Added support for null values for nullable enums in lanient mode (#2176)

Fixed #2170

Co-authored-by: Leonid Startsev <[email protected]>

formats/json-tests/commonTest/src/kotlinx/serialization/json/JsonCoerceInputValuesTest.kt

@@ -5,7 +5,6 @@
 package kotlinx.serialization.json
 
 import kotlinx.serialization.*
-import kotlinx.serialization.json.internal.*
 import kotlinx.serialization.test.assertFailsWithSerial
 import kotlin.test.*
 
@@ -25,6 +24,11 @@ class JsonCoerceInputValuesTest : JsonTestBase() {
  val foo: String
  )
 
+ @Serializable
+ data class NullableEnumHolder(
+ val enum: SampleEnum?
+ )
+
  val json = Json {
  coerceInputValues = true
  isLenient = true
@@ -99,4 +103,13 @@ class JsonCoerceInputValuesTest : JsonTestBase() {
  assertEquals(expected, json.decodeFromString(MultipleValues.serializer(), input), "Failed on input: $input")
  }
  }
+
+ @Test
+ fun testNullSupportForEnums() = parametrizedTest(json) {
+ var decoded = decodeFromString<NullableEnumHolder>("""{"enum": null}""")
+ assertNull(decoded.enum)
+
+ decoded = decodeFromString<NullableEnumHolder>("""{"enum": OptionA}""")
+ assertEquals(SampleEnum.OptionA, decoded.enum)
+ }
 }

formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonNamesMap.kt

@@ -98,12 +98,16 @@ internal fun SerialDescriptor.getJsonNameIndexOrThrow(json: Json, name: String,
 @OptIn(ExperimentalSerializationApi::class)
 internal inline fun Json.tryCoerceValue(
  elementDescriptor: SerialDescriptor,
- peekNull: () -> Boolean,
+ peekNull: (consume: Boolean) -> Boolean,
  peekString: () -> String?,
  onEnumCoercing: () -> Unit = {}
 ): Boolean {
- if (!elementDescriptor.isNullable && peekNull()) return true
+ if (!elementDescriptor.isNullable && peekNull(true)) return true
  if (elementDescriptor.kind == SerialKind.ENUM) {
+ if (elementDescriptor.isNullable && peekNull(false)) {
+ return false
+ }
+
  val enumValue = peekString()
  ?: return false // if value is not a string, decodeEnum() will throw correct exception
  val enumIndex = elementDescriptor.getJsonNameIndex(this, enumValue)

formats/json/commonMain/src/kotlinx/serialization/json/internal/StreamingJsonDecoder.kt

@@ -133,7 +133,7 @@ internal open class StreamingJsonDecoder(
  }
 
  override fun decodeNotNullMark(): Boolean {
- return !(elementMarker?.isUnmarkedNull ?: false) && lexer.tryConsumeNotNull()
+ return !(elementMarker?.isUnmarkedNull ?: false) && !lexer.tryConsumeNull()
  }
 
  override fun decodeNull(): Nothing? {
@@ -208,7 +208,7 @@ internal open class StreamingJsonDecoder(
  */
  private fun coerceInputValue(descriptor: SerialDescriptor, index: Int): Boolean = json.tryCoerceValue(
  descriptor.getElementDescriptor(index),
- { !lexer.tryConsumeNotNull() },
+ { lexer.tryConsumeNull(it) },
  { lexer.peekString(configuration.isLenient) },
  { lexer.consumeString() /* skip unknown enum string*/ }
  )

formats/json/commonMain/src/kotlinx/serialization/json/internal/lexer/AbstractJsonLexer.kt

@@ -244,25 +244,28 @@ internal abstract class AbstractJsonLexer {
 
  /**
  * Tries to consume `null` token from input.
- * Returns `true` if the next 4 chars in input are not `null`,
- * `false` otherwise and consumes it.
+ * Returns `false` if the next 4 chars in input are not `null`,
+ * `true` otherwise and consumes it if [doConsume] is `true`.
  */
- fun tryConsumeNotNull(): Boolean {
+ fun tryConsumeNull(doConsume: Boolean = true): Boolean {
  var current = skipWhitespaces()
  current = prefetchOrEof(current)
  // Cannot consume null due to EOF, maybe something else
  val len = source.length - current
- if (len < 4 || current == -1) return true
+ if (len < 4 || current == -1) return false
  for (i in 0..3) {
- if (NULL[i] != source[current + i]) return true
+ if (NULL[i] != source[current + i]) return false
  }
  /*
  * If we're in lenient mode, this might be the string with 'null' prefix,
  * distinguish it from 'null'
  */
- if (len > 4 && charToTokenClass(source[current + 4]) == TC_OTHER) return true
- currentPosition = current + 4
- return false
+ if (len > 4 && charToTokenClass(source[current + 4]) == TC_OTHER) return false
+
+ if (doConsume) {
+ currentPosition = current + 4
+ }
+ return true
  }
 
  open fun skipWhitespaces(): Int {