history form renders incorrect if readonly (and pre-commit-ci)

.pre-commit-config.yaml

@@ -10,7 +10,7 @@ repos:
     rev: 24.8.0
     hooks:
       - id: black
-        language_version: python3.8
+        language_version: python3.9
 
   - repo: https://github.com/pycqa/flake8
     rev: 7.1.1

simple_history/admin.py

@@ -5,7 +5,7 @@
 from django.conf import settings
 from django.contrib import admin
 from django.contrib.admin import helpers
-from django.contrib.admin.utils import unquote
+from django.contrib.admin.utils import flatten_fieldsets, unquote
 from django.contrib.auth import get_permission_codename, get_user_model
 from django.core.exceptions import PermissionDenied
 from django.db.models import QuerySet
@@ -240,11 +240,18 @@ def history_form_view(self, request, object_id, version_id, extra_context=None):
         else:
             form = form_class(instance=obj)
 
+        fieldsets = self.get_fieldsets(request, obj)
+
+        if object_id and not self.has_change_permission(request, obj):
+            readonly_fields = flatten_fieldsets(fieldsets)
+        else:
+            readonly_fields = self.get_readonly_fields(request, obj)
+
         admin_form = helpers.AdminForm(
             form,
-            self.get_fieldsets(request, obj),
+            fieldsets,
             self.prepopulated_fields,
-            self.get_readonly_fields(request, obj),
+            readonly_fields,
             model_admin=self,
         )