Latex3: Runaway argument with fontspec/LuaLaTeX after installing l3kernel 2018-10-17

Note: the CONTRIBUTING document says to add “bug” label for this, but how do I do that?

I could be mistaken but I don't think there's enough information here to know what could be triggering the bug. Can you provide a minimal example that demonstrates the problem?

@wspr a minimal example for me is

~~~~
documentclass{book}
usepackage{fontspec}
%tracingmacros=1
newfontfamilyarabicfont{Amiri}

begin{document}
abc
end{document}
~~~~

I get a similar error if I load \usepackage{libertine}.

OK, this is LuaTeX-specific so I wonder if it's something in the message text that is dependent on the form of the font-loading command.

The break seems to depend on the length of the module name. With 8 chars it breaks:

~~~~
documentclass{book}
usepackage{fontspec}
ExplSyntaxOn
%suppress fontspec message
msg_set:nnn {fontspec}{defining-font}{}

%new test message
msg_set:nnn {testtest} {defining-font} %works with testtests and testtes
{
g__fontspec_defined_shapes_tl
}

newfontfamilyarabicfont{Amiri}

msg_info:nn {testtest} {defining-font} %breaks
ExplSyntaxOff

begin{document}
abc
end{document}
~~~~

The message from xelatex is a longer than the one from lualatex, but beside this I don't see anything obvious.

@u-fischer I think I have an idea on the source of the issue ... need to work a few things through.

@josephwright and I get the error in xelatex now too with a suitable message.

~~~~
msg_set:nnn {testtest} {defining-font} %works with testtests and testtes
{
(m/n)~with~
<->"Amiri:mode=node;script=latn;language=DFLT;"
}

~~~~

@u-fischer Yeah, fits with my guess as to the issue: I need to trace the wrapping through, but I think I can fix after work.

Cutting down further, one can get to for example

\RequirePackage{expl3}
\ExplSyntaxOn
\iow_wrap:nnnN
  {
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx~
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  }
  { xxxxxxxxxxxxxxxxxxxxxxx }
  { }
  \iow_term:n

_i.e._ it's an engine-neutral issue caused by the exact line lengths involved.

From CTeX issue 384. I originally tested article, book, etc, which worked fine with unicode-math. But switching document class to ctexart, ctexbook produces similar problem as the OP. Initially I assumed it was a bug in CTeX. But now it appears to be a l3kernel bug.

% !TeX program = XeLaTeX
% l3kernel update, 2018-10-17:
% https://ctan.org/ctan-ann/id/[email protected]
\documentclass{ctexart}
\usepackage{unicode-math}
\begin{document}
$e^{i\pi} = -1$
\end{document}

with error messages:

...
Runaway argument?
76543210\q_stop newline - 'bold' (bx/n) with NFSS spec.: <->s*[0.9999\ETC.
! File ended while scanning use of \__iow_wrap_end_chunk:w.
<inserted text> 
                \par 
<*> ./test-ctex-unicode-math.tex

?

@RuixiZhang42 I'm working on it: I'd expect to fix it today.