Assignments and switch role to student: Error with viewing assignment with group submitting

Hi there,

we encountered a bug with the "switch role to" feature together with assignments that can be submitted in group mode.

• Steps to reproduce:

1. Login as teacher in a course and turn editing on
2. Create a new assignment activity, enter a title and just set the following option in the section Group submission settings: Students submit in groups: Yes.
3. Save and return to course
4. Switch role to...: Student
5. Click on the newly added assignment

Result:
It opens a page with broken CSS with the error message: You can't add comments:

This also happens if you create a group and enrole yourself as a teacher in this group and also if setting Require group to make submission is set to yes.

• Cause:
  In the function assignsubmission_comments_comment_validate() in mod/assign/submission/comments/lib.php we ran into this error:

  66 if (!$canview) {

  67 throw new comment_exception('nopermissiontocomment');

  68 }

  The cause is that $canview will be false because the teacher will never be added as a submitting member for an assignment in the called line $canview = $assignment->can_view_submission($submission->userid);
  Here's the corresponding code:
  mod/assign/locallib.php:

  4367 public function can_view_group_submission($groupid) {

  4368 global $USER;

  4369

  4370 $members = $this->get_submission_group_members($groupid, true);

  4371 foreach ($members as $member) {

  4372 if($member->id == 11964) {

  4373 error_log($member->id);

  4374 error_log("Can view submission: " . $this->can_view_submission($member->id));

  4375 }

  4376 // If we can view any members submission, we can view the submission for the group.

  4377 if ($this->can_view_submission($member->id)) {

  4378 return true;

  4379 }

  4380 }

  4381 return false;

  4382 }