Fixed #26162 -- Checked query name clashes of hidden relationships.

Although reverse accessor clashes should be skipped query name can't be hidden.

Thanks to Ian Foote and Tim Graham for the review.

django/db/models/fields/related.py

@@ -194,12 +194,6 @@ class RelatedField(Field):
         if not isinstance(self.remote_field.model, ModelBase):
             return []
 
-        # If the field doesn't install backward relation on the target model (so
-        # `is_hidden` returns True), then there are no clashes to check and we
-        # can skip these fields.
-        if self.remote_field.is_hidden():
-            return []
-
         # Consider that we are checking field `Model.foreign` and the models
         # are:
         #
@@ -211,12 +205,15 @@ class RelatedField(Field):
         #         foreign = models.ForeignKey(Target)
         #         m2m = models.ManyToManyField(Target)
 
-        rel_opts = self.remote_field.model._meta
         # rel_opts.object_name == "Target"
+        rel_opts = self.remote_field.model._meta
+        # If the field doesn't install a backward relation on the target model
+        # (so `is_hidden` returns True), then there are no clashes to check
+        # and we can skip these fields.
+        rel_is_hidden = self.remote_field.is_hidden()
         rel_name = self.remote_field.get_accessor_name()  # i. e. "model_set"
         rel_query_name = self.related_query_name()  # i. e. "model"
-        field_name = "%s.%s" % (opts.object_name,
-            self.name)  # i. e. "Model.field"
+        field_name = "%s.%s" % (opts.object_name, self.name)  # i. e. "Model.field"
 
         # Check clashes between accessor or reverse query name of `field`
         # and any other field name -- i.e. accessor for Model.foreign is
@@ -225,7 +222,7 @@ class RelatedField(Field):
         for clash_field in potential_clashes:
             clash_name = "%s.%s" % (rel_opts.object_name,
                 clash_field.name)  # i. e. "Target.model_set"
-            if clash_field.name == rel_name:
+            if not rel_is_hidden and clash_field.name == rel_name:
                 errors.append(
                     checks.Error(
                         "Reverse accessor for '%s' clashes with field name '%s'." % (field_name, clash_name),
@@ -255,7 +252,7 @@ class RelatedField(Field):
             clash_name = "%s.%s" % (  # i. e. "Model.m2m"
                 clash_field.related_model._meta.object_name,
                 clash_field.field.name)
-            if clash_field.get_accessor_name() == rel_name:
+            if not rel_is_hidden and clash_field.get_accessor_name() == rel_name:
                 errors.append(
                     checks.Error(
                         "Reverse accessor for '%s' clashes with reverse accessor for '%s'." % (field_name, clash_name),

docs/releases/1.8.10.txt

@@ -11,3 +11,6 @@ Bugfixes
 
 * Fixed a crash on PostgreSQL that prevented using ``TIME_ZONE=None`` and
   ``USE_TZ=False`` (:ticket:`26177`).
+
+* Added system checks for query name clashes of hidden relationships
+  (:ticket:`26162`).

docs/releases/1.9.3.txt

@@ -14,3 +14,6 @@ Bugfixes
 
 * Fixed a crash on PostgreSQL that prevented using ``TIME_ZONE=None`` and
   ``USE_TZ=False`` (:ticket:`26177`).
+
+* Added system checks for query name clashes of hidden relationships
+  (:ticket:`26162`).

tests/invalid_models_tests/test_relative_fields.py

@@ -1008,45 +1008,69 @@ class ExplicitRelatedNameClashTests(SimpleTestCase):
 @isolate_apps('invalid_models_tests')
 class ExplicitRelatedQueryNameClashTests(SimpleTestCase):
 
-    def test_fk_to_integer(self):
+    def test_fk_to_integer(self, related_name=None):
         self._test_explicit_related_query_name_clash(
             target=models.IntegerField(),
             relative=models.ForeignKey('Target',
                 models.CASCADE,
+                related_name=related_name,
                 related_query_name='clash'))
 
-    def test_fk_to_fk(self):
+    def test_hidden_fk_to_integer(self, related_name=None):
+        self.test_fk_to_integer(related_name='+')
+
+    def test_fk_to_fk(self, related_name=None):
         self._test_explicit_related_query_name_clash(
             target=models.ForeignKey('Another', models.CASCADE),
             relative=models.ForeignKey('Target',
                 models.CASCADE,
+                related_name=related_name,
                 related_query_name='clash'))
 
-    def test_fk_to_m2m(self):
+    def test_hidden_fk_to_fk(self):
+        self.test_fk_to_fk(related_name='+')
+
+    def test_fk_to_m2m(self, related_name=None):
         self._test_explicit_related_query_name_clash(
             target=models.ManyToManyField('Another'),
             relative=models.ForeignKey('Target',
                 models.CASCADE,
+                related_name=related_name,
                 related_query_name='clash'))
 
-    def test_m2m_to_integer(self):
+    def test_hidden_fk_to_m2m(self):
+        self.test_fk_to_m2m(related_name='+')
+
+    def test_m2m_to_integer(self, related_name=None):
         self._test_explicit_related_query_name_clash(
             target=models.IntegerField(),
             relative=models.ManyToManyField('Target',
+                related_name=related_name,
                 related_query_name='clash'))
 
-    def test_m2m_to_fk(self):
+    def test_hidden_m2m_to_integer(self):
+        self.test_m2m_to_integer(related_name='+')
+
+    def test_m2m_to_fk(self, related_name=None):
         self._test_explicit_related_query_name_clash(
             target=models.ForeignKey('Another', models.CASCADE),
             relative=models.ManyToManyField('Target',
+                related_name=related_name,
                 related_query_name='clash'))
 
-    def test_m2m_to_m2m(self):
+    def test_hidden_m2m_to_fk(self):
+        self.test_m2m_to_fk(related_name='+')
+
+    def test_m2m_to_m2m(self, related_name=None):
         self._test_explicit_related_query_name_clash(
             target=models.ManyToManyField('Another'),
             relative=models.ManyToManyField('Target',
+                related_name=related_name,
                 related_query_name='clash'))
 
+    def test_hidden_m2m_to_m2m(self):
+        self.test_m2m_to_m2m(related_name='+')
+
     def _test_explicit_related_query_name_clash(self, target, relative):
         class Another(models.Model):
             pass