bug#26996: 25.1; doc-view-revert-buffer doesn't detect file change while using tramp

bug#26996: 25.1; doc-view-revert-buffer doesn't detect file change while using tramp

[Iakov Davydov]

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Hi,
I have problem with reverting buffer when opening pdf via tramp.
This happens in emacs 24 and emacs 25, with different version of tramp.

Steps to reproduce are like this:
1. Open pdf with tramp over ssh -> DocView mode.
2. Update the pdf somehow on the server.
3. Press 'g' to revert buffer (doc-view-revert-buffer) -> "yes".

If the pdf was updated, I expect to see an updated pdf. Instead I see an
old pdf.

On tramp-mailing list I was told that this is a bug in
doc-view-revert-buffer and therefore I have to report is as emacs bug.

Here's a response from Michael Albinus:
<===>
I've checked doc-view-revert-buffer. It works over
doc-view--buffer-file-name. So it doesn't detect a changed pdf, see its
docstring:

--8<---------------cut here---------------start------------->8---
doc-view--buffer-file-name is a variable defined in ‘doc-view.el’.
Its value is "/tmp/docview1000/123.pdf"
Local in buffer 123.pdf</ssh:host:>; global value is nil

Documentation:
Only used internally.
The file name used for conversion. Normally it’s the same as
‘buffer-file-name’, but for remote files, compressed files and
files inside an archive it is a temporary copy of
the (uncompressed, extracted) file residing in
‘doc-view-cache-directory’.
--8<---------------cut here---------------end--------------->8---

Nothing Tramp could do. I recommend to write an Emacs bug.
<===>

Is there a way to correct this behavior?

Thank you,
Iakov





In GNU Emacs 25.1.2 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
of 2016-09-29 built on lcy01-19
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description: Ubuntu 16.04.2 LTS

Configured using:
'configure --build=x86_64-linux-gnu --prefix=/usr
'--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
'--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
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'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
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Important settings:
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value of $LANG: en_US.UTF-8
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Major mode: DocView

Minor modes in effect:
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Memory information:
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-- 
Iakov Davydov
Postdoc, Department of Ecology and Evolution, University of Lausanne
Swiss Institute of Bioinformatics

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bug#26996: 25.1; doc-view-revert-buffer doesn't detect file change while using tramp

[Lars Ingebrigtsen]

Iakov Davydov <dav02.davs@myths.ru> writes:

> I have problem with reverting buffer when opening pdf via tramp. 
> This happens in emacs 24 and emacs 25, with different version of tramp. 
>
> Steps to reproduce are like this: 
> 1. Open pdf with tramp over ssh -> DocView mode. 
> 2. Update the pdf somehow on the server. 
> 3. Press 'g' to revert buffer (doc-view-revert-buffer) -> "yes". 
>
> If the pdf was updated, I expect to see an updated pdf. Instead I see an 
> old pdf. 

I managed to reproduce this in Emacs 27, and it should now be fixed.

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

bug#26996: 25.1; doc-view-revert-buffer doesn't detect file change while using tramp

[Stefan Monnier]

>> I have problem with reverting buffer when opening pdf via tramp. 
>> This happens in emacs 24 and emacs 25, with different version of tramp. 
>>
>> Steps to reproduce are like this: 
>> 1. Open pdf with tramp over ssh -> DocView mode. 
>> 2. Update the pdf somehow on the server. 
>> 3. Press 'g' to revert buffer (doc-view-revert-buffer) -> "yes". 
>>
>> If the pdf was updated, I expect to see an updated pdf. Instead I see an 
>> old pdf. 
>
> I managed to reproduce this in Emacs 27, and it should now be fixed.

Hmm... but now auto-revert loops forever:
updating the file -> triggers auto-revert -> your new code
saves the buffer to the file -> triggers auto-revert -> ...

I think the patch below is needed.

But I wonder why you added:

    (doc-view-make-safe-dir doc-view-cache-directory)

did it just seemed safer or have you found a concrete case that
needed it?


        Stefan


diff --git a/lisp/doc-view.el b/lisp/doc-view.el
index 5f9d4fcc2f..457e4325cf 100644
--- a/lisp/doc-view.el
+++ b/lisp/doc-view.el
@@ -457,9 +457,11 @@ doc-view--revert-buffer
                         (apply orig-fun args)
                         ;; Update the cached version of the pdf file,
                         ;; too.  This is the one that's used when
-                        ;; rendering.
-                        (doc-view-make-safe-dir doc-view-cache-directory)
-                        (write-region nil nil doc-view--buffer-file-name))))
+                        ;; rendering (bug#26996).
+                        (unless (equal buffer-file-name
+                                       doc-view--buffer-file-name)
+                          (doc-view-make-safe-dir doc-view-cache-directory)
+                          (write-region nil nil doc-view--buffer-file-name)))))
     (if (and (eq 'pdf doc-view-doc-type)
              (executable-find "pdfinfo"))
         ;; We don't want to revert if the PDF file is corrupted which

bug#26996: 25.1; doc-view-revert-buffer doesn't detect file change while using tramp

[Lars Ingebrigtsen]

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

> Hmm... but now auto-revert loops forever:
> updating the file -> triggers auto-revert -> your new code
> saves the buffer to the file -> triggers auto-revert -> ...
>
> I think the patch below is needed.

Sounds good; please

> But I wonder why you added:
>
>     (doc-view-make-safe-dir doc-view-cache-directory)
>
> did it just seemed safer or have you found a concrete case that
> needed it?

It been so long I barely remember.  I mean, the patch is more than a
month old.  :-)

Let's see...  Yes, I think I remember the directory having been removed
while I was playing with this stuff, so I had to make sure it existed
before writing to it.

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

bug#26996: 25.1; doc-view-revert-buffer doesn't detect file change while using tramp

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>> Hmm... but now auto-revert loops forever:
>> updating the file -> triggers auto-revert -> your new code
>> saves the buffer to the file -> triggers auto-revert -> ...
>>
>> I think the patch below is needed.
>
> Sounds good; please

apply.

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