Supress some protected-access warnings when django-simple-history is …

…installed.

django-simple-hisory is a fairly popular [1] package for keeping track
of changes in django objects. Setting the `_change_reason` property of
an object is the officially documented way to provide a value for the
`history_change_reason` field of historical objects [2].

When django-simple-hisory is installed, protected-access warnings for
setting `_change_reason` is most likely a false positive, and should be
supressed.

Because of inherent limitations of pylint, this may lead to some false
negatives if `_change_reason` is used elsewhere.

[1] https://pypistats.org/packages/django-simple-history
[2] https://django-simple-history.readthedocs.io/en/latest/historical_model.html#change-reason

pylint_django/augmentations/__init__.py

@@ -9,6 +9,7 @@
 from astroid.nodes.scoped_nodes import Module
 from astroid.objects import Super
 from django import VERSION as django_version
+from django.conf import settings
 from django.utils import termcolors
 from django.views.generic.base import ContextMixin, RedirectView, View
 from django.views.generic.dates import DateMixin, DayMixin, MonthMixin, WeekMixin, YearMixin
@@ -752,6 +753,23 @@ def allow_meta_protected_access(node):
     return False
 
 
+def allow_simple_history_protected_access(assign_node):
+    # NOTE: Only consider the first assignment target, mirroring current pylint behavior.
+    # See pylint ClassChecker::visit_assign().
+    # Because the type of assign_target typically cannot be inferred, this will suppress
+    # the warning even in assignments on objects not related to simple_history.
+    assign_target = assign_node.targets[0]
+    assign_target_attrname = getattr(assign_target, "attrname", None)
+
+    if assign_target_attrname is None or assign_target_attrname not in ("_change_reason",):
+        return False
+
+    if "simple_history" not in settings.INSTALLED_APPS:
+        return False
+
+    return True
+
+
 class IsClass:  # pylint: disable=too-few-public-methods
     def __init__(self, class_name):
         self.class_name = class_name
@@ -968,6 +986,14 @@ def apply_augmentations(linter):
         is_model_mpttmeta_subclass,
     )
 
+    # django-simple-history
+    suppress_message(
+        linter,
+        ClassChecker.visit_assign,
+        "protected-access",
+        allow_simple_history_protected_access,
+    )
+
     # factory_boy's DjangoModelFactory
     suppress_message(linter, TypeChecker.visit_attribute, "no-member", is_model_factory)
     suppress_message(