Macros with optional arguments do not work in TikZ commands [Semi-patch]

[ilyaza]

Brief outline of the bug

The TikZ command loop fails handling LaTeX macros with optional arguments. It gives a cryptic error message (like Did you forget to insert a semicolon). (A “semi-patch” included — it works for the older version of the scan loop.)

Minimal working example (MWE)

(The following example includes also a \global\def chunk to illustrate another functionality of the patch.)

\documentclass{article}
\usepackage{tikz}

\begin{document}

\newcommand\foo[1][node {123}]{#1}

\tikz \draw (0,0) node {123} -- ++(1,1);.

\tikz \draw (0,0) \foo \foo[-- ++(1,1)] \global\def\BAR{node {yyy}};.

\tikz \draw (0,0) node {123} -- ++(1,1);.

\tikz \draw \BAR;

\end{document}

How to fix

Right now I cannot test with the latest version. I include the patch for the version in TeXLive2021. I expect the first and the third chunks would work in the bleeding-edge version too (they are only 4 LoCs), and the dispatcher would need an extra chunk like

    {\global}{\let\pgfutil@next\tikz@global}%
    {\let}{\let\pgfutil@next\tikz@assignment}%
    {\futurelet}{\let\pgfutil@next\tikz@assignment}%
    {\def}{\let\pgfutil@next\tikz@assignment}%
    {\gdef}{\let\pgfutil@next\tikz@assignment}%
    {\edef}{\let\pgfutil@next\tikz@assignment}%
    {\xdef}{\let\pgfutil@next\tikz@assignment}%

diff-tikz.code.tex.txt

[hmenke]

You cannot use unexpandable material on a path and that is also documented. I'm not going to change that.

[ilyaza]

I do not follow: with the given patch, you can use this particular kind of unexpandable “material”. So your statement would be valid only in the past tense.

[hmenke]

If you want to perform semantic actions (like assignments) on a path use \pgfextra. Macros with unexpandable material are intentionally unsupported, because you will quickly run into problems with incomplete \if or dangling \else.

See also #967

[muzimuzhi]

A workaround

• \newcommand\foo[1][...]{...} is replaced with option insert path and key handler /.default,
• \global\def\BAR{..} is wrapped in \pgfextra

\documentclass{article}
\usepackage{tikz}

\tikzset{
  foo/.style={insert path={#1}},
  foo/.default={node {123}}
}

\begin{document}
\tikz \draw (0,0) node {123} -- ++(1,1);.

\tikz \draw (0,0) [foo] [foo={-- ++(1,1)}]
  \pgfextra{\global\def\BAR{node {yyy}}};.

\tikz \draw (0,0) node {123} -- ++(1,1);.

\tikz \draw \BAR;
\end{document}