bug#2058: 23.0.60; bewildering behavior when visit new file throw.pdf

[Alan Mackenzie]

Hi, Tassilo,

On Tue, Jan 27, 2009 at 10:55:40AM +0100, Tassilo Horn wrote:
> "Drew Adams" <drew.adams@oracle.com> writes:

> Hi Drew,

> > emacs -Q

> > I did C-x C-f throw.pdf, with no existing file throw.pdf. The ensuing
> > messages and interaction were bewildering.

> Is that really a use-case?

No, it's an error case.  The user wanted to visit throw.ldf, which is a
text based document format used only in his own company.  But he mistyped
it.  He also knows nothing about png images, and really doesn't want to
have to learn.

> > An extremely long message appeared in the echo area:
> > "No image (png) support available or some conversion utility for pdf
> > files is missing.  Type C-c C-c to switch to an editing mode or C-c
> > C-t to open a buffer showing the doc as text."

It's particularly long and confusing for a non-existent document.  Emacs
shouldn't alarm users.

> > But the new, empty file throw.pdf appeared to be visited with no
> > problem. I tried to type into it. That threw me back to the previous
> > buffer I had been in (Dired), and crazy error msgs were displayed.

> The buffer was in doc-view-mode which has its own keymap, and most
> probably you've hit k or q, which kills/buries the buffer.

What on earth is doc-view-mode?  Hmm.  C-h f doc-view-mode <CR>.  ;-(

> > I tried again, and this time I tried to type `C-c C-t', since the 
> > message indicated that that would open the buffer as text. That too
> > led to errors.

> Yeah, in the background it tries to run pdftotext on the pdf, to extract
> the plain text contents.

> > I don't know exactly what happened, but you will, as soon as you try
> > it. ;-)

> Sure.  So what's your advice how to handle this situation?  Check if the
> file is existent (and non-empty) and if not, print a message and
> fallback to fundamental mode?

Whatever is done, don't force the poor bewildered user to make a
decision.  Perform whatever error handling is appropriate and display a
message, and let her get out without further ado.

"... to switch to an editing mode " is particularly bad.  It should be
less vague, stating the mode (text mode?).

"... to open a buffer showing the doc as text" would be better as "to
show the doc as text".

> Bye,
> Tassilo

-- 
Alan Mackenzie (Nürnberg, Germany).