Don't create useless transitions between identical states and clean previous ones with migration

A FIXED -> FIXED transition happens, e.g., here:
  https://todo.sr.ht/~sircmpwn/meta.sr.ht/46#event-47525
because I fucked up a link and listed this one twice,
and Drew opened each link first, then closed them,
hence marking the ticket as FIXED twice

With this patch, we just do nothing if there's nothing to do

todosrht/alembic/versions/6742af305c73_clean_no-comment_isostatus-change_events.py

@@ -0,0 +1,31 @@
+"""Clean no-comment isostatus-change events
+
+Revision ID: 6742af305c73
+Revises: c32f13924e46
+Create Date: 2020-08-25 23:50:49.940532
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '6742af305c73'
+down_revision = 'c32f13924e46'
+
+from alembic import op
+from todosrht.types import Event, EventType
+from sqlalchemy.orm import sessionmaker
+
+Session = sessionmaker()
+
+
+def upgrade():
+    bind = op.get_bind()
+    session = Session(bind=bind)
+    (session.query(Event)
+        .filter(Event.comment_id == None)
+        .filter(Event.event_type == EventType.status_change)
+        .filter(Event.old_status == Event.new_status)
+        .filter(Event.old_resolution == Event.new_resolution)).delete()
+
+
+def downgrade():
+    pass

todosrht/blueprints/ticket.py

@@ -193,6 +193,8 @@ def ticket_comment_POST(owner, name, ticket_id):
     participant = get_participant_for_user(current_user)
     event = add_comment(participant, ticket,
         text=text, resolve=resolve, resolution=resolution, reopen=reopen)
+    if not event:
+        return redirect(ticket_url(ticket))
 
     TicketWebhook.deliver(TicketWebhook.Events.event_create,
             event.to_dict(),

todosrht/tickets.py

@@ -197,10 +197,14 @@ def _change_ticket_status(ticket, resolve, resolution, reopen):
     old_resolution = ticket.resolution
 
     if resolve:
+        if old_status == TicketStatus.resolved and old_resolution == resolution:
+            return None
         ticket.status = TicketStatus.resolved
         ticket.resolution = resolution
 
     if reopen:
+        if old_status == TicketStatus.reported:
+            return None
         ticket.status = TicketStatus.reported
 
     return StatusChange(old_status, ticket.status,
@@ -303,6 +307,8 @@ def add_comment(submitter, ticket,
 
     comment = _create_comment(ticket, submitter, text) if text else None
     status_change = _change_ticket_status(ticket, resolve, resolution, reopen)
+    if not comment and not status_change:
+        return None
     event = _create_comment_event(ticket, submitter, comment, status_change)
     notified_participants = _send_comment_notifications(
         submitter, ticket, event, comment, resolution)