Missing character: There is no ; in font nullfont!

[nschloe]

When using pgfplots with tectonic, I'm getting errors like

Running TeX ...
warning: c.tex:16: Missing character: There is no ; in font nullfont!
warning: could not represent character ";" (0x3b) in font "nullfont"
warning:   you may need to load the `fontspec` package and use (e.g.) \setmainfont to
warning:   choose a different font that covers the unrepresentable character(s)

MWE:

\documentclass{article}

\usepackage{pgfplots}

\begin{document}

% warning
% \begin{tikzpicture}
% \begin{axis}
% ;
% \end{axis}
% \end{tikzpicture}

% warning
\begin{tikzpicture}
\begin{axis}[]
\draw[draw=none,fill=red] (axis cs:-0.4,0) rectangle (axis cs:-0.1,3.2);
\addlegendimage{ybar,ybar legend,draw=none,fill=red};
\end{axis}
\end{tikzpicture}

% no warning
% \begin{tikzpicture}
% \begin{axis}[]
% \addplot [
% red,
% domain=-3e-3:3e-3,
% samples=201,
% ]
% {exp(-x^2 / (2e-3^2)) / (1e-3 * sqrt(2*pi))};
% \end{axis}
% \end{tikzpicture}

\end{document}

It is indeed possible to remove some semicolons in the tikzpicture, but the official documentation uses semicolons everywhere. (They don't hurt.) pdflatex doesn't warn, either.

[pkgw]

Thanks for reporting. Are the results OK or is there something wrong with them? I think this might be a case where Tectonic is just surfacing a warning that normally remains hidden.

[nschloe]

Output looks okay. The weird thing is that this

\draw[draw=none,fill=red] (axis cs:-0.4,0) rectangle (axis cs:-0.1,3.2);
\addlegendimage{ybar,ybar legend,draw=none,fill=red};

gives the warning, but when removing both or either one of the semicolons, the warning goes away.

[blefloch]

This is not a bug.

The \draw command (from the tikz package) expects to be ended by a semicolon, but \addlegendimage from pgfplots does not expect a semicolon. So the second semicolon gets typeset. But the tikzpicture environment sets the font to \nullfont to avoid accidentally typesetting text outside of the tikz commands, so the semicolon gets typeset in \nullfont, which does not have any character, hence the Missing character information message.

When compiling with pdflatex/xelatex/lualatex instead of tectonic, this information message is only put in the log. (This default behavior can be changed by putting \tracinglostchars=2 near the start of the file, which makes the information message appear in the terminal too.) The only difference in tectonic is to show the message more explicitly, which I think is a better default.

If you remove the second semicolon, it doesn't get typeset, so there is no message. If you remove the first one, the \draw command ends at the second semicolon (since the first is missing), so there is no message (it's surprising that there is no error, but not relevant here).

[nschloe]

Thanks @blefloch for the concise explanation!

The only difference in tectonic is to show the message more explicitly, which I think is a better default.

I agree. Let's close this.