Fixed #30393 -- Added validation of startapp's directory option.

django/core/management/templates.py

@@ -74,6 +74,8 @@ class TemplateCommand(BaseCommand):
             except OSError as e:
                 raise CommandError(e)
         else:
+            if app_or_project == 'app':
+                self.validate_name(os.path.basename(target), 'directory')
             top_dir = os.path.abspath(path.expanduser(target))
             if not os.path.exists(top_dir):
                 raise CommandError("Destination directory '%s' does not "
@@ -205,7 +207,7 @@ class TemplateCommand(BaseCommand):
         raise CommandError("couldn't handle %s template %s." %
                            (self.app_or_project, template))
 
-    def validate_name(self, name):
+    def validate_name(self, name, name_or_dir='name'):
         if name is None:
             raise CommandError('you must provide {an} {app} name'.format(
                 an=self.a_or_an,
@@ -214,10 +216,11 @@ class TemplateCommand(BaseCommand):
         # Check it's a valid directory name.
         if not name.isidentifier():
             raise CommandError(
-                "'{name}' is not a valid {app} name. Please make sure the "
-                "name is a valid identifier.".format(
+                "'{name}' is not a valid {app} {type}. Please make sure the "
+                "{type} is a valid identifier.".format(
                     name=name,
                     app=self.app_or_project,
+                    type=name_or_dir,
                 )
             )
         # Check it cannot be imported.
@@ -228,11 +231,12 @@ class TemplateCommand(BaseCommand):
         else:
             raise CommandError(
                 "'{name}' conflicts with the name of an existing Python "
-                "module and cannot be used as {an} {app} name. Please try "
-                "another name.".format(
+                "module and cannot be used as {an} {app} {type}. Please try "
+                "another {type}.".format(
                     name=name,
                     an=self.a_or_an,
                     app=self.app_or_project,
+                    type=name_or_dir,
                 )
             )
 

tests/admin_scripts/tests.py

@@ -2132,6 +2132,25 @@ class StartApp(AdminScriptTestCase):
         )
         self.assertFalse(os.path.exists(testproject_dir))
 
+    def test_invalid_target_name(self):
+        for bad_target in ('invalid.dir_name', '7invalid_dir_name', '.invalid_dir_name'):
+            with self.subTest(bad_target):
+                _, err = self.run_django_admin(['startapp', 'app', bad_target])
+                self.assertOutput(
+                    err,
+                    "CommandError: '%s' is not a valid app directory. Please "
+                    "make sure the directory is a valid identifier." % bad_target
+                )
+
+    def test_importable_target_name(self):
+        _, err = self.run_django_admin(['startapp', 'app', 'os'])
+        self.assertOutput(
+            err,
+            "CommandError: 'os' conflicts with the name of an existing Python "
+            "module and cannot be used as an app directory. Please try "
+            "another directory."
+        )
+
     def test_overlaying_app(self):
         self.run_django_admin(['startapp', 'app1'])
         out, err = self.run_django_admin(['startapp', 'app2', 'app1'])