GNU bug report logs - #4616
23.1.50; empty script files

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Package: emacs; Severity: minor; Reported by: Markus Rost <rost@HIDDEN>; dated Fri, 2 Oct 2009 14:10:06 UTC; Maintainer for emacs is bug-gnu-emacs@HIDDEN.

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From: Lars Ingebrigtsen <larsi@HIDDEN>
To: Markus Rost <rost@HIDDEN>
Subject: Re: bug#4616: 23.1.50; empty script files
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 <20091004150617.5367DEFB40@HIDDEN>
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In-Reply-To: <20091004150617.5367DEFB40@HIDDEN> (Markus
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 Content preview: Markus Rost <rost@HIDDEN> writes: >> The Emacs
 Lisp reader always requires at least one sexp in the input. >> This is
 independent
 of the source of the input. > > Oh yes. My patch would violate this. But
 the Emacs Lisp "loader" > doesn [...] 
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Markus Rost <rost@HIDDEN> writes:

>> The Emacs Lisp reader always requires at least one sexp in the input.
>> This is independent of the source of the input.
>
> Oh yes.  My patch would violate this.  But the Emacs Lisp "loader"
> doesn't require any input.
>
> I think, somebody without knowledge of Emacs internals will be
> surprised that
>
> ===File ~/x.el==============================================
> #!/home/rost/build/cvs/emacs/src/emacs --script
> ;; (some-valid-elisp-expression)
> ============================================================
>
> yields an "End of file during parsing" error and returns with positive
> exit status.

It's not quite clear to me what the issue here is.

--script requires at least one readable form in the script, and that
seems OK to me.  Is the problem the exit status?

> And I think, somebody executing pure elisp will be surprised that
>
> (read "#!\n(foo)")
>
> does not yield an "Invalid read syntax" error.
>
> It seems that the basic read function has a *general* feature in order
> to get --script and the "#!"-syntax working.

Heh.  That is quite amusing...

But can we change that at this point?  Presumably Emacs has had this
quirk for generations, so perhaps there's some code out there that
relies on the accidental comment-ness of #!...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Information forwarded to bug-gnu-emacs@HIDDEN:
bug#4616; Package emacs. Full text available.

Message received at 4616@HIDDEN:

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From: Markus Rost <rost@HIDDEN>
To: 4616 <at> debbugs.gnu.org
Subject: bug#4616: 23.1.50; empty script files
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Message-Id: <20091008174333.11AC9EFE6B@HIDDEN>
Date: Thu,  8 Oct 2009 19:43:32 +0200 (CEST)

What is the best way to implement --script?  Let me discuss some
possibilities:

1. The current implementation.  It consists of the lines

      if (c == '!')
	{
	  /* #! appears at the beginning of an executable file.
	     Skip the first line.  */
	  while (c != '\n' && c >= 0)
	    c = READCHAR;
	  goto retry;
	}

   in function read1 in lread.c.  This is appealing by its brevity.
   However it has the disadvantage that the basic read function has a
   *general* feature in order to get --script and the "#!"-syntax
   working.  Further it leads to the bug originally posted:  Execution
   of an empty script file like

   ===File ~/x.el==============================================
   #!/home/rost/build/cvs/emacs/src/emacs --script
   ============================================================

   yields an "End of file during parsing" error and returns with positive
   exit status.

2. One may think of handling --script by first removing a first
   #!-line before passing the file to load.  This seems to be very
   hard to implement because the load routine is complicated
   (switching back and forth between C and Elisp functions).  Besides
   this practical problem, there is the following disadvantage:  In
   some circumstances one may want to load a script file directly, as
   in

   emacs -batch ... -l ~/x.el ...

   Moreover, when editing the file one may want to test it with
   eval-buffer.

3. This leaves the possibility to handle #!-lines when running
   eval-region.  It should skip a #!-line at the beginning of the
   region.  It could skip any #!-line in the region, which is what
   read1 does right now, but I see no necessity for that.  This would
   be implemented by my two previous patches

   <URL:http://lists.gnu.org/archive/html/bug-gnu-emacs/2009-10/msg00082.html>
   <URL:http://lists.gnu.org/archive/html/bug-gnu-emacs/2009-10/msg00124.html>

   Of course making a change in readevalloop/read1 needs a careful
   check, maybe by several people.  However, the patch is a very
   "local" one around the variable unread_char and there are only a
   few places where unread_char appears, so checking the patch is not
   too much work.  Moreover, if something would be wrong with the
   change, very likely emacs would not even compile as many files are
   loaded during the build process.

Acknowledgement sent to Markus Rost <rost@HIDDEN>:
Extra info received and forwarded to list. Copy sent to Emacs Bugs <bug-gnu-emacs@HIDDEN>. Full text available.