[2.1.x] Fixed #29469 -- Added a helpful makemigrations error if app_label contains dots.

Backport of 78972af367 from master

django/core/management/commands/makemigrations.py

@@ -73,6 +73,14 @@ class Command(BaseCommand):
                 bad_app_labels.add(app_label)
         if bad_app_labels:
             for app_label in bad_app_labels:
+                if '.' in app_label:
+                    self.stderr.write(
+                        "'%s' is not a valid app label. Did you mean '%s'?" % (
+                            app_label,
+                            app_label.split('.')[-1],
+                        )
+                    )
+                else:
                     self.stderr.write("App '%s' could not be found. Is it in INSTALLED_APPS?" % app_label)
             sys.exit(2)
 

tests/migrations/test_commands.py

@@ -786,6 +786,12 @@ class MakeMigrationsTests(MigrationTestBase):
             call_command("makemigrations", "this_app_does_not_exist", stderr=err)
         self.assertIn("'this_app_does_not_exist' could not be found.", err.getvalue())
 
+    def test_makemigrations_app_name_with_dots(self):
+        err = io.StringIO()
+        with self.assertRaises(SystemExit):
+            call_command('makemigrations', 'invalid.app.label', stderr=err)
+        self.assertIn("'invalid.app.label' is not a valid app label. Did you mean 'label'?", err.getvalue())
+
     def test_makemigrations_empty_no_app_specified(self):
         """
         makemigrations exits if no app is specified with 'empty' mode.