Mail: Handle all rendering in mail.py, return values for log (#5895)

* Mail: Handle all rendering in mail.py, return values for log

* Apply suggestions from code review

src/pretix/base/services/cancelevent.py

@@ -45,7 +45,6 @@ from pretix.base.services.tax import split_fee_for_taxes
 from pretix.base.templatetags.money import money_filter
 from pretix.celery_app import app
 from pretix.helpers import OF_SELF
-from pretix.helpers.format import format_map
 
 logger = logging.getLogger(__name__)
 
@@ -55,7 +54,7 @@ def _send_wle_mail(wle: WaitingListEntry, subject: LazyI18nString, message: Lazy
         email_context = get_email_context(event_or_subevent=subevent or wle.event, event=wle.event)
         mail(
             wle.email,
-            format_map(subject, email_context),
+            str(subject),
             message,
             email_context,
             wle.event,
@@ -73,9 +72,8 @@ def _send_mail(order: Order, subject: LazyI18nString, message: LazyI18nString, s
 
         email_context = get_email_context(event_or_subevent=subevent or order.event, refund_amount=refund_amount,
                                           order=order, position_or_address=ia, event=order.event)
-        real_subject = format_map(subject, email_context)
         order.send_mail(
-            real_subject, message, email_context,
+            subject, message, email_context,
             'pretix.event.order.email.event_canceled',
             user,
         )
@@ -85,14 +83,13 @@ def _send_mail(order: Order, subject: LazyI18nString, message: LazyI18nString, s
                 continue
 
             if p.addon_to_id is None and p.attendee_email and p.attendee_email != order.email:
-                real_subject = format_map(subject, email_context)
                 email_context = get_email_context(event_or_subevent=p.subevent or order.event,
                                                   event=order.event,
                                                   refund_amount=refund_amount,
                                                   position_or_address=p,
                                                   order=order, position=p)
                 order.send_mail(
-                    real_subject, message, email_context,
+                    subject, message, email_context,
                     'pretix.event.order.email.event_canceled',
                     position=p,
                     user=user

src/pretix/base/services/mail.py

@@ -149,13 +149,13 @@ def prefix_subject(settings_holder, subject, highlight=False):
     return subject
 
 
-def mail(email: Union[str, Sequence[str]], subject: str, template: Union[str, LazyI18nString],
+def mail(email: Union[str, Sequence[str]], subject: Union[str, FormattedString], template: Union[str, LazyI18nString],
          context: Dict[str, Any] = None, event: Event = None, locale: str = None, order: Order = None,
          position: OrderPosition = None, *, headers: dict = None, sender: str = None, organizer: Organizer = None,
          customer: Customer = None, invoices: Sequence = None, attach_tickets=False, auto_email=True, user=None,
          attach_ical=False, attach_cached_files: Sequence = None, attach_other_files: list=None,
          plain_text_only=False, no_order_links=False, cc: Sequence[str]=None, bcc: Sequence[str]=None,
-         sensitive: bool=False):
+         sensitive: bool=False) -> Optional[OutgoingMail]:
     """
     Sends out an email to a user. The mail will be sent synchronously or asynchronously depending on the installation.
 
@@ -335,14 +335,26 @@ def mail(email: Union[str, Sequence[str]], subject: str, template: Union[str, La
             should_attach_other_files=attach_other_files or [],
             sensitive=sensitive,
         )
+        m._prefetched_objects_cache = {}
         if invoices and not position:
             m.should_attach_invoices.add(*invoices)
+            # Hack: For logging, we'll later make a `should_attach_invoices.all()` call. We can prevent a useless
+            # DB query by filling the cache
+            m._prefetched_objects_cache[m.should_attach_invoices.prefetch_cache_name] = invoices
+        else:
+            m._prefetched_objects_cache[m.should_attach_invoices.prefetch_cache_name] = Invoice.objects.none()
         if attach_cached_files:
+            cf_list = []
             for cf in attach_cached_files:
                 if not isinstance(cf, CachedFile):
-                    m.should_attach_cached_files.add(CachedFile.objects.get(pk=cf))
-                else:
-                    m.should_attach_cached_files.add(cf)
+                    cf = CachedFile.objects.get(pk=cf)
+                m.should_attach_cached_files.add(cf)
+                cf_list.append(cf)
+            # Hack: For logging, we'll later make a `should_attach_cached_files.all()` call. We can prevent a useless
+            # DB query by filling the cache
+            m._prefetched_objects_cache[m.should_attach_cached_files.prefetch_cache_name] = cf_list
+        else:
+            m._prefetched_objects_cache[m.should_attach_cached_files.prefetch_cache_name] = CachedFile.objects.none()
 
         send_task = mail_send_task.si(
             outgoing_mail=m.id
@@ -364,6 +376,8 @@ def mail(email: Union[str, Sequence[str]], subject: str, template: Union[str, La
                 lambda: chain(*task_chain).apply_async()
             )
 
+    return m
+
 
 class CustomEmail(EmailMultiAlternatives):
     def _create_mime_attachment(self, content, mimetype):

src/pretix/base/services/vouchers.py

@@ -39,7 +39,7 @@ def vouchers_send(event: Event, vouchers: list, subject: str, message: str, reci
         with language(event.settings.locale):
             email_context = get_email_context(event=event, name=r.get('name') or '',
                                               voucher_list=[v.code for v in voucher_list])
-            mail(
+            outgoing_mail = mail(
                 r['email'],
                 subject,
                 LazyI18nString(message),
@@ -60,8 +60,8 @@ def vouchers_send(event: Event, vouchers: list, subject: str, message: str, reci
                     data={
                         'recipient': r['email'],
                         'name': r.get('name'),
-                        'subject': subject,
-                        'message': message,
+                        'subject': outgoing_mail.subject,
+                        'message': outgoing_mail.body_plain,
                     },
                     save=False
                 ))