tikz graphs library: Edge label syntax

Question

I'm using tikz and its "graph" library, and I'd like to label some of my graph's edges. The tikz manual (pgfmanual.pdf v3.0.1, p. 364) suggests the syntax

\documentclass{scrartcl}
\usepackage{tikz}
\usetikzlibrary{graphs}

\begin{document}
\tikz \graph
{
  a ->["foo"] b
};
\end{document}

However, this doesn't work; upon compilation I get the error message

! Package pgfkeys Error: I do not know the key '/tikz/"{foo}"' and I am going t
 o ignore it. Perhaps you misspelled it.

Am I doing something wrong, or is this a bug in tikz or its documentation?

By the way, the alternative syntax ->[edge label=foo] works fine.

Answer 1

You need to load the quotes library.

\RequirePackage{luatex85}
\documentclass[border=12pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{graphs,graphdrawing,quotes}
\begin{document}
\tikz \graph
{
  a ->["foo"] b
};
\end{document}