bug#65308: (find-file) botches buffer-file-name in -batch mode

bug#65308: (find-file) botches buffer-file-name in -batch mode

[Konstantin Kharlamov]

This was found while trying to use Emacs in `-batch` mode to regexp-
replace many files in a project. Turns out calling `(save-buffer)` will
make it say that directory does not exist, and the reason for that is
that `buffer-file-name` gets mangled filename.

# Steps to reproduce

	$ mkdir dir && touch dir/1 dir/2
	$ emacs -batch --eval '(progn (dolist (file command-line-args-left) (find-file file) (print buffer-file-name))))' dir/1 dir/2                                    

	"/tmp/dir/1"

	"/tmp/dir/dir/2"

## Expected

Second print would say `/tmp/dir/2`

## Actual

Second print refers to non-existing `/tmp/dir/dir/2`.

# Versions tested

Reproducible with stable 29.1 and somewhat old master as of commit
04710bd01b2

bug#65308: (find-file) botches buffer-file-name in -batch mode

[Eli Zaretskii]

tags 65308 notabug
thanks

> From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> Date: Tue, 15 Aug 2023 14:25:16 +0300
> 
> 	$ mkdir dir && touch dir/1 dir/2
> 	$ emacs -batch --eval '(progn (dolist (file command-line-args-left) (find-file file) (print buffer-file-name))))' dir/1 dir/2                                    
> 
> 	"/tmp/dir/1"
> 
> 	"/tmp/dir/dir/2"
> 
> ## Expected
> 
> Second print would say `/tmp/dir/2`
> 
> ## Actual
> 
> Second print refers to non-existing `/tmp/dir/dir/2`.

IMO, this is the expected behavior: relative file names are
interpreted relative to the current buffer's default-directory.  After
the first find-file, the current buffer visits the file "/tmp/dir/1",
whose default-directory is "/tmp/dir/".

There's no bug here.  To get what you want, run the command-line
arguments through expand-file-name _before_ calling find-file.

bug#65308: (find-file) botches buffer-file-name in -batch mode

[Konstantin Kharlamov]

On Tue, 2023-08-15 at 15:03 +0300, Eli Zaretskii wrote:
> tags 65308 notabug
> thanks
> 
> > From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> > Date: Tue, 15 Aug 2023 14:25:16 +0300
> > 
> >         $ mkdir dir && touch dir/1 dir/2
> >         $ emacs -batch --eval '(progn (dolist (file command-line-
> > args-left) (find-file file) (print buffer-file-name))))' dir/1
> > dir/2                                    
> > 
> >         "/tmp/dir/1"
> > 
> >         "/tmp/dir/dir/2"
> > 
> > ## Expected
> > 
> > Second print would say `/tmp/dir/2`
> > 
> > ## Actual
> > 
> > Second print refers to non-existing `/tmp/dir/dir/2`.
> 
> IMO, this is the expected behavior: relative file names are
> interpreted relative to the current buffer's default-directory. 
> After
> the first find-file, the current buffer visits the file "/tmp/dir/1",
> whose default-directory is "/tmp/dir/".
> 
> There's no bug here.  To get what you want, run the command-line
> arguments through expand-file-name _before_ calling find-file.

Oh, okay, thank you, I see. I settled with calling a `(kill-buffer)`
after `(save-buffer)`, which I guess works because each time the buffer
is killed we get back to the *scratch* buffer that has the original
"current directory".

bug#65308: (find-file) botches buffer-file-name in -batch mode

[Eli Zaretskii]

> From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> Cc: 65308@debbugs.gnu.org
> Date: Tue, 15 Aug 2023 15:17:00 +0300
> 
> On Tue, 2023-08-15 at 15:03 +0300, Eli Zaretskii wrote:
> > There's no bug here.  To get what you want, run the command-line
> > arguments through expand-file-name _before_ calling find-file.
> 
> Oh, okay, thank you, I see. I settled with calling a `(kill-buffer)`
> after `(save-buffer)`, which I guess works because each time the buffer
> is killed we get back to the *scratch* buffer that has the original
> "current directory".

Yes, that will work, as will using save-current-buffer etc.  But
please note that relying on the default-directory of some random
buffer when using relative file names is always fraught with surprises
in Emacs, which is why I suggested to use expand-file-name instead.

Closing.