diff --git a/libraries/kotlinx-metadata/jvm/api/kotlinx-metadata-jvm.api b/libraries/kotlinx-metadata/jvm/api/kotlinx-metadata-jvm.api
index b78e9f6b9ad..7034d869246 100644
--- a/libraries/kotlinx-metadata/jvm/api/kotlinx-metadata-jvm.api
+++ b/libraries/kotlinx-metadata/jvm/api/kotlinx-metadata-jvm.api
@@ -1584,11 +1584,8 @@ public final class kotlinx/metadata/jvm/KotlinModuleMetadata$Companion {
 	public static synthetic fun write$default (Lkotlinx/metadata/jvm/KotlinModuleMetadata$Companion;Lkotlinx/metadata/jvm/KmModule;[IILjava/lang/Object;)[B
 }
 
-public final class kotlinx/metadata/jvm/KotlinModuleMetadata$Writer : kotlinx/metadata/jvm/KmModuleVisitor {
+public final class kotlinx/metadata/jvm/KotlinModuleMetadata$Writer {
 	public fun <init> ()V
-	public fun visitAnnotation (Lkotlinx/metadata/KmAnnotation;)V
-	public fun visitOptionalAnnotationClass ()Lkotlinx/metadata/KmClassVisitor;
-	public fun visitPackageParts (Ljava/lang/String;Ljava/util/List;Ljava/util/Map;)V
 	public final fun write ([I)[B
 	public static synthetic fun write$default (Lkotlinx/metadata/jvm/KotlinModuleMetadata$Writer;[IILjava/lang/Object;)[B
 }
diff --git a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/JvmExtensionVisitors.kt b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/JvmExtensionVisitors.kt
index 89ff3a9e63c..ac64ce6a913 100644
--- a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/JvmExtensionVisitors.kt
+++ b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/JvmExtensionVisitors.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata.jvm
 
@@ -12,7 +12,7 @@ import org.jetbrains.kotlin.metadata.jvm.deserialization.JvmProtoBufUtil
 /**
  * A visitor containing the common code to visit JVM extensions for Kotlin declaration containers, such as classes and package fragments.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public abstract class JvmDeclarationContainerExtensionVisitor @JvmOverloads constructor(
     protected open val delegate: JvmDeclarationContainerExtensionVisitor? = null
 ) : KmDeclarationContainerExtensionVisitor {
@@ -46,7 +46,7 @@ public abstract class JvmDeclarationContainerExtensionVisitor @JvmOverloads cons
 /**
  * A visitor to visit JVM extensions for a class.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmClassExtensionVisitor @JvmOverloads constructor(
     delegate: JvmClassExtensionVisitor? = null
 ) : KmClassExtensionVisitor, JvmDeclarationContainerExtensionVisitor(delegate) {
@@ -92,7 +92,7 @@ public open class JvmClassExtensionVisitor @JvmOverloads constructor(
 /**
  * A visitor to visit JVM extensions for a package fragment.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmPackageExtensionVisitor @JvmOverloads constructor(
     delegate: JvmPackageExtensionVisitor? = null
 ) : KmPackageExtensionVisitor, JvmDeclarationContainerExtensionVisitor(delegate) {
@@ -123,7 +123,7 @@ public open class JvmPackageExtensionVisitor @JvmOverloads constructor(
 /**
  * A visitor to visit JVM extensions for a function.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmFunctionExtensionVisitor @JvmOverloads constructor(
     private val delegate: JvmFunctionExtensionVisitor? = null
 ) : KmFunctionExtensionVisitor {
@@ -170,7 +170,7 @@ public open class JvmFunctionExtensionVisitor @JvmOverloads constructor(
 /**
  * A visitor to visit JVM extensions for a property.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmPropertyExtensionVisitor @JvmOverloads constructor(
     private val delegate: JvmPropertyExtensionVisitor? = null
 ) : KmPropertyExtensionVisitor {
@@ -259,7 +259,7 @@ public open class JvmPropertyExtensionVisitor @JvmOverloads constructor(
 /**
  * A visitor to visit JVM extensions for a constructor.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmConstructorExtensionVisitor @JvmOverloads constructor(
     private val delegate: JvmConstructorExtensionVisitor? = null
 ) : KmConstructorExtensionVisitor {
@@ -291,7 +291,7 @@ public open class JvmConstructorExtensionVisitor @JvmOverloads constructor(
 /**
  * A visitor to visit JVM extensions for a type parameter.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmTypeParameterExtensionVisitor @JvmOverloads constructor(
     private val delegate: JvmTypeParameterExtensionVisitor? = null
 ) : KmTypeParameterExtensionVisitor {
@@ -328,7 +328,7 @@ public open class JvmTypeParameterExtensionVisitor @JvmOverloads constructor(
 /**
  * A visitor to visit JVM extensions for a type.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public open class JvmTypeExtensionVisitor @JvmOverloads constructor(
     private val delegate: JvmTypeExtensionVisitor? = null
 ) : KmTypeExtensionVisitor {
diff --git a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinClassMetadata.kt b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinClassMetadata.kt
index 628dd354a01..f4ff16fc951 100644
--- a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinClassMetadata.kt
+++ b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinClassMetadata.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR", "UNUSED_PARAMETER")
 
 package kotlinx.metadata.jvm
 
@@ -58,9 +58,9 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * Returns the same (mutable) [KmClass] instance every time.
          */
-        public val kmClass: KmClass = KmClass().apply {
+        public val kmClass: KmClass = run {
             val (strings, proto) = JvmProtoBufUtil.readClassDataFrom(annotationData.requireNotEmpty(), annotationData.data2)
-            proto.accept(this, strings)
+            proto.toKmClass(strings)
         }
 
         /**
@@ -78,7 +78,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * @param v the visitor that must visit this class
          */
-        @Deprecated(VISITOR_API_MESSAGE)
+        @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
         public fun accept(v: KmClassVisitor): Unit = kmClass.accept(v)
 
         /**
@@ -86,6 +86,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          */
         @Deprecated(
             "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeClass(kmClass, metadataVersion, extraInt)",
+            level = DeprecationLevel.ERROR
         )
         public class Writer : ClassWriter(JvmStringTable()) {
             /**
@@ -99,15 +100,13 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             @JvmOverloads
             @Deprecated(
                 "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeClass(kmClass, metadataVersion, extraInt)",
+                level = DeprecationLevel.ERROR
             )
             public fun write(
                 metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
                 extraInt: Int = 0
             ): Class {
-                checkMetadataVersion(metadataVersion)
-                val (d1, d2) = writeProtoBufData(t.build(), c)
-                val metadata = Metadata(CLASS_KIND, metadataVersion, d1, d2, extraInt = extraInt)
-                return Class(metadata)
+                error("This method is no longer implemented. Migrate to KotlinClassMetadata.writeClass.")
             }
         }
     }
@@ -127,9 +126,9 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * Returns the same (mutable) [KmPackage] instance every time.
          */
-        public val kmPackage: KmPackage = KmPackage().apply {
+        public val kmPackage: KmPackage = run {
             val (strings, proto) = JvmProtoBufUtil.readPackageDataFrom(annotationData.requireNotEmpty(), annotationData.data2)
-            proto.accept(this, strings)
+            proto.toKmPackage(strings)
         }
 
         /**
@@ -147,7 +146,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * @param v the visitor that must visit this file facade
          */
-        @Deprecated(VISITOR_API_MESSAGE)
+        @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
         public fun accept(v: KmPackageVisitor): Unit = kmPackage.accept(v)
 
         /**
@@ -155,6 +154,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          */
         @Deprecated(
             "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeFileFacade(kmPackage, metadataVersion, extraInt)",
+            level = DeprecationLevel.ERROR
         )
         public class Writer : PackageWriter(JvmStringTable()) {
             /**
@@ -168,15 +168,13 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             @JvmOverloads
             @Deprecated(
                 "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeFileFacade(kmPackage, metadataVersion, extraInt)",
+                level = DeprecationLevel.ERROR
             )
             public fun write(
                 metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
                 extraInt: Int = 0
             ): FileFacade {
-                checkMetadataVersion(metadataVersion)
-                val (d1, d2) = writeProtoBufData(t.build(), c)
-                val metadata = Metadata(FILE_FACADE_KIND, metadataVersion, d1, d2, extraInt = extraInt)
-                return FileFacade(metadata)
+                error("This method is no longer implemented. Migrate to KotlinClassMetadata.writeFileFacade.")
             }
         }
     }
@@ -203,9 +201,9 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * Returns the same (mutable) [KmLambda] instance every time.
          */
-        public val kmLambda: KmLambda? = if (!isLambda) null else KmLambda().apply {
+        public val kmLambda: KmLambda? = if (!isLambda) null else {
             val (strings, proto) = functionData!!
-            proto.accept(this, strings)
+            proto.toKmLambda(strings)
         }
 
         /**
@@ -227,7 +225,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * @param v the visitor that must visit this lambda
          */
-        @Deprecated(VISITOR_API_MESSAGE)
+        @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
         public fun accept(v: KmLambdaVisitor) {
             if (!isLambda) throw IllegalArgumentException(
                 "accept(KmLambdaVisitor) is only possible for synthetic classes which are lambdas (isLambda = true)"
@@ -244,6 +242,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
         @Deprecated(
             WRITER_API_MESSAGE + ": KotlinClassMetadata.writeLambda(kmLambda, metadataVersion, extraInt) " +
                     "or KotlinClassMetadata.writeSyntheticClass(metadataVersion, extraInt) for a non-lambda synthetic class",
+            level = DeprecationLevel.ERROR
         )
         public class Writer : LambdaWriter(JvmStringTable()) {
             /**
@@ -257,19 +256,14 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             @Deprecated(
                 WRITER_API_MESSAGE + ": KotlinClassMetadata.writeLambda(kmLambda, metadataVersion, extraInt) " +
                         "or KotlinClassMetadata.writeSyntheticClass(metadataVersion, extraInt) for a non-lambda synthetic class",
+                level = DeprecationLevel.ERROR
             )
             @JvmOverloads
             public fun write(
                 metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
                 extraInt: Int = 0
             ): SyntheticClass {
-                checkMetadataVersion(metadataVersion)
-                val proto = t?.build()
-                val (d1, d2) =
-                    if (proto != null) writeProtoBufData(proto, c)
-                    else Pair(emptyArray(), emptyArray())
-                val metadata = Metadata(SYNTHETIC_CLASS_KIND, metadataVersion, d1, d2, extraInt = extraInt)
-                return SyntheticClass(metadata)
+                error("This method is no longer implemented. Migrate to KotlinClassMetadata.writeLambda or KotlinClassMetadata.writeSyntheticClass.")
             }
         }
     }
@@ -316,6 +310,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          */
         @Deprecated(
             "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeMultiFileClassFacade(partClassNames, metadataVersion, extraInt)",
+            level = DeprecationLevel.ERROR
         )
         public class Writer {
             /**
@@ -329,6 +324,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
              */
             @Deprecated(
                 "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeMultiFileClassFacade(partClassNames, metadataVersion, extraInt)",
+                level = DeprecationLevel.ERROR
             )
             @JvmOverloads
             public fun write(
@@ -336,12 +332,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
                 metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
                 extraInt: Int = 0
             ): MultiFileClassFacade {
-                checkMetadataVersion(metadataVersion)
-                val metadata = Metadata(
-                    MULTI_FILE_CLASS_FACADE_KIND, metadataVersion,
-                    partClassNames.toTypedArray(), extraInt = extraInt
-                )
-                return MultiFileClassFacade(metadata)
+                error("This method is no longer implemented. Migrate to KotlinClassMetadata.writeMultiFileClassFacade.")
             }
         }
     }
@@ -363,9 +354,9 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * Returns the same (mutable) [KmPackage] instance every time.
          */
-        public val kmPackage: KmPackage = KmPackage().apply {
+        public val kmPackage: KmPackage = run {
             val (strings, proto) = JvmProtoBufUtil.readPackageDataFrom(annotationData.requireNotEmpty(), annotationData.data2)
-            proto.accept(this, strings)
+            proto.toKmPackage(strings)
         }
 
