Checked unicity of app config names when populating the app registry.

This check will miss duplicates until the check for duplicate labels is
added.

Refs #21679.

django/apps/registry.py

@@ -1,4 +1,4 @@
-from collections import defaultdict, OrderedDict
+from collections import Counter, defaultdict, OrderedDict
 import os
 import sys
 import warnings
@@ -79,8 +79,19 @@ class Apps(object):
                     app_config = entry
                 else:
                     app_config = AppConfig.create(entry)
+                # TODO: check for duplicate app labels here (#21679).
                 self.app_configs[app_config.label] = app_config
 
+            # Check for duplicate app names.
+            counts = Counter(
+                app_config.name for app_config in self.app_configs.values())
+            duplicates = [
+                name for name, count in counts.most_common() if count > 1]
+            if duplicates:
+                raise ImproperlyConfigured(
+                    "Application names aren't unique, "
+                    "duplicates: %s" % ", ".join(duplicates))
+
             # Load models.
             for app_config in self.app_configs.values():
                 all_models = self.all_models[app_config.label]