Free price: Allow to suggest a different price than the minimum (#3666)

* Free price: Allow to suggest a different price than the minimum

* Full implementation

* Widget tests

* Add min values to titles

src/pretix/base/migrations/0248_item_free_price_suggestion.py

@@ -0,0 +1,22 @@
+# Generated by Django 4.2.4 on 2023-10-25 12:01
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("pretixbase", "0247_checkinlist"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="item",
+            name="free_price_suggestion",
+            field=models.DecimalField(decimal_places=2, max_digits=13, null=True),
+        ),
+        migrations.AddField(
+            model_name="itemvariation",
+            name="free_price_suggestion",
+            field=models.DecimalField(decimal_places=2, max_digits=13, null=True),
+        ),
+    ]

src/pretix/base/models/items.py

@@ -431,6 +431,12 @@ class Item(LoggedModel):
                     "additional donations for your event. This is currently not supported for products that are "
                     "bought as an add-on to other products.")
     )
+    free_price_suggestion = models.DecimalField(
+        verbose_name=_("Suggested price"),
+        help_text=_("This price will be used as the default value of the input field. The user can choose a lower "
+                    "value, but not lower than the price this product would have without the free price option."),
+        max_digits=13, decimal_places=2, null=True, blank=True,
+    )
     tax_rule = models.ForeignKey(
         'TaxRule',
         verbose_name=_('Sales tax'),
@@ -1021,6 +1027,12 @@ class ItemVariation(models.Model):
         help_text=_('If set, this will be displayed next to the current price to show that the current price is a '
                     'discounted one. This is just a cosmetic setting and will not actually impact pricing.')
     )
+    free_price_suggestion = models.DecimalField(
+        verbose_name=_("Suggested price"),
+        help_text=_("This price will be used as the default value of the input field. The user can choose a lower "
+                    "value, but not lower than the price this product would have without the free price option."),
+        max_digits=13, decimal_places=2, null=True, blank=True,
+    )
     require_approval = models.BooleanField(
         verbose_name=_('Require approval'),
         default=False,