Fixed #27436 -- Fixed makemigrations crash when creating migrations on a…

Fixed #27436 -- Fixed makemigrations crash when creating migrations on a separate drive than where Django is installed.

django/core/management/commands/makemigrations.py

@@ -208,7 +208,10 @@ class Command(BaseCommand):
                 if self.verbosity >= 1:
                     # Display a relative path if it's below the current working
                     # directory, or an absolute path otherwise.
-                    migration_string = os.path.relpath(writer.path)
+                    try:
+                        migration_string = os.path.relpath(writer.path)
+                    except ValueError:
+                        migration_string = writer.path
                     if migration_string.startswith('..'):
                         migration_string = writer.path
                     self.stdout.write("  %s:\n" % (self.style.MIGRATE_LABEL(migration_string),))

tests/migrations/test_commands.py

@@ -1152,6 +1152,19 @@ class MakeMigrationsTests(MigrationTestBase):
             call_command("makemigrations", "migrations", stdout=out)
             self.assertIn(os.path.join(migration_dir, '0001_initial.py'), out.getvalue())
 
+    def test_makemigrations_migration_path_output_valueerror(self):
+        """
+        makemigrations prints the absolute path if os.path.relpath() raises a
+        ValueError when it's impossible to obtain a relative path, e.g. on
+        Windows if Django is installed on a different drive than where the
+        migration files are created.
+        """
+        out = six.StringIO()
+        with self.temporary_migration_module() as migration_dir:
+            with mock.patch('os.path.relpath', side_effect=ValueError):
+                call_command('makemigrations', 'migrations', stdout=out)
+        self.assertIn(os.path.join(migration_dir, '0001_initial.py'), out.getvalue())
+
     def test_makemigrations_inconsistent_history(self):
         """
         makemigrations should raise InconsistentMigrationHistory exception if