Pandoc numbered section links

numbered-links.lua

--[[
Based on [this](https://stackoverflow.com/a/54130482) stack overfloaw answer which no longer works

License: CC BY-SA 4.0

Usage:

See Section [](#some-section-name)

# Some section name

text text text

---------

`[](#some-section-name)` will be replaced by the number of the section.

`numbersections` is not required, but the links will not make much sense without it.
]]

local make_sections = (require 'pandoc').utils.make_sections

local section_numbers = {}

local function populate_section_numbers(doc)
    local function populate(elements)
        for _, elem in pairs(elements) do
            if elem.t == "Div" then
                section_numbers["#" .. elem.identifier] = elem.attributes.number
                populate(elem.content)
            end
        end
    end

    populate(make_sections(true, nil, doc.blocks))
end

local function resolve_section_ref(link)
    if #link.content > 0 or link.target:sub(1, 1) ~= '#' then
        return nil
    end
    local num = section_numbers[link.target]
    local section_number = nil
    if not num then
        section_number = pandoc.Str("??")
        warn("Could not identify section number for targer `" ..
            link.target .. "`. Possibly trying to link unnumbered section")
    else
        section_number = pandoc.Str(num)
    end
    return pandoc.Link(section_number, link.target, link.title, link.attr)
end

return {
    { Pandoc = populate_section_numbers },
    { Link = resolve_section_ref }
}