Backend UX: Hide advanced tax rule settings

src/pretix/base/models/tax.py

@@ -125,6 +125,10 @@ class TaxRule(LoggedModel):
             s += ' ({})'.format(_('reverse charge enabled'))
         return str(s)
 
+    @property
+    def has_custom_rules(self):
+        return self.custom_rules and self.custom_rules != '[]'
+
     def tax(self, base_price, base_price_is='auto'):
         if self.rate == Decimal('0.00'):
             return TaxedPrice(

src/pretix/control/templates/pretixcontrol/event/tax_edit.html

@@ -20,11 +20,24 @@
         {% bootstrap_form_errors form %}
         {% bootstrap_field form.name layout="control" %}
         {% bootstrap_field form.rate addon_after="%" layout="control" %}
+
+        <div class="panel panel-default">
+            <div class="panel-heading">
+                <h4 class="panel-title">
+                    <a data-toggle="collapse" href="#advanced">
+                        <strong>{% trans "Advanced settings" %}</strong>
+                        <i class="fa fa-angle-down collapse-indicator"></i>
+                    </a>
+                </h4>
+            </div>
+            <div id="advanced" class="panel-collapse collapsed {% if rule.eu_reverse_charge or rule.has_custom_rules or form.errors %}in{% endif %}">
+                <div class="panel-body">
                     <legend>{% trans "Advanced settings" %}</legend>
                     <div class="alert alert-warning">
                         <span class="fa fa-fw fa-legal fa-4x pull-left"></span>
                         {% blocktrans trimmed with docs="https://docs.pretix.eu/en/latest/user/events/taxes.html" %}
-                These settings are intended for advanced users. See the <a href="{{ docs }}">documentation</a>
+                            These settings are intended for advanced users. See the
+                            <a href="{{ docs }}">documentation</a>
                             for more information. Note that we are not responsible for the correct handling
                             of taxes in your ticket shop. If in doubt, please contact a lawyer or tax consultant.
                         {% endblocktrans %}
@@ -100,6 +113,9 @@
                                 <i class="fa fa-plus"></i> {% trans "Add a new rule" %}</button>
                         </p>
                     </div>
+                </div>
+            </div>
+        </div>
 
 
         <div class="form-group submit-group">