Add "old email address" field

src/pretix/base/forms/user.py

@@ -190,6 +190,7 @@ class UserEmailChangeForm(forms.Form):
         'duplicate_identifier': _("There already is an account associated with this email address. "
                                   "Please choose a different one."),
     }
+    old_email = forms.EmailField(label=_('Old email address'), disabled=True)
     new_email = forms.EmailField(label=_('New email address'))
 
     def __init__(self, *args, **kwargs):

src/pretix/control/templates/pretixcontrol/user/change_email.html

@@ -12,6 +12,7 @@
         <p class="text-muted">
             {% trans "This changes the email address used to login to your account, as well as where we send email notifications." %}
         </p>
+        {% bootstrap_field form.old_email %}
         {% bootstrap_field form.new_email %}
         <p>
             {% trans "We will send a confirmation code to your new email address, which you need to enter in the next step to confirm the email address is correct." %}

src/pretix/control/views/user.py

@@ -864,6 +864,11 @@ class UserEmailChangeView(RecentAuthenticationRequiredMixin, FormView):
             "user": self.request.user,
         }
 
+    def get_initial(self):
+        return {
+            "old_email": self.request.user.email
+        }
+
     def form_valid(self, form):
         self.request.user.send_confirmation_code('email_change', form.cleaned_data['new_email'])
         return redirect(reverse('control:user.settings.email.confirm', kwargs={}))