[lltx] microtype's \textls command broken in current TeX Live

[Robert]

On 10.02.17 22:22, Reinhard Kotucha wrote:
 > Dear Sirs,
 > the minimal example below doesn't work anymore.
 >
 > ---------------------------------------------------------------
 > \documentclass{article}
 > \usepackage{fontspec} \setmainfont{TeX Gyre Pagella}
 > \usepackage{microtype}
 > \usepackage{unicode-math} \setmathfont{texgyrepagella-math.otf}
 >
 > \begin{document}
 > \textls[30]{$x$}
 > \end{document}
 > ---------------------------------------------------------------
 >
 > The problem occurs if the mandatory argument of \textls contains
 > stuff in math mode.  Any idea?

It's actually not the math mode, but the file spec that microtype 
stumbles over. Try with:

\def\MT at ls@fontspec at colon#1:#2:#3:#4\@nil{%
   \ifx\\#3\\#1:#2\else#1:#2:#3\fi}
\def\MT at ls@fontspec at font#1 #2\@nil{%
   "\MT at ls@fontspec at colon#1:::\relax\@nil
     kernfactor=\MT at minus \ifnum\MT at letterspace@=1000 1\else 0.%
          \ifnum\MT at minus\MT at letterspace@<100 0\fi
          \ifnum\MT at minus\MT at letterspace@<10  0\fi
         \number\MT at minus\MT at letterspace@ \fi;"
   \ifx\\#2\\ at \f at size pt\else#2\fi\relax
}

after microtype.

Best,
-- 
  Robert