GNU bug report logs - #64281
[Feature Request] Recognize “#” syntax when reading local-variables

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Shynur Xie <one.last.kiss <at> outlook.com>
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: [Feature Request] Recognize “#” syntax when reading local-variables
Date: Sun, 25 Jun 2023 11:54:02 +0000

For example, if I want to use UTF-8-UNIX only for files directly under
directory DIR, and those under DIR/SUBDIR/ or its subdirectories, I
can write this way:

    ((nil . ((subdirs . nil)
               . #1=((coding . utf-8-unix))))
     ("SUBDIR" . ((nil . #1#))))

If “#” can be recognized when reading local-variables, we can write
“((coding . utf-8-unix))” only once.  Thanks.

--
shynur

Message #8 received at 64281 <at> debbugs.gnu.org (full text, mbox):

From: Shynur Xie <one.last.kiss <at> outlook.com>
To: "64281 <at> debbugs.gnu.org" <64281 <at> debbugs.gnu.org>
Subject: Re: [Feature Request] Recognize “#” syntax
Date: Sun, 25 Jun 2023 13:53:30 +0000

It seems that this is a intentional behavior:

<https://www.gnu.org/software/emacs/manual/html_node/elisp/File-Local-Variables.html>:

> For additional safety, read-circle is temporarily bound to nil when
> Emacs reads file-local variables.

No further question; can be closed now.

(I wonder if we can treat ~/.emacs.d/.dir-locals.el specially, or tell
 Emacs which files can be treated specially -- enable read-circle.)

Message #11 received at 64281 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Shynur Xie <one.last.kiss <at> outlook.com>,
 Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 64281 <at> debbugs.gnu.org
Subject: Re: bug#64281: [Feature Request] Recognize
 “#” syntax
Date: Sun, 25 Jun 2023 18:08:21 +0300

> From: Shynur Xie <one.last.kiss <at> outlook.com>
> Date: Sun, 25 Jun 2023 13:53:30 +0000
> msip_labels: 
> 
> It seems that this is a intentional behavior:
> 
> <https://www.gnu.org/software/emacs/manual/html_node/elisp/File-Local-Variables.html>:
> 
> > For additional safety, read-circle is temporarily bound to nil when
> > Emacs reads file-local variables.
> 
> No further question; can be closed now.
> 
> (I wonder if we can treat ~/.emacs.d/.dir-locals.el specially, or tell
>  Emacs which files can be treated specially -- enable read-circle.)

Stefan, any comments before we close this?

Message #14 received at 64281 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Shynur Xie <one.last.kiss <at> outlook.com>, 64281 <at> debbugs.gnu.org
Subject: Re: bug#64281: [Feature Request] Recognize “#”
 syntax
Date: Sun, 25 Jun 2023 11:46:13 -0400

>> It seems that this is a intentional behavior:
>>
>> <https://www.gnu.org/software/emacs/manual/html_node/elisp/File-Local-Variables.html>:
>>
>> > For additional safety, read-circle is temporarily bound to nil when
>> > Emacs reads file-local variables.
>>
>> No further question; can be closed now.
>>
>> (I wonder if we can treat ~/.emacs.d/.dir-locals.el specially, or tell
>>  Emacs which files can be treated specially -- enable read-circle.)
>
> Stefan, any comments before we close this?

file/dir-local variables are dangerous enough as it is, I think.  If you
want to do better, you can use an actual ELisp file.


        Stefan

Message #17 received at 64281 <at> debbugs.gnu.org (full text, mbox):

From: Drew Adams <drew.adams <at> oracle.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>, Eli Zaretskii <eliz <at> gnu.org>
Cc: Shynur Xie <one.last.kiss <at> outlook.com>,
 "64281 <at> debbugs.gnu.org" <64281 <at> debbugs.gnu.org>
Subject: RE: [External] : bug#64281: [Feature Request] Recognize “#” syntax
Date: Sun, 25 Jun 2023 16:16:47 +0000

> >> It seems that this is a intentional behavior:
> >> .../File-Local-Variables.html:
> >>
> >> > For additional safety, read-circle is temporarily bound
> >> > to nil when Emacs reads file-local variables.
> >>
> >> No further question; can be closed now.
> >>
> >> (I wonder if we can treat ~/.emacs.d/.dir-locals.el specially, or tell
> >>  Emacs which files can be treated specially -- enable read-circle.)
> >
> > Stefan, any comments before we close this?
> 
> file/dir-local variables are dangerous enough as it is, I think.  If you
> want to do better, you can use an actual ELisp file.

