GNU bug report logs - #5312
Why is ‘show-trailing-whitespace’ considered unsafe?

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

From: ludo <at> gnu.org (Ludovic Courtès)
To: bug-emacs <at> gnu.org
Subject: Why is ‘show-trailing-whitespace’
	considered unsafe?
Date: Mon, 04 Jan 2010 14:11:29 +0100

Hello, and best wishes,

Why is ‘show-trailing-whitespace’ considered unsafe?

I find it inconvenient since adding it to a per-file or per-directory
local variable list will (by default) ask users whether they want to
apply the dreaded setting.

Thanks,
Ludo’.

Message #8 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: ludo <at> gnu.org (Ludovic =?UTF-8?Q?Court=C3=A8s)
Cc: ?=@iro.umontreal.ca, 5312 <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Tue, 05 Jan 2010 13:56:38 -0500

> Why is ‘show-trailing-whitespace’ considered unsafe?

Because all vars are unsafe by default (i.e. unless someone tells Emacs
explicitly that this var is safe).

> I find it inconvenient since adding it to a per-file or per-directory
> local variable list will (by default) ask users whether they want to
> apply the dreaded setting.

Arguably this var is more a personal user preference than a property of
a file, so maybe the lack of a `safe-local-variable' property is
actually a feature ;-0


        Stefan

Message #13 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: ludo <at> gnu.org (Ludovic Courtès)
Cc: 5312 <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Wed, 06 Jan 2010 09:24:03 -0500

>>> I find it inconvenient since adding it to a per-file or per-directory
>>> local variable list will (by default) ask users whether they want to
>>> apply the dreaded setting.
>> Arguably this var is more a personal user preference than a property of
>> a file, so maybe the lack of a `safe-local-variable' property is
>> actually a feature ;-0
> Yeah, I see what you mean.  OTOH the same could be said of, say,
> ‘indent-tabs-mode’, which /is/ safe.  I don’t find
> ‘show-trailing-whitespace’ any different.

You might be right.  But I do know of several file formats where TABs
are seriously problematic so you could argue that indent-tabs-mode in
those files is linked to the file's content rather than some mere
user preference.
Of course, maybe you can come up with file formats where trailing
whitespaces are seriously problematic as well.  I just can't think of
any off the top of my head.


        Stefan

Message #16 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 5312 <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Wed, 06 Jan 2010 09:31:42 +0100

Hi,

[There was a bug in the Cc: list.]

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

>> I find it inconvenient since adding it to a per-file or per-directory
>> local variable list will (by default) ask users whether they want to
>> apply the dreaded setting.
>
> Arguably this var is more a personal user preference than a property of
> a file, so maybe the lack of a `safe-local-variable' property is
> actually a feature ;-0

Yeah, I see what you mean.  OTOH the same could be said of, say,
‘indent-tabs-mode’, which /is/ safe.  I don’t find
‘show-trailing-whitespace’ any different.

Thanks,
Ludo’.

Message #19 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 5312 <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Wed, 06 Jan 2010 16:13:14 +0100

Hi,

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> Of course, maybe you can come up with file formats where trailing
> whitespaces are seriously problematic as well.  I just can't think of
> any off the top of my head.

Trailing whitespaces can lead to pointless conflicts when applying
patches.  See, e.g.,
http://www.mail-archive.com/libvir-list <at> redhat.com/msg04896.html .

In this thread, the project’s policy is to get rid of them, and
‘show-trailing-whitespace’ in ‘.dir-locals.el’ or similar would
definitely help.

Thanks,
Ludo’.

Message #22 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: James Cloos <cloos <at> jhcloos.com>
To: 5312 <at> debbugs.gnu.org
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Wed, 06 Jan 2010 14:33:00 -0500

>>>>> "Stefan" == Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

Stefan> Of course, maybe you can come up with file formats where trailing
Stefan> whitespaces are seriously problematic as well.  I just can't think
Stefan> of any off the top of my head.

One seen recently -- on the groff list, IIRC -- involved continuation
lines.  <\><NL> works, <\><SP><NL> does not.

-JimC
-- 
James Cloos <cloos <at> jhcloos.com>         OpenPGP: 1024D/ED7DAEA6

Message #25 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: James Cloos <cloos <at> jhcloos.com>
Cc: 5312 <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Wed, 06 Jan 2010 15:25:27 -0500

Stefan> Of course, maybe you can come up with file formats where trailing
Stefan> whitespaces are seriously problematic as well.  I just can't think
Stefan> of any off the top of my head.

> One seen recently -- on the groff list, IIRC -- involved continuation
> lines.  <\><NL> works, <\><SP><NL> does not.

That also affects C, C++, Elisp, and many other formats.  The fact that we
haven't mentioned them indicates that it's not considered "seriously
problematic" enough.
Actually, font-lock can also be used in those modes to highlight such
suspicious forms: it's more useful than show-trailing-whitespace since
it can more specifically target those trailing whitespaces that are
semantically significant.


        Stefan

Message #28 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Kevin Rodgers <kevin.d.rodgers <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Thu, 07 Jan 2010 07:17:29 -0700

Stefan Monnier wrote:
> Stefan> Of course, maybe you can come up with file formats where trailing
> Stefan> whitespaces are seriously problematic as well.  I just can't think
> Stefan> of any off the top of my head.
> 
>> One seen recently -- on the groff list, IIRC -- involved continuation
>> lines.  <\><NL> works, <\><SP><NL> does not.
> 
> That also affects C, C++, Elisp, and many other formats.  The fact that we
> haven't mentioned them indicates that it's not considered "seriously
> problematic" enough.
> Actually, font-lock can also be used in those modes to highlight such
> suspicious forms: it's more useful than show-trailing-whitespace since
> it can more specifically target those trailing whitespaces that are
> semantically significant.

Regardless, show-trailing-whitespace is safe.

-- 
Kevin Rodgers
Denver, Colorado, USA

Message #31 received at 5312 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: Kevin Rodgers <kevin.d.rodgers <at> gmail.com>
Cc: 5312 <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Thu, 07 Jan 2010 14:40:18 -0500

> Regardless, show-trailing-whitespace is safe.

Agreed,


        Stefan

Message #36 received at 5312-done <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: 5312-done <at> debbugs.gnu.org
Subject: Re: bug#5312: Why is ‘show-trailing-whitespace’ considered unsafe?
Date: Thu, 14 Jan 2010 01:15:33 -0500

  * frame.el (show-trailing-whitespace): Safe if boolean.

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