         /**
@@ -389,7 +380,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          *
          * @param v the visitor that must visit this multi-file class part
          */
-        @Deprecated(VISITOR_API_MESSAGE)
+        @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
         public fun accept(v: KmPackageVisitor) {
             kmPackage.accept(v)
         }
@@ -398,7 +389,8 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
          * A [KmPackageVisitor] that generates the metadata of a multi-file class part.
          */
         @Deprecated(
-            "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeMultiFileClassPart(kmPackage, facadeClassName, metadataVersion, extraInt)"
+            "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeMultiFileClassPart(kmPackage, facadeClassName, metadataVersion, extraInt)",
+            level = DeprecationLevel.ERROR
         )
         public class Writer : PackageWriter(JvmStringTable()) {
             /**
@@ -411,7 +403,8 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
              *   0 by default
              */
             @Deprecated(
-                "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeMultiFileClassPart(kmPackage, facadeClassName, metadataVersion, extraInt)"
+                "$WRITER_API_MESSAGE, such as KotlinClassMetadata.writeMultiFileClassPart(kmPackage, facadeClassName, metadataVersion, extraInt)",
+                level = DeprecationLevel.ERROR
             )
             @JvmOverloads
             public fun write(
@@ -419,12 +412,7 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
                 metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
                 extraInt: Int = 0
             ): MultiFileClassPart {
-                checkMetadataVersion(metadataVersion)
-                val (d1, d2) = writeProtoBufData(t.build(), c)
-                val metadata = Metadata(
-                    MULTI_FILE_CLASS_PART_KIND, metadataVersion, d1, d2, facadeClassName, extraInt = extraInt
-                )
-                return MultiFileClassPart(metadata)
+                error("This method is no longer implemented. Migrate to KotlinClassMetadata.writeMultifileClassPart.")
             }
         }
     }
@@ -457,7 +445,11 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
             extraInt: Int = 0,
         ): Metadata = wrapWriteIntoIAE {
-            Class.Writer().also { kmClass.accept(it) }.write(metadataVersion, extraInt).annotationData
+            checkMetadataVersion(metadataVersion)
+            val writer = ClassWriter(JvmStringTable())
+            writer.writeClass(kmClass)
+            val (d1, d2) = writeProtoBufData(writer.t.build(), writer.c)
+            Metadata(CLASS_KIND, metadataVersion, d1, d2, extraInt = extraInt)
         }
 
         /**
@@ -477,7 +469,11 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
             extraInt: Int = 0,
         ): Metadata = wrapWriteIntoIAE {
-            FileFacade.Writer().also { kmPackage.accept(it) }.write(metadataVersion, extraInt).annotationData
+            checkMetadataVersion(metadataVersion)
+            val writer = PackageWriter(JvmStringTable())
+            writer.writePackage(kmPackage)
+            val (d1, d2) = writeProtoBufData(writer.t.build(), writer.c)
+            Metadata(FILE_FACADE_KIND, metadataVersion, d1, d2, extraInt = extraInt)
         }
 
         /**
@@ -497,7 +493,14 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
             extraInt: Int = 0,
         ): Metadata = wrapWriteIntoIAE {
-            SyntheticClass.Writer().also { kmLambda.accept(it) }.write(metadataVersion, extraInt).annotationData
+            checkMetadataVersion(metadataVersion)
+            val writer = LambdaWriter(JvmStringTable())
+            writer.writeLambda(kmLambda)
+            val proto = writer.t?.build()
+            val (d1, d2) =
+                if (proto != null) writeProtoBufData(proto, writer.c)
+                else Pair(emptyArray(), emptyArray())
+            Metadata(SYNTHETIC_CLASS_KIND, metadataVersion, d1, d2, extraInt = extraInt)
         }
 
         /**
@@ -515,7 +518,10 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
         public fun writeSyntheticClass(
             metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
             extraInt: Int = 0,
-        ): Metadata = SyntheticClass.Writer().write(metadataVersion, extraInt).annotationData
+        ): Metadata {
+            checkMetadataVersion(metadataVersion)
+            return Metadata(SYNTHETIC_CLASS_KIND, metadataVersion, emptyArray(), emptyArray(), extraInt = extraInt)
+        }
 
         /**
          * Writes metadata of the multi-file class facade.
@@ -533,7 +539,13 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
         public fun writeMultiFileClassFacade(
             partClassNames: List<String>, metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
             extraInt: Int = 0,
-        ): Metadata = MultiFileClassFacade.Writer().write(partClassNames, metadataVersion, extraInt).annotationData
+        ): Metadata {
+            checkMetadataVersion(metadataVersion)
+            return Metadata(
+                MULTI_FILE_CLASS_FACADE_KIND, metadataVersion,
+                partClassNames.toTypedArray(), extraInt = extraInt
+            )
+        }
 
         /**
          * Writes the metadata of the multi-file class part.
@@ -554,7 +566,13 @@ public sealed class KotlinClassMetadata(internal val annotationData: Metadata) {
             metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION,
             extraInt: Int = 0,
         ): Metadata = wrapWriteIntoIAE {
-            MultiFileClassPart.Writer().also { kmPackage.accept(it) }.write(facadeClassName, metadataVersion, extraInt).annotationData
+            checkMetadataVersion(metadataVersion)
+            val writer = PackageWriter(JvmStringTable())
+            writer.writePackage(kmPackage)
+            val (d1, d2) = writeProtoBufData(writer.t.build(), writer.c)
+            Metadata(
+                MULTI_FILE_CLASS_PART_KIND, metadataVersion, d1, d2, facadeClassName, extraInt = extraInt
+            )
         }
 
         /**
diff --git a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinModuleMetadata.kt b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinModuleMetadata.kt
index ccb6aca8e11..95d70cf4de4 100644
--- a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinModuleMetadata.kt
+++ b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/KotlinModuleMetadata.kt
@@ -6,15 +6,16 @@
 @file:Suppress(
     "MemberVisibilityCanBePrivate",
     "DEPRECATION",
+    "DEPRECATION_ERROR",
     "INVISIBLE_MEMBER", // InconsistentKotlinMetadataException
-    "INVISIBLE_REFERENCE"
+    "INVISIBLE_REFERENCE",
+    "UNUSED_PARAMETER"
 )
 
 package kotlinx.metadata.jvm
 
 import kotlinx.metadata.*
-import kotlinx.metadata.internal.accept
-import kotlinx.metadata.jvm.internal.IgnoreInApiDump
+import kotlinx.metadata.internal.toKmClass
 import kotlinx.metadata.jvm.KotlinClassMetadata.Companion.COMPATIBLE_METADATA_VERSION
 import kotlinx.metadata.jvm.KotlinClassMetadata.Companion.throwIfNotCompatible
 import kotlinx.metadata.jvm.internal.wrapIntoMetadataExceptionWhenNeeded
@@ -47,7 +48,7 @@ public class KotlinModuleMetadata private constructor(
      *
      * Returns the same (mutable) [KmModule] instance every time.
      */
-    public val kmModule: KmModule = KmModule().apply(this::accept)
+    public val kmModule: KmModule = readImpl()
 
     /**
      * Visits metadata of this module with a new [KmModule] instance and returns that instance.
@@ -57,39 +58,42 @@ public class KotlinModuleMetadata private constructor(
         ReplaceWith("kmModule"),
         DeprecationLevel.WARNING
     )
-    public fun toKmModule(): KmModule = KmModule().apply(kmModule::accept)
+    public fun toKmModule(): KmModule = KmModule().apply { kmModule.accept(this) }
 
 
     /**
      * A [KmModuleVisitor] that generates the metadata of a Kotlin JVM module file.
      */
-    @Deprecated("Writer API is deprecated as excessive and cumbersome. Please use KotlinModuleMetadata.write(kmModule, metadataVersion)")
-    public class Writer : KmModuleVisitor() {
+    @Deprecated(
+        "Writer API is deprecated as excessive and cumbersome. Please use KotlinModuleMetadata.write(kmModule, metadataVersion)",
+        level = DeprecationLevel.ERROR
+    )
+    public class Writer {
         private val b = JvmModuleProtoBuf.Module.newBuilder()
 
-        override fun visitPackageParts(fqName: String, fileFacades: List<String>, multiFileClassParts: Map<String, String>) {
-            PackageParts(fqName).apply {
-                for (fileFacade in fileFacades) {
-                    addPart(fileFacade, null)
-                }
-                for ((multiFileClassPart, multiFileFacade) in multiFileClassParts) {
-                    addPart(multiFileClassPart, multiFileFacade)
-                }
+        private fun writeModule(kmModule: KmModule) {
+            kmModule.packageParts.forEach { (fqName, packageParts) ->
+                PackageParts(fqName).apply {
+                    for (fileFacade in packageParts.fileFacades) {
+                        addPart(fileFacade, null)
+                    }
+                    for ((multiFileClassPart, multiFileFacade) in packageParts.multiFileClassParts) {
+                        addPart(multiFileClassPart, multiFileFacade)
+                    }
 
-                addTo(b)
+                    addTo(b)
+                }
             }
-        }
 
-        override fun visitAnnotation(annotation: KmAnnotation) {
+            // visitAnnotation
             /*
             // TODO: move StringTableImpl to module 'metadata' and support module annotations here
             b.addAnnotation(ProtoBuf.Annotation.newBuilder().apply {
                 id = annotation.className.name // <-- use StringTableImpl here
             })
             */
-        }
 
-        override fun visitOptionalAnnotationClass(): KmClassVisitor? {
+            // visitOptionalAnnotationClass
             /*
             return object : ClassWriter(TODO() /* use StringTableImpl here */) {
                 override fun visitEnd() {
@@ -97,7 +101,6 @@ public class KotlinModuleMetadata private constructor(
                 }
             }
             */
-            return null
         }
 
         /**
@@ -106,9 +109,12 @@ public class KotlinModuleMetadata private constructor(
          * @param metadataVersion metadata version to be written to the metadata (see [Metadata.metadataVersion]),
          *   [KotlinClassMetadata.COMPATIBLE_METADATA_VERSION] by default
          */
-        @Deprecated("Writer API is deprecated as excessive and cumbersome. Please use KotlinModuleMetadata.write(kmModule, metadataVersion)")
+        @Deprecated(
+            "Writer API is deprecated as excessive and cumbersome. Please use KotlinModuleMetadata.write(kmModule, metadataVersion)",
+            level = DeprecationLevel.ERROR
+        )
         public fun write(metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION): ByteArray {
-            return b.build().serializeToByteArray(JvmMetadataVersion(*metadataVersion), 0)
+            error("This method is no longer implemented. Migrate to KotlinModuleMetadata.write.")
         }
     }
 
