Generating tikz graphics fails with chunk before preamble

[ClaudiusL]

The following MWE runs without problems:

\documentclass{article}

<<knitr-setup, echo=FALSE, cache=FALSE, message=FALSE>>=
library(knitr)

opts_chunk$set(
  echo = FALSE,
  dev = "tikz"
)
@

\begin{document}
<<test>>=
plot(1)
@
\end{document}

As soon as the chunk knitr-setup is moved before the preamble, compilation fails with the following error: Error in getMetricsFromLatex(TeXMetrics).

The following code can be used to reproduce the issue:

<<knitr-setup, echo=FALSE, cache=FALSE, message=FALSE>>=
library(knitr)

opts_chunk$set(
  echo = FALSE,
  dev = "tikz"
)
@

\documentclass{article}

\begin{document}
<<test>>=
plot(1)
@
\end{document}

The problem seems to be that the knitr copies whole chunk knitr-setup to test-1.tikz which is invalid TEX code. Therefore I suppose this is a bug in knitr.

[yihui]

Yes, it may be a bug. Forgive my laziness, but perhaps it is easier for you to move the code chunk after \documentclass{article}? :)

[ClaudiusL]

I would not say that you are lazy – after all you developed knitr. ;) (That's a hidden "thank you").

Of course, moving the code after \documentclass is easy and works. But maybe it would be usefull to mention this somewhere in the documentation. Is the graphics manual the right place for such things? As soon as I have time I could propose an amendment (and as soon as I found out how to make pull requests).
I would also recommend to mention that windows users need to update filehash when using tikz. These two problems drove me crazy before I found out how to easily fix them and it would be a pitty if people didn't use tikz just because of them.

[yihui]

It should not be too difficult to fix the bug. I just don't have the time at the moment and it does not sound like a terrible bug.

Re: filehash, I guess the easiest way is to ask @rdpeng to release a new version of filehash to CRAN, and we update the version requirement in tikzDevice.

[yihui]

Should be fixed now. Thanks!

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