_post', 'filter_function_name_7326', 10, 2 );
function filter_function_name_7326( $trash, $post ){
	// filter...

	return $trash;
}
$trash(true/false)
Whether to go forward with trashing.
$post(WP_Post)
Post object.

Where the hook is called

wp_trash_post()
pre_trash_post
WP_Customize_Manager::trash_changeset_post()
pre_trash_post
wp-includes/post.php 2808
$check = apply_filters( 'pre_trash_post', null, $post );
wp-includes/class-wp-customize-manager.php 2948
$check = apply_filters( 'pre_trash_post', null, $post );

Where the hook is used (in WP core)

Does not used.