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With TikZ library shadows, a space immediately after the curly bracket in drop shadow = { shadow... throws an error. If there is no space after the bracket, there is no error, i.e. drop shadow = {shadow... works. Is this a bug or is there a rationale behind the intolerance to space? 

Package pgfkeys Error: I am the key '/tikz/ shadow xshift', to which
 you passed '1ex', and I am going to ignore it. Perhaps you misspelled it.

MWE

\documentclass[border=10]{standalone}
\usepackage[svgnames]{xcolor}
\usepackage{tikz}
\usetikzlibrary{shadows}
\tikzset{test1/.style = {drop shadow = { shadow xshift = 1ex}}}% test1 styles fail
\tikzset{
    test2/.style = {% test2 styles work
        drop shadow = {shadow xshift = 1ex
        },
    }
}
\begin{document}
    \begin{tikzpicture}
        \fill[test1] (0,0) rectangle (1,1);
    \end{tikzpicture}
\end{document}
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  • 2
    TikZ syntax generally is sensitive to spaces - it wants them or wants them not, for example. Sometimes, it is indifferent. But I don't see how you could call it a 'bug'. Is it really a problem? – cfr May 20 '16 at 21:05
  • 1
    @cfr, I am not qualified to say if it might be a bug, a limitation or a feature by design. It seemed strange to me that line breaks and spaces were feasible just about everywhere (see test2) except in one place (see test1). It took me a good 15 minutes to locate the space I had intentionally placed, not knowing it could cause a problem. Also, the error message is sometimes quite scary, along the lines that the tikz shadow command is not recognized. – PatrickT May 20 '16 at 21:26
  • As I understand it, it is probably more-or-less inevitable that the parser will sometimes be fussy because of the way in which arguments get bounced around, basically. There are certainly weirder cases than this ;). – cfr May 20 '16 at 22:21
  • @cfr, I see! Perhaps you can make that an answer: give another example of a weird space-related situation we should be aware of? – PatrickT May 21 '16 at 11:02
  • See e.g. tex.stackexchange.com/questions/266148/…. – cfr May 22 '16 at 0:16
2

In reply to @cfr's comment, I think this is a serious problem because people (at least me) love fancy indentation:

\tikzset{
  test1/.style={
    drop shadow={
      shadow xshift=1ex
    }
  }
}

In such case, TikZ got redundant spaces inevitably because of new lines.

Unfortunately, this seems to be a deep bug of pgfkeys. Consider the following example

\documentclass[tikz]{standalone}
\tikzset{
    option a/.style={
        #1
    }
}
\tikzset{
    option b/.style={
        option a={
            #1
        }
    }
}
\tikzset{
    option c/.style={
        option b={
            red
        }
    }
}
\begin{document}
    \tikz\fill[          red ]circle(1);
    \tikz\fill[option a={red}]circle(1);
    \tikz\fill[option b={red}]circle(1);
    \tikz\fill[option c      ]circle(1);
\end{document}

It produces two errors: One at option b={red}

I do not know the key '/tikz/ red '

And the other at option c:

I do not know the key '/tikz/  red  '

One can accumulate spaces as follows

\documentclass[tikz]{standalone}
\tikzset{option a/.style={ #1 } }
\tikzset{option b/.style={option a={ #1 } } }
\tikzset{option c/.style={option b={ #1 } } }
\tikzset{option d/.style={option c={ #1 } } }
\tikzset{option e/.style={option d={ #1 } } }
\tikzset{option f/.style={option e={ #1 } } }
\tikzset{option g/.style={option f={ #1 } } }
\tikzset{option h/.style={option g={ #1 } } }
\tikzset{option i/.style={option h={ #1 } } }
\tikzset{option j/.style={option i={ #1 } } }
\tikzset{option k/.style={option j={ #1 } } }
\begin{document}
\tikz\fill[option k=red]circle(1);
\end{document}

 I do not know the key '/tikz/          red          '

A partial solution

This trick is so fragile that if one replace } } } by }} } or } }}, the corresponding spaces disappear.

Probably this is the why the source code of TikZ contains so many lonely %. For instance tikz.code.tex line 1209-1215

\tikzset{
  no marks/.style={mark=none},%
  no markers/.style={mark=none},%
  every mark/.style={},
  mark options/.style={%
      every mark/.style={#1}%
  }}

Appendix

drop shadow is defined in tikzlibraryshadows.code.tex

\tikzset{
  /tikz/drop shadow/.style={
    general shadow={%
      shadow scale=1,
      shadow xshift=.5ex,
      shadow yshift=-.5ex,
      opacity=.5,
      fill=black!50,
      every shadow,
      #1
    }
  }
}

Here, general shadow is option a, drop shadow is option b, and test1 is option c.

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