Is this a bug with fancyvrb, fancyhdr and fontspec?

Question

Consider the following (hopefully minimal) non-working example and compile with luatex (TeXlive 2016):

\documentclass{article}
\usepackage{fontspec}
\setmainfont{texgyrebonum-regular.otf}
\usepackage{fancyvrb}
\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyfoot[C]{{\addfontfeature{Numbers = SlashedZero}0}}
\begin{document}
\begin{Verbatim}[frame = single]
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\end{Verbatim}
\end{document}

One can see this in the footer of the first page:

There is obviously something wrong. Is this a bug or am I doing something wrong?

Answer 1

It is a fontspec/lua problem in the distribution. The file .../texmf-dist/tex/latex/fontspec/fontspec.lua on line 29/30 has the following code

local function tempswatrue()  tex.sprint([[\FontspecSetCheckBoolTrue ]]) end
local function tempswafalse() tex.sprint([[\FontspecSetCheckBoolFalse]]) end

This code, however uses the catcodes that are current instead of the standard LaTeX catcodes. These two lines should be replaced by

local latex = luatexbase.registernumber("catcodetable@latex")
local function tempswatrue()  tex.sprint(latex,[[\FontspecSetCheckBoolTrue ]]) end
local function tempswafalse() tex.sprint(latex,[[\FontspecSetCheckBoolFalse]]) end

which uses the standard LaTeX code. Of course this should be changed in the official distribution.

See https://github.com/wspr/fontspec/issues/230.