Using TikZ Chains Library with labeled edges extension

The other day I need to create a diagram, and went in the TikZ way. I was using the chains library to produce the diagram. But I face some problems, I needed to add labels to the edges created by the chain. However, this is not supported natively by the library.

I found a cool code that exemplifies how to add the edges to the chain, but it removes the old notation

\chainin (node) [join=with srcNode by style]

and make you use a new definition. However, I still need to use the styles and the source node notation. So, I start digging in the chains library code and modify it to allow the use of the label notation from other examples. The fix is

\makeatletter
\def\tikz@lib@parse@join#1{%
  \def\tikz@temp{#1}%
  \ifx\tikz@temp\pgfutil@empty%
    \tikz@lib@parse@join@by by \pgf@stop%
  \else%
    \pgfutil@in@{with }{#1}%
    \ifpgfutil@in@% 'with [by] [label]'
      \pgfutil@in@{by }{#1}%
      \ifpgfutil@in@% 'with by [label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'with by label'
          \tikz@lib@parse@join@with@by@label#1\pgf@stop%
        \else% 'with by'
          \tikz@lib@parse@join@with@by#1\pgf@stop%
        \fi%
      \else% 'with [label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'with label'
          \tikz@lib@parse@join@with@label#1\pgf@stop%
        \else% with
          \tikz@lib@parse@join@with@by#1 by \pgf@stop%
        \fi%
      \fi%
    \else% '[by] [label]'
      \pgfutil@in@{by }{#1}%
      \ifpgfutil@in@% 'by [label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'by label'
          \tikz@lib@parse@join@by@label#1\pgf@stop%
        \else% 'by'
          \tikz@lib@parse@join@by#1\pgf@stop%
        \fi%
      \else% '[label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'label'
          \tikz@lib@parse@join@label#1\pgf@stop%
        \else%
          \tikz@lib@parse@join@by#1 by \pgf@stop%
        \fi%
      \fi%
    \fi%
  \fi%
}
\def\tikz@lib@parse@join@with@by@label with #1 by #2 label #3\pgf@stop{%
  \tikzset{after node path={(#1)edge[every join,#2]#3(\tikzchaincurrent)}}%
}
\def\tikz@lib@parse@join@with@label with #1 label #2\pgf@stop{%
  \tikzset{after node path={(#1)edge[every join]#2(\tikzchaincurrent)}}%
}
\def\tikz@lib@parse@join@by@label by #1 label #2\pgf@stop{%
  \tikzset{after node path={\ifx\tikzchainprevious\pgfutil@empty\else(\tikzchainprevious)edge[every join,#1]#2(\tikzchaincurrent)\fi}}%
}
\def\tikz@lib@parse@join@label label #1\pgf@stop{%
  \tikzset{after node path={\ifx\tikzchainprevious\pgfutil@empty\else(\tikzchainprevious)edge[every join]#1(\tikzchaincurrent)\fi}}%
}
\makeatother

This allows one to use the chains like:

\chainin (node) [join=with anotherNode by myStyle label {node[above] {some Tag}}];
\chainin (node) [join=by myStyle label {node[above] {some Tag}}];

Note that the order needs to be maintained, so you can use [with] [label] [tag] and omit any of those, while the order is maintained. A minimal working example is below:

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{shapes,% for the rectangle
                chains,% provides the chains
                scopes}% allows to replace \begin{scope} \end{scope} with {}

\makeatletter
\def\tikz@lib@parse@join#1{%
  \def\tikz@temp{#1}%
  \ifx\tikz@temp\pgfutil@empty%
    \tikz@lib@parse@join@by by \pgf@stop%
  \else%
    \pgfutil@in@{with }{#1}%
    \ifpgfutil@in@% 'with [by] [label]'
      \pgfutil@in@{by }{#1}%
      \ifpgfutil@in@% 'with by [label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'with by label'
          \tikz@lib@parse@join@with@by@label#1\pgf@stop%
        \else% 'with by'
          \tikz@lib@parse@join@with@by#1\pgf@stop%
        \fi%
      \else% 'with [label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'with label'
          \tikz@lib@parse@join@with@label#1\pgf@stop%
        \else% with
          \tikz@lib@parse@join@with@by#1 by \pgf@stop%
        \fi%
      \fi%
    \else% '[by] [label]'
      \pgfutil@in@{by }{#1}%
      \ifpgfutil@in@% 'by [label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'by label'
          \tikz@lib@parse@join@by@label#1\pgf@stop%
        \else% 'by'
          \tikz@lib@parse@join@by#1\pgf@stop%
        \fi%
      \else% '[label]'
        \pgfutil@in@{label }{#1}%
        \ifpgfutil@in@% 'label'
          \tikz@lib@parse@join@label#1\pgf@stop%
        \else%
          \tikz@lib@parse@join@by#1 by \pgf@stop%
        \fi%
      \fi%
    \fi%
  \fi%
}
\def\tikz@lib@parse@join@with@by@label with #1 by #2 label #3\pgf@stop{%
  \tikzset{after node path={(#1)edge[every join,#2]#3(\tikzchaincurrent)}}%
}
\def\tikz@lib@parse@join@with@label with #1 label #2\pgf@stop{%
  \tikzset{after node path={(#1)edge[every join]#2(\tikzchaincurrent)}}%
}
\def\tikz@lib@parse@join@by@label by #1 label #2\pgf@stop{%
  \tikzset{after node path={\ifx\tikzchainprevious\pgfutil@empty\else(\tikzchainprevious)edge[every join,#1]#2(\tikzchaincurrent)\fi}}%
}
\def\tikz@lib@parse@join@label label #1\pgf@stop{%
  \tikzset{after node path={\ifx\tikzchainprevious\pgfutil@empty\else(\tikzchainprevious)edge[every join]#1(\tikzchaincurrent)\fi}}%
}
\makeatother

\begin{document}
\begin{tikzpicture}[
  nonterminal/.style={
    rectangle,
    minimum size=6mm,
    very thick,
    draw=red!50!black!50,
    top color=white, % a shading that is white at the top...
    bottom color=red!50!black!20, % and something else at the bottom
    font=\itshape
  },
  terminal/.style={
    rectangle,minimum size=6mm,rounded corners=3mm,
    very thick,draw=black!50,
    top color=white,bottom color=black!20,
    font=\ttfamily
  },
  every on chain/.style={join}, every join/.style={->}
]

\matrix[column sep=4mm] {
  % First row:
  & & & & \node (plus) [terminal] {+};&\\
  % Second row:
  \node (ui1)   [nonterminal] {unsigned integer};&
  \node (dot)   [terminal]    {.};               &
  \node (digit) [terminal]    {digit};           &
  \node (e)     [terminal]    {E};               &
  & % space in between
  \node (ui2) [nonterminal] {unsigned integer};\\
  % Third row:
  & & & & \node (minus)[terminal] {-};&\\
  };

{ [start chain]
  \chainin (ui1);
  \chainin (dot);
  \chainin (digit);
  \chainin (e);
  { [start branch=plus]
    \chainin (plus) [join=label {node[above left]{a label}}];
  }
  { [start branch=minus]
    \chainin (minus);
  }
  \chainin (ui2) [join=with chain/plus-end label {node[above right] {plus label}}, join=with chain/minus-end by dashed label {node [below right]{minus label}}];
}
\end{tikzpicture}
\end{document}

HTH…

PS. This post was inspired by this TeX.SX question, and I put this answer also there. You can found more about (La)TeX there.