bug#81648: 32.0.50; Running LaTeX on files with non-ASCII chars in the name

X-Debbugs-CC: Stefan Monnier <[email protected]>

Hi all,

compiling LaTeX files with non-ASCII characters in their file names
fails.   Steps to reproduce:

• Save the file attached in a temp directory
• Start Emacs as 'emacs -Q'
• Open the file and hit 'C-c C-c RET' or 'C-c C-f' to compile
• This is what I see after 'C-c C-c RET':

--8<---------------cut here---------------start------------->8---
$ pdflatex  \\nonstopmode\\input \ä.tex
This is pdfTeX, Version 3.141592653-2.6-1.40.29 (TeX Live 2026) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
LaTeX2e <2026-06-01>
L3 programming layer <2026-08-10>

(/usr/local/texlive/2026/texmf-dist/tex/latex/tools/.tex File ignored)

! LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
<*> \nonstopmode\input ä
                         .tex

LaTeX Font Warning: Font shape `/cmr/m/n' undefined
(Font)              using `/cmr/m/n' instead on input line 0.

! Corrupted NFSS tables.
wrong@fontshape ...message {Corrupted NFSS tables}
                                                  error@fontshape else let f...
<*> \nonstopmode\input ä
                         .tex

LaTeX Font Warning: Font shape `/cmr/m/n' undefined
(Font)              using `OT1/cmr/m/n' instead on input line 0.

Missing character: There is no . in font nullfont!
Missing character: There is no t in font nullfont!
Missing character: There is no e in font nullfont!
Missing character: There is no x in font nullfont!
! Emergency stop.
<*> \nonstopmode\input ä.tex
                             
!  ==> Fatal error occurred, no output PDF file produced!
Transcript written on .log.
--8<---------------cut here---------------end--------------->8---

This is on macOS; same on GNU/Linux as confirmed here[1].

Best, Arash


Footnotes:
[1]  https://lists.gnu.org/archive/html/bug-gnu-emacs/2026-08/msg00960.html