LaTeX throws error on \heightof

Question

I'm trying use \heightof in my document but XeLaTeX throws an error. Both minimal code end errors are below. Ubuntu 20.04 with latest updates

\documentclass[14pt,a4paper]{extarticle}
\usepackage{calc}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node[minimum height=\heightof{A}]{A};
\end{tikzpicture}
\end{document}

ABD: EveryShipout initializing macros
! Undefined control sequence.
\pgfmath@dimen@ ...men@@ #1=0.0pt\relax \pgfmath@ 
                                                  
l.6 \node[minimum height=\heightof{A}]{A};

UPD. The height of bold text is height("{\textbf{A}}").

Answer 1

\heighof doesn't work inside tikz, use the functions provided by it. See the section "Mathematical Expressions" in the documentation.

\documentclass[14pt,a4paper]{extarticle}
\usepackage{calc}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node[minimum height=height("A")]{A};
\end{tikzpicture}
\end{document}

Addition: minimum height does not describe the height of the node content, in the sense of the height of a TeX box, but the total height:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node[draw,inner sep=0,minimum height=10pt] (A) {.};

\draw[red,<->] ([xshift=-2pt]A.south west) --++ (0,10pt);
\end{tikzpicture}
\begin{tikzpicture}
\node[draw,minimum height=10pt] (A) {.};

\draw[red,<->] ([xshift=-2pt]A.south west) --++ (0,10pt);
\end{tikzpicture}

\end{document}

Answer 2

The command \heightof only works in calc package expressions.

You can use height{"A"}, but this wouldn't take care of the inner sep, so you should add it to the minimum height.

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
\node[draw,minimum height=height("A")+2*(\pgfkeysvalueof{/pgf/inner ysep})]{A};
\end{tikzpicture}
\begin{tikzpicture}
\node[draw,minimum height=height("A")+2*(\pgfkeysvalueof{/pgf/inner ysep})]{x};
\end{tikzpicture}

\begin{tikzpicture}[inner sep=1pt]
\node[draw,minimum height=height("A")+2*(\pgfkeysvalueof{/pgf/inner ysep})]{A};
\end{tikzpicture}
\begin{tikzpicture}[inner sep=1pt]
\node[draw,minimum height=height("A")+2*(\pgfkeysvalueof{/pgf/inner ysep})]{x};
\end{tikzpicture}

\end{document}