1. That Elisp manual node (`File Local Variables')
doesn't say what danger is avoided by disabling
`read-circle', but it seems to suggest that that
danger is pointed out in node `Read Syntax for
Circular Objects':

  For additional safety, read-circle is temporarily
  bound to nil when Emacs reads file-local variables
  (see Input Functions). This prevents the Lisp reader
  from recognizing circular and shared Lisp structures
  (see Read Syntax for Circular Objects).

Yes, that's what it does, but why?  What's the
"additional safety" about?  What danger's involved?

Node `Read Syntax for Circular Objects' says nothing
about any possible danger (security/safety problem)
circular objects can introduce.  Can we please say
something about the danger in that node?

2. Wouldn't it make sense (be useful) to let users
and code decide whether to allow this for particular
file-local variables?

A question from ignorance - see #1, above.  Is it
helpful to talk about danger and avoiding it,
without giving readers some idea of what's involved?

Message #20 received at 64281 <at> debbugs.gnu.org (full text, mbox):

From: Shynur Xie <one.last.kiss <at> outlook.com>
To: Drew Adams <drew.adams <at> oracle.com>, Stefan Monnier
 <monnier <at> iro.umontreal.ca>, Eli Zaretskii <eliz <at> gnu.org>
Cc: "64281 <at> debbugs.gnu.org" <64281 <at> debbugs.gnu.org>
Subject: Re: [External] : bug#64281: [Feature Request] Recognize “#” syntax
Date: Mon, 26 Jun 2023 10:21:25 +0000

To: Drew

> drew> Node `Read Syntax for Circular Objects' says nothing about any
> drew> possible danger (security/safety problem) circular objects can
> drew> introduce.

I guess that “.dir-locals.el” _isn’t_ read by ELisp syntax, so if you
visit a “.dir-locals.el” file, Emacs will choose “Lisp-Data mode” for
it.  And (info "(elisp)Circular Objects") _is_ about Elisp read
syntax.

> stefan> To: Eli
> stefan> If you want to do better, you can use an actual ELisp file.
                                                ^^^^^^^^^^^^^^^^^^^^

Seems like it is indeed not now, though uses a “.el” postfix.

____________________

To: ALL

> drew> Wouldn't it make sense (be useful) to let users and code
> drew> decide whether to allow this for particular file-local
> drew> variables?

Agree.

There have already been numerous potential dangerous behaviors,
perhaps one more won’t make much of a difference.  I think as long as
users are provided with appropriate warnings, it should suffice.   For
instance, the following code snippet can cause Emacs to crash
instantly, but we still shouldn’t deprive users of their right to
execute it:

    (clear-string (symbol-name t))

Luckily, manual contains a corresponding warning.

--
shynur

Message #25 received at 64281-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: one.last.kiss <at> outlook.com, 64281-done <at> debbugs.gnu.org
Subject: Re: bug#64281: [Feature Request] Recognize “#”
 syntax
Date: Mon, 26 Jun 2023 15:21:36 +0300

> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Cc: Shynur Xie <one.last.kiss <at> outlook.com>,  64281 <at> debbugs.gnu.org
> Date: Sun, 25 Jun 2023 11:46:13 -0400
> 
> >> It seems that this is a intentional behavior:
> >>
> >> <https://www.gnu.org/software/emacs/manual/html_node/elisp/File-Local-Variables.html>:
> >>
> >> > For additional safety, read-circle is temporarily bound to nil when
> >> > Emacs reads file-local variables.
> >>
> >> No further question; can be closed now.
> >>
> >> (I wonder if we can treat ~/.emacs.d/.dir-locals.el specially, or tell
> >>  Emacs which files can be treated specially -- enable read-circle.)
> >
> > Stefan, any comments before we close this?
> 
> file/dir-local variables are dangerous enough as it is, I think.  If you
> want to do better, you can use an actual ELisp file.

Agreed.

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