Improve test for JVM intrinsics:

build.gradle

@@ -252,4 +252,4 @@ tasks.named("dokkaHtmlMultiModule") {
 
 tasks.withType(org.jetbrains.kotlin.gradle.targets.js.npm.tasks.KotlinNpmInstallTask).configureEach {
     args.add("--ignore-engines")
-}
+}

core/commonMain/src/kotlinx/serialization/SerializersCache.kt

@@ -19,7 +19,7 @@ import kotlin.reflect.KType
  * Cache for non-null non-parametrized and non-contextual serializers.
  */
 @ThreadLocal
-private val SERIALIZERS_CACHE = createCache { it.serializerOrNull() ?: it.polymorphicIfInterface() }
+internal val SERIALIZERS_CACHE = createCache { it.serializerOrNull() ?: it.polymorphicIfInterface() }
 
 /**
  * Cache for nullable non-parametrized and non-contextual serializers.

core/commonMain/src/kotlinx/serialization/internal/Platform.common.kt

@@ -6,7 +6,6 @@ package kotlinx.serialization.internal
 
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
-import kotlin.native.concurrent.*
 import kotlin.reflect.*
 
 internal object InternalHexConverter {
@@ -169,6 +168,13 @@ internal interface SerializerCache<T> {
      * Returns cached serializer or `null` if serializer not found.
      */
     fun get(key: KClass<Any>): KSerializer<T>?
+
+    /**
+     * Use SOLELY for test purposes.
+     * May return `false` even if `get` returns value. It means that entry was computed, but not
+     *  stored (behavior for all non-JVM platforms).
+     */
+    fun isStored(key: KClass<*>): Boolean = false
 }
 
 /**

core/commonTest/src/kotlinx/serialization/CachedSerializersTest.kt

@@ -61,21 +61,5 @@ class CachedSerializersTest {
     fun testAbstractSerializersAreSame() {
         assertSame(Abstract.serializer(), Abstract.serializer())
     }
-
-
-    @OptIn(ExperimentalTime::class)
-    @Test
-    fun testSerializersAreIntrinsified() = jvmOnly {
-        val m = SerializersModule {  }
-        val direct = measureTime {
-            Object.serializer()
-        }
-        val directMs = direct.inWholeMicroseconds
-        val indirect = measureTime {
-            m.serializer<Object>()
-        }
-        val indirectMs = indirect.inWholeMicroseconds
-        if (indirectMs > directMs + (directMs / 4)) error("Direct ($directMs) and indirect ($indirectMs) times are too far apart")
-    }
 }
 

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

@@ -52,6 +52,10 @@ private class ClassValueCache<T>(val compute: (KClass<*>) -> KSerializer<T>?) :
             .getOrSet(key.java) { CacheEntry(compute(key)) }
             .serializer
     }
+
+    override fun isStored(key: KClass<*>): Boolean {
+        return classValue.isStored(key.java)
+    }
 }
 
 /**
@@ -85,6 +89,11 @@ private class ClassValueReferences<T> : ClassValue<MutableSoftReference<T>>() {
         return ref.getOrSetWithLock { factory() }
     }
 
+    fun isStored(key: Class<*>): Boolean {
+        val ref = get(key)
+        return ref.reference.get() != null
+    }
+
 }
 
 /**
@@ -134,6 +143,10 @@ private class ConcurrentHashMapCache<T>(private val compute: (KClass<*>) -> KSer
             CacheEntry(compute(key))
         }.serializer
     }
+
+    override fun isStored(key: KClass<*>): Boolean {
+        return cache.containsKey(key.java)
+    }
 }
 
 

core/jvmTest/src/kotlinx/serialization/CachingTest.kt

@@ -6,9 +6,9 @@ package kotlinx.serialization
 
 import kotlinx.serialization.internal.*
 import kotlinx.serialization.modules.*
-import org.junit.Test
 import kotlin.reflect.*
 import kotlin.test.*
+import kotlin.test.Test
 
 class CachingTest {
     @Test
@@ -43,4 +43,21 @@ class CachingTest {
 
         assertEquals(1, factoryCalled)
     }
+
+    @Serializable
+    class Target
+
+    @Test
+    fun testJvmIntrinsics() {
+        val ser1 = Target.serializer()
+        assertFalse(SERIALIZERS_CACHE.isStored(Target::class), "Cache shouldn't have values before call to serializer<T>()")
+        val ser2 = serializer<Target>()
+        assertFalse(
+            SERIALIZERS_CACHE.isStored(Target::class),
+            "Serializer for Target::class is stored in the cache, which means that runtime lookup was performed and call to serializer<Target> was not intrinsified." +
+                "Check that compiler plugin intrinsics are enabled and working correctly."
+        )
+        val ser3 = serializer(typeOf<Target>())
+        assertTrue(SERIALIZERS_CACHE.isStored(Target::class), "Serializer should be stored in cache after typeOf-based lookup")
+    }
 }