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

[Eli Zaretskii <eliz@gnu.org>]

> From: Rupert Swarbrick <rswarbrick@gmail.com>
> Date: Fri, 12 Jul 2019 16:14:33 +0100
> 
> 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)
>        ("\\.g?z\\(~\\|\\.~[0-9]+~\\)?\\'" no-conversion . 
>        no-conversion)
>        ("\\.tgz\\'" no-conversion . no-conversion)
>        ("\\.tbz\\'" no-conversion . no-conversion)
>        ("\\.bz2\\(~\\|\\.~[0-9]+~\\)?\\'" no-conversion . 
>        no-conversion)
>        ("\\.Z\\(~\\|\\.~[0-9]+~\\)?\\'" no-conversion . 
>        no-conversion)
>        ("\\.elc\\'" emacs-mule . emacs-mule)
>        ("\\.utf\\(-8\\)?\\'" . utf-8)
>        ("\\(\\`\\|/\\)loaddefs.el\\'" raw-text . raw-text-unix)
>        ("\\.tar\\'" no-conversion . no-conversion)
>        ("\\.po[tx]?\\'\\|\\.po\\." . po-find-file-coding-system)
>        ("\\.lisp\\'" . utf-8-unix))))

Was the Info file compressed, i.e. did it have one of extensions that
caused no-conversion to be used?

> 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.
> 
> 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.

Yes, something should be done there, thanks.