bug#64939: 30.0.50; The default auto-mode-interpreter-regexp does not match env with flags

[Eli Zaretskii]

> From: Wilhelm Kirschbaum <wkirschbaum@gmail.com>
> Date: Sat, 29 Jul 2023 23:38:07 +0200
> 
> This is a very naive solution to the above, but I am probably
> missing some knowledge here and will break for anyone setting the
> var to something custom.

Feel free to make this change locally, but I don't see how this can be
general enough for us to install it as the default value.

For starters, 'env' can be invoked with several options, not just with
one.  Also, some 'env' options accept arguments, and how do we know if
the word that follows "env -OPTION" is the command to check against
interpreter-mode-alist or an argument of an option?

IOW, I don't think this is a problem for a regexp-based solution.  If
we want to support such complex shebang lines (btw, does the Posix or
GNU/Linux shell support them?), we should analyze the text after "env"
to find the candidate interpreter.  Not sure whether even that will
provide a robust solution.

Btw, can't you satisfy your needs via file-local variables?