Remove special casing for Unit in kotlinx.serialization

Unignore test since it is in muted list and auto-generated

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/TypeUtil.kt

@@ -41,8 +41,7 @@ import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializationPackage
 open class SerialTypeInfo(
     val property: SerializableProperty,
     val elementMethodPrefix: String,
-    val serializer: ClassDescriptor? = null,
+    val serializer: ClassDescriptor? = null
-    val unit: Boolean = false
 )
 
 fun AbstractSerialGenerator.findAddOnSerializer(propertyType: KotlinType, module: ModuleDescriptor): ClassDescriptor? {
@@ -75,7 +74,6 @@ fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty): S
 //          alternative:  KotlinBuiltIns.getPrimitiveType(T)!!.typeName.identifier
         )
         KotlinBuiltIns.isString(T) -> SerialTypeInfo(property, "String")
-        KotlinBuiltIns.isUnit(T) -> SerialTypeInfo(property, "Unit", unit = true)
         KotlinBuiltIns.isNonPrimitiveArray(T.toClassDescriptor!!) -> {
             val serializer = property.serializableWith?.toClassDescriptor ?: property.module.findClassAcrossModuleDependencies(
                 referenceArraySerializerId

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializerJsTranslator.kt

@@ -335,13 +335,6 @@ open class SerializerJsTranslator(
                             localProps[i],
                             call
                         ).makeStmt()
-                        // need explicit unit instance
-                        if (sti.unit) {
-                            +JsAstUtils.assignment(
-                                localProps[i],
-                                context.getQualifiedReference(property.type.builtIns.unit)
-                            ).makeStmt()
-                        }
                         // char unboxing crutch
                         if (KotlinBuiltIns.isCharOrNullableChar(property.type)) {
                             val coerceTo = TranslationUtils.getReturnTypeForCoercion(property.descriptor)

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt

@@ -101,21 +101,21 @@ fun InstructionAdapter.genKOutputMethodCall(
     val sti = generator.getSerialTypeInfo(property, propertyType)
     val useSerializer = if (fromClassStartVar == null) stackValueSerializerInstanceFromSerializer(classCodegen, sti, generator)
     else stackValueSerializerInstanceFromClass(classCodegen, sti, fromClassStartVar, generator)
-    val actualType = if (!sti.unit) ImplementationBodyCodegen.genPropertyOnStack(
+    val actualType = ImplementationBodyCodegen.genPropertyOnStack(
         this,
         expressionCodegen.context,
         property.descriptor,
         propertyOwnerType,
         ownerVar,
         classCodegen.state
-    ) else null
+    )
     actualType?.type?.let { type -> StackValue.coerce(type, sti.type, this) }
     invokeinterface(
         kOutputType.internalName,
         CallingConventions.encode + sti.elementMethodPrefix + (if (useSerializer) "Serializable" else "") + CallingConventions.elementPostfix,
         "(" + descType.descriptor + "I" +
                 (if (useSerializer) kSerialSaverType.descriptor else "") +
-                (if (sti.unit) "" else sti.type.descriptor) + ")V"
+                (sti.type.descriptor) + ")V"
     )
 }
 
@@ -394,9 +394,8 @@ class JVMSerialTypeInfo(
     property: SerializableProperty,
     val type: Type,
     nn: String,
-    serializer: ClassDescriptor? = null,
+    serializer: ClassDescriptor? = null
-    unit: Boolean = false
+) : SerialTypeInfo(property, nn, serializer)
-) : SerialTypeInfo(property, nn, serializer, unit)
 
 fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty, type: Type): JVMSerialTypeInfo {
     fun SerializableInfo(serializer: ClassDescriptor?) =
@@ -451,8 +450,6 @@ fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty, ty
             // no explicit serializer for this property. Check other built in types
             if (KotlinBuiltIns.isString(property.type))
                 return JVMSerialTypeInfo(property, Type.getType("Ljava/lang/String;"), "String")
-            if (KotlinBuiltIns.isUnit(property.type))
-                return JVMSerialTypeInfo(property, Type.getType("Lkotlin/Unit;"), "Unit", unit = true)
             // todo: more efficient enum support here, but only for enums that don't define custom serializer
             // otherwise, it is a serializer for some other type
             val serializer = property.serializableWith?.toClassDescriptor

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/SerializerCodegenImpl.kt

@@ -486,7 +486,7 @@ open class SerializerCodegenImpl(
                         (if (useSerializer) kSerialLoaderType.descriptor else "")
                         + (if (unknownSer) AsmTypes.K_CLASS_TYPE.descriptor else "")
                         + (if (update) sti.type.descriptor else "")
-                        + ")" + (if (sti.unit) "V" else sti.type.descriptor)
+                        + ")" + (sti.type.descriptor)
             )
         }
 
@@ -508,11 +508,7 @@ open class SerializerCodegenImpl(
             produceCall(false)
         }
 
-        if (sti.unit) {
+        StackValue.coerce(sti.type, propertyType, this)
-            StackValue.putUnitInstance(this)
-        } else {
-            StackValue.coerce(sti.type, propertyType, this)
-        }
         store(propertyVar, propertyType)
     }
 

plugins/kotlin-serialization/kotlin-serialization-compiler/test/org/jetbrains/kotlinx/serialization/SerializationIrBytecodeListingTestGenerated.java

@@ -9,7 +9,6 @@ import com.intellij.testFramework.TestDataPath;
 import org.jetbrains.kotlin.test.JUnit3RunnerWithInners;
 import org.jetbrains.kotlin.test.KotlinTestUtils;
 import org.jetbrains.kotlin.test.TestMetadata;
-import org.junit.Ignore;
 import org.junit.runner.RunWith;
 
 import java.io.File;
@@ -20,7 +19,6 @@ import java.util.regex.Pattern;
 @TestMetadata("plugins/kotlin-serialization/kotlin-serialization-compiler/testData/codegen")
 @TestDataPath("$PROJECT_ROOT")
 @RunWith(JUnit3RunnerWithInners.class)
-@Ignore // todo: unignore when new serialziation version will be publicly available & update it in build.gradle.kts
 public class SerializationIrBytecodeListingTestGenerated extends AbstractSerializationIrBytecodeListingTest {
     private void runTest(String testDataFilePath) throws Exception {
         KotlinTestUtils.runTest(this::doTest, this, testDataFilePath);

tests/mute-common.csv

@@ -54,6 +54,6 @@ org.jetbrains.kotlin.psi.injection.StringInterpolationInjectionTest.testInterpol
 org.jetbrains.kotlin.nj2k.NewJavaToKotlinConverterSingleFileTestGenerated.Issues.testKt_8170, KT-36459
 org.jetbrains.kotlin.shortenRefs.ShortenRefsTestGenerated.testExtensionForObject2, Always red
 org.jetbrains.kotlin.util.KotlinVersionsTest.testVersionsAreConsistent, KT-35567
-org.jetbrains.kotlinx.serialization.SerializationIrBytecodeListingTestGenerated.testBasic, Broken between 20 nov and 10 dec
+org.jetbrains.kotlinx.serialization.SerializationIrBytecodeListingTestGenerated.testBasic, wait until new serialziation runtime version will be publicly available
 org.jetbrains.kotlin.jvm.compiler.CompileKotlinAgainstJavaTestGenerated.WithAPT.testClassWithTypeParameter, KT-36448
 org.jetbrains.kotlin.jvm.compiler.CompileKotlinAgainstJavaTestGenerated.WithoutAPT.testClassWithTypeParameter, KT-36448