LaTeX: To combine ul-lua and LuaTeX-ja

lua-ul-japanese-1.tex

% LuaLaTeX document
\documentclass[a6paper]{ltjsarticle}%for Japanese
\usepackage{lua-ul}
\begin{document}% mix of Japanese and English phrases
色は匂へど、
\underLine{散りぬるを（alas）、
「我が世」誰ぞ、“常”ならむ？
有為の奥山今日越えて（go on!）、
浅き夢見じwow yeah}酔ひもせず……。
\end{document}

lua-ul-japanese-1

Got:

Expected:

The document class ltjsarticle loads the package luatexja for proper typesetting of the Japanese language, which involves the insertion of glues between characters. I’m afraid luatexja is huge and highly complicated, but the issue can be as simple as the matter of execution order of callbacks.

The document class ltjsarticle loads the package luatexja for proper typesetting of the Japanese language, which involves the insertion of glues between characters. I’m afraid luatexja is huge and highly complicated, but the issue can be as simple as the matter of execution order of callbacks.

The callbacks are executed in the right order, but luatexja sets the new glue attributes to the attributes active at the end of the paragraph and not at the point of the insertion. (That also means that if the \par is in the \underLine argument, you get the reverse issue: The glue is underlined even if it shouldn't be.)

That's straight-forward to fix, but it has to happen in luatexja. I'll prepare a patch for them.

ooh a fix 🦆