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Bug fixed in version 11

In adapting some plotting functions to utilize the PlotLegends option of version 9, I came across the following errors:

f[x_] := Legended[Plot[Sin[t], {t, 0, Pi}], x]
f[1];
Information[f]

TextForm[First::first: StandardForm[Short[Shallow[HoldForm[{}], {10, 50}], 5]] has a length of zero and no first element. >>]

This is just a toy example for a more complex situation where I can't directly use the PlotLegends option but have to use Legended explicitly.

What is the best way to catch this error when a user invokes the above or types ?f to see the code for this function. It seems the output of Definition works as expected (it formats the Legended contents, and that happens for other constructs such as Framed too).

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    $\begingroup$ For the error in ?f, specifying usage message is enough f::usage = "bla";. $\endgroup$
    – swish
    May 5, 2013 at 20:48
  • $\begingroup$ Wierd.. I can reproduce the problem at first time. But after doing some tracing, I quit the kernel, then the problem is gone! I restarted the whole mma, still no problem now! $\endgroup$
    – Silvia
    May 5, 2013 at 20:52
  • $\begingroup$ @Silvia Yeah, me too! Weird indeed... $\endgroup$
    – swish
    May 5, 2013 at 20:57
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    $\begingroup$ Mmm not sure whether this one needs to be reported as a bug or exorcized $\endgroup$
    – Dr. belisarius
    May 5, 2013 at 21:07
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    $\begingroup$ @swish Guess evaluating f introduced something to box functions. Check this: System`Dump`makeusageboxes[f[x_] := Legended["123", x]]. $\endgroup$
    – Silvia
    May 5, 2013 at 21:14

1 Answer 1

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I Trace-ed the Information[ f ] command both before and after an invocation of f (with a simpler definition f[x_] := Legended["123", x]). By comparing the results, I found a function System`Dump`makeusageboxes:

trace comparison

which reduces to another function BoxForm`MakeBoxesWithTextFormatting:

Attributes[BoxForm`MakeBoxesWithTextFormatting] = {HoldAllComplete}

BoxForm`MakeBoxesWithTextFormatting[BoxForm`args___] := 
          Block[Evaluate[BoxForm`$TextFormattingForms], 
                Block[{BoxForm`UseTextFormattingQ = True}, MakeBoxes[BoxForm`args]]]

By setting BoxForm`UseTextFormattingQ to False (which is its default global value), the problem seems to be bypassed:

Unprotect[BoxForm`MakeBoxesWithTextFormatting]

BoxForm`MakeBoxesWithTextFormatting[BoxForm`args___] := 
 Block[Evaluate[BoxForm`$TextFormattingForms], MakeBoxes[BoxForm`args]]

Protect[BoxForm`MakeBoxesWithTextFormatting]

correct result

Edit

As it might be safer not to modify system functions, here is another possible workaround (the disadvantage is an extra UpValue item):

f /: Information[f, opt_] := 
 Block[{Internal`ConvertFormTest = (InputForm &)}, Information[f, opt]] /; 
  Internal`ConvertFormTest[] === None

Information[f]

I don't know why, but somehow Internal`ConvertFormTest[] is called after an invocation of f. Playing around it reveals its connection to some box formatting.

trace comparison 2

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  • $\begingroup$ Unfortunately, your edited solution doesn't work with my original function. And your first solution (using Unprotect) still doesn't work with the function I defined in this answer which motivated my question. But certainly some kind of UpValues solution will be the way to go, even if it has to be more hand-tuned... so I upvoted this. I'll wait a little more before accepting it. $\endgroup$
    – Jens
    May 6, 2013 at 3:16
  • $\begingroup$ @Jens Hmm.. More and more looks like a bug, I guess? Will try digging deeper tomorrow.. $\endgroup$
    – Silvia
    May 6, 2013 at 15:31
  • $\begingroup$ I agree it behaves like a bug. Would you mind adding the bug tag to the question (so I don't get in trouble for doing it myself)? $\endgroup$
    – Jens
    May 7, 2013 at 2:38
  • $\begingroup$ @Jens Of course not. Done. $\endgroup$
    – Silvia
    May 7, 2013 at 5:12

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