DeserializationProblemHandler is not invoked when trying to deserializing String

[zigzago]

Describe the bug
KMongo (https://github.com/Litote/kmongo) uses DeserializationProblemHandler in order to patch some unexpected deserialization issue (see https://github.com/Litote/kmongo/blob/master/kmongo-jackson-mapping/src/main/kotlin/org/litote/kmongo/jackson/StringDeserializationProblemHandler.kt#L38 )

in 2.12.0 I got this stacktrace (and DeserializationProblemHandler is not called)

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`)
 at [Source: de.undercouch.bson4jackson.io.LittleEndianInputStream@2c7d121c; pos: 24] (through reference chain: org.litote.kmongo.issues.Issue85ObjectIdIsNotProperlyDeserializedInAStringPropertyWhenPropertyIsInherited$MainData["_id"])

	at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
	at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1590)
	at com.fasterxml.jackson.databind.DeserializationContext.extractScalarFromObject(DeserializationContext.java:872)
	at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:62)
	at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:11)
	at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:542)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:565)

Version information
Which Jackson version(s) was this for? 2.12.0
2.11.3 is ok

To Reproduce

This KMongo test fails: https://github.com/Litote/kmongo/blob/master/kmongo/src/test/kotlin/org/litote/kmongo/issues/Issue85ObjectIdIsNotProperlyDeserializedInAStringPropertyWhenPropertyIsInherited.kt#L70

Expected behavior
DeserializationProblemHandler invoked

Additional context
Digging in the code (StringDeserializer line 61):

// 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
        if (t == JsonToken.START_OBJECT) {
            return ctxt.extractScalarFromObject(p, this, _valueClass);
        }
(...)
 return (String) ctxt.handleUnexpectedToken(_valueClass, p);

[cowtowncoder]

Thank you for reporting this: sounds like a regression in that DeserializationProblemHandler.handleUnexpectedToken(..) used to be called earlier but now new default extractScalarFromObject does not call it.

[cowtowncoder]

Fixed for 2.12.1 -- thank you for reporting this!