I believe a change has been made so that Lua filters now traverse the
document in linear order. If this is the case in the latest version of
Pandoc it should be doable with a two-pass filter: first a pass which
collects the headings and then a pass which inserts the TsoC. If you want
hierarchical section numbering you probably also need to do a first pandoc
run which inserts the numbering and then a second pandoc run with the
filter to insert the TsoC.  Something like this:

(Warning 1: Untested code!
  Warning 2: Make sure not to overwrite any existing file!
  Warning 3: Assumes that all chapters are heading level 2 — change the
chapter_level and toc_level variables to match!
   Warning 4: Assumes that each section/chapter has a unique identifier!
)

local chapter_level = 2
local toc_level = 3
local headings = {}
local current_chapter = nil

local function collect_headings (head)
  if head.level == chapter_level then
    local id = head.identifier
    current_chapter = {
      chapter = id
      toc = {}
    }
    headings[id] = current_chapter
  elseif head.level = toc_level then
    if current_chapter then
      local toc = current_chapter.toc
      toc[#toc+1] = head
    end
  end
  return nil
end

local function build_toc (heads)
  local toc = {}
  for _,head in ipairs(heads) do
    local entry = {
      pandoc.Plain{
        pandoc.Link(
          head.content:clone(), -- text
          head.identifier, -- target
          "", -- empty title
          pandoc.Attr(
            "", -- empty identifier
            {'local-toc-link'} -- class
          )
        )
      }
    }
    toc[#toc+1] = entry
  end
  return pandoc.Div(
    { pandoc.BulletList(toc) },
    pandoc.Attr( "", {'local-toc'} )
  )
end


local function insert_toc (head)
  if head.level = chapter_level then
    local id = head.identifier
    if headings[id] then
      local toc = build_toc(
        headings[id].toc
      )
      return {head,toc}
    end
  end
  return nil
end

return {
  { Header = collect_headings },
  { Header = insert_toc },
}


Den fre 31 jan. 2020 19:27Szabolcs Horvát <szhorvat-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> Hello everyone,
>
> I am converting a Markdown file to HTML.
>
> I can insert a table of contents at the beginning using the --toc option.
>
> Is it possible to insert additional tables of contents under each
> level-two or level-three heading?
>
> I am looking to create something similar to the organization of this page:
> https://igraph.org/c/doc/igraph-Visitors.html#idm209455316208
>
> Szabolcs
>
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>

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