@@ -117,24 +123,27 @@ public class KotlinModuleMetadata private constructor(
      *
      * @param v the visitor that must visit this module file
      */
-    @Deprecated(VISITOR_API_MESSAGE)
-    public fun accept(v: KmModuleVisitor) {
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+    public fun accept(v: KmModuleVisitor): Unit = kmModule.accept(v)
+
+    private fun readImpl(): KmModule {
+        val v = KmModule()
         for ((fqName, parts) in data.packageFqName2Parts) {
             val (fileFacades, multiFileClassParts) = parts.parts.partition { parts.getMultifileFacadeName(it) == null }
-            v.visitPackageParts(fqName, fileFacades, multiFileClassParts.associateWith { parts.getMultifileFacadeName(it)!! })
+            v.packageParts[fqName] = KmPackageParts(
+                fileFacades.toMutableList(),
+                multiFileClassParts.associateWith { parts.getMultifileFacadeName(it)!! }.toMutableMap()
+            )
         }
 
         for (annotation in data.moduleData.annotations) {
-            v.visitAnnotation(KmAnnotation(annotation, emptyMap()))
+            v.annotations.add(KmAnnotation(annotation, emptyMap()))
         }
 
         for (classProto in data.moduleData.optionalAnnotations) {
-            v.visitOptionalAnnotationClass()?.let {
-                classProto.accept(it, data.moduleData.nameResolver)
-            }
+            v.optionalAnnotationClasses.add(classProto.toKmClass(data.moduleData.nameResolver))
         }
-
-        v.visitEnd()
+        return v
     }
 
     /**
@@ -173,7 +182,8 @@ public class KotlinModuleMetadata private constructor(
         @JvmStatic
         @JvmOverloads
         public fun write(kmModule: KmModule, metadataVersion: IntArray = COMPATIBLE_METADATA_VERSION): ByteArray = wrapWriteIntoIAE {
-            Writer().also { kmModule.accept(it) }.write(metadataVersion)
+            val w = Writer().also { it.writeModule(kmModule) }
+            return w.b.build().serializeToByteArray(JvmMetadataVersion(*metadataVersion), 0)
         }
 
         private fun dataFromBytes(bytes: ByteArray): ModuleMapping {
@@ -190,7 +200,7 @@ public class KotlinModuleMetadata private constructor(
  *
  * When using this class, [visitEnd] must be called exactly once and after calls to all other visit* methods.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 @UnstableMetadataApi
 public abstract class KmModuleVisitor(private val delegate: KmModuleVisitor? = null) {
     /**
@@ -265,17 +275,17 @@ public class KmModule : KmModuleVisitor() {
      */
     public val optionalAnnotationClasses: MutableList<KmClass> = ArrayList(0)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitPackageParts(fqName: String, fileFacades: List<String>, multiFileClassParts: Map<String, String>) {
         packageParts[fqName] = KmPackageParts(fileFacades.toMutableList(), multiFileClassParts.toMutableMap())
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitAnnotation(annotation: KmAnnotation) {
         annotations.add(annotation)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitOptionalAnnotationClass(): KmClass =
         KmClass().also(optionalAnnotationClasses::add)
 
@@ -284,7 +294,7 @@ public class KmModule : KmModuleVisitor() {
      *
      * @param visitor the visitor which will visit data in this module.
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmModuleVisitor) {
         for ((fqName, parts) in packageParts) {
             visitor.visitPackageParts(fqName, parts.fileFacades, parts.multiFileClassParts)
diff --git a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmExtensionNodes.kt b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmExtensionNodes.kt
index e88c8b8a17c..c5e28531812 100644
--- a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmExtensionNodes.kt
+++ b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmExtensionNodes.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION","DEPRECATION_ERROR")
 
 package kotlinx.metadata.jvm.internal
 
diff --git a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmMetadataExtensions.kt b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmMetadataExtensions.kt
index 8cca51409f6..dbd0212d1c7 100644
--- a/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmMetadataExtensions.kt
+++ b/libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/internal/JvmMetadataExtensions.kt
@@ -15,10 +15,11 @@ import org.jetbrains.kotlin.metadata.deserialization.getExtensionOrNull
 import org.jetbrains.kotlin.metadata.jvm.JvmProtoBuf
 import org.jetbrains.kotlin.metadata.jvm.deserialization.JvmProtoBufUtil
 
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION_ERROR")
 internal class JvmMetadataExtensions : MetadataExtensions {
     override fun readClassExtensions(v: KmClassVisitor, proto: ProtoBuf.Class, c: ReadContext) {
         val ext = v.visitExtensions(JvmClassExtensionVisitor.TYPE) as? JvmClassExtensionVisitor ?: return
+        ext as JvmClassExtension
 
         val anonymousObjectOriginName = proto.getExtensionOrNull(JvmProtoBuf.anonymousObjectOriginName)
         if (anonymousObjectOriginName != null) {
@@ -26,9 +27,7 @@ internal class JvmMetadataExtensions : MetadataExtensions {
         }
 
         for (property in proto.getExtension(JvmProtoBuf.classLocalVariable)) {
-            ext.visitLocalDelegatedProperty(
-                property.flags, c[property.name], property.getPropertyGetterFlags(), property.getPropertySetterFlags()
-            )?.let { property.accept(it, c) }
+            ext.localDelegatedProperties.add(property.toKmProperty(c))
         }
 
         ext.visitModuleName(proto.getExtensionOrNull(JvmProtoBuf.classModuleName)?.let(c::get) ?: JvmProtoBufUtil.DEFAULT_MODULE_NAME)
@@ -40,11 +39,10 @@ internal class JvmMetadataExtensions : MetadataExtensions {
 
     override fun readPackageExtensions(v: KmPackageVisitor, proto: ProtoBuf.Package, c: ReadContext) {
         val ext = v.visitExtensions(JvmPackageExtensionVisitor.TYPE) as? JvmPackageExtensionVisitor ?: return
+        ext as JvmPackageExtension
 
         for (property in proto.getExtension(JvmProtoBuf.packageLocalVariable)) {
-            ext.visitLocalDelegatedProperty(
-                property.flags, c[property.name], property.getPropertyGetterFlags(), property.getPropertySetterFlags()
-            )?.let { property.accept(it, c) }
+            ext.localDelegatedProperties.add(property.toKmProperty(c))
         }
 
         ext.visitModuleName(proto.getExtensionOrNull(JvmProtoBuf.packageModuleName)?.let(c::get) ?: JvmProtoBufUtil.DEFAULT_MODULE_NAME)
@@ -119,50 +117,34 @@ internal class JvmMetadataExtensions : MetadataExtensions {
 
     override fun readValueParameterExtensions(v: KmValueParameterVisitor, proto: ProtoBuf.ValueParameter, c: ReadContext) {}
 
-    override fun writeClassExtensions(type: KmExtensionType, proto: ProtoBuf.Class.Builder, c: WriteContext): KmClassExtensionVisitor? {
-        if (type != JvmClassExtensionVisitor.TYPE) return null
-        return object : JvmClassExtensionVisitor() {
-            override fun visitAnonymousObjectOriginName(internalName: String) {
-                proto.setExtension(JvmProtoBuf.anonymousObjectOriginName, c[internalName])
-            }
-
-            override fun visitLocalDelegatedProperty(
-                flags: Int, name: String, getterFlags: Int, setterFlags: Int
-            ): KmPropertyVisitor = writeProperty(c, flags, name, getterFlags, setterFlags) {
-                proto.addExtension(JvmProtoBuf.classLocalVariable, it.build())
-            }
-
-            override fun visitModuleName(name: String) {
-                if (name != JvmProtoBufUtil.DEFAULT_MODULE_NAME) {
-                    proto.setExtension(JvmProtoBuf.classModuleName, c[name])
-                }
-            }
-
-            override fun visitJvmFlags(flags: Int) {
-                if (flags != 0) {
-                    proto.setExtension(JvmProtoBuf.jvmClassFlags, flags)
-                }
-            }
+    override fun writeClassExtensions(extension: KmClassExtension, proto: ProtoBuf.Class.Builder, c: WriteContext): Boolean {
+        if (extension.type != JvmClassExtensionVisitor.TYPE) return false
+        extension as JvmClassExtension
+        extension.anonymousObjectOriginName?.let { proto.setExtension(JvmProtoBuf.anonymousObjectOriginName, c[it]) }
+        extension.localDelegatedProperties.forEach {
+            proto.addExtension(JvmProtoBuf.classLocalVariable, c.writeProperty(it).build())
         }
+        extension.moduleName?.let { moduleName ->
+            if (moduleName != JvmProtoBufUtil.DEFAULT_MODULE_NAME) proto.setExtension(JvmProtoBuf.classModuleName, c[moduleName])
+        }
+        if (extension.jvmFlags != 0) proto.setExtension(JvmProtoBuf.jvmClassFlags, extension.jvmFlags)
+        return true
     }
 
     override fun writePackageExtensions(
-        type: KmExtensionType, proto: ProtoBuf.Package.Builder, c: WriteContext
-    ): KmPackageExtensionVisitor? {
-        if (type != JvmPackageExtensionVisitor.TYPE) return null
-        return object : JvmPackageExtensionVisitor() {
-            override fun visitLocalDelegatedProperty(
-                flags: Int, name: String, getterFlags: Int, setterFlags: Int
-            ): KmPropertyVisitor = writeProperty(c, flags, name, getterFlags, setterFlags) {
-                proto.addExtension(JvmProtoBuf.packageLocalVariable, it.build())
-            }
-
-            override fun visitModuleName(name: String) {
-                if (name != JvmProtoBufUtil.DEFAULT_MODULE_NAME) {
-                    proto.setExtension(JvmProtoBuf.packageModuleName, c[name])
-                }
+        extension: KmPackageExtension, proto: ProtoBuf.Package.Builder, c: WriteContext
+    ): Boolean {
+        if (extension.type != JvmPackageExtensionVisitor.TYPE) return false
+        extension as JvmPackageExtension
+        extension.localDelegatedProperties.forEach {
+            proto.addExtension(JvmProtoBuf.packageLocalVariable, c.writeProperty(it).build())
+        }
+        extension.moduleName?.let { name ->
+            if (name != JvmProtoBufUtil.DEFAULT_MODULE_NAME) {
+                proto.setExtension(JvmProtoBuf.packageModuleName, c[name])
             }
         }
+        return true
     }
 
     // PackageFragment is not used by JVM backend.
diff --git a/libraries/kotlinx-metadata/jvm/test/kotlinx/metadata/test/MetadataSmokeTest.kt b/libraries/kotlinx-metadata/jvm/test/kotlinx/metadata/test/MetadataSmokeTest.kt
index cde6c35794d..bea33732355 100644
--- a/libraries/kotlinx-metadata/jvm/test/kotlinx/metadata/test/MetadataSmokeTest.kt
+++ b/libraries/kotlinx-metadata/jvm/test/kotlinx/metadata/test/MetadataSmokeTest.kt
@@ -124,27 +124,15 @@ class MetadataSmokeTest {
 
     @Test
     fun jvmInternalName() {
-        class ClassNameReader : KmClassVisitor() {
-            lateinit var className: ClassName
-
-            override fun visit(flags: Int, name: ClassName) {
-                className = name
-            }
-        }
 
         class L
 
-        val l = ClassNameReader().run {
-            (KotlinClassMetadata.read(L::class.java.getMetadata()) as KotlinClassMetadata.Class).accept(this)
-            className
-        }
+        val l = (KotlinClassMetadata.read(L::class.java.getMetadata()) as KotlinClassMetadata.Class).kmClass.name
         assertEquals(".kotlinx/metadata/test/MetadataSmokeTest\$jvmInternalName\$L", l)
         assertEquals("kotlinx/metadata/test/MetadataSmokeTest\$jvmInternalName\$L", l.toJvmInternalName())
 
