Re: executable-set-magic update

[Andrew L. Moore]

>> It would also be nice if `executable-set-magic’ were supported beyond
>> `sh-set-shell’ (in lisp/progmodes/sh-script.el), so I implemented
>> a minor mode that adds the following hook to find-file:
>>
>> (defun script-set-magic ()
>>   "Look up interpreter associated with current major mode in
>> `script-set-magic-alist' and call `executable-set-magic'."
>>   (let ((interpreter (alist-get major-mode script-set-magic-alist)))
>>     (if interpreter (executable-set-magic interpreter)))
>>   )

> Stefan Monnier wrote:
> Doesn't this add a #! to every file using modes like
> js/ruby/awk/perl/python/...?
> 
> In multi-file programs, only the main file needs a "#!", so I don't
> understand why adding #! to all files would make sense.

Stefan,
Sorry I missed your comment.  Yeah, script libraries don’t use magic numbers, so
I updated the minor mode with a variable that allows skipping files in “project”
directories.  And since the minor mode leverages executable-set-magic, it's been
renamed `executable-set-magic-mode’:

 https://github.com/slewsys/emacs-extensions/blob/master/executable-set-magic.el

The current implementation searches for a “project root” in the file path
by brute force. Hopefully that can be updated with something more elegant.

In the mean time, function `executable-set-magic' only seems to be leveraged
by lisp/progmodes/sh-script.el for shell scripts.  So an alternative to
extending it might be removing it, e.g., to an external library.
-AM