Tax rules: add custom rules for country subdivision (e.g. state) (Z#23111850) (#3520)

src/pretix/control/forms/event.py

@@ -38,6 +38,7 @@ from decimal import Decimal
 from urllib.parse import urlencode, urlparse
 from zoneinfo import ZoneInfo
 
+import pycountry
 from django import forms
 from django.conf import settings
 from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
@@ -65,7 +66,8 @@ from pretix.base.models import Event, Organizer, TaxRule, Team
 from pretix.base.models.event import EventFooterLink, EventMetaValue, SubEvent
 from pretix.base.reldate import RelativeDateField, RelativeDateTimeField
 from pretix.base.settings import (
-    PERSON_NAME_SCHEMES, PERSON_NAME_TITLE_GROUPS, validate_event_settings,
+    COUNTRIES_WITH_STATE_IN_ADDRESS, PERSON_NAME_SCHEMES,
+    PERSON_NAME_TITLE_GROUPS, validate_event_settings,
 )
 from pretix.base.validators import multimail_validate
 from pretix.control.forms import (
@@ -1428,9 +1430,20 @@ class CountriesAndEU(CachedCountries):
     cache_subkey = 'with_any_or_eu'
 
 
+class CountriesAndEUAndStates(CountriesAndEU):
+    def __iter__(self):
+        for country_code, country_name in super().__iter__():
+            yield country_code, country_name
+            if country_code in COUNTRIES_WITH_STATE_IN_ADDRESS:
+                types, form = COUNTRIES_WITH_STATE_IN_ADDRESS[country_code]
+                yield from sorted(((state.code, country_name + " - " + state.name)
+                                   for state in pycountry.subdivisions.get(country_code=country_code)
+                                   if state.type in types), key=lambda s: s[1])
+
+
 class TaxRuleLineForm(I18nForm):
     country = LazyTypedChoiceField(
-        choices=CountriesAndEU(),
+        choices=CountriesAndEUAndStates(),
         required=False
     )
     address_type = forms.ChoiceField(