GNU bug report logs - #79277
31.0.50; Dired errors when trying to overwrite broken symlink

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

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 31.0.50; Dired errors when trying to overwrite broken symlink
Date: Wed, 20 Aug 2025 11:25:28 +0200

Hello,

In dired call S or Y and specify a file name that names a broken
symlink.  This just raises a 'file-already-exists' error.

Of course we want the user to be asked whether the file should be
overwritten, as in all similar cases.

The reason for the different handling is that this test in
`dired-create-files':

   (let* ((overwrite (file-exists-p to)) ...

is wrong because it doesn't handle symlinks as intended.  We
want the test to succeed.  If TO is a symlink it is irrelevant
whether the link target exists.  The fix is obvious.

But since this case is a recurring source of confusion and coding errors
I wonder if we want to introduce a new test function (at least to dired)
that would handle this case directly.  Something named
`dired-file-name-exists-p' maybe?  It would not follow symlinks but just
tell whether a specified file name is already in use.


TIA,

Michael.


In GNU Emacs 31.0.50 (build 10, x86_64-pc-linux-gnu, cairo version
 1.16.0) of 2025-08-19 built on drachen
Repository revision: ced457fd86f90b035e1f40186f4ff957f82e715e
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
 'configure --with-x-toolkit=no --with-native-compilation=no'

Message #8 received at 79277 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 79277 <at> debbugs.gnu.org
Subject: Re: bug#79277: 31.0.50;
 Dired errors when trying to overwrite broken symlink
Date: Sun, 24 Aug 2025 12:58:33 +0300

> Date: Wed, 20 Aug 2025 11:25:28 +0200
> From:  Michael Heerdegen via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> 
> In dired call S or Y and specify a file name that names a broken
> symlink.  This just raises a 'file-already-exists' error.
> 
> Of course we want the user to be asked whether the file should be
> overwritten, as in all similar cases.
> 
> The reason for the different handling is that this test in
> `dired-create-files':
> 
>    (let* ((overwrite (file-exists-p to)) ...
> 
> is wrong because it doesn't handle symlinks as intended.  We
> want the test to succeed.  If TO is a symlink it is irrelevant
> whether the link target exists.  The fix is obvious.

What kind of fix did you have in mind?

> But since this case is a recurring source of confusion and coding errors
> I wonder if we want to introduce a new test function (at least to dired)
> that would handle this case directly.

Can you point to other places where this issue arises?

> Something named `dired-file-name-exists-p' maybe?  It would not
> follow symlinks but just tell whether a specified file name is
> already in use.

If it turns out there are enough users for this, it sounds to me like
a useful utility on its own right, not specific to Dired, suitable to
files.el or maybe files-x.el.  (If we do that, we should update the
ELisp manual as well.)

Thanks.

Message #11 received at 79277 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 79277 <at> debbugs.gnu.org
Subject: Re: bug#79277: 31.0.50; Dired errors when trying to overwrite
 broken symlink
Date: Sat, 13 Sep 2025 08:25:07 +0200

Eli Zaretskii <eliz <at> gnu.org> writes:

> > Date: Wed, 20 Aug 2025 11:25:28 +0200
> > From:  Michael Heerdegen via "Bug reports for GNU Emacs,
> >  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> > 
> > In dired call S or Y and specify a file name that names a broken
> > symlink.  This just raises a 'file-already-exists' error.
> > 
> > Of course we want the user to be asked whether the file should be
> > overwritten, as in all similar cases.
> > 
> > The reason for the different handling is that this test in
> > `dired-create-files':
> > 
> >    (let* ((overwrite (file-exists-p to)) ...
> > 
> > is wrong because it doesn't handle symlinks as intended.  We
> > want the test to succeed.  If TO is a symlink it is irrelevant
> > whether the link target exists.  The fix is obvious.
>
> What kind of fix did you have in mind?

Using (or (file-symlink-p to) (file-exists-p to)) would be correct -
right?

> > But since this case is a recurring source of confusion and coding errors
> > I wonder if we want to introduce a new test function (at least to dired)
> > that would handle this case directly.
>
> Can you point to other places where this issue arises?

It seems it doesn't occur that often.  Very few occurrences are in
Tramp.  2 or so.

> > Something named `dired-file-name-exists-p' maybe?  It would not
> > follow symlinks but just tell whether a specified file name is
> > already in use.
>
> If it turns out there are enough users for this, it sounds to me like
> a useful utility on its own right, not specific to Dired, suitable to
> files.el or maybe files-x.el.  (If we do that, we should update the
> ELisp manual as well.)

If "users" means Emacs own Elisp sources than there are probably not
enough users.  So I would be fine with just fixing the issue.


Thanks,

Michael.

Message #14 received at 79277 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 79277 <at> debbugs.gnu.org
Subject: Re: bug#79277: 31.0.50; Dired errors when trying to overwrite
 broken symlink
Date: Sat, 13 Sep 2025 10:21:29 +0300

> From: Michael Heerdegen <michael_heerdegen <at> web.de>
> Cc: 79277 <at> debbugs.gnu.org
> Date: Sat, 13 Sep 2025 08:25:07 +0200
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> > > Date: Wed, 20 Aug 2025 11:25:28 +0200
> > > From:  Michael Heerdegen via "Bug reports for GNU Emacs,
> > >  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> > > 
> > > In dired call S or Y and specify a file name that names a broken
> > > symlink.  This just raises a 'file-already-exists' error.
> > > 
> > > Of course we want the user to be asked whether the file should be
> > > overwritten, as in all similar cases.
> > > 
> > > The reason for the different handling is that this test in
> > > `dired-create-files':
> > > 
> > >    (let* ((overwrite (file-exists-p to)) ...
> > > 
> > > is wrong because it doesn't handle symlinks as intended.  We
> > > want the test to succeed.  If TO is a symlink it is irrelevant
> > > whether the link target exists.  The fix is obvious.
> >
> > What kind of fix did you have in mind?
> 
> Using (or (file-symlink-p to) (file-exists-p to)) would be correct -
> right?

Feel free to suggest a patch along these lines.

> > > But since this case is a recurring source of confusion and coding errors
> > > I wonder if we want to introduce a new test function (at least to dired)
> > > that would handle this case directly.
> >
> > Can you point to other places where this issue arises?
> 
> It seems it doesn't occur that often.  Very few occurrences are in
> Tramp.  2 or so.
> 
> > > Something named `dired-file-name-exists-p' maybe?  It would not
> > > follow symlinks but just tell whether a specified file name is
> > > already in use.
> >
> > If it turns out there are enough users for this, it sounds to me like
> > a useful utility on its own right, not specific to Dired, suitable to
> > files.el or maybe files-x.el.  (If we do that, we should update the
> > ELisp manual as well.)
> 
> If "users" means Emacs own Elisp sources than there are probably not
> enough users.  So I would be fine with just fixing the issue.

Agreed, thanks.

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