Fixed #19724 -- Output note when showing only core management commands

When listing available management commands, only core commands are
listed if settings have any error. This commit adds a note in this
case so errors are not totally silently skipped.
Thanks Peter Davis for the report.

django/core/management/__init__.py

@@ -249,6 +249,15 @@ class ManagementUtility(object):
                 usage.append(style.NOTICE("[%s]" % app))
                 for name in sorted(commands_dict[app]):
                     usage.append("    %s" % name)
+            # Output an extra note if settings are not properly configured
+            try:
+                from django.conf import settings
+                settings.INSTALLED_APPS
+            except ImproperlyConfigured as e:
+                usage.append(style.NOTICE(
+                    "Note that only Django core commands are listed as settings "
+                    "are not properly configured (error: %s)." % e))
+
         return '\n'.join(usage)
 
     def fetch_command(self, subcommand):

tests/admin_scripts/tests.py

@@ -1055,6 +1055,17 @@ class ManageSettingsWithSettingsErrors(AdminScriptTestCase):
         self.assertNoOutput(out)
         self.assertOutput(err, "KeyError: 'blah'")
 
+    def test_help(self):
+        """
+        Test listing available commands output note when only core commands are
+        available.
+        """
+        self.write_settings('settings.py', sdict={'MEDIA_URL': '"/no_ending_slash"'})
+        args = ['help']
+        out, err = self.run_manage(args)
+        self.assertOutput(out, 'only Django core commands are listed')
+        self.assertNoOutput(err)
+
 
 class ManageValidate(AdminScriptTestCase):
     def tearDown(self):