“Hobby” library stopped working after updating to TeXLive 2014

Question

After upgrading to TeXLive 2014 compiling my TikZ pictures prepared with the hobby library stopped working.

Consider the following MWE:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{hobby,positioning}

\begin{document}
    \begin{tikzpicture}[%
        scale=1, 
        % circlenodes/.style={circle, draw, font=\footnotesize},
        circlenodes/.style={circle, draw, font=\footnotesize, inner sep=0.1em,
            minimum width=1.5em},
        % midnodes/.style={midway, circle, fill=white, font=\tiny},
        midnodes/.style={midway, font=\tiny, above},
        >=latex,
        ]
        \fill[gray!20](-3, 3) to[curve through={%
            (-2, 1.5) (0,0) (0.5, 0.5) (1, 1.5) (3,3) 
        }] (4, 4) --(4,-0.5) -- (-3, -0.5) -- (-3, 3);
        \draw[thick, ->] (-3,-0.5) -- (4, -0.5) node[at end, anchor=west] {$tgo$};
        \draw[thick, ->] (-3,-0.5) -- (-3, 4) node[at end, anchor=south] {$J(tgo)$};
        \draw[very thick] (-3, 3) to[curve through={%
            (-2, 1.5) (0,0) (0.5, 0.5) (1, 1.5) (3,3) 
        }] (4, 4);
        \node[circlenodes, fill=red!20] (one) at (-3,3) {$a_0$};
        \node[circlenodes, fill=green!20, below=0pt of one] (a1) {$a_1$};
        \node[circlenodes, fill=yellow!20] (five)  at (-2,1.5) {$a_2$};
        \node[circlenodes, fill=blue!20, below=0pt of five] (a3) {$a_3$};
        \node[circlenodes, below=0pt of one] {$a_1$};
        \node[circlenodes, fill=red!20] (three) at (0.5,0.5) {$c_0$};
        \node[circlenodes, fill=green!20, right=0pt of three] (c1) {$c_1$};
        \node[circlenodes, fill=yellow!20, right=0pt of c1] (c2) {$c_2$};
        \node[circlenodes, fill=blue!20, right=0pt of c2] (c3) {$c_3$};
        \node[circlenodes, fill=green!20] (four)  at (3,3) {$b_1$};
        \node[circlenodes, fill=yellow!20, below=0pt of four] (b2) {$b_2$};
        \node[circlenodes, fill=blue!20,] (six)   at (1,1.5) {$b_3$};
        \node[circlenodes, fill=red!20] (two)  at (4,4) {$b_0$};
        \path[->] (two) edge[bend left=30]  node[midnodes] {1} (four);
        \path[->] (b2) edge[bend left=30] node[midnodes] {3} (six);
        \path[->] (a1) edge[bend right=30] node[midnodes] {2} (five);
    \end{tikzpicture}
\end{document}

This gives the following error message with the lualatex compiler:

! Undefined control sequence.
<argument> \fp_if_undefined:NTF 
                     \l_hobby_out_angle_fp {\array_put:Nnx \l_hobby_matrix_b_ar
l.18         }] (4, 4)
                     --(4,-0.5) -- (-3, -0.5) -- (-3, 3);
? 

With a deadline drawing close, I am getting nervous :-). The wise man might say: ¨Never change a running system.“ I should have listened, but here I am:

Do you have any idea how to fix this?

Answer 1

This is now fixed in the version of hobby on CTAN and the change has propagated to TeXLive 14 (I can't say for MikTeX).

If you have an older version, see egreg's post.

Answer 2

The function \fp_if_undefined:NTF (and siblings) have been deprecated several months ago and removed from the last revision of the expl3 suite. Unfortunately, hobby wasn't updated timely.

You can momentarily solve the issue by defining in a suitable way the now inexistent functions:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{hobby,positioning}

\ExplSyntaxOn
\cs_set_eq:NN \fp_if_undefined:NTF \cs_if_free:NTF
\cs_set_eq:NN \fp_if_undefined:NT \cs_if_free:NT
\ExplSyntaxOff

After an examination of hobby.code.tex they seem the only functions that need to be provided back.