Macro default argument support

I'm trying to write some custom plugins for transforming latex, and so far, I really liked your work, especially in how you provide every required toolsets via modular package structure. While experimenting with it, I noticed that currently there's no support for macros with default arguments.

% input.tex
\documentclass{article}
% \newcommand\foo[2][bar]{#1,#2}
\begin{document}
    \foo[bar]{baz}
    \foo{baz}
\end{document}

unified-latex input.tex -e "\\newcommand\\foo[2][bar]{#1,#2}"

Then the result will be

\documentclass{article}

%\newcommand\foo[2][bar]{#1,#2}

\begin{document}
        bar,baz

        ,baz
\end{document}

where the expected output would have two identical lines of bar,baz.

In unified-latex-util-macros, an xpase-style signature is computed, but it produces o irrespective of the presence of a default argument. I've also noticed that manually passing O{bar} m via \NewDocumentCommand still produces unexpected results, so there should be another issue regarding macro expanders.

It'd be nice if this support can be added. I'm wondering to know if there's any blocker for implementing it, I'm interested in sending a PR.

siefkenj / unified-latex

Macro default argument support #24