Fix IllegalAccessException being thrown on an attempt to retrieve ser…

…ializer for some private implementation classes from stdlib.

Fixes #2449

core/jvmMain/src/kotlinx/serialization/internal/Platform.kt

@@ -153,6 +153,9 @@ private fun <T : Any> Class<T>.createEnumSerializer(): KSerializer<T> {
 }
 
 private fun <T : Any> Class<T>.findObjectSerializer(): KSerializer<T>? {
+    // Special case to avoid IllegalAccessException on Java11+
+    // There are no serializable objects in the stdlib anyway.
+    if (this.canonicalName.let { it.startsWith("java.") || it.startsWith("kotlin.") }) return null
     // Check it is an object without using kotlin-reflect
     val field =
         declaredFields.singleOrNull { it.name == "INSTANCE" && it.type == this && Modifier.isStatic(it.modifiers) }

formats/json-tests/jvmTest/src/kotlinx/serialization/JavaCollectionsTest.kt

@@ -17,14 +17,16 @@
 package kotlinx.serialization
 
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.test.typeTokenOf
 import org.junit.Test
 import java.util.HashMap
 import java.util.HashSet
 import kotlin.collections.LinkedHashMap
 import kotlin.collections.Map
 import kotlin.collections.hashMapOf
 import kotlin.collections.hashSetOf
-import kotlin.test.assertEquals
+import kotlin.reflect.*
+import kotlin.test.*
 
 
 class JavaCollectionsTest {
@@ -38,7 +40,7 @@ class JavaCollectionsTest {
     )
 
     @Test
-    fun test() {
+    fun testJavaCollectionsInsideClass() {
         val original = HasHashMap("42", hashMapOf(1 to "1", 2 to "2"), hashSetOf(11), LinkedHashMap(), null)
         val serializer = HasHashMap.serializer()
         val string = Json.encodeToString(serializer = serializer, value = original)
@@ -49,4 +51,55 @@ class JavaCollectionsTest {
         val restored = Json.decodeFromString(deserializer = serializer, string = string)
         assertEquals(expected = original, actual = restored)
     }
+
+    @Test
+    fun testTopLevelMaps() {
+        // Returning null here is a deliberate choice: map constructor functions may return different specialized
+        // implementations (e.g., kotlin.collections.EmptyMap or java.util.Collections.SingletonMap)
+        // that may or may not be generic. Since we generally cannot return a generic serializer using Java class only,
+        // all attempts to get map serializer using only .javaClass should return null.
+        assertNull(serializerOrNull(emptyMap<String, String>().javaClass))
+        assertNull(serializerOrNull(mapOf<String, String>("a" to "b").javaClass))
+        assertNull(serializerOrNull(mapOf<String, String>("a" to "b", "b" to "c").javaClass))
+        // Correct ways of retrieving map serializer:
+        assertContains(
+            serializer(typeTokenOf<Map<String, String>>()).descriptor.serialName,
+            "kotlin.collections.LinkedHashMap"
+        )
+        assertContains(
+            serializer(typeTokenOf<java.util.LinkedHashMap<String, String>>()).descriptor.serialName,
+            "kotlin.collections.LinkedHashMap"
+        )
+        assertContains(
+            serializer(typeOf<LinkedHashMap<String, String>>()).descriptor.serialName,
+            "kotlin.collections.LinkedHashMap"
+        )
+    }
+
+    @Test
+    fun testTopLevelSetsAndLists() {
+        // Same reasoning as for maps
+        assertNull(serializerOrNull(emptyList<String>().javaClass))
+        assertNull(serializerOrNull(listOf<String>("a").javaClass))
+        assertNull(serializerOrNull(listOf<String>("a", "b").javaClass))
+        assertNull(serializerOrNull(emptySet<String>().javaClass))
+        assertNull(serializerOrNull(setOf<String>("a").javaClass))
+        assertNull(serializerOrNull(setOf<String>("a", "b").javaClass))
+        assertContains(
+            serializer(typeTokenOf<Set<String>>()).descriptor.serialName,
+            "kotlin.collections.LinkedHashSet"
+        )
+        assertContains(
+            serializer(typeTokenOf<List<String>>()).descriptor.serialName,
+            "kotlin.collections.ArrayList"
+        )
+        assertContains(
+            serializer(typeTokenOf<java.util.LinkedHashSet<String>>()).descriptor.serialName,
+            "kotlin.collections.LinkedHashSet"
+        )
+        assertContains(
+            serializer(typeTokenOf<java.util.ArrayList<String>>()).descriptor.serialName,
+            "kotlin.collections.ArrayList"
+        )
+    }
 }

formats/json-tests/jvmTest/src/kotlinx/serialization/features/SerializerByTypeTest.kt

@@ -209,15 +209,6 @@ class SerializerByTypeTest {
         assertEquals(expected, json.encodeToString(serial2 as KSerializer<T>, value))
     }
 
-    @PublishedApi
-    internal open class TypeBase<T>
-
-    public inline fun <reified T> typeTokenOf(): Type {
-        val base = object : TypeBase<T>() {}
-        val superType = base::class.java.genericSuperclass!!
-        return (superType as ParameterizedType).actualTypeArguments.first()!!
-    }
-
     class IntBox(val i: Int)
 
     object CustomIntSerializer : KSerializer<IntBox> {

formats/json-tests/jvmTest/src/kotlinx/serialization/test/TypeToken.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2017-2023 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.serialization.test
+
+import java.lang.reflect.*
+
+
+@PublishedApi
+internal open class TypeBase<T>
+
+public inline fun <reified T> typeTokenOf(): Type {
+    val base = object : TypeBase<T>() {}
+    val superType = base::class.java.genericSuperclass!!
+    return (superType as ParameterizedType).actualTypeArguments.first()!!
+}