Wrong path reported by json parser for unknown key

[larshagencognite]

Describe the bug
When parsing json with unknown key, the path in the error message will only be correct if the unknown key is the first key in the object. If it is not the first key, the reported path will include the previous key at the same level as the unknown key.

To Reproduce

package ...

import kotlinx.serialization.Serializable
import kotlinx.serialization.SerializationException
import kotlinx.serialization.json.Json
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.assertThrows

class UnknownKeyParsingTest {
    @Serializable
    data class MyClass(val field: String)

    @Test
    fun testUnknownKey() {
        assertThrows<SerializationException> {
            Json.decodeFromString<MyClass>("""{ "unknownField": 123 }""")
        }.also {
            assertEquals(
                """
                    Unexpected JSON token at offset 3: Encountered an unknown key 'unknownField' at path: $
                    Use 'ignoreUnknownKeys = true' in 'Json {}' builder to ignore unknown keys.
                    JSON input: { "unknownField": 123 }
                """.trimIndent(),
                it.message
            )
        }
    }

    @Test
    fun testUnknownKeyAsSecondKey() {
        assertThrows<SerializationException> {
            Json.decodeFromString<MyClass>("""{ "field": "value", "unknownField": 123 }""")
        }.also {
            assertEquals(
                """
                    Unexpected JSON token at offset 21: Encountered an unknown key 'unknownField' at path: $.field
                    Use 'ignoreUnknownKeys = true' in 'Json {}' builder to ignore unknown keys.
                    JSON input: { "field": "value", "unknownField": 123 }
                """.trimIndent(),
                it.message
            )
        }
    }
}

Expected behavior
The expected behaviour is that the reported path is for the object that contains the unknown key, not for a sibling key.

Environment

• Kotlin version: 2.0.21
• Library version: 1.7.3
• Kotlin platforms: JVM

[sandwwraith]

Thanks for the report, I'll take a look