Improve detection of "is a NaN" to only consider explicit cases, not `double` overflow/underflow

[cowtowncoder]

Currently it appears that too big (overflow) and too small (underflow) values can produce "Not a Number" (NaN) values from JsonParser, in addition to optionally supported tokens -- only allowed if enabled -- like +INF / -INF / NaN).

But doing this causes problem with BigDecimal handling since such "too big"/"too small" values CAN be represented as BigDecimal, whereas "true" Not-a-Numbers cannot.

So we should improve handling of JsonParser.isNaN() method so that it ONLY indicates explicit Not-a-Number cases, and not overflows.

[pjfanning]

There is similar NaN checking in many Jackson modules. If we want to sort this for 2.16, we should delay the release to look at all the modules. I think NaN handling is a rarely needed use case and that it be better to leave this till after 2.16 release.

[pjfanning]

If we were to tackle this, I would suggest adding isNaNOrInfinite(String) public static method to NumberInput class that does simple String checks instead of trying to parse the input as a number. This could be used in different Jackson modules.

Most of our parsers keep the data as Strings/char[] and only parse to number representation if needed.

[cowtowncoder]

Forgot to tag this as 2.17, I 100% agree that due to timing we would increase risk by making changes now.

I don't have a complete idea on how to go about this, due to differences between Double/double/Float/float (with NaN marker values, but limited ranges) vs BigDecimal (unlimited range but no NaN values).

One existing example of what might be doable are methods canConvertToXxx in JsonNode (canConvertToInt(), canConvertToLong(), canConvertToExactIntegral()).
So could potentially add something like

JsonParser.isInDoubleRange();

which would be roughly same as !isNaNOrInfiniteForDouble(). But also potentially expensive depending on conversion.

But then again there is the question of changing observed behavior of isNaN even if not changing documented one -- Javadocs do not say that isNaN should return true in case value is outside range of Double and that just occurs as a side-effect of parsing into double.

[cowtowncoder]

Was implemented a while ago (forgot to add reference from commit). Tested via

src/test/java/com/fasterxml/jackson/core/read/NonStandardNumberParsingTest.java