MDL-24951 mod_forum: Check user capability to know what message to show.

If the user has the following capabilty: mod/forum:canposttomygroups then show them
the more technical of the strings. Otherwise we use something a bit easier for them to ask their
tutor or teacher about.

mod/forum/lang/en/forum.php

@@ -53,6 +53,7 @@ $string['bynameondate'] = 'by {$a->name} - {$a->date}';
 $string['cannotadd'] = 'Could not add the discussion for this forum';
 $string['cannotadddiscussion'] = 'Adding discussions to this forum requires group membership.';
 $string['cannotadddiscussionall'] = 'You do not have permission to add a new discussion topic for all participants.';
+$string['cannotadddiscussiongroup'] = 'You are not able to create a discussion because you are not a member of any group.';
 $string['cannotaddsubscriber'] = 'Could not add subscriber with id {$a} to this forum!';
 $string['cannotaddteacherforumto'] = 'Could not add converted teacher forum instance to section 0 in the course';
 $string['cannotcreatediscussion'] = 'Could not create new discussion';

mod/forum/lib.php

@@ -5528,7 +5528,11 @@ function forum_print_latest_discussions($course, $forum, $maxdiscussions = -1, $
     } else if ($groupmode and !has_capability('moodle/site:accessallgroups', $context)) {
         // inform users why they can not post new discussion
         if (!$currentgroup) {
-            echo $OUTPUT->notification(get_string('cannotadddiscussionall', 'forum'));
+            if (!has_capability('mod/forum:canposttomygroups', $context)) {
+                echo $OUTPUT->notification(get_string('cannotadddiscussiongroup', 'forum'));
+            } else {
+                echo $OUTPUT->notification(get_string('cannotadddiscussionall', 'forum'));
+            }
         } else if (!groups_is_member($currentgroup)) {
             echo $OUTPUT->notification(get_string('cannotadddiscussion', 'forum'));
         }