option to preserve yaml front matter for md_document

rstudio · Mar 27, 2014 · 9a5d207 · 9a5d207
1 parent 190246f
commit 9a5d207
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Showing 2 changed files with 28 additions and 4 deletions.
diff --git a/R/md_document.R b/R/md_document.R
@@ -12,6 +12,8 @@
 #'   \href{http://johnmacfarlane.net/pandoc/demo/example9/pandocs-markdown.html}{pandoc's
 #'    markdown} for details.
 #'
+#' @param preserve_yaml Preserve YAML front matter in final document.
+#'
 #' @param fig_retina Scaling to perform for retina displays. Defaults to
 #'   \code{NULL} which performs no scaling. A setting of 2 will work for all
 #'   widely used retina displays, but will also result in the output of
@@ -41,6 +43,7 @@
 #'
 #' @export
 md_document <- function(variant = "markdown_strict",
+                        preserve_yaml = FALSE,
                         toc = FALSE,
                         toc_depth = 3,
                         fig_width = 7,
@@ -66,11 +69,28 @@ md_document <- function(variant = "markdown_strict",
   # pandoc args
   args <- c(args, pandoc_args)
 
+  # add post_processor for yaml preservation
+  if (preserve_yaml) {
+    post_processor <- function(input_file, output_file, verbose) {
+      input_lines <- readLines(input_file, warn = FALSE)
+      partitioned <- partition_yaml_front_matter(input_lines)
+      if (!is.null(partitioned$front_matter)) {
+        output_lines <- c(partitioned$front_matter,
+                          "",
+                          readLines(output_file, warn = FALSE))
+        writeLines(output_lines, output_file, useBytes = TRUE)
+      }
+    }
+  } else {
+    post_processor <- NULL
+  }
+
   # return format
   output_format(
     knitr = knitr_options_html(fig_width, fig_height, fig_retina),
     pandoc = pandoc_options(to = variant,
                             from = from_rmarkdown(),
-                            args = args)
+                            args = args),
+    post_processor = post_processor
   )
 }
diff --git a/man/md_document.Rd b/man/md_document.Rd
@@ -2,9 +2,10 @@
 \alias{md_document}
 \title{Convert to a markdown document}
 \usage{
-md_document(variant = "markdown_strict", toc = FALSE, toc_depth = 3,
-  fig_width = 7, fig_height = 5, fig_retina = NULL, includes = NULL,
-  data_dir = NULL, pandoc_args = NULL)
+md_document(variant = "markdown_strict", preserve_yaml = FALSE,
+  toc = FALSE, toc_depth = 3, fig_width = 7, fig_height = 5,
+  fig_retina = NULL, includes = NULL, data_dir = NULL,
+  pandoc_args = NULL)
 }
 \arguments{
   \item{variant}{Markdown variant to produce (defaults to
@@ -16,6 +17,9 @@ md_document(variant = "markdown_strict", toc = FALSE, toc_depth = 3,
   \href{http://johnmacfarlane.net/pandoc/demo/example9/pandocs-markdown.html}{pandoc's
   markdown} for details.}
 
+  \item{preserve_yaml}{Preserve YAML front matter in final
+  document.}
+
   \item{fig_retina}{Scaling to perform for retina displays.
   Defaults to \code{NULL} which performs no scaling. A
   setting of 2 will work for all widely used retina