bug#81606: Mojibake with UTF-8 file names

> From: Arash Esbati <[email protected]>
> Cc: [email protected],  [email protected]
> Date: Fri, 14 Aug 2026 01:02:54 +0200
> 
> Eli Zaretskii <[email protected]> writes:
> 
> > If you instrument latexenc-find-file-coding-system with Edebug, does
> > it get called in the above scenario?
> 
> Yes, it gets called inside the files I sent.
> 
> > If so, can you step through the code and tell what happens, and also
> > show the Lisp backtrace, so we know how this function is called and by
> > what code?
> 
> I can't tell how where the caller is, it doesn't throw an error so I
> don't see a backtrace.

Edebug has a command to produce a backtrace; please use that.

> What I can tell is that while the funcion is
> called, the problematic part is:
> 
>   (let ((file (if (re-search-forward
>                    "^%+ *\\(TeX-master\\|tex-main-file\\): *\"\\(.+\\)\""
>                    nil t)
>                   (match-string 2)
> 
> The search is successful and (match-string 2) returns
> 
>   Result: "\303\244.tex"
> 
> I would have expected a plain "ä.tex".

You are aware that \303\244 is the UTF-8 sequence for ä, are you?

The above seems to mean that the search is done on a unibyte buffer or
something.