title: RMarkdown PDF "LaTeX3 error: Erroneous variable"
body: <p>I've been creating PDF reports via RMarkdown for a couple months now, but after installing MikTex, R and the rmarkdown and tidyverse packages on a new machine today, I received the following error message when attemping to knit a PDF:</p>
  
  <pre><code>"C:/PROGRA~2/Pandoc/pandoc" +RTS -K512m -RTS Test.utf8.md --to latex --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output test.pdf --template "C:\Users\drewm\Documents\R\win-library\3.4\rmarkdown\rmd\latex\default-1.17.0.2.tex" --highlight-style tango --latex-engine xelatex --variable graphics=yes --variable "geometry:margin=1in" 
  ! Undefined control sequence.
  &lt;argument&gt; \LaTeX3 error: 
                             Erroneous variable \c__fontspec_shape_n_n_tl used!
   l.3806 \emfontdeclare{ \emshape, \eminnershape }
  
  pandoc.exe: Error producing PDF
  Error: pandoc document conversion failed with error 43
  In addition: Warning message:
  running command '"C:/PROGRA~2/Pandoc/pandoc" +RTS -K512m -RTS Test.utf8.md --to latex --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output test.pdf --template "C:\Users\drewm\Documents\R\win-library\3.4\rmarkdown\rmd\latex\default-1.17.0.2.tex" --highlight-style tango --latex-engine xelatex --variable graphics=yes --variable "geometry:margin=1in"' had status 43
  </code></pre>
  
  <p>I was able to recreate the error with the simple example below:</p>
  
  <p><strong>Test.R</strong></p>
  
  <pre><code>library(rmarkdown)
  library(knitr)
  
  setwd(C:/something)
  
  render("Test.rmd", output_format=pdf_document(latex_engine="xelatex"), output_file="test.pdf")
  </code></pre>
  
  <p><strong>Test.Rmd</strong></p>
  
  <pre><code>---
  title: "Habits"
  output:
    pdf_document:
      latex_engine: xelatex
  ---
  
  Hello World!
  </code></pre>
  
  <p>I also see the error when I knit Test.Rmd directly in RStudio instead of using a separate .R file with <code>render()</code>. I also tried using the lualatex pdf engine and received the same error as above. I am able to generate PDFs using the RMarkdown PDF example built into RStudio.</p>
  
  <p><a href="https://sourceforge.net/p/miktex/discussion/33790/thread/fcf98fa1/?limit=25" rel="noreferrer">This post</a> on Sourceforge seems relevant, but not useful since the solution was to update the fontspec package and I'm already using an updated fontspec package.</p>
  
  <p><strong>Session Info</strong></p>
  
  <pre><code>&gt; sessionInfo()
  R version 3.4.1 (2017-06-30)
  Platform: x86_64-w64-mingw32/x64 (64-bit)
  Running under: Windows 10 x64 (build 15063)
  
  Matrix products: default
  
  locale:
  [1] LC_COLLATE=English_United States.1252 
  [2] LC_CTYPE=English_United States.1252   
  [3] LC_MONETARY=English_United States.1252
  [4] LC_NUMERIC=C                          
  [5] LC_TIME=English_United States.1252    
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] knitr_1.17    rmarkdown_1.6
  
  loaded via a namespace (and not attached):
   [1] compiler_3.4.1  backports_1.1.0 magrittr_1.5    rprojroot_1.2  
   [5] tools_3.4.1     htmltools_0.3.6 yaml_2.1.14     Rcpp_0.12.12   
   [9] stringi_1.1.5   stringr_1.2.0   digest_0.6.12   evaluate_0.10.1
  </code></pre>
  
  <p>Any help or advice is greatly appreciated!</p>