Do not automatically trim trailing whitespace from `java.util.regex.Pattern` values

[jberger]

Is your feature request related to a problem? Please describe.
I have a large JSON structure containing arrays of Patterns to match as part of a lookup. Some contain patterns that end in an escaped literal space, ie \\ . When this happens the trim behavior (that I had to search rather hard to find) causes the pattern to now end in an escape character which then fails to compile as a Pattern.

Describe the solution you'd like
While I can understand trimming string values in XML as an unfortunate side-effect of the whitespace independent structure, in JSON I would have expected to be somewhat more literal. Even so if this is the behavior that more people want, can you please at least add an attribute that would prevent trimming?

Usage example
Something like .with(DeserializationFeature.NO_TRIM) would be sufficient.

Additional context
I'm sure I must have missed something in the documentation but I was not easy to find that values were supposed to be trimmed. Indeed my searching mostly found people asking in various forums how to cause the values to be trimmed, not to prevent them from being trimmed. Clarifying that behavior in the documentation would be nice as well.

Thanks

[cowtowncoder]

(EDITED)

I can't promise I'll have time to work on this, but one thing that would help whoever had time to tackle this feature request would be to file a failing unit test showing expected behavior that is not occurring.
That is, case of giving what is deemed invalid input, and expecting an exception (which will not happen by default).
This would help also verify understanding of what is being asked.

Oh: I suspect there might already be a way to reconfigure new-ish "Coercion Config" setting -- by default it is rather permissive, but it may be possible to change that easily.
Given a test case this could be tested relatively easily.

[cowtowncoder]

Hmmmh. Looking at reference FromStringDeserializer, realized that I misunderstood the issue.
It is NOT about empty vs blank Strings (for which Coercion Config setting matters), but actual behavior for a set of "simple" JDK scalar types, as support from FromStringDeserializer.

This is both easier and more difficult thing since it is sort of irregular...

@jberger how about an alternative of specifically disabling trimming for Pattern (and if you can think of other JDK types handled for which similar issues might occur) instead? I understand the issue wrt trailing space, but I think it is in general dangerous for that type.

[cowtowncoder]

I think that an improvement to handling Patterns, specifically, would fit in 2.13(.1) patch, changing target.