--wraps argument only accepts a bare command. You can use
--wraps='pikaur' but not
If the completions you want are only triggered when the
-R flag is given, using
--wraps may not be enough. You would need to add your own completions file. Fortunately, Fish makes this very simple.
Is there a command that lets you query or list the valid options? I'm not familiar with
pikaur, but for example, let's say the valid arguments to your function were given given by a command like
pikaur ls or
pikaur query, or perhaps they're subdirectories of
/etc/pikaur. If there is such a command, you can create a completions file for your function (i.e. if your function is located in
~/.config/fish/functions/remove.fish, then create
~/.config/fish/completions/remove.fish) with the following contents:
complete -c remove --no-files --arguments "(<query command>)"
Note: If you'd like to refer to existing completions, you can see inspect the directories listed by