-        val coroutineContextKey = ClassNameReader().run {
-            (KotlinClassMetadata.read(CoroutineContext.Key::class.java.getMetadata()) as KotlinClassMetadata.Class).accept(this)
-            className
-        }
+        val coroutineContextKey = (KotlinClassMetadata.read(CoroutineContext.Key::class.java.getMetadata()) as KotlinClassMetadata.Class).kmClass.name
+
         assertEquals("kotlin/coroutines/CoroutineContext.Key", coroutineContextKey)
         assertEquals("kotlin/coroutines/CoroutineContext\$Key", coroutineContextKey.toJvmInternalName())
     }
@@ -154,7 +142,7 @@ class MetadataSmokeTest {
         val x: suspend Int.(String, String) -> Unit = { _, _ -> }
         val annotation = x::class.java.getMetadata()
         val metadata = KotlinClassMetadata.read(annotation) as KotlinClassMetadata.SyntheticClass
-        metadata.accept(KmLambda())
+        assertNotNull(metadata.kmLambda)
     }
 
     @Test
@@ -172,19 +160,10 @@ class MetadataSmokeTest {
         classWithStableParameterNames.constructors.forEach { assertFalse(it.hasNonStableParameterNames) }
         classWithStableParameterNames.functions.forEach { assertFalse(it.hasNonStableParameterNames) }
 
-        val newMetadata = KotlinClassMetadata.writeClass(
-            KmClass().apply {
-                classWithStableParameterNames.accept(
-                    object : KmClassVisitor(this) {
-                        override fun visitConstructor(flags: Int) =
-                            super.visitConstructor(flags + flagsOf(Flag.Constructor.HAS_NON_STABLE_PARAMETER_NAMES))
+        classWithStableParameterNames.constructors.forEach { it.hasNonStableParameterNames = true }
+        classWithStableParameterNames.functions.forEach { it.hasNonStableParameterNames = true }
 
-                        override fun visitFunction(flags: Int, name: String) =
-                            super.visitFunction(flags + flagsOf(Flag.Function.HAS_NON_STABLE_PARAMETER_NAMES), name)
-                    }
-                )
-            }
-        )
+        val newMetadata = KotlinClassMetadata.writeClass(classWithStableParameterNames)
 
         val classWithUnstableParameterNames = newMetadata.readAsKmClass()
 
diff --git a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/KlibModuleMetadata.kt b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/KlibModuleMetadata.kt
index 79fcfbc1c73..2492b4e1571 100644
--- a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/KlibModuleMetadata.kt
+++ b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/KlibModuleMetadata.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata.klib
 
@@ -90,7 +90,7 @@ class KlibModuleMetadata(
                 library.packageMetadataParts(packageFqName).map { part ->
                     val packageFragment = parsePackageFragment(library.packageMetadata(packageFqName, part))
                     val nameResolver = NameResolverImpl(packageFragment.strings, packageFragment.qualifiedNames)
-                    KmModuleFragment().apply { packageFragment.accept(this, nameResolver, listOf(fileIndex)) }
+                    packageFragment.toKmModuleFragment(nameResolver, listOf(fileIndex))
                 }.let(readStrategy::processModuleParts)
             }
             return KlibModuleMetadata(moduleHeader.moduleName, moduleFragments, moduleHeader.annotation)
@@ -119,9 +119,9 @@ class KlibModuleMetadata(
             annotations
         )
         val groupedProtos = groupedFragments.mapValues { (_, fragments) ->
-            fragments.map {
+            fragments.map { mf ->
                 val c = WriteContext(ApproximatingStringTable(), listOf(reverseIndex))
-                KlibModuleFragmentWriter(c.strings as ApproximatingStringTable, c.contextExtensions).also(it::accept).write()
+                KlibModuleFragmentWriter(c.strings as ApproximatingStringTable, c.contextExtensions).also { it.writeModuleFragment(mf) }.write()
             }
         }
         // This context and string table is only required for module-level annotations.
diff --git a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibExtensionNodes.kt b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibExtensionNodes.kt
index ff46b24afbc..635a9bbd322 100644
--- a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibExtensionNodes.kt
+++ b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibExtensionNodes.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata.klib.impl
 
diff --git a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibMetadataExtensions.kt b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibMetadataExtensions.kt
index 2697f849f68..273e74a72f2 100644
--- a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibMetadataExtensions.kt
+++ b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibMetadataExtensions.kt
@@ -151,9 +151,9 @@ internal class KlibMetadataExtensions : MetadataExtensions {
         }
     }
 
-    override fun writeClassExtensions(type: KmExtensionType, proto: ProtoBuf.Class.Builder, c: WriteContext): KmClassExtensionVisitor? {
-        if (type != KlibClassExtensionVisitor.TYPE) return null
-        return object : KlibClassExtensionVisitor() {
+    override fun writeClassExtensions(extension: KmClassExtension, proto: ProtoBuf.Class.Builder, c: WriteContext): Boolean {
+        if (extension.type != KlibClassExtensionVisitor.TYPE) return false
+        extension.accept(object : KlibClassExtensionVisitor() {
             override fun visitAnnotation(annotation: KmAnnotation) {
                 proto.addExtension(
                     KlibMetadataProtoBuf.classAnnotation,
@@ -191,21 +191,23 @@ internal class KlibMetadataExtensions : MetadataExtensions {
                     proto.setEnumEntry(entryIndex, entryProto.build())
                 }
             }
-        }
+        })
+        return true
     }
 
     override fun writePackageExtensions(
-        type: KmExtensionType,
+        extension: KmPackageExtension,
         proto: ProtoBuf.Package.Builder,
         c: WriteContext
-    ): KmPackageExtensionVisitor? {
-        if (type != KlibPackageExtensionVisitor.TYPE) return null
-        return object : KlibPackageExtensionVisitor() {
+    ): Boolean {
+        if (extension.type != KlibPackageExtensionVisitor.TYPE) return false
+        extension.accept(object : KlibPackageExtensionVisitor() {
             override fun visitFqName(name: String) {
                 val nameIdx = (c.strings as StringTableImpl).getPackageFqNameIndex(FqName(name))
                 proto.setExtension(KlibMetadataProtoBuf.packageFqName, nameIdx)
             }
-        }
+        })
+        return true
     }
 
     override fun writeModuleFragmentExtensions(
diff --git a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibWriters.kt b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibWriters.kt
index c08b7f1f8e6..b8af17c3afa 100644
--- a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibWriters.kt
+++ b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/impl/klibWriters.kt
@@ -2,11 +2,11 @@
  * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
 
 package kotlinx.metadata.klib.impl
 
 import kotlinx.metadata.internal.*
+import kotlinx.metadata.internal.common.KmModuleFragment
 import kotlinx.metadata.klib.KlibSourceFile
 import org.jetbrains.kotlin.library.metadata.KlibMetadataProtoBuf
 import org.jetbrains.kotlin.metadata.ProtoBuf
@@ -34,7 +34,8 @@ class KlibModuleFragmentWriter(
     fun write(): ProtoBuf.PackageFragment =
         t.build()
 
-    override fun visitEnd() {
+    override fun writeModuleFragment(kmPackageFragment: KmModuleFragment) {
+        super.writeModuleFragment(kmPackageFragment)
 
         // TODO: This should be moved to ModuleFragmentWriter.
         val (strings, qualifiedNames) = (c.strings as ApproximatingStringTable).buildProto()
@@ -49,4 +50,4 @@ class KlibModuleFragmentWriter(
         val isEmpty = t.class_Count == 0 && isPackageEmpty
         t.setExtension(KlibMetadataProtoBuf.isEmpty, isEmpty)
     }
-}
\ No newline at end of file
+}
diff --git a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/klibMetadataExtensionVisitors.kt b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/klibMetadataExtensionVisitors.kt
index 856ec20f3b2..488c41339d6 100644
--- a/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/klibMetadataExtensionVisitors.kt
+++ b/libraries/kotlinx-metadata/klib/src/kotlinx/metadata/klib/klibMetadataExtensionVisitors.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata.klib
 
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/Extensions.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/Extensions.kt
index 89920d77f09..fdef8e5c29a 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/Extensions.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/Extensions.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata
 
