New data model for default tax rule and new options for cancellation fees (#4962)

* New data model for default tax rule

* Remove misleading empty label when field is not optional

* Allow to split cancellation fee

* Fix API and tests

* Update migration

* Update src/tests/api/test_taxrules.py

Co-authored-by: luelista <weller@rami.io>

* Update src/tests/api/test_taxrules.py

Co-authored-by: luelista <weller@rami.io>

* Review note

* Update src/pretix/base/models/tax.py

Co-authored-by: luelista <weller@rami.io>

* Flip API behaviour for default

* Fix failing tests

* Fix failing test

* Split migration

---------

Co-authored-by: luelista <weller@rami.io>

src/pretix/control/forms/event.py

@@ -761,6 +761,7 @@ class CancelSettingsForm(SettingsForm):
         'change_allow_user_addons',
         'change_allow_user_if_checked_in',
         'change_allow_attendee',
+        'tax_rule_cancellation',
     ]
 
     def __init__(self, *args, **kwargs):
@@ -783,14 +784,8 @@ class PaymentSettingsForm(EventSettingsValidationMixin, SettingsForm):
         'payment_term_accept_late',
         'payment_pending_hidden',
         'payment_explanation',
+        'tax_rule_payment',
     ]
-    tax_rate_default = forms.ModelChoiceField(
-        queryset=TaxRule.objects.none(),
-        label=_('Tax rule for payment fees'),
-        required=False,
-        help_text=_("The tax rule that applies for additional fees you configured for single payment methods. This "
-                    "will set the tax rate and reverse charge rules, other settings of the tax rule are ignored.")
-    )
 
     def clean_payment_term_days(self):
         value = self.cleaned_data.get('payment_term_days')
@@ -804,10 +799,6 @@ class PaymentSettingsForm(EventSettingsValidationMixin, SettingsForm):
             raise ValidationError(_("This field is required."))
         return value
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-        self.fields['tax_rate_default'].queryset = self.obj.tax_rules.all()
-
 
 class ProviderForm(SettingsForm):
     """

src/pretix/control/forms/item.py

@@ -406,7 +406,6 @@ class ItemCreateForm(I18nModelForm):
 
         self.fields['tax_rule'].queryset = self.instance.event.tax_rules.all()
         change_decimal_field(self.fields['default_price'], self.instance.event.currency)
-        self.fields['tax_rule'].empty_label = _('No taxation')
         self.fields['copy_from'] = forms.ModelChoiceField(
             label=_("Copy product information"),
             queryset=self.event.items.all(),
@@ -416,6 +415,8 @@ class ItemCreateForm(I18nModelForm):
         )
         if self.event.tax_rules.exists():
             self.fields['tax_rule'].required = True
+        else:
+            self.fields['tax_rule'].empty_label = _('No taxation')
 
         if not self.event.has_subevents:
             choices = [

src/pretix/control/forms/orders.py

@@ -174,8 +174,7 @@ class CancelForm(forms.Form):
         label=_('Keep a cancellation fee of'),
         help_text=_('If you keep a fee, all positions within this order will be canceled and the order will be reduced '
                     'to a cancellation fee. Payment and shipping fees will be canceled as well, so include them '
-                    'in your cancellation fee if you want to keep them. Please always enter a gross value, '
-                    'tax will be calculated automatically.'),
+                    'in your cancellation fee if you want to keep them.'),
     )
     cancel_invoice = forms.BooleanField(
         label=_('Generate cancellation for invoice'),
@@ -200,6 +199,19 @@ class CancelForm(forms.Form):
         self.fields['cancellation_fee'].max_value = self.instance.total
         if not self.instance.invoices.exists():
             del self.fields['cancel_invoice']
+        if self.instance.event.settings.tax_rule_cancellation == 'split':
+            self.fields['cancellation_fee'].help_text = str(self.fields['cancellation_fee'].help_text) + ' ' + _(
+                'Please enter a gross amount. As per your event settings, the taxes will be split the same way as the '
+                'order positions.'
+            )
+        elif self.instance.event.settings.tax_rule_cancellation == 'default':
+            self.fields['cancellation_fee'].help_text = str(self.fields['cancellation_fee'].help_text) + ' ' + _(
+                'Please enter a gross amount. As per your event settings, the default tax rate will be charged.'
+            )
+        elif self.instance.event.settings.tax_rule_cancellation == 'none':
+            self.fields['cancellation_fee'].help_text = str(self.fields['cancellation_fee'].help_text) + ' ' + _(
+                'As per your event settings, no tax will be charged.'
+            )
 
     def clean_cancellation_fee(self):
         val = self.cleaned_data['cancellation_fee'] or Decimal('0.00')