Drop synthetic class kind Function, drop Metadata#xi

compiler/backend/src/org/jetbrains/kotlin/codegen/ClosureCodegen.java

@@ -231,7 +231,6 @@ public class ClosureCodegen extends MemberCodegen<KtElement> {
             @Override
             public Unit invoke(AnnotationVisitor av) {
                 writeAnnotationData(av, serializer, functionProto, false);
-                av.visit(JvmAnnotationNames.SYNTHETIC_CLASS_KIND_FIELD_NAME, KotlinClassHeader.SyntheticClassKind.FUNCTION.getId());
                 return Unit.INSTANCE;
             }
         });

compiler/testData/codegen/boxWithStdlib/reflection/lambdaClasses/parameterNamesAndNullability.kt

@@ -34,17 +34,10 @@ fun extensionFunExpr() {
     assertEquals(null, g.parameters.single().name)
 }
 
-fun customFunction() {
-    val f = object : Function<String> {}
-    assertNull(f.reflect())
-}
-
 fun box(): String {
     lambda()
     funExpr()
     extensionFunExpr()
 
-    customFunction()
-
     return "OK"
 }

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/JvmAnnotationNames.java

@@ -44,7 +44,6 @@ public final class JvmAnnotationNames {
     public static final String KIND_FIELD_NAME = "k";
     public static final String METADATA_DATA_FIELD_NAME = "d1";
     public static final String METADATA_STRINGS_FIELD_NAME = "d2";
-    public static final String SYNTHETIC_CLASS_KIND_FIELD_NAME = "xi";
     public static final String METADATA_MULTIFILE_CLASS_NAME_FIELD_NAME = "xs";
     public static final String DATA_FIELD_NAME = "data";
     public static final String STRINGS_FIELD_NAME = "strings";

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/header/KotlinClassHeader.kt

@@ -44,9 +44,5 @@ class KotlinClassHeader(
         }
     }
 
-    enum class SyntheticClassKind(val id: Int) {
-        FUNCTION(1),
-    }
-
     override fun toString() = "$kind version=$metadataVersion"
 }

core/reflection.jvm/src/kotlin/reflect/jvm/reflectLambda.kt

@@ -19,7 +19,6 @@
 package kotlin.reflect.jvm
 
 import org.jetbrains.kotlin.load.kotlin.JvmNameResolver
-import org.jetbrains.kotlin.load.kotlin.header.KotlinClassHeader
 import org.jetbrains.kotlin.serialization.ProtoBuf
 import org.jetbrains.kotlin.serialization.deserialization.DeserializationContext
 import org.jetbrains.kotlin.serialization.deserialization.MemberDeserializer
@@ -39,7 +38,6 @@ import kotlin.reflect.jvm.internal.getOrCreateModule
  */
 fun <R> Function<R>.reflect(): KFunction<R>? {
     val annotation = javaClass.getAnnotation(Metadata::class.java) ?: return null
-    if (annotation.xi != KotlinClassHeader.SyntheticClassKind.FUNCTION.id) return null
     val input = BitEncoding.decodeBytes(annotation.d1).inputStream()
     val nameResolver = JvmNameResolver(
             JvmProtoBuf.StringTableTypes.parseDelimitedFrom(input, JvmProtoBufUtil.EXTENSION_REGISTRY), annotation.d2

core/runtime.jvm/src/kotlin/Metadata.kt

@@ -55,14 +55,5 @@ internal annotation class Metadata(
         /**
          * An extra string. For a multi-file part class, internal name of the facade class.
          */
-        val xs: String = "",
+        val xs: String = ""
-        /**
-         * An extra integer. For a synthetic class, the specific kind of this class which is one of the following:
-         *
-         * 1 Anonymous class for a lambda or a function reference
-         *
-         * A value other than this (e.g. 0) or a missing value means this is a synthetic class of some other sort.
-         * This kind has no effect on the compiler because it doesn't read synthetic class metadata. It may be used in IDEs and tools.
-         */
-        val xi: Int = 0
 )