[ticket/12407] Allow changing of post_data, etc. at end of posting.php

The current event core.posting_modify_template_vars is just ran using dispatch
but it doesn't pass any data from posting.php to the listener. Because of that,
it's not possible to know anything from posting.php and therefore limits the
use cases of this event. This will change it to allow similar actions as with
the event core.modify_posting_parameters.

PHPBB3-12407

phpBB/posting.php

@@ -1473,8 +1473,8 @@ $form_enctype = (@ini_get('file_uploads') == '0' || strtolower(@ini_get('file_up
 add_form_key('posting');
 
 
-// Start assigning vars for main posting page ...
+// Build array of variables for main posting page
-$template->assign_vars(array(
+$page_data = array(
 	'L_POST_A'					=> $page_title,
 	'L_ICON'					=> ($mode == 'reply' || $mode == 'quote' || ($mode == 'edit' && $post_id != $post_data['topic_first_post_id'])) ? $user->lang['POST_ICON'] : $user->lang['TOPIC_ICON'],
 	'L_MESSAGE_BODY_EXPLAIN'	=> $user->lang('MESSAGE_BODY_EXPLAIN', (int) $config['max_post_chars']),
@@ -1542,15 +1542,42 @@ $template->assign_vars(array(
 	'S_HIDDEN_FIELDS'		=> $s_hidden_fields,
 	'S_ATTACH_DATA'			=> json_encode($message_parser->attachment_data),
 	'S_IN_POSTING'			=> true,
-));
+);
 
 /**
 * This event allows you to modify template variables for the posting screen
 *
 * @event core.posting_modify_template_vars
+* @var	int	post_id		ID of the post
+* @var	int	topic_id	ID of the topic
+* @var	int	forum_id	ID of the forum
+* @var	bool	submit		Whether or not the form has been submitted
+* @var	bool	preview		Whether or not the post is being previewed
+* @var	bool	save		Whether or not a draft is being saved
+* @var	bool	load		Whether or not a draft is being loaded
+* @var	bool	delete		Whether or not the post is being deleted
+* @var	bool	cancel		Whether or not to cancel the form (returns to
+*				viewtopic or viewforum depending on if the user
+*				is posting a new topic or editing a post)
+* @var	bool	refresh		Whether or not to retain previously submitted data
+* @var	string	mode		What action to take if the form has been sumitted
+*				post|reply|quote|edit|delete|bump|smilies|popup
+* @var	array	error		Any error strings; a non-empty array aborts
+*				form submission.
+*				NOTE: Should be actual language strings, NOT
+*				language keys.
+* @var	array	s_hidden_fields	Hidden fields of posting form
+* @var	array	post_data	Post data of the post to create, edit, etc.
+* @var	array	page_data	Posting page data that should be passed to the
+*				posting page via $template->assign_vars()
 * @since 3.1-A1
+* @changed 3.1.0-b3 Introduced variables passed to listener
 */
-$phpbb_dispatcher->dispatch('core.posting_modify_template_vars');
+$vars = array('post_id', 'topic_id', 'forum_id', 'submit', 'preview', 'save', 'load', 'delete', 'cancel', 'refresh', 'mode', 'error', 's_hidden_fields', 'post_data', 'page_data');
+extract($phpbb_dispatcher->trigger_event('core.posting_modify_template_vars', compact($vars)));
+
+// Start assigning vars for main posting page ...
+$template->assign_vars($page_data);
 
 // Build custom bbcodes array
 display_custom_bbcodes();