Mecabを使って改行位置をいい感じに調整する（LuaTeX）

wakati-test.tex

% inspired by https://tech.aptpod.co.jp/entry/2020/11/20/160000
% with http://taku910.github.io/mecab/
% ref. https://tex.stackexchange.com/questions/500372/conditional-string-replacements-in-lualatex

\documentclass[a4paper]{ltjsarticle}
\usepackage[no-math]{luatexja-fontspec}
\usepackage{luacode,luatexbase}
%\usepackage[callback={preline},verbosity=1]{nodetree}
%\usepackage{lipsum}
\usepackage[textwidth=32em,textheight=5cm,paperwidth=32em,paperheight=5cm]{geometry}

\title{\wakatiBreak{とても長いタイトルを持ち秋の夜に世界の片隅で作成されたPDF出力テストのためのドキュメント}}
%\stitle{とても長いタイトルを持ち秋の夜に世界の片隅で作成されたPDF出力テストのためのドキュメント}

\begin{document}

\begingroup
\ttfamily
\let\\\relax
\catcode`\^^M=12
\catcode`\%=12
\luaexec{
  mecab = require("lua-mecab")
  parser = mecab:new("-Owakati")
  function break_at_wakachi (s)
    if s ~= "\\wakatiBreakOff" then
      local t = {}
      split_tex (t, s)
      return table.concat (t)
    end
  end

  function split_tex (t, s, is_cmd)
    if s == nil then
      return t
    else
      local c = string.sub (s, 0, 1)
      if c == '\\' then
        found, rest = string_find (s, "\\[%a]+")
        if not found then
          found, rest = string_find (s, "\\[^%a]")
        end
        table.insert(t, found)
        split_tex (t, rest, true)
      elseif c == '[' then
        if is_cmd then
          found, rest = string_find (s, "[^\\]]")
          table.insert(t, found)
          split_tex (t, rest, false)
        else
          table.insert(t, "[")
          split_tex (t, string.sub(s, 1, -1), 0)
        end
      else
        found, rest = string_find (s, "[^\\\\]+")
        if found ~= nil then
          table.insert(t, setBreak(parser:parse(found)))
        end
        split_tex (t, rest, false)
      end
    end
  end

  function string_find (s, pattern)
    found = string.match (s, pattern)
    if found ~= nil then
      rest = string.sub (s, string.len(found) + 1, -1)
      if rest == "" then
        rest = nil
      end
      return found, rest
    else
      return nil
    end
  end

  function setBreak (s)
    f, r = string_find (s, "[^%s]+")
    if f == nil then
      s = ""
    elseif r == nil then
      s = f
    elseif string.match(string.sub(string.reverse(f), 1, 1), "%w")
             and string.match(string.sub(r, 2, 2), "%w") then
      s = f .. " " .. setBreak(string.sub(r, 2, -1))
    else
      print (f)
      print (r)
      s = f .. "\\penalty -5{}" .. setBreak(string.sub(r, 2, -1))
    end
    return s
  end
}

\endgroup

\newcommand\wakatiBreakOn{\directlua{luatexbase.add_to_callback("process_input_buffer", break_at_wakachi, "break_at_wakachi" )}}
\newcommand\wakatiBreakOff{\directlua{luatexbase.remove_from_callback("process_input_buffer", "break_at_wakachi" )}}
\newcommand\wakatiBreak[1]{\directlua{tex.sprint(break_at_wakachi(\luastringN{#1}))}}

\wakatiBreakOn
\maketitle

あなたとJAVA, 今すぐダウンロード.
\wakatiBreakOff
%\directlua{tex.print(parser:parse("あなたとJAVA, 今すぐダウンロード. "))}
\end{document}