Fixed #24776 -- Improved apps.get_app_config() error message on fully-qualified package names.

django/apps/registry.py

@@ -147,7 +147,12 @@ class Apps(object):
         try:
             return self.app_configs[app_label]
         except KeyError:
-            raise LookupError("No installed app with label '%s'." % app_label)
+            message = "No installed app with label '%s'." % app_label
+            for app_config in self.get_app_configs():
+                if app_config.name == app_label:
+                    message += " Did you mean '%s'?" % app_config.label
+                    break
+            raise LookupError(message)
 
     # This method is performance-critical at least for Django's test suite.
     @lru_cache.lru_cache(maxsize=None)

django/core/management/commands/dumpdata.py

@@ -68,8 +68,8 @@ class Command(BaseCommand):
             else:
                 try:
                     app_config = apps.get_app_config(exclude)
-                except LookupError:
-                    raise CommandError('Unknown app in excludes: %s' % exclude)
+                except LookupError as e:
+                    raise CommandError(str(e))
                 excluded_apps.add(app_config)
 
         if len(app_labels) == 0:
@@ -87,8 +87,8 @@ class Command(BaseCommand):
                     app_label, model_label = label.split('.')
                     try:
                         app_config = apps.get_app_config(app_label)
-                    except LookupError:
-                        raise CommandError("Unknown application: %s" % app_label)
+                    except LookupError as e:
+                        raise CommandError(str(e))
                     if app_config.models_module is None or app_config in excluded_apps:
                         continue
                     try:
@@ -111,8 +111,8 @@ class Command(BaseCommand):
                     app_label = label
                     try:
                         app_config = apps.get_app_config(app_label)
-                    except LookupError:
-                        raise CommandError("Unknown application: %s" % app_label)
+                    except LookupError as e:
+                        raise CommandError(str(e))
                     if app_config.models_module is None or app_config in excluded_apps:
                         continue
                     app_list[app_config] = None

tests/apps/tests.py

@@ -121,6 +121,10 @@ class AppsTests(SimpleTestCase):
         with self.assertRaises(LookupError):
             apps.get_app_config('webdesign')
 
+        msg = "No installed app with label 'django.contrib.auth'. Did you mean 'myauth'"
+        with self.assertRaisesMessage(LookupError, msg):
+            apps.get_app_config('django.contrib.auth')
+
     @override_settings(INSTALLED_APPS=SOME_INSTALLED_APPS)
     def test_is_installed(self):
         """

tests/fixtures/tests.py

@@ -216,7 +216,7 @@ class FixtureLoadingTests(DumpDataAssertMixin, TestCase):
 
         # Excluding a bogus app should throw an error
         with six.assertRaisesRegex(self, management.CommandError,
-                "Unknown app in excludes: foo_app"):
+                "No installed app with label 'foo_app'."):
             self._dumpdata_assert(['fixtures', 'sites'], '', exclude_list=['foo_app'])
 
         # Excluding a bogus model should throw an error