close #358: when bibliography or references is detected in the .Rmark…

…down post, use Pandoc to convert .markdown to .markdown and process the citations during the conversion

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: blogdown
 Type: Package
 Title: Create Blogs and Websites with R Markdown
-Version: 0.21.37
+Version: 0.21.38
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "xie@yihui.name", comment = c(ORCID = "0000-0003-0645-5666")),
     person("Beilei", "Bian", role = "ctb"),

NEWS.md

@@ -20,7 +20,7 @@
 
 - Documented and exported the internal function `find_hugo()` to find the Hugo executable. If multiple versions of Hugo are installed, `find_hugo()` can also find a specific version of Hugo, e.g., `blogdown::find_hugo('0.25.1')`. You may use `blogdown::find_hugo('all')` to find all possible versions of Hugo currently installed.
 
-- The file format `.Rmarkdown` supports HTML widgets now, just like the `.Rmd` format. If you are not familiar with the `.Rmarkdown` format, you may see https://bookdown.org/yihui/blogdown/output-format.html.
+- The file format `.Rmarkdown` supports HTML widgets and citations now, just like the `.Rmd` format. If you are not familiar with the `.Rmarkdown` format, you may see https://bookdown.org/yihui/blogdown/output-format.html.
 
 ## MAJOR CHANGES
 

R/render.R

@@ -215,6 +215,18 @@ process_markdown = function(x, res) {
   x = xfun::protect_math(x)
   # remove the special comments from HTML dependencies
   x = gsub('<!--/?html_preserve-->', '', x)
+  # render citations
+  if (length(grep('^(references|bibliography):($| )', x))) {
+    # temporary .md files to generate citations
+    mds = replicate(2, wd_tempfile('.md~', pattern = 'citation'))
+    on.exit(unlink(mds), add = TRUE)
+    write_utf8(x, mds[1])
+    rmarkdown::pandoc_convert(
+      mds[1], from = 'markdown', to = 'gfm+tex_math_dollars+footnotes', output = mds[2],
+      options = c('--atx-headers', '--wrap=preserve'), citeproc = TRUE
+    )
+    x = c(bookdown:::fetch_yaml(x), '', read_utf8(mds[2]))
+  }
   x
 }
 

docs/01-introduction.Rmd

@@ -192,10 +192,10 @@ Table: (\#tab:md-diff) Differences among the three document formats.
 |Feature      |.Rmd |.Rmarkdown |.md  |
 |:------------|:----|:----------|:----|
 |Run R code   |yes  |yes        |no   |
-|Bibliography |yes  |no         |no   |
+|Bibliography |yes  |yes        |no   |
 |Task list    |maybe|yes        |yes  |
 |MathJax      |yes  |maybe      |maybe|
-|HTML widgets |yes  |no         |no   |
+|HTML widgets |yes  |yes        |no   |
 
 1. You cannot execute any R code in a plain Markdown document, whereas in an R Markdown document, you can embed R code chunks (```` ```{r} ````). However, you can still embed R code in plain Markdown using the syntax for fenced code blocks ```` ```r ```` (note there are no curly braces `{}`). Such code blocks will not be executed and may be suitable for pure demonstration purposes. Below is an example of an R code chunk in R Markdown: