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

[Eli Zaretskii <eliz@gnu.org>]

> From: Wilhelm Kirschbaum <wkirschbaum@gmail.com>
> Date: Sat, 29 Jul 2023 22:08:19 +0200
> 
> 
> A file without an extension will load ruby-mode if the first line 
> is:
> 
>     #!/usr/bin/env ruby
> 
> but not when the first line is:
> 
>     #!/usr/bin/env -S ruby -e 'puts 123'
> 
> Is there any reason why the latter should not be matched by the 
> default
> `auto-mode-interpreter-regexp' value in 'files.el'?

That line _is_ matched by auto-mode-interpreter-regexp:

  (string-match-p auto-mode-interpreter-regexp "#!/usr/bin/env -S ruby -e 'puts 123'") => 0

The problem is how to find the name of the interpreter if the text
after "/usr/bin/env" includes more than one word?  Once we start using
command-line switches and their arguments, and take into consideration
that many GNU/Linux programs can freely intersperse options and
non-option arguments on the command line in any order, where does this
end?

> A more useful example I stumbled on today while working on a 
> language
> server after adding:
> 
> `(add-to-list 'interpreter-mode-alist '("elixir" 
> . elixir-ts-mode))'
> 
> 
>     #!/usr/bin/env -S elixir --erl "-kernel standard_io_encoding 
>     latin1"

How about making a script that invokes elixir with those arguments,
and then augment interpreter-mode-alist to name that script instead?