Serialization of isXXX fields changed in 2.10.1, adding is prefix which was previously absent

[LichKing-lee]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
failure on jackson-module-kotlin 2.10.1 or higher

class JacksonTest {
    private lateinit var objectMapper: ObjectMapper

    @BeforeEach
    fun setUp() {
        objectMapper = jacksonObjectMapper()
    }

    @Test
    fun json() {
        val p = Person(32, "changyong", true)
        val json = objectMapper.writeValueAsString(p)

        val expected = """
            {"age":32,"name":"changyong","junior":true}
        """.trimIndent()

        assertThat(json).isEqualTo(expected)
    }
}

This result is {"age":32,"name":"changyong","isJunior":true}

Expected behavior
pass on jackson-module-kotlin 2.10.0 or lower

class JacksonTest {
    private lateinit var objectMapper: ObjectMapper

    @BeforeEach
    fun setUp() {
        objectMapper = jacksonObjectMapper()
    }

    @Test
    fun json() {
        val p = Person(32, "changyong", true)
        val json = objectMapper.writeValueAsString(p)

        val expected = """
            {"age":32,"name":"changyong","junior":true}
        """.trimIndent()

        assertThat(json).isEqualTo(expected)
    }
}

This result is {"age":32,"name":"changyong","junior":true}

Versions
Kotlin:
Jackson-module-kotlin: 2.10.1 or higher
Jackson-databind: 2.10.4

Additional context
Does changed spec on serialize isXXX properties? or bug?

Thank you.

[LichKing-lee]

Attach Person class

data class Person(
    val age: Int,
    val name: String,
    val isJunior: Boolean
)

[LichKing-lee]

I looked #80 and release note at https://github.com/FasterXML/jackson-module-kotlin/blob/master/release-notes/VERSION-2.x
Is there a way to keep it existing on 2.10.1 or higher?

[usulkies]

Hi @LichKing-lee .
We also experienced some severe bugs when we upgraded to Jackson 2.10.
But after all, this is the right behavior. The property name should be serialized as-is and the "is" should not be omitted. Also, this was not working on both serialization and deserialization. So services could not talk to each other because the receiving service didn't knew the property name without the "is".

There is a workaround if it's breaking things, and this is to add the @JsonProperty ("junior") annotation on the property and then it'll be serialized like before.
You can also configure a custom strategy to your mapper when the function name is starting with "is" and it's a boolean (Jackson sees Kotlin's properties as functions).

[dinomite]

@tokuhirom described it succinctly in #394:

Serialization result of the following code is incompatible between jackson-module-kotlin 2.10.0 and 2.10.1.

data class FooKt(var isUsingBar: Boolean)

Jackson version: 2.10.0
{"usingBar":true}
Jackson version: 2.10.1
{"isUsingBar":true}

They also create a repro https://github.com/tokuhirom/jackson-field-name-incompatiblity

[dinomite]

We will track this in #337