! is required but not allowed for custom command

Question

I'm using Neovim 0.3.7. I have a default session file that loads up a number of files I'm working on at the moment. To save and load the sessions I have the following custom commands defined:

let sessionlocation = maindir.'/basetest.vim'
exe 'command Sdfs mks' sessionlocation
exe 'command Ldfs source' sessionlocation

This worked fine when I first saved the session. But now I have closed some tabs and opened some new ones and I want the current file layout to be the default session. When I try to run :Sdfs I get the error message:

E189 "..." exists (add ! to overwrite)

where ... is the session file directory. That makes sense. But when I run :Sdfs! I get another error message:

E447: No ! allowed

How can I allow ! in my custom command so that I can overwrite my default session file?

Answer 1

E189 "..." exists (add ! to overwrite) is reported by :h :mksession if session file exists , add ! after mks should fix that:

exe 'command Sdfs mks!' sessionlocation

If you want to pass ! from Sdfs to mks, use this:

exe 'command -bang Sdfs mks<bang>' sessionlocation

:h :command-bang
:h <bang>