Strange interaction between fontspec, lua and pgfplots

Question

While trying to combine some Lua code with plots written in pgfplots something went completely wrong. I have no idea what causes the problem, as the error message is a bit opaque to me. Here is the example which compiles nicely in luatex without the fontspec package:

\documentclass[12pt]{article}
\usepackage{pgfplots}

\usepackage{fontspec}
\usepackage{luacode}
\usepackage{filecontents}

\begin{filecontents*}{test.txt}
some text
\end{filecontents*}

\begin{luacode*}
  function readtxt()
    file = io.open("test.txt", "r")
    text = file:read("*all")
    return tex.print(text) 
  end
\end{luacode*}

\begin{document}
\directlua{readtxt()} 

\begin{tikzpicture}
  \begin{axis}
    \addplot[] coordinates {(0.0, 0.0) (1,1)};
  \end{axis}
\end{tikzpicture}

\end{document}

With fontspec enabled the first error messages of a total of 58 are:

! LuaTeX error ...)/MiKTeX 2.9/tex/luatex/luaotfload/otfl-font-def.lua:239: att
empt to call field 'suffix' (a nil value).
<to be read again> 
                   relax 
l.26   \end{axis}

The lua interpreter ran into a problem, so the
remainder of this lua chunk will be ignored.

! Font \EU2/lmr/m/n/8=file:lmroman8-regular:script=latn;+trep;+tlig; at 8pt not
 loadable: metric data not found or bad.
<to be read again> 
                   relax 
l.26   \end{axis}

I wasn't able to read the size data for this font,
so I will ignore the font specification.    

Somehow there is some negative interaction between the three components, Lua, pgfplots and fontspec. Individually they all work nicely. Some interaction was reported in this question: Bad interaction between fontspec and some lua code that performs string-related search and replace operations but this seems unrelated.

Any ideas what is going on here?

Answer 1

The problem has nothing to do with pgfplots: You get the same error if you simply try to change the font after your \directlua e.g. by issuing a \tiny.

The source of the problem is the name of your file handle. Probably luaotfload is using this name too. Every thing works if I change the name to e.g. fileA:

\documentclass[12pt]{article}

\usepackage{fontspec}
\usepackage{luacode}
\usepackage{filecontents}

\begin{filecontents*}{test.txt}
some text
\end{filecontents*}

\begin{luacode*}
  function readtxt()
    fileA = io.open("test.txt", "r") --changed
    text = fileA:read("*all")
    return tex.print(text)
  end
\end{luacode*}

\begin{document}
\directlua{readtxt()}

\tiny abc
\end{document}