[XeTeX] Xetex, Latex3, unicode-math and Math font not found

[Pierre Dupond]

Hi All,
      I want to use the command "\setmathfont" when the font name
is in a LaTeX3 variable.

When the name of the math font (Asana-Math.otf) is in
the LaTeX3 variable, the font is not found.
But when the name of the font is directly passed
as the parameter (instead of expanding a variable first),
the font is correctly found.

What is curious is that the name of the font seems to be correctly
recognised like it is shown in this log extract:
   (/opt/texlive/2019/texmf-local/tex/latex/unicode-math/unicode-math-table.tex)))
   )
   kpathsea: Running mktextfm Asana-Math.otf/OT

With LuaLatex, an error message indicating that the font
is not found is displayed but after a reload of the cache
the font is found.

Any ideas?

Thanks for your help,

Best regards

Here is the code to reproduce the problem:

-----------------------------------------test.sty------------------------------------
\RequirePackage{expl3}
\ProvidesExplPackage {test} {2020-05-12} {1.0}
                     {to test some commands}
\AtBeginDocument{\ExplSyntaxOff}

\RequirePackage{fontspec}
\RequirePackage{unicode-math}
\str_const:Nn \c__test_MathFont_str {Asana-Math.otf}

\setmathfont{\str_use:N \c__test_MathFont_str}
%\setmathfont{Asana-Math.otf}

------------------------------------------test.tex--------------------------------------
\documentclass{article}
\usepackage{test}

\begin{document}
     Some text and some math $e^{iπ}+1=0$.
\end{document}


--
Pierre Dupond <76nemo76 at gmx.ch>