[gentoo-user] Problems with LyX and xetex-2021

[Stefano Crocco]

Hello to everyone,
since upgrading my ~arch system to TeXLive-2021 I'm having problems using 
XeLaTeX to compile LyX documents. Has someone else experienced this issue? I'd 
like to file a bug report about it, but before doing so I'd like to be sure 
that there isn't something wrong with my system.

Below you'll find the details of my problem.

Thanks in advance

Stefano

DETAILS

When I use LyX to create a PDF using XeLaTeX from the attached test.lyx file 
(using the default LaTeX (XeTeX) -> PDF (XeTeX) converter), I get an error 
dialog with the following text:

The external program
xelatex 
finished with an error. It is recommended you fix the cause of the external 
program's error (check the logs). 

As far as I can see, the log (attached as log_from_lyx) don't mention any 
error, except for the generic (at least to my eyes) line
"Error 256 (driver return code) generating output;"
near the end.

Trying to obtain a better error message, I exported the LyX file as a XeLaTeX 
file using the File/Export LaTeX (xetex) menu entry and run xelatex on it. Of 
course, it failed, but this time the log (in the log_from_xelatex attachment) 
contains a more meaningful message:
"xdvipdfmx:fatal: Cannot proceed without .vf or "physical" font for PDF 
output..."

Unfortunately, I'm not expert enough in the inner works of (xe)latex to 
understand this message. I tried searching google for it but didn't find 
anything useful. However, looking at the tex file generated by LyX (the 
test.tex attachment), I noticed the line 

\usepackage[T1]{fontenc}

which seemed strange to me, as I thought that the fontenc package shouldn't be 
used with XeLaTeX. Indeed, after commenting this line, xelatex successfully 
created the correct PDF.

This problem has almost certainly been caused by switching texlive and the 
related packages from 2020 to 2021, since on another computer where I masked 
the 2021 version of app-text/texlive-core, app-text/texlive and all packages 
in category dev-texlive, everything works correctly.