allow -x argument for migrate command

flask_migrate/__init__.py

@@ -171,11 +171,14 @@ def revision(directory=None, message=None, autogenerate=False, sql=False,
 @MigrateCommand.option('-d', '--directory', dest='directory', default=None,
                        help=("migration script directory (default is "
                              "'migrations')"))
+@MigrateCommand.option('-x', '--x-arg', dest='x_arg', default=None,
+                       action='append', help=("Additional arguments consumed "
+                                              "by custom env.py scripts"))
 def migrate(directory=None, message=None, sql=False, head='head', splice=False,
-            branch_label=None, version_path=None, rev_id=None):
+            branch_label=None, version_path=None, rev_id=None, x_arg=None):
     """Alias for 'revision --autogenerate'"""
     config = current_app.extensions['migrate'].migrate.get_config(
-        directory, opts=['autogenerate'])
+        directory, opts=['autogenerate'], x_arg=x_arg)
     if alembic_version >= (0, 7, 0):
         command.revision(config, message, autogenerate=True, sql=sql,
                          head=head, splice=splice, branch_label=branch_label,

flask_migrate/cli.py

@@ -80,12 +80,14 @@ def revision(directory, message, autogenerate, sql, head, splice, branch_label,
 @click.option('--rev-id', default=None,
               help=('Specify a hardcoded revision id instead of generating '
                     'one'))
+@click.option('-x', '--x-arg', multiple=True,
+              help='Additional arguments consumed by custom env.py scripts')
 @with_appcontext
 def migrate(directory, message, sql, head, splice, branch_label, version_path,
-            rev_id):
+            rev_id, x_arg):
     """Autogenerate a new revision file (Alias for 'revision --autogenerate')"""
     _migrate(directory, message, sql, head, splice, branch_label, version_path,
-             rev_id)
+             rev_id, x_arg)
 
 
 @db.command()