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

[Wilhelm Kirschbaum <wkirschbaum@gmail.com>]

> 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'?
>
>
> 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"
>
>    Node.start(:"next-ls-#{System.system_time()}", :shortnames)
>    ....
>
>
>
> Wilhelm

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.

modified   lisp/files.el
@@ -3243,7 +3243,7 @@ inhibit-local-variables-p
 
 (defvar auto-mode-interpreter-regexp
   (purecopy "#![ \t]?\\([^ \t\n]*\
-/bin/env[ \t]\\)?\\([^ \t\n]+\\)")
+/bin/env[ \t]\\)?\\(-\\{1,2\\}[a-zA-Z1-9=]+[ \t]+\\)?\\([^ 
\t\n]+\\)")
   "Regexp matching interpreters, for file mode determination.
 This regular expression is matched against the first line of a 
 file
 to determine the file's mode in `set-auto-mode'.  If it matches, 
 the file
@@ -3445,7 +3445,7 @@ set-auto-mode
 	 (setq mode (save-excursion
 		      (goto-char (point-min))
 		      (if (looking-at 
 auto-mode-interpreter-regexp)
-			  (match-string 2))))
+			  (match-string 3))))
 	 ;; Map interpreter name to a mode, signaling we're done 
 at the
 	 ;; same time.
 	 (setq done (assoc-default

modified   lisp/progmodes/sh-script.el
@@ -1481,7 +1481,7 @@ sh--guess-shell
   (cond ((save-excursion
            (goto-char (point-min))
            (looking-at auto-mode-interpreter-regexp))
-         (match-string 2))
+         (match-string 3))
         ((not buffer-file-name) sh-shell-file)
         ;; Checks that use `buffer-file-name' follow.
         ((string-match "\\.m?spec\\'" buffer-file-name) "rpm")