Add radix property to JsonFormat (#320)

[tiger9800]

To implement FasterXML/jackson-databind#5317, we would like to use radix property of the @JsonFromat annotation. We make sure to add it to JsonFormat.Value to parallel the behavior of other properties of the @jsonformat annotation.

[cowtowncoder]

We have one potential problem here: there's no real "default" marker here, so any use of @JsonFormat would cause override with radix 10 -- since there's no way to tell explicit "10" from default (when radix omitted. That is these are equivalent:

@JsonFormat(shape=Shape.STRING, radix=10)
@JsonFormat(shape=Shape.STRING)

which becomes problem when using global or per-type defaults.

So I think it is necessary to instead use "magic constant" to indicate "use default"; -1 would be traditional choice. This would need to be translated when requested (separate accessor for translating and "raw" value?), and considered when merging Value instances.

[tiger9800]

Wouldn't we be fine with 10 being a default? Radix only becomes relevant when we are serializing a Number and shape is String, and currently we always serialize numbers as strings in base 10. We will keep doing so if @JsonFormat(shape=Shape.STRING, radix=10) or @JsonFormat(shape=Shape.STRING). My plan was to even check in NumberSerializer against @JsonFromat.DEFAULT_RADIX and decide if we need to employ the special DifferentRadixSerializer.

[cowtowncoder]

@tiger9800 Problem is not direct @JsonFormat usage but the case where global/type defaults are set to, for example, use radix 16 (for hex). If so, that'd be overwritten by @JsonFormat without radix property (or rather, one for which default of 10 is applied).
Behavior in such cases should vary b/w explicit radix value and default.
Bit like why OptBoolean is used instead of boolean for some annotation to distinguish between "true", "false" and "default".

[tiger9800]

Oh I see, we can put a global config override of 16 and then apply an annotation @JsonFormat(shape=Shape.STRING) to some property that is a subclass of Number. We would expect the Number to be serialized as a hex string, but it will be serialized as a base-10 string because @JsonFormat(shape=Shape.STRING) with a default radix of 10 had higher precedence.

Great catch, thank you. Will fix!

[cowtowncoder]

@tiger9800 Exactly! We have had this challenge for some annotations before which is why I recognized it :)

[tiger9800]

Added the marker default value. For translating from raw value, we have JsonFormat.Value#hasNonDefaultRadix, so I imagine this is enough. Please let me know what you think.

[cowtowncoder]

Should not check against 10 as ObjectMapper may specify other default radix

[cowtowncoder]

Close; left couple of notes for changes.

[cowtowncoder]

A unit test failure wrt String representation.