Expose change reason to admin form

Fixes jazzband#853

CHANGES.rst

@@ -15,6 +15,7 @@ Unreleased
 - Added temporary requirement on ``asgiref>=3.6`` while the minimum required Django
   version is lower than 4.2 (gh-1261)
 - Small performance optimization of the ``clean-duplicate_history`` command (gh-1015)
+- Allow setting change reason through ``SimpleHistoryAdmin``'s change form (gh-1232)
 
 3.4.0 (2023-08-18)
 ------------------

simple_history/admin.py

@@ -1,4 +1,4 @@
-from django import http
+from django import forms, http
 from django.apps import apps as django_apps
 from django.conf import settings
 from django.contrib import admin
@@ -17,6 +17,8 @@
 
 SIMPLE_HISTORY_EDIT = getattr(settings, "SIMPLE_HISTORY_EDIT", False)
 
+class HistoryChangeReasonForm(forms.ModelForm):
+    history_change_reason = forms.CharField(required=False)
 
 class SimpleHistoryAdmin(admin.ModelAdmin):
     object_history_template = "simple_history/object_history.html"
@@ -224,9 +226,30 @@ def render_history_view(self, request, template, context, **kwargs):
 
     def save_model(self, request, obj, form, change):
         """Set special model attribute to user for reference after save"""
+        obj._change_reason = form.cleaned_data.get("history_change_reason")
         obj._history_user = request.user
         super().save_model(request, obj, form, change)
 
+    form = HistoryChangeReasonForm
+
+    def get_fields(self, request, obj=None):
+        return [
+            field
+            for field in super().get_fields(request, obj)
+            if field != "history_change_reason"
+        ]
+
+    def get_fieldsets(self, request, obj=None):
+        return super().get_fieldsets(request, obj) + ([
+            (
+                "History",
+                {
+                    "classes": ["collapse"],
+                    "fields": ["history_change_reason"],
+                },
+            )
+        ] if 'history_change_reason' in self.form.declared_fields else [])
+
     @property
     def content_type_model_cls(self):
         """Returns the ContentType model class."""

simple_history/tests/tests/test_admin.py

@@ -218,6 +218,50 @@ def test_history_user_on_save_in_admin(self):
             [p.history_user for p in Poll.history.all()], [self.user, self.user]
         )
 
+    def test_history_change_reason_on_save_in_admin(self):
+        self.login()
+
+        # Ensure polls created via admin interface save correct change reason
+        change_reason = "New change reason"
+        initial_data = poll_data = {
+            "question": "new poll?",
+            "pub_date_0": "2012-01-01",
+            "pub_date_1": "10:00:00",
+            "history_change_reason": change_reason,
+        }
+        self.client.post(reverse("admin:tests_poll_add"), data=poll_data)
+        poll = Poll.objects.get()
+        self.assertEqual(poll.history.get().history_change_reason, change_reason)
+
+
+        # Ensure polls modified via admin interface save correct change reason
+        change_reason = "Edited change reason"
+        poll_data = {
+            "question": "new poll?",
+            "pub_date_0": "2011-01-01",
+            "pub_date_1": "10:00:00",
+            "history_change_reason": change_reason,
+        }
+        self.client.post(reverse("admin:tests_poll_change", args=[poll.id]), data=poll_data)
+        poll.refresh_from_db()
+        self.assertEqual(poll.pub_date.year, 2011)
+        self.assertEqual(poll.history.count(), 2)
+        self.assertEqual(poll.history.latest().history_change_reason, change_reason)
+
+        # Let's emulate a revert
+        change_reason = "Revert to history record 0"
+        response = self.client.get(get_history_url(poll, 0))
+        form = response.context.get("adminform").form
+        self.assertEqual(form["history_change_reason"].value(), None)  # Always starts empty
+        self.assertEqual(form["pub_date"].value().year, 2012)
+
+        self.client.post(get_history_url(poll, 0), data=initial_data | {"history_change_reason": change_reason})
+
+        poll.refresh_from_db()
+        self.assertEqual(poll.pub_date.year, 2012)
+        self.assertEqual(poll.history.count(), 3)
+        self.assertEqual(poll.history.latest().history_change_reason, change_reason)
+
     def test_underscore_in_pk(self):
         self.login()
         book = Book(isbn="9780147_513731")