Allow plugins to disable and pre-fill questions and contact form fields (#1824)

Co-authored-by: Raphael Michel <michel@rami.io>
Co-authored-by: Raphael Michel <mail@raphaelmichel.de>

src/pretix/presale/checkoutflow.py

@@ -32,7 +32,9 @@ from pretix.presale.forms.checkout import (
 )
 from pretix.presale.signals import (
     checkout_all_optional, checkout_confirm_messages, checkout_flow_steps,
-    contact_form_fields, order_meta_from_request, question_form_fields,
+    contact_form_fields, contact_form_fields_overrides,
+    order_meta_from_request, question_form_fields,
+    question_form_fields_overrides,
 )
 from pretix.presale.views import (
     CartMixin, get_cart, get_cart_is_free, get_cart_total,
@@ -423,6 +425,16 @@ class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
                 return True
         return False
 
+    @cached_property
+    def _contact_override_sets(self):
+        return [
+            resp for recv, resp in contact_form_fields_overrides.send(
+                self.request.event,
+                request=self.request,
+                order=None,
+            )
+        ]
+
     @cached_property
     def contact_form(self):
         wd = self.cart_session.get('widget_data', {})
@@ -433,14 +445,36 @@ class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
             )
         }
         initial.update(self.cart_session.get('contact_form_data', {}))
+
+        override_sets = self._contact_override_sets
+        for overrides in override_sets:
+            initial.update({
+                k: v['initial'] for k, v in overrides.items() if 'initial' in v
+            })
+
         f = ContactForm(data=self.request.POST if self.request.method == "POST" else None,
                         event=self.request.event,
                         request=self.request,
                         initial=initial, all_optional=self.all_optional)
         if wd.get('email', '') and wd.get('fix', '') == "true":
             f.fields['email'].disabled = True
+
+        for overrides in override_sets:
+            for fname, val in overrides.items():
+                if 'disabled' in val and fname in f.fields:
+                    f.fields[fname].disabled = val['disabled']
+
         return f
 
+    def get_question_override_sets(self, cart_position):
+        return [
+            resp for recv, resp in question_form_fields_overrides.send(
+                self.request.event,
+                position=cart_position,
+                request=self.request
+            )
+        ]
+
     @cached_property
     def eu_reverse_charge_relevant(self):
         return any([p.item.tax_rule and (p.item.tax_rule.eu_reverse_charge or p.item.tax_rule.custom_rules)
@@ -466,6 +500,13 @@ class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
         else:
             wd_initial = {}
         initial = dict(wd_initial)
+
+        override_sets = self._contact_override_sets
+        for overrides in override_sets:
+            initial.update({
+                k: v['initial'] for k, v in overrides.items() if 'initial' in v
+            })
+
         if not self.address_asked and self.request.event.settings.invoice_name_required:
             f = InvoiceNameForm(data=self.request.POST if self.request.method == "POST" else None,
                                 event=self.request.event,
@@ -483,6 +524,12 @@ class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
         for name, field in f.fields.items():
             if wd_initial.get(name) and wd.get('fix', '') == 'true':
                 field.disabled = True
+
+        for overrides in override_sets:
+            for fname, val in overrides.items():
+                if 'disabled' in val and fname in f.fields:
+                    f.fields[fname].disabled = val['disabled']
+
         return f
 
     @cached_property