4 test failures for master due to default change (see https://github.com/FasterXML/jackson-databind/issues/3406)

[cowtowncoder]

So, looks like some tests need changes now that DeserializationFeature.FAIL_ON_TRAILING_TOKENS is enabled by default.
Databind had a few, mostly bad json in test (trailing quotes or duplicated ']/}at the end). Can also just ensure default for setting isfalse` if that makes more sense.

[pjfanning]

I'll look into the issue. At least 1 of the failing tests serializes an object instance with Jackson and tries to deserialize the resultant json with Jackson as a round trip. Could be an edge case where empty json is created.

[pjfanning]

I can confirm one test seralizes an object with no fields and the resultant json is {}.
The test then fails when we try to deserialize {}. @cowtowncoder is this possibly a bug in Jackson-Databind? Isn't {} valid json? Is it not a valid representation of empty data for a class with no fields?

[pjfanning]

I have a similar test in the same test class that serializes an object instance as {"field":"bar"}. Jackson fails to parse this now when I try to get Jackson to deserialize this json.

This error looks like:

Trailing token (of type PROPERTY_NAME) found after value (bound as `tools.jackson.module.scala.deser.CaseObjectDeserializerTest$Foo$`): not allowed as per `DeserializationFeature.FAIL_ON_TRAILING_TOKENS`
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); byte offset: #UNKNOWN]
tools.jackson.databind.exc.MismatchedInputException: Trailing token (of type PROPERTY_NAME) found after value (bound as `tools.jackson.module.scala.deser.CaseObjectDeserializerTest$Foo$`): not allowed as per `DeserializationFeature.FAIL_ON_TRAILING_TOKENS`
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); byte offset: #UNKNOWN]
	at tools.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:56)
	at tools.jackson.databind.DeserializationContext.reportTrailingTokens(DeserializationContext.java:1829)
	at tools.jackson.databind.ObjectMapper._verifyNoTrailingTokens(ObjectMapper.java:2687)
	at tools.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2581)
	at tools.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1570)
	at tools.jackson.module.scala.deser.CaseObjectDeserializerTest.$anonfun$new$2(CaseObjectDeserializerTest.scala:36)

[cowtowncoder]

{} is definitely legal. But most commonly these seem to be from either actual extra fluff -- I noticed that single opening quote can be detected and reported as likely trailing JsonToken.VALUE_STRING -- or Deserializer actually not consuming content.

In case of PROPERTY_NAME it could specifically happen.
So maybe digging bit into CaseObjectDeserializer would work -- is there any chance of it leaving content unread?

In case of {"field":"bar"} that'd mean that deserializer simply returns something without consuming "field":"bar"} part (opening { has been consumed).

[pjfanning]

Reasonable point. The ScalaObjectDeserializer was not consuming the tokens. e755834 fixes the tests but sort of shows that deserializing Scala Objects (singleton class instances in Java) is a bit of an edge case and the code in ScalaObjectDeserializer is just not right. I'll see if it can be improved. The change I've added gets around the immediate issue. I will backport it to branch 2.19.

[cowtowncoder]

Excellent! We did find a few test problems in jackson-databind, was useful. But no actual bugs (as far as I remember).