Refs #18012 -- Accounted for reverse proxy relations in migrations.

Thanks to Markus for the suggestion and Tim for the review.

django/db/migrations/state.py

@@ -41,13 +41,21 @@ def get_related_models_recursive(model):
     its superclass through the implicit *_ptr OneToOneField on the subclass.
     """
     def _related_models(m):
-        return [
-            f.related_model for f in m._meta.get_fields(include_parents=True, include_hidden=True)
-            if f.is_relation and f.related_model is not None and not isinstance(f.related_model, six.string_types)
-        ] + [
+        related_models = [
             subclass for subclass in m.__subclasses__()
             if issubclass(subclass, models.Model)
         ]
+        related_fields_models = set()
+        for f in m._meta.get_fields(include_parents=True, include_hidden=True):
+            if f.is_relation and f.related_model is not None and not isinstance(f.related_model, six.string_types):
+                related_fields_models.add(f.model)
+                related_models.append(f.related_model)
+        # Reverse accessors of foreign keys to proxy models
+        # are attached to their concrete proxied model.
+        opts = m._meta
+        if opts.proxy and m in related_fields_models:
+            related_models.append(opts.concrete_model)
+        return related_models
 
     seen = set()
     queue = _related_models(model)

tests/migrations/test_state.py

@@ -960,6 +960,16 @@ class RelatedModelsTests(SimpleTestCase):
         self.assertRelated(A, [B])
         self.assertRelated(B, [A])
 
+    def test_fk_through_proxy(self):
+        A = self.create_model("A")
+        B = self.create_model("B", bases=(A,), proxy=True)
+        C = self.create_model("C", bases=(B,), proxy=True)
+        D = self.create_model("D", foreign_keys=[models.ForeignKey('C', models.CASCADE)])
+        self.assertRelated(A, [B, C, D])
+        self.assertRelated(B, [A, C, D])
+        self.assertRelated(C, [A, B, D])
+        self.assertRelated(D, [A, B, C])
+
     def test_nested_fk(self):
         A = self.create_model("A", foreign_keys=[models.ForeignKey('B', models.CASCADE)])
         B = self.create_model("B", foreign_keys=[models.ForeignKey('C', models.CASCADE)])