Pandoc filter which prevents code blocks containing backticks being mangled in Markdown output

pandoc-fix-backtick-codeblocks.lua

--[[

Pandoc filter which prevents code blocks containing backticks being mangled in Markdown output.


| This software is Copyright (c) 2019 by Benct Philip Jonsson.
| 
| This is free software, licensed under:
| 
|   The MIT (X11) License
| 
| The MIT License
| 
| Permission is hereby granted, free of charge, to any person
| obtaining a copy of this software and associated
| documentation files (the "Software"), to deal in the Software
| without restriction, including without limitation the rights to
| use, copy, modify, merge, publish, distribute, sublicense,
| and/or sell copies of the Software, and to permit persons to
| whom the Software is furnished to do so, subject to the
| following conditions:
| 
| The above copyright notice and this permission notice shall
| be included in all copies or substantial portions of the
| Software.
| 
| THE SOFTWARE IS PROVIDED "AS IS", WITHOUT
| WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
| INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
| MERCHANTABILITY, FITNESS FOR A PARTICULAR
| PURPOSE AND NONINFRINGEMENT. IN NO EVENT
| SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
| LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
| LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
| TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
| CONNECTION WITH THE SOFTWARE OR THE USE OR
| OTHER DEALINGS IN THE SOFTWARE.
]]

local function fix_backticks (elem)
    local code = elem.text:gsub('%s*$','\n')
    local max = 0
    for ticks in code:gmatch('%`+') do
        local this = ticks:len()
        if this > max then
            max = this
        end
    end
    if max > 0 then
        local ticks = string.rep('`', max * 2)
        code = code .. ticks .. "\n"
        classes = elem.classes
        if 'markdown' == FORMAT then
            local attr = {}
            if elem.identifier:len() > 0 then
                attr[#attr+1] = '#' .. elem.identifier
            end
            for _,class in ipairs(classes) do
                attr[#attr+1] = '.' .. class
            end
            for k, v in pairs(elem.attributes) do
                v = v:gsub('%"', '"')
                attr[#attr+1] = k .. '="' .. v .. '"'
            end
            if #attr > 0 then
                ticks = ticks .. " {" .. table.concat(attr, " ") .. "}"
            end
        elseif 'markdown_github' == FORMAT then
            if #classes > 0 then
                ticks = ticks .. classes[1]
            end
        else
            return nil
        end
        code = ticks .. "\n" .. code
        return pandoc.RawBlock(FORMAT, code)
    end
end

function Pandoc (doc)
    if FORMAT == 'markdown' or FORMAT == 'markdown_github' then
        local filter = { CodeBlock = fix_backticks }
        local temp = pandoc.Div(doc.blocks)
        doc.blocks = pandoc.walk_block(temp, filter).content
        return doc
    else
        return nil
    end
end