knitr file ended while scanning use of \@xverbatim

Question

I have the following .Rnw file:

\documentclass{article}

\usepackage[table]{xcolor}
\usepackage{multicol}

\begin{document}

\begin{multicols}{2}
\hskip-3.5cm\begin{tabular}{|l|}
\hline
\cellcolor[RGB]{0,0,140}{\large\textbf{\textcolor{white}{Bill To: }}}\\
\hline

\textbf{
"asdf"
}\\
\\[-1em]
\textbf{[email protected]} \\
\hline
\end{tabular}
\hskip6cm\begin{tabular}{|l|l|}
\hline
Date: & 05/31/2018 \\
\hline
Invoice \#: & 1234asdf \\
\hline
\end{tabular}
\end{multicols}


\end{document}

which gives me the expected pdf:

However, when I replace the "asdf" with R code:

\documentclass{article}

\usepackage[table]{xcolor}
\usepackage{multicol}

\begin{document}

\begin{multicols}{2}
\hskip-3.5cm\begin{tabular}{|l|}
\hline
\cellcolor[RGB]{0,0,140}{\large\textbf{\textcolor{white}{Bill To: }}}\\
\hline

\textbf{
<<asdf>>=
cat("asdf")
@
}\\
\\[-1em]
\textbf{[email protected]} \\
\hline
\end{tabular}
\hskip6cm\begin{tabular}{|l|l|}
\hline
Date: & 05/31/2018 \\
\hline
Invoice \#: & 1234asdf \\
\hline
\end{tabular}
\end{multicols}


\end{document}

I get the following error:

File ended while scanning use of \@xverbatim

Looking at the generated .tex file, this is the relevant part:

\textbf{
\begin{knitrout}
\definecolor{shadecolor}{rgb}{0.969, 0.969, 0.969}\color{fgcolor}\begin{kframe}
\begin{alltt}
\hlkwd{cat}\hlstd{(}\hlstr{"asdf"}\hlstd{)}
\end{alltt}
\begin{verbatim}
## asdf
\end{verbatim}
\end{kframe}
\end{knitrout}
}\\

and this is what the .log file says:

Runaway argument?
 #### asdf \end {verbatim} \end {kframe} \end {knitrout} \check@icr \expandafte
r \ETC.
! File ended while scanning use of \@xverbatim.
<inserted text> 
                \par 
<*> test2.tex

I suspect you have forgotten a `}', causing me
to read past where you wanted me to stop.
I'll try to recover; but if the error is serious,
you'd better type `E' or `X' now and fix your file.

! Emergency stop.
<*> test2.tex

What am I doing wrong?

Answer 1

By default, R output is wrapped in a LaTeX verbatim environment, and you can't put one of those inside \textbf. There are a couple of different approaches to fix this.

The simplest is just to use the chunk option results='asis', i.e.

\textbf{
<<asdf,results='asis',echo=FALSE>>=
cat("asdf")
@
}

This will prevent knitr from adding the environment around the output; the LaTeX code will just be

\textbf{
asdf
}

which should be fine.

If you want the default formatting but just want to change the font or style of text, things are harder. You need to tell knitr to use a different environment instead of verbatim, e.g. the Verbatim environment provided by the fancyvrb package. You can do this by changing the output hook. For example, this should work

% in the preamble:
\usepackage{fancyvrb}
<<include=FALSE>>=
oldhook <- knitr::knit_hooks$get("output")
bold <- function(x, options)
  paste0("\\begin{Verbatim}[fontseries=b]\n", x, "\\end{Verbatim}")
@

% in the body:
<<asdf,echo=FALSE>>=
knitr::knit_hooks$set(output = bold)
cat("asdf")
@
% Optionally restore the old hook...
<<include=FALSE>>=
knitr::knit_hooks$set(output = oldhook)
@

However, it doesn't always work, because some options (like fontseries=b) conflict with settings that knitr makes. You can change to italic (using fontshape=it), but not to bold. So stick with the first suggestion.