No toc generated with output: md_document

[stla]

Hello,

I've tried the latest CRAN version and the dev version. While setting toc: true for a md_document, the table of contents is not generated.

---
title: "No toc"
author: "Stéphane Laurent"
date: "12 décembre 2017"
output:
  md_document:
    toc: true
    variant: markdown
    preserve_yaml: true
---


# Part 1

This is an R Markdown document. 

# Part 2

You can also embed plots.

[stla]

I can get the toc by doing
render("myfile.Rmd", md_document(variant="markdown", toc=TRUE, preserve_yaml = TRUE, pandoc_args="--template=toctemplate.txt"))
with the toctemplate.txt file

$toc$

$body$

[yihui]

Did this work before but stopped working recently? If not, please see #1211. We cannot support it unless Pandoc supports it.

[stla]

Yes, this worked before. This is what I always used for my Hakyll blog.
Pandoc supports it, it suffices to have the template I posted.

[stla]

I've looked at #1211
This is not the problem here:

> rmarkdown::pandoc_version()
[1] ‘1.19.2.1’

[stla]

I've tried with the default variant.
This generates a TOC:

output:
  md_document:
    toc: true

But this doesn't generate a TOC:

output:
  md_document:
    toc: true
    preserve_yaml: true

There's something abnormal.

[stla]

The smoking gun is here, in the md_document function:

  # base pandoc options for all markdown output
  args <- c(if (variant != "markdown" && !preserve_yaml) "--standalone")

Looks like Pandoc does not generate the TOC if there isn't the option --standalone.

[stla]

I've tried to understand why you remove --standalone.

This generates the TOC:
render("bugtocmd.Rmd", md_document("markdown", preserve_yaml=TRUE, toc=TRUE, pandoc_args="--standalone")) but the YAML block is duplicated.

This generates the TOC and the YAML block is not duplicated:
render("bugtocmd.Rmd", md_document("markdown", preserve_yaml=FALSE, toc=TRUE, pandoc_args="--standalone"))

Thus, when variant=markdown, the YAML block is preserved if there is the option --standalone.

Therefore I would propose this solution, but I have not seriously tested it:

# base pandoc options for all markdown output
args <- if (variant != "markdown" || preserve_yaml) "--standalone"
.......
# add post_processor for yaml preservation
  if (preserve_yaml && variant != "markdown") {
    ......

[yihui]

Okay, I'll take a look at your proposal soon.

[yihui]

Should be fixed now. Thanks for the report and investigation!

[github-actions]

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