bug#36573: 26.1; bufferpos-to-filepos assumes coding-system-eol-type gives integer

[Lars Ingebrigtsen <larsi@gnus.org>]

Rupert Swarbrick <rswarbrick@gmail.com> writes:

> Thank you for the reply. I've now found the "culprit" (bisecting my
> init.el starting with emacs -Q). The dubious setting was:
>
>  '(file-coding-system-alist
>     (quote
>      (("\\.dz\\'" no-conversion . no-conversion)

(etc)

Even with this setting, I'm not able to reproduce the problem.  It would
be helpful with a recipe, starting from "emacs -Q", to verify that we're
fixing this in the correct way.

> I think it probably still makes sense to add a note to the manual for
> bufferpos-to-filepos and filepos-to-bufferpos to point out that they
> don't work if the line ending convention is unknown.

Well, manual does say that the coding system has to be known (which
implies that the line ending convention should also be known)...

> For bonus points, maybe it makes sense to add something to fail
> earlier (and more understandably!) in the info reading code. I'm not
> sure exactly where that would be, though.

I think those functions probably shouldn't signal an error in this
situation if asked to do an approximate calculation (but just guess at a
one-byte ending), perhaps.  But give a better error message when asked
to do an exact calculation.

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