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

[Wilhelm Kirschbaum]

> 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")