Problem with DateHistogram Epilog

Question

Bug introduced in 11.3 or earlier and persisting through 13.3.0

@Szabolcs reported this bug on the WRI Redmine bug tracker 11 months ago. It is still "In Progress".

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Epilog in DateHistogram is incorrectly rendered.

$Version
(* "12.2.0 for Mac OS X x86 (64-bit) (December 12, 2020)" *)    

dates = {DateObject[{2021, 01, 10}], DateObject[{2021, 01, 10}], DateObject[{2021, 01, 12}]}

epilog = Inset[Framed[Grid[{{"Mean", 1.5}}, Alignment -> {{Left, Right}}]], Scaled[{1, 1}], ImageScaled[{1, 1}]];

The epilog looks fine

Graphics@epilog

When it is used in DateHistogram, AbsoluteTime is evaluated on the text.

DateHistogram[dates, "Day", Epilog -> epilog]

Reproducible on Wolfram Cloud "12.2.0 for Linux x86 (64-bit) (November 16, 2020)"

This only happens with DateHistogram, it works fine with Histogram. I could find nothing in the documentation regarding the special behavior of Epilog in DateHistogram.

Is this a bug? Any workarounds?

Answer 1

This is certainly a bug: All pairs {a:(_String|_List), b_?(NumberQ[N@#]&)} that appear anywhere in epilog/prolog are replaced with {AbsoluteTime[a], b}.

An example that shows various cases that trigger the mysterious behavior as well as possible work-arounds:

epilog2 = Inset[Framed[
    Grid[{{"FOO", 1.5}, 
        {"FOO", BAR[1.5]},
        {"FOO", "1.5"}, 
        {Defer@"FOO", 1.5},
        {FOO, 1.5},
        {{2021, 1, 1}, 1.5}, 
        {{2021, 1, 1}, "1.5"},
        {{2021, 1, 1}, 1.5, ""},
        {Defer@{2021, 1, 1}, 1.5}
        {{100}, 1.5},
        {Defer@{100}, 1.5}}, 
   Alignment -> {{Left, Right}}]], Scaled[{1, 1}],  ImageScaled[{1, 1}]];

DateHistogram[dates, "Day", Epilog -> epilog2]

$Version

 "11.3.0 for Microsoft Windows (64-bit) (March 7, 2018)"

An alternative work-around is to remove the option Epilog from DateHistogram, wrap it with Show and add the epilog in Show:

Show[DateHistogram[dates, "Day",  ImageSize -> Large], Epilog -> epilog2]

or

Show[DateHistogram[dates, "Day",  ImageSize -> Large], Graphics@epilog2]

The culprit is the replacement rule Charting`timeCoordRule applied to epilog (also prolog and axes origin) expressions inside the function Charting`iDateHistogram:

epilog2 /. Charting`timeCoordRule

Its definition:

GeneralUtilities`PrintDefinitionsLocal[Charting`timeCoordRule]