@@ -29,7 +29,7 @@ import kotlin.reflect.KClass
  * ```
  * In case an extension visitor of an unrelated type is returned, the code using the visitor API must ignore that visitor.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public class KmExtensionType(private val klass: KClass<out KmExtensionVisitor>) {
     override fun equals(other: Any?): Boolean =
         other is KmExtensionType && klass == other.klass
@@ -44,7 +44,7 @@ public class KmExtensionType(private val klass: KClass<out KmExtensionVisitor>)
 /**
  * A base interface for all extension visitors.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmExtensionVisitor {
     /**
      * Type of this extension visitor.
@@ -55,59 +55,59 @@ public interface KmExtensionVisitor {
 /**
  * A visitor to visit platform-specific extensions for a declaration container, such as a class or a package fragment.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmDeclarationContainerExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a class.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmClassExtensionVisitor : KmDeclarationContainerExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a package fragment.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmPackageExtensionVisitor : KmDeclarationContainerExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a function.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmFunctionExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a property.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmPropertyExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a constructor.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmConstructorExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a type parameter.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmTypeParameterExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a type.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmTypeExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a type alias.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmTypeAliasExtensionVisitor : KmExtensionVisitor
 
 /**
  * A visitor to visit platform-specific extensions for a value parameter.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmValueParameterExtensionVisitor : KmExtensionVisitor
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/Nodes.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/Nodes.kt
index 3db8b41a87f..34f2fbfb861 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/Nodes.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/Nodes.kt
@@ -38,7 +38,7 @@ public interface KmDeclarationContainer {
  * Precise kind of the class can be obtained via [KmClass.kind].
  * Various class attributes can be read and manipulated via extension properties, such as [KmClass.visibility] or [KmClass.isData].
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmClass : KmClassVisitor(), KmDeclarationContainer {
     /**
      * Class flags, consisting of [Flag.HAS_ANNOTATIONS], visibility flag, modality flag and [Flag.Class] flags.
@@ -122,78 +122,78 @@ public class KmClass : KmClassVisitor(), KmDeclarationContainer {
      */
     public val versionRequirements: MutableList<KmVersionRequirement> = ArrayList(0)
 
-    private val extensions: List<KmClassExtension> =
+    internal val extensions: List<KmClassExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createClassExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visit(flags: Int, name: ClassName) {
         this.flags = flags
         this.name = name
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor =
         KmTypeParameter(flags, name, id, variance).addTo(typeParameters)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitSupertype(flags: Int): KmTypeVisitor =
         KmType(flags).addTo(supertypes)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitFunction(flags: Int, name: String): KmFunctionVisitor =
         KmFunction(flags, name).addTo(functions)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitProperty(flags: Int, name: String, getterFlags: Int, setterFlags: Int): KmPropertyVisitor =
         KmProperty(flags, name, getterFlags, setterFlags).addTo(properties)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeAlias(flags: Int, name: String): KmTypeAliasVisitor =
         KmTypeAlias(flags, name).addTo(typeAliases)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitConstructor(flags: Int): KmConstructorVisitor =
         KmConstructor(flags).addTo(constructors)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitCompanionObject(name: String) {
         this.companionObject = name
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitNestedClass(name: String) {
         nestedClasses.add(name)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitEnumEntry(name: String) {
         enumEntries.add(name)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitSealedSubclass(name: ClassName) {
         sealedSubclasses.add(name)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitInlineClassUnderlyingPropertyName(name: String) {
         inlineClassUnderlyingPropertyName = name
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitInlineClassUnderlyingType(flags: Int): KmTypeVisitor =
         KmType(flags).also { inlineClassUnderlyingType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     @ExperimentalContextReceivers
     override fun visitContextReceiverType(flags: Int): KmTypeVisitor =
         KmType(flags).addTo(contextReceiverTypes)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVersionRequirement(): KmVersionRequirementVisitor =
         KmVersionRequirement().addTo(versionRequirements)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmClassExtensionVisitor =
         extensions.singleOfType(type)
 
@@ -202,7 +202,7 @@ public class KmClass : KmClassVisitor(), KmDeclarationContainer {
      *
      * @param visitor the visitor which will visit data in this class
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     @OptIn(ExperimentalContextReceivers::class)
     public fun accept(visitor: KmClassVisitor) {
         visitor.visit(flags, name)
@@ -230,7 +230,7 @@ public class KmClass : KmClassVisitor(), KmDeclarationContainer {
  * Package fragments are produced from single file facades and multi-file class parts.
  * Note that a package fragment does not contain any classes, as classes are not a part of file facades and have their own metadata.
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmPackage : KmPackageVisitor(), KmDeclarationContainer {
     /**
      * Functions in the package fragment.
@@ -247,22 +247,22 @@ public class KmPackage : KmPackageVisitor(), KmDeclarationContainer {
      */
     override val typeAliases: MutableList<KmTypeAlias> = ArrayList(0)
 
-    private val extensions: List<KmPackageExtension> =
+    internal val extensions: List<KmPackageExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createPackageExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitFunction(flags: Int, name: String): KmFunctionVisitor =
         KmFunction(flags, name).addTo(functions)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitProperty(flags: Int, name: String, getterFlags: Int, setterFlags: Int): KmPropertyVisitor =
         KmProperty(flags, name, getterFlags, setterFlags).addTo(properties)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeAlias(flags: Int, name: String): KmTypeAliasVisitor =
         KmTypeAlias(flags, name).addTo(typeAliases)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmPackageExtensionVisitor =
         extensions.singleOfType(type)
 
@@ -271,7 +271,7 @@ public class KmPackage : KmPackageVisitor(), KmDeclarationContainer {
      *
      * @param visitor the visitor which will visit data in this package fragment
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmPackageVisitor) {
         functions.forEach { visitor.visitFunction(it.flags, it.name)?.let(it::accept) }
         properties.forEach { visitor.visitProperty(it.flags, it.name, it.getter.flags, it.setterFlags)?.let(it::accept) }
@@ -284,14 +284,14 @@ public class KmPackage : KmPackageVisitor(), KmDeclarationContainer {
 /**
  * Represents a synthetic class generated for a Kotlin lambda.
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmLambda : KmLambdaVisitor() {
     /**
      * Signature of the synthetic anonymous function, representing the lambda.
      */
     public lateinit var function: KmFunction
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitFunction(flags: Int, name: String): KmFunctionVisitor =
         KmFunction(flags, name).also { function = it }
 
@@ -300,7 +300,7 @@ public class KmLambda : KmLambdaVisitor() {
      *
      * @param visitor the visitor which will visit data in this lambda
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmLambdaVisitor) {
         visitor.visitFunction(function.flags, function.name)?.let(function::accept)
         visitor.visitEnd()
@@ -313,7 +313,7 @@ public class KmLambda : KmLambdaVisitor() {
  * Various constructor attributes can be read and manipulated via extension properties,
  * such as [KmConstructor.visibility] or [KmConstructor.isSecondary].
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmConstructor @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmConstructor, such as KmConstructor.visibility") public var flags: Int,
 ) :
@@ -330,18 +330,18 @@ public class KmConstructor @Deprecated(flagsCtorDeprecated) constructor(
      */
     public val versionRequirements: MutableList<KmVersionRequirement> = ArrayList(0)
 
-    private val extensions: List<KmConstructorExtension> =
+    internal val extensions: List<KmConstructorExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createConstructorExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitValueParameter(flags: Int, name: String): KmValueParameterVisitor =
         KmValueParameter(flags, name).addTo(valueParameters)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVersionRequirement(): KmVersionRequirementVisitor =
         KmVersionRequirement().addTo(versionRequirements)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmConstructorExtensionVisitor =
         extensions.singleOfType(type)
 
@@ -350,7 +350,7 @@ public class KmConstructor @Deprecated(flagsCtorDeprecated) constructor(
      *
      * @param visitor the visitor which will visit data in this class
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmConstructorVisitor) {
         valueParameters.forEach { visitor.visitValueParameter(it.flags, it.name)?.let(it::accept) }
         versionRequirements.forEach { visitor.visitVersionRequirement()?.let(it::accept) }
@@ -367,7 +367,7 @@ public class KmConstructor @Deprecated(flagsCtorDeprecated) constructor(
  *
  * @property name the name of the function
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmFunction @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmFunction, such as KmFunction.visibility") public var flags: Int,
     public var name: String,
@@ -412,40 +412,40 @@ public class KmFunction @Deprecated(flagsCtorDeprecated) constructor(
     @ExperimentalContracts
     public var contract: KmContract? = null
 
-    private val extensions: List<KmFunctionExtension> =
+    internal val extensions: List<KmFunctionExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createFunctionExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor =
         KmTypeParameter(flags, name, id, variance).addTo(typeParameters)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitReceiverParameterType(flags: Int): KmTypeVisitor =
         KmType(flags).also { receiverParameterType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     @ExperimentalContextReceivers
     override fun visitContextReceiverType(flags: Int): KmTypeVisitor =
         KmType(flags).addTo(contextReceiverTypes)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitValueParameter(flags: Int, name: String): KmValueParameterVisitor =
         KmValueParameter(flags, name).addTo(valueParameters)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitReturnType(flags: Int): KmTypeVisitor =
         KmType(flags).also { returnType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVersionRequirement(): KmVersionRequirementVisitor =
         KmVersionRequirement().addTo(versionRequirements)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     @ExperimentalContracts
     override fun visitContract(): KmContractVisitor =
         KmContract().also { contract = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmFunctionExtensionVisitor =
         extensions.singleOfType(type)
 
@@ -455,7 +455,7 @@ public class KmFunction @Deprecated(flagsCtorDeprecated) constructor(
      * @param visitor the visitor which will visit data in this function
      */
     @OptIn(ExperimentalContextReceivers::class)
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmFunctionVisitor) {
         typeParameters.forEach { visitor.visitTypeParameter(it.flags, it.name, it.id, it.variance)?.let(it::accept) }
         receiverParameterType?.let { visitor.visitReceiverParameterType(it.flags)?.let(it::accept) }
@@ -489,7 +489,7 @@ public class KmPropertyAccessorAttributes internal constructor(internal var flag
  *
  * @property name the name of the property
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmProperty @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmProperty, such as KmProperty.visibility") public var flags: Int,
     public var name: String,
@@ -593,35 +593,35 @@ public class KmProperty @Deprecated(flagsCtorDeprecated) constructor(
      */
     public val versionRequirements: MutableList<KmVersionRequirement> = ArrayList(0)
 
-    private val extensions: List<KmPropertyExtension> =
+    internal val extensions: List<KmPropertyExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createPropertyExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor =
         KmTypeParameter(flags, name, id, variance).addTo(typeParameters)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitReceiverParameterType(flags: Int): KmTypeVisitor =
         KmType(flags).also { receiverParameterType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     @ExperimentalContextReceivers
     override fun visitContextReceiverType(flags: Int): KmTypeVisitor =
         KmType(flags).addTo(contextReceiverTypes)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitSetterParameter(flags: Int, name: String): KmValueParameterVisitor =
         KmValueParameter(flags, name).also { setterParameter = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitReturnType(flags: Int): KmTypeVisitor =
         KmType(flags).also { returnType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVersionRequirement(): KmVersionRequirementVisitor =
         KmVersionRequirement().addTo(versionRequirements)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmPropertyExtensionVisitor =
         extensions.singleOfType(type)
 
@@ -631,7 +631,7 @@ public class KmProperty @Deprecated(flagsCtorDeprecated) constructor(
      * @param visitor the visitor which will visit data in this property
      */
     @OptIn(ExperimentalContextReceivers::class)
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmPropertyVisitor) {
         typeParameters.forEach { visitor.visitTypeParameter(it.flags, it.name, it.id, it.variance)?.let(it::accept) }
         receiverParameterType?.let { visitor.visitReceiverParameterType(it.flags)?.let(it::accept) }
@@ -652,7 +652,7 @@ public class KmProperty @Deprecated(flagsCtorDeprecated) constructor(
  *
  * @property name the name of the type alias
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmTypeAlias @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmTypeAlias, such as KmTypeAlias.visibility") public var flags: Int,
     public var name: String,
@@ -686,31 +686,31 @@ public class KmTypeAlias @Deprecated(flagsCtorDeprecated) constructor(
      */
     public val versionRequirements: MutableList<KmVersionRequirement> = ArrayList(0)
 
-    private val extensions: List<KmTypeAliasExtension> =
+    internal val extensions: List<KmTypeAliasExtension> =
         MetadataExtensions.INSTANCES.mapNotNull(MetadataExtensions::createTypeAliasExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor =
         KmTypeParameter(flags, name, id, variance).addTo(typeParameters)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitUnderlyingType(flags: Int): KmTypeVisitor =
         KmType(flags).also { underlyingType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExpandedType(flags: Int): KmTypeVisitor =
         KmType(flags).also { expandedType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitAnnotation(annotation: KmAnnotation) {
         annotations.add(annotation)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmTypeAliasExtensionVisitor? =
         extensions.singleOfType(type)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVersionRequirement(): KmVersionRequirementVisitor =
         KmVersionRequirement().addTo(versionRequirements)
 
@@ -719,7 +719,7 @@ public class KmTypeAlias @Deprecated(flagsCtorDeprecated) constructor(
      *
      * @param visitor the visitor which will visit data in this type alias
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmTypeAliasVisitor) {
         typeParameters.forEach { visitor.visitTypeParameter(it.flags, it.name, it.id, it.variance)?.let(it::accept) }
         visitor.visitUnderlyingType(underlyingType.flags)?.let(underlyingType::accept)
@@ -739,7 +739,7 @@ public class KmTypeAlias @Deprecated(flagsCtorDeprecated) constructor(
  *
  * @property name the name of the value parameter
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmValueParameter @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmValueParameter, such as KmValueParameter.declaresDefaultValue") public var flags: Int,
     public var name: String,
@@ -758,18 +758,18 @@ public class KmValueParameter @Deprecated(flagsCtorDeprecated) constructor(
      */
     public var varargElementType: KmType? = null
 
-    private val extensions: List<KmValueParameterExtension> =
+    internal val extensions: List<KmValueParameterExtension> =
         MetadataExtensions.INSTANCES.mapNotNull(MetadataExtensions::createValueParameterExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitType(flags: Int): KmTypeVisitor =
         KmType(flags).also { type = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVarargElementType(flags: Int): KmTypeVisitor =
         KmType(flags).also { varargElementType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmValueParameterExtensionVisitor? =
         extensions.singleOfType(type)
 
@@ -778,7 +778,7 @@ public class KmValueParameter @Deprecated(flagsCtorDeprecated) constructor(
      *
      * @param visitor the visitor which will visit data in this value parameter
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmValueParameterVisitor) {
         visitor.visitType(type.flags)?.let(type::accept)
         varargElementType?.let { visitor.visitVarargElementType(it.flags)?.let(it::accept) }
@@ -798,7 +798,7 @@ public class KmValueParameter @Deprecated(flagsCtorDeprecated) constructor(
  *           the name is not enough (e.g. `class A<T> { fun <T> foo(t: T) }`)
  * @property variance the declaration-site variance of the type parameter
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmTypeParameter @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmTypeParameter, such as KmTypeParameter.isReified") public var flags: Int,
     public var name: String,
@@ -813,14 +813,14 @@ public class KmTypeParameter @Deprecated(flagsCtorDeprecated) constructor(
      */
     public val upperBounds: MutableList<KmType> = ArrayList(1)
 
-    private val extensions: List<KmTypeParameterExtension> =
+    internal val extensions: List<KmTypeParameterExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createTypeParameterExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitUpperBound(flags: Int): KmTypeVisitor =
         KmType(flags).addTo(upperBounds)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmTypeParameterExtensionVisitor? =
         extensions.singleOfType(type)
 
@@ -829,7 +829,7 @@ public class KmTypeParameter @Deprecated(flagsCtorDeprecated) constructor(
      *
      * @param visitor the visitor which will visit data in this type parameter
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmTypeParameterVisitor) {
         upperBounds.forEach { visitor.visitUpperBound(it.flags)?.let(it::accept) }
         extensions.forEach { visitor.visitExtensions(it.type)?.let(it::accept) }
@@ -843,7 +843,7 @@ public class KmTypeParameter @Deprecated(flagsCtorDeprecated) constructor(
  * Various type attributes can be read and manipulated via extension properties,
  * such as [KmType.isNullable].
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmType @Deprecated(flagsCtorDeprecated) constructor(
     @Deprecated("$flagAccessPrefix KmType, such as KmType.isNullable") public var flags: Int
 ) : KmTypeVisitor() {
@@ -890,46 +890,46 @@ public class KmType @Deprecated(flagsCtorDeprecated) constructor(
      */
     public var flexibleTypeUpperBound: KmFlexibleTypeUpperBound? = null
 
-    private val extensions: List<KmTypeExtension> =
+    internal val extensions: List<KmTypeExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createTypeExtension)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitClass(name: ClassName) {
         classifier = KmClassifier.Class(name)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeAlias(name: ClassName) {
         classifier = KmClassifier.TypeAlias(name)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitTypeParameter(id: Int) {
         classifier = KmClassifier.TypeParameter(id)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitArgument(flags: Int, variance: KmVariance): KmTypeVisitor =
         KmType(flags).also { arguments.add(KmTypeProjection(variance, it)) }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitStarProjection() {
         arguments.add(KmTypeProjection.STAR)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitAbbreviatedType(flags: Int): KmTypeVisitor =
         KmType(flags).also { abbreviatedType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitOuterType(flags: Int): KmTypeVisitor =
         KmType(flags).also { outerType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitFlexibleTypeUpperBound(flags: Int, typeFlexibilityId: String?): KmTypeVisitor =
         KmType(flags).also { flexibleTypeUpperBound = KmFlexibleTypeUpperBound(it, typeFlexibilityId) }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmTypeExtensionVisitor =
         extensions.singleOfType(type)
 
@@ -939,7 +939,7 @@ public class KmType @Deprecated(flagsCtorDeprecated) constructor(
      * @param visitor the visitor which will visit data in this type
      * @throws IllegalArgumentException if type metadata is inconsistent
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmTypeVisitor) {
         when (val classifier = classifier) {
             is KmClassifier.Class -> visitor.visitClass(classifier.name)
@@ -969,7 +969,7 @@ public class KmType @Deprecated(flagsCtorDeprecated) constructor(
  * Version requirement is an internal feature of the Kotlin compiler and the standard Kotlin library,
  * enabled, for example, with the internal [kotlin.internal.RequireKotlin] annotation.
  */
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmVersionRequirement : KmVersionRequirementVisitor() {
     /**
      * Kind of the version that this declaration requires.
@@ -996,7 +996,7 @@ public class KmVersionRequirement : KmVersionRequirementVisitor() {
      */
     public lateinit var version: KmVersion
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visit(kind: KmVersionRequirementVersionKind, level: KmVersionRequirementLevel, errorCode: Int?, message: String?) {
         this.kind = kind
         this.level = level
@@ -1004,7 +1004,7 @@ public class KmVersionRequirement : KmVersionRequirementVisitor() {
         this.message = message
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitVersion(major: Int, minor: Int, patch: Int) {
         this.version = KmVersion(major, minor, patch)
     }
@@ -1014,7 +1014,7 @@ public class KmVersionRequirement : KmVersionRequirementVisitor() {
      *
      * @param visitor the visitor which will visit data in this version requirement
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmVersionRequirementVisitor) {
         visitor.visit(kind, level, errorCode, message)
         visitor.visitVersion(version.major, version.minor, version.patch)
@@ -1029,14 +1029,14 @@ public class KmVersionRequirement : KmVersionRequirementVisitor() {
  * may change in a subsequent release.
  */
 @ExperimentalContracts
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmContract : KmContractVisitor() {
     /**
      * Effects of this contract.
      */
     public val effects: MutableList<KmEffect> = ArrayList(1)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitEffect(type: KmEffectType, invocationKind: KmEffectInvocationKind?): KmEffectVisitor =
         KmEffect(type, invocationKind).addTo(effects)
 
@@ -1045,7 +1045,7 @@ public class KmContract : KmContractVisitor() {
      *
      * @param visitor the visitor which will visit data in this contract
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmContractVisitor) {
         effects.forEach { visitor.visitEffect(it.type, it.invocationKind)?.let(it::accept) }
         visitor.visitEnd()
@@ -1063,7 +1063,7 @@ public class KmContract : KmContractVisitor() {
  *   specified further in the effect expression
  */
 @ExperimentalContracts
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmEffect(
     public var type: KmEffectType,
     public var invocationKind: KmEffectInvocationKind?
@@ -1079,11 +1079,11 @@ public class KmEffect(
      */
     public var conclusion: KmEffectExpression? = null
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitConstructorArgument(): KmEffectExpressionVisitor =
         KmEffectExpression().addTo(constructorArguments)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitConclusionOfConditionalEffect(): KmEffectExpressionVisitor =
         KmEffectExpression().also { conclusion = it }
 
@@ -1092,7 +1092,7 @@ public class KmEffect(
      *
      * @param visitor the visitor which will visit data in this effect
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmEffectVisitor) {
         constructorArguments.forEach { visitor.visitConstructorArgument()?.let(it::accept) }
         conclusion?.let { visitor.visitConclusionOfConditionalEffect()?.let(it::accept) }
@@ -1110,7 +1110,7 @@ public class KmEffect(
  * such as [KmEffectExpression.isNegated].
  */
 @ExperimentalContracts
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION", "DEPRECATION_ERROR")
 public class KmEffectExpression : KmEffectExpressionVisitor() {
     /**
      * Effect expression flags, consisting of [Flag.EffectExpression] flags.
@@ -1146,26 +1146,26 @@ public class KmEffectExpression : KmEffectExpressionVisitor() {
      */
     public val orArguments: MutableList<KmEffectExpression> = ArrayList(0)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visit(flags: Int, parameterIndex: Int?) {
         this.flags = flags
         this.parameterIndex = parameterIndex
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitConstantValue(value: Any?) {
         constantValue = KmConstantValue(value)
     }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitIsInstanceType(flags: Int): KmTypeVisitor =
         KmType(flags).also { isInstanceType = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitAndArgument(): KmEffectExpressionVisitor =
         KmEffectExpression().addTo(andArguments)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitOrArgument(): KmEffectExpressionVisitor =
         KmEffectExpression().addTo(orArguments)
 
@@ -1174,7 +1174,7 @@ public class KmEffectExpression : KmEffectExpressionVisitor() {
      *
      * @param visitor the visitor which will visit data in this effect expression
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmEffectExpressionVisitor) {
         visitor.visit(flags, parameterIndex)
         constantValue?.let { visitor.visitConstantValue(it.value) }
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/Visitors.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/Visitors.kt
index bbee0a48fbc..ef67af299df 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/Visitors.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/Visitors.kt
@@ -13,8 +13,8 @@ internal const val VISITOR_API_MESSAGE =
 /**
  * A visitor containing the common code to visit Kotlin declaration containers, such as classes and package fragments.
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmDeclarationContainerVisitor @JvmOverloads constructor(protected open val delegate: KmDeclarationContainerVisitor? = null) {
     /**
      * Visits a function in the container.
@@ -61,8 +61,8 @@ public abstract class KmDeclarationContainerVisitor @JvmOverloads constructor(pr
  * When using this class, [visit] must be called first, followed by zero or more [visitTypeParameter] calls, followed by zero or more calls
  * to other visit* methods, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmClassVisitor @JvmOverloads constructor(delegate: KmClassVisitor? = null) : KmDeclarationContainerVisitor(delegate) {
     override val delegate: KmClassVisitor?
         get() = super.delegate as KmClassVisitor?
@@ -194,8 +194,8 @@ public abstract class KmClassVisitor @JvmOverloads constructor(delegate: KmClass
  *
  * When using this class, [visitEnd] must be called exactly once and after calls to all other visit* methods.
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmPackageVisitor @JvmOverloads constructor(delegate: KmPackageVisitor? = null) :
     KmDeclarationContainerVisitor(delegate) {
     override val delegate: KmPackageVisitor?
@@ -222,8 +222,8 @@ public abstract class KmPackageVisitor @JvmOverloads constructor(delegate: KmPac
  *
  * When using this class, [visitFunction] must be called first, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmLambdaVisitor @JvmOverloads constructor(private val delegate: KmLambdaVisitor? = null) {
     /**
      * Visits the signature of a synthetic anonymous function, representing the lambda.
@@ -247,8 +247,8 @@ public abstract class KmLambdaVisitor @JvmOverloads constructor(private val dele
  *
  * When using this class, [visitEnd] must be called exactly once and after calls to all other visit* methods.
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmConstructorVisitor @JvmOverloads constructor(private val delegate: KmConstructorVisitor? = null) {
     /**
      * Visits a value parameter of the constructor.
@@ -287,8 +287,8 @@ public abstract class KmConstructorVisitor @JvmOverloads constructor(private val
  * When using this class, zero or more calls to [visitTypeParameter] must be done first, followed by zero or more calls
  * to other visit* methods, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmFunctionVisitor @JvmOverloads constructor(private val delegate: KmFunctionVisitor? = null) {
     /**
      * Visits a type parameter of the function.
@@ -371,8 +371,8 @@ public abstract class KmFunctionVisitor @JvmOverloads constructor(private val de
  * When using this class, zero or more calls to [visitTypeParameter] must be done first, followed by zero or more calls
  * to other visit* methods, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmPropertyVisitor @JvmOverloads constructor(private val delegate: KmPropertyVisitor? = null) {
     /**
      * Visits a type parameter of the property.
@@ -448,8 +448,8 @@ public abstract class KmPropertyVisitor @JvmOverloads constructor(private val de
  * When using this class, zero or more calls to [visitTypeParameter] must be done first, followed by zero or more calls
  * to other visit* methods, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmTypeAliasVisitor @JvmOverloads constructor(private val delegate: KmTypeAliasVisitor? = null) {
     /**
      * Visits a type parameter of the type alias.
@@ -517,8 +517,8 @@ public abstract class KmTypeAliasVisitor @JvmOverloads constructor(private val d
  * When using this class, either [visitType] or [visitVarargElementType] must be called first (depending on whether the value parameter
  * is `vararg` or not), followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmValueParameterVisitor @JvmOverloads constructor(private val delegate: KmValueParameterVisitor? = null) {
     /**
      * Visits the type of the value parameter, if this is **not** a `vararg` parameter.
@@ -557,8 +557,8 @@ public abstract class KmValueParameterVisitor @JvmOverloads constructor(private
  *
  * When using this class, zero or more [visitUpperBound] calls must be done first, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmTypeParameterVisitor @JvmOverloads constructor(private val delegate: KmTypeParameterVisitor? = null) {
     /**
      * Visits the upper bound of the type parameter.
@@ -595,8 +595,8 @@ public abstract class KmTypeParameterVisitor @JvmOverloads constructor(private v
  *
  * When using this class, [visitEnd] must be called exactly once and after calls to all other visit* methods.
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 public abstract class KmTypeVisitor @JvmOverloads constructor(private val delegate: KmTypeVisitor? = null) {
     /**
      * Visits the name of the class, if this type's classifier is a class.
@@ -708,8 +708,8 @@ public abstract class KmTypeVisitor @JvmOverloads constructor(private val delega
  *
  * When using this class, [visit] must be called first, followed by [visitVersion], followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-public abstract class KmVersionRequirementVisitor @JvmOverloads constructor(@Suppress("DEPRECATION") private val delegate: KmVersionRequirementVisitor? = null) {
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+public abstract class KmVersionRequirementVisitor @JvmOverloads constructor(@Suppress("DEPRECATION_ERROR") private val delegate: KmVersionRequirementVisitor? = null) {
     /**
      * Visits the description of this version requirement.
      *
@@ -750,8 +750,8 @@ public abstract class KmVersionRequirementVisitor @JvmOverloads constructor(@Sup
  *
  * When using this class, zero or more calls to [visitEffect] must be done first, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 @ExperimentalContracts
 public abstract class KmContractVisitor @JvmOverloads constructor(private val delegate: KmContractVisitor? = null) {
     /**
@@ -781,8 +781,8 @@ public abstract class KmContractVisitor @JvmOverloads constructor(private val de
  * When using this class, zero or more calls to [visitConstructorArgument] or [visitConclusionOfConditionalEffect] must be done first,
  * followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 @ExperimentalContracts
 public abstract class KmEffectVisitor @JvmOverloads constructor(private val delegate: KmEffectVisitor? = null) {
     /**
@@ -815,8 +815,8 @@ public abstract class KmEffectVisitor @JvmOverloads constructor(private val dele
  *
  * When using this class, [visit] must be called first, followed by zero or more calls to other visit* methods, followed by [visitEnd].
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+@Suppress("DEPRECATION_ERROR")
 @ExperimentalContracts
 public abstract class KmEffectExpressionVisitor @JvmOverloads constructor(private val delegate: KmEffectExpressionVisitor? = null) {
     /**
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Readers.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Readers.kt
index 7feccde1cd6..7c328ac5110 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Readers.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Readers.kt
@@ -2,13 +2,13 @@
  * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION") // flags
 
 package kotlinx.metadata.internal
 
 import kotlinx.metadata.*
+import kotlinx.metadata.internal.common.KmModuleFragment
 import kotlinx.metadata.internal.extensions.MetadataExtensions
-import kotlinx.metadata.internal.common.KmModuleFragmentVisitor
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.deserialization.*
 import kotlin.contracts.ExperimentalContracts
@@ -49,11 +49,11 @@ public class ReadContext(
 }
 
 @OptIn(ExperimentalContextReceivers::class)
-public fun ProtoBuf.Class.accept(
-    v: KmClassVisitor,
+public fun ProtoBuf.Class.toKmClass(
     strings: NameResolver,
-    contextExtensions: List<ReadContextExtension> = emptyList()
-) {
+    contextExtensions: List<ReadContextExtension> = emptyList(),
+): KmClass {
+    val v = KmClass()
     val c = ReadContext(
         strings,
         TypeTable(typeTable),
@@ -61,61 +61,36 @@ public fun ProtoBuf.Class.accept(
         contextExtensions = contextExtensions
     ).withTypeParameters(typeParameterList)
 
-    v.visit(flags, c.className(fqName))
-
-    for (typeParameter in typeParameterList) {
-        typeParameter.accept(v::visitTypeParameter, c)
-    }
-
-    for (supertype in supertypes(c.types)) {
-        v.visitSupertype(supertype.typeFlags)?.let { supertype.accept(it, c) }
-    }
-
-    for (constructor in constructorList) {
-        v.visitConstructor(constructor.flags)?.let { constructor.accept(it, c) }
-    }
+    v.flags = flags
+    v.name = c.className(fqName)
 
+    typeParameterList.mapTo(v.typeParameters) { it.toKmTypeParameter(c) }
+    supertypes(c.types).mapTo(v.supertypes) { it.toKmType(c) }
+    constructorList.mapTo(v.constructors) { it.toKmConstructor(c) }
     v.visitDeclarations(functionList, propertyList, typeAliasList, c)
-
     if (hasCompanionObjectName()) {
-        v.visitCompanionObject(c[companionObjectName])
-    }
-
-    for (nestedClassName in nestedClassNameList) {
-        v.visitNestedClass(c[nestedClassName])
+        v.companionObject = c[companionObjectName]
     }
 
+    nestedClassNameList.mapTo(v.nestedClasses) { c[it] }
     for (enumEntry in enumEntryList) {
-        if (!enumEntry.hasName()) {
-            throw InconsistentKotlinMetadataException("No name for EnumEntry")
-        }
-        v.visitEnumEntry(c[enumEntry.name])
+        if (!enumEntry.hasName()) throw InconsistentKotlinMetadataException("No name for EnumEntry")
+        v.enumEntries.add(c[enumEntry.name])
     }
-
-    for (sealedSubclassFqName in sealedSubclassFqNameList) {
-        v.visitSealedSubclass(c.className(sealedSubclassFqName))
-    }
-
+    sealedSubclassFqNameList.mapTo(v.sealedSubclasses) { c.className(it) }
     if (hasInlineClassUnderlyingPropertyName()) {
-        v.visitInlineClassUnderlyingPropertyName(c[inlineClassUnderlyingPropertyName])
-    }
-    loadInlineClassUnderlyingType(c)?.let { underlyingType ->
-        v.visitInlineClassUnderlyingType(underlyingType.typeFlags)?.let { underlyingType.accept(it, c) }
+        v.inlineClassUnderlyingPropertyName = c[inlineClassUnderlyingPropertyName]
     }
+    v.inlineClassUnderlyingType = loadInlineClassUnderlyingType(c)?.toKmType(c)
 
-    for (contextReceiverType in contextReceiverTypes(c.types)) {
-        v.visitContextReceiverType(contextReceiverType.typeFlags)?.let { contextReceiverType.accept(it, c) }
-    }
-
-    for (versionRequirement in versionRequirementList) {
-        v.visitVersionRequirement()?.let { acceptVersionRequirementVisitor(versionRequirement, it, c) }
-    }
+    contextReceiverTypes(c.types).mapTo(v.contextReceiverTypes) { it.toKmType(c) }
+    versionRequirementList.mapTo(v.versionRequirements) { readVersionRequirement(it, c) }
 
     for (extension in c.extensions) {
         extension.readClassExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
 private fun ProtoBuf.Class.loadInlineClassUnderlyingType(c: ReadContext): ProtoBuf.Type? {
@@ -130,11 +105,11 @@ private fun ProtoBuf.Class.loadInlineClassUnderlyingType(c: ReadContext): ProtoB
         ?.returnType(c.types)
 }
 
-public fun ProtoBuf.Package.accept(
-    v: KmPackageVisitor,
+public fun ProtoBuf.Package.toKmPackage(
     strings: NameResolver,
-    contextExtensions: List<ReadContextExtension> = emptyList()
-) {
+    contextExtensions: List<ReadContextExtension> = emptyList(),
+): KmPackage {
+    val v = KmPackage()
     val c = ReadContext(
         strings,
         TypeTable(typeTable),
@@ -148,14 +123,14 @@ public fun ProtoBuf.Package.accept(
         extension.readPackageExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
-public fun ProtoBuf.PackageFragment.accept(
-    v: KmModuleFragmentVisitor,
+public fun ProtoBuf.PackageFragment.toKmModuleFragment(
     strings: NameResolver,
-    contextExtensions: List<ReadContextExtension> = emptyList()
-) {
+    contextExtensions: List<ReadContextExtension> = emptyList(),
+): KmModuleFragment {
+    val v = KmModuleFragment()
     val c = ReadContext(
         strings,
         TypeTable(ProtoBuf.TypeTable.newBuilder().build()),
@@ -163,223 +138,155 @@ public fun ProtoBuf.PackageFragment.accept(
         contextExtensions = contextExtensions
     )
 
-    v.visitPackage()?.let { `package`.accept(it, strings, contextExtensions) }
-
-    class_List.forEach { clazz ->
-        v.visitClass()?.let { clazz.accept(it, strings, contextExtensions) }
-    }
+    v.pkg = `package`.toKmPackage(strings, contextExtensions)
+    class_List.mapTo(v.classes) { it.toKmClass(strings, contextExtensions) }
 
     for (extension in c.extensions) {
         extension.readModuleFragmentExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
-private fun KmDeclarationContainerVisitor.visitDeclarations(
-    functions: List<ProtoBuf.Function>,
-    properties: List<ProtoBuf.Property>,
-    typeAliases: List<ProtoBuf.TypeAlias>,
-    c: ReadContext
+private fun KmDeclarationContainer.visitDeclarations(
+    protoFunctions: List<ProtoBuf.Function>,
+    protoProperties: List<ProtoBuf.Property>,
+    protoTypeAliases: List<ProtoBuf.TypeAlias>,
+    c: ReadContext,
 ) {
-    for (function in functions) {
-        visitFunction(function.flags, c[function.name])?.let { function.accept(it, c) }
-    }
-
-    for (property in properties) {
-        visitProperty(
-            property.flags, c[property.name], property.getPropertyGetterFlags(), property.getPropertySetterFlags()
-        )?.let { property.accept(it, c) }
-    }
-
-    for (typeAlias in typeAliases) {
-        visitTypeAlias(typeAlias.flags, c[typeAlias.name])?.let { typeAlias.accept(it, c) }
-    }
+    protoFunctions.mapTo(functions) { it.toKmFunction(c) }
+    protoProperties.mapTo(properties) { it.toKmProperty(c) }
+    protoTypeAliases.mapTo(typeAliases) { it.toKmTypeAlias(c) }
 }
 
-public fun ProtoBuf.Function.accept(v: KmLambdaVisitor, strings: NameResolver) {
+public fun ProtoBuf.Function.toKmLambda(strings: NameResolver): KmLambda {
+    val v = KmLambda()
     val c = ReadContext(strings, TypeTable(typeTable), VersionRequirementTable.EMPTY)
-
-    v.visitFunction(flags, c[name])?.let { accept(it, c) }
-
-    v.visitEnd()
+    v.function = this.toKmFunction(c)
+    return v
 }
 
-private fun ProtoBuf.Constructor.accept(v: KmConstructorVisitor, c: ReadContext) {
-    for (parameter in valueParameterList) {
-        v.visitValueParameter(parameter.flags, c[parameter.name])?.let { parameter.accept(it, c) }
-    }
-
-    for (versionRequirement in versionRequirementList) {
-        v.visitVersionRequirement()?.let { acceptVersionRequirementVisitor(versionRequirement, it, c) }
-    }
+private fun ProtoBuf.Constructor.toKmConstructor(c: ReadContext): KmConstructor {
+    val v = KmConstructor(flags)
+    valueParameterList.mapTo(v.valueParameters) { it.toKmValueParameter(c) }
+    versionRequirementList.mapTo(v.versionRequirements) { readVersionRequirement(it, c) }
 
     for (extension in c.extensions) {
         extension.readConstructorExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
 @OptIn(ExperimentalContextReceivers::class)
-private fun ProtoBuf.Function.accept(v: KmFunctionVisitor, outer: ReadContext) {
+private fun ProtoBuf.Function.toKmFunction(outer: ReadContext): KmFunction {
+    val v = KmFunction(flags, outer[name])
     val c = outer.withTypeParameters(typeParameterList)
 
-    for (typeParameter in typeParameterList) {
-        typeParameter.accept(v::visitTypeParameter, c)
-    }
-
-    receiverType(c.types)?.let { receiverType ->
-        v.visitReceiverParameterType(receiverType.typeFlags)?.let { receiverType.accept(it, c) }
-    }
-
-    for (contextReceiverType in contextReceiverTypes(c.types)) {
-        v.visitContextReceiverType(contextReceiverType.typeFlags)?.let { contextReceiverType.accept(it, c) }
-    }
-
-    for (parameter in valueParameterList) {
-        v.visitValueParameter(parameter.flags, c[parameter.name])?.let { parameter.accept(it, c) }
-    }
-
-    returnType(c.types).let { returnType ->
-        v.visitReturnType(returnType.typeFlags)?.let { returnType.accept(it, c) }
-    }
+    typeParameterList.mapTo(v.typeParameters) { it.toKmTypeParameter(c) }
+    v.receiverParameterType = receiverType(c.types)?.toKmType(c)
+    contextReceiverTypes(c.types).mapTo(v.contextReceiverTypes) { it.toKmType(c) }
+    valueParameterList.mapTo(v.valueParameters) { it.toKmValueParameter(c) }
+    v.returnType = returnType(c.types).toKmType(c)
 
+    @OptIn(ExperimentalContracts::class)
     if (hasContract()) {
-        @OptIn(ExperimentalContracts::class) v.visitContract()?.let { contract.accept(it, c) }
+        v.contract = contract.toKmContract(c)
     }
 
-    for (versionRequirement in versionRequirementList) {
-        v.visitVersionRequirement()?.let { acceptVersionRequirementVisitor(versionRequirement, it, c) }
-    }
+    versionRequirementList.mapTo(v.versionRequirements) { readVersionRequirement(it, c) }
 
     for (extension in c.extensions) {
         extension.readFunctionExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
 @OptIn(ExperimentalContextReceivers::class)
-public fun ProtoBuf.Property.accept(v: KmPropertyVisitor, outer: ReadContext) {
+public fun ProtoBuf.Property.toKmProperty(outer: ReadContext): KmProperty {
+    val v = KmProperty(flags, outer[name], getPropertyGetterFlags(), getPropertySetterFlags())
     val c = outer.withTypeParameters(typeParameterList)
 
-    for (typeParameter in typeParameterList) {
-        typeParameter.accept(v::visitTypeParameter, c)
-    }
-
-    receiverType(c.types)?.let { receiverType ->
-        v.visitReceiverParameterType(receiverType.typeFlags)?.let { receiverType.accept(it, c) }
-    }
-
-    for (contextReceiverType in contextReceiverTypes(c.types)) {
-        v.visitContextReceiverType(contextReceiverType.typeFlags)?.let { contextReceiverType.accept(it, c) }
-    }
-
+    typeParameterList.mapTo(v.typeParameters) { it.toKmTypeParameter(c) }
+    v.receiverParameterType = receiverType(c.types)?.toKmType(c)
+    contextReceiverTypes(c.types).mapTo(v.contextReceiverTypes) { it.toKmType(c) }
     if (hasSetterValueParameter()) {
-        val parameter = setterValueParameter
-        v.visitSetterParameter(parameter.flags, c[parameter.name])?.let { parameter.accept(it, c) }
-    }
-
-    returnType(c.types).let { returnType ->
-        v.visitReturnType(returnType.typeFlags)?.let { returnType.accept(it, c) }
-    }
-
-    for (versionRequirement in versionRequirementList) {
-        v.visitVersionRequirement()?.let { acceptVersionRequirementVisitor(versionRequirement, it, c) }
+        v.setterParameter = setterValueParameter.toKmValueParameter(c)
     }
+    v.returnType = returnType(c.types).toKmType(c)
+    versionRequirementList.mapTo(v.versionRequirements) { readVersionRequirement(it, c) }
 
     for (extension in c.extensions) {
         extension.readPropertyExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
-private fun ProtoBuf.TypeAlias.accept(v: KmTypeAliasVisitor, outer: ReadContext) {
+private fun ProtoBuf.TypeAlias.toKmTypeAlias(outer: ReadContext): KmTypeAlias {
+    val v = KmTypeAlias(flags, outer[name])
+
     val c = outer.withTypeParameters(typeParameterList)
 
-    for (typeParameter in typeParameterList) {
-        typeParameter.accept(v::visitTypeParameter, c)
-    }
+    typeParameterList.mapTo(v.typeParameters) { it.toKmTypeParameter(c) }
+    v.underlyingType = underlyingType(c.types).toKmType(c)
+    v.expandedType = expandedType(c.types).toKmType(c)
+    annotationList.mapTo(v.annotations) { it.readAnnotation(c.strings) }
 
-    underlyingType(c.types).let { underlyingType ->
-        v.visitUnderlyingType(underlyingType.typeFlags)?.let { underlyingType.accept(it, c) }
-    }
-
-    expandedType(c.types).let { expandedType ->
-        v.visitExpandedType(expandedType.typeFlags)?.let { expandedType.accept(it, c) }
-    }
-
-    for (annotation in annotationList) {
-        v.visitAnnotation(annotation.readAnnotation(c.strings))
-    }
-
-    for (versionRequirement in versionRequirementList) {
-        v.visitVersionRequirement()?.let { acceptVersionRequirementVisitor(versionRequirement, it, c) }
-    }
+    versionRequirementList.mapTo(v.versionRequirements) { readVersionRequirement(it, c) }
 
     for (extension in c.extensions) {
         extension.readTypeAliasExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
-private fun ProtoBuf.ValueParameter.accept(v: KmValueParameterVisitor, c: ReadContext) {
-    type(c.types).let { type ->
-        v.visitType(type.typeFlags)?.let { type.accept(it, c) }
-    }
+private fun ProtoBuf.ValueParameter.toKmValueParameter(c: ReadContext): KmValueParameter {
+    val v = KmValueParameter(flags, c[name])
+    v.type = type(c.types).toKmType(c)
 
-    varargElementType(c.types)?.let { varargElementType ->
-        v.visitVarargElementType(varargElementType.typeFlags)?.let { varargElementType.accept(it, c) }
-    }
+    v.varargElementType = varargElementType(c.types)?.toKmType(c)
 
     for (extension in c.extensions) {
         extension.readValueParameterExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
-private inline fun ProtoBuf.TypeParameter.accept(
-    visit: (flags: Int, name: String, id: Int, variance: KmVariance) -> KmTypeParameterVisitor?,
-    c: ReadContext
-) {
+private fun ProtoBuf.TypeParameter.toKmTypeParameter(
+    c: ReadContext,
+): KmTypeParameter {
     val variance = when (requireNotNull(variance)) {
         ProtoBuf.TypeParameter.Variance.IN -> KmVariance.IN
         ProtoBuf.TypeParameter.Variance.OUT -> KmVariance.OUT
         ProtoBuf.TypeParameter.Variance.INV -> KmVariance.INVARIANT
     }
+    val ktp = KmTypeParameter(typeParameterFlags, c[name], id, variance)
 
-    visit(typeParameterFlags, c[name], id, variance)?.let { accept(it, c) }
-}
-
-private fun ProtoBuf.TypeParameter.accept(v: KmTypeParameterVisitor, c: ReadContext) {
-    for (upperBound in upperBounds(c.types)) {
-        v.visitUpperBound(upperBound.typeFlags)?.let { upperBound.accept(it, c) }
-    }
+    upperBounds(c.types).mapTo(ktp.upperBounds) { it.toKmType(c) }
 
     for (extension in c.extensions) {
-        extension.readTypeParameterExtensions(v, this, c)
+        extension.readTypeParameterExtensions(ktp, this, c)
     }
 
-    v.visitEnd()
+    return ktp
 }
 
-private fun ProtoBuf.Type.accept(v: KmTypeVisitor, c: ReadContext) {
-    when {
-        hasClassName() -> v.visitClass(c.className(className))
-        hasTypeAliasName() -> v.visitTypeAlias(c.className(typeAliasName))
-        hasTypeParameter() -> v.visitTypeParameter(typeParameter)
+private fun ProtoBuf.Type.toKmType(c: ReadContext): KmType {
+    val v = KmType(typeFlags)
+    v.classifier = when {
+        hasClassName() -> KmClassifier.Class(c.className(className))
+        hasTypeAliasName() -> KmClassifier.TypeAlias(c.className(typeAliasName))
+        hasTypeParameter() -> KmClassifier.TypeParameter(typeParameter)
         hasTypeParameterName() -> {
             val id = c.getTypeParameterId(typeParameterName)
                 ?: throw InconsistentKotlinMetadataException("No type parameter id for ${c[typeParameterName]}")
-            v.visitTypeParameter(id)
-        }
-        else -> {
-            throw InconsistentKotlinMetadataException("No classifier (class, type alias or type parameter) recorded for Type")
+            KmClassifier.TypeParameter(id)
         }
+        else -> throw InconsistentKotlinMetadataException("No classifier (class, type alias or type parameter) recorded for Type")
     }
 
     for (argument in argumentList) {
@@ -393,35 +300,28 @@ private fun ProtoBuf.Type.accept(v: KmTypeVisitor, c: ReadContext) {
         if (variance != null) {
             val argumentType = argument.type(c.types)
                 ?: throw InconsistentKotlinMetadataException("No type argument for non-STAR projection in Type")
-            v.visitArgument(argumentType.typeFlags, variance)?.let { argumentType.accept(it, c) }
+            v.arguments.add(KmTypeProjection(variance, argumentType.toKmType(c)))
         } else {
-            v.visitStarProjection()
+            v.arguments.add(KmTypeProjection.STAR)
         }
     }
 
-    abbreviatedType(c.types)?.let { abbreviatedType ->
-        v.visitAbbreviatedType(abbreviatedType.typeFlags)?.let { abbreviatedType.accept(it, c) }
-    }
+    v.abbreviatedType = abbreviatedType(c.types)?.toKmType(c)
+    v.outerType = outerType(c.types)?.toKmType(c)
 
-    outerType(c.types)?.let { outerType ->
-        v.visitOuterType(outerType.typeFlags)?.let { outerType.accept(it, c) }
-    }
-
-    flexibleUpperBound(c.types)?.let { upperBound ->
-        v.visitFlexibleTypeUpperBound(
-            upperBound.typeFlags,
-            if (hasFlexibleTypeCapabilitiesId()) c[flexibleTypeCapabilitiesId] else null
-        )?.let { upperBound.accept(it, c) }
+    v.flexibleTypeUpperBound = flexibleUpperBound(c.types)?.toKmType(c)?.let {
+        KmFlexibleTypeUpperBound(it, if (hasFlexibleTypeCapabilitiesId()) c[flexibleTypeCapabilitiesId] else null)
     }
 
     for (extension in c.extensions) {
         extension.readTypeExtensions(v, this, c)
     }
 
-    v.visitEnd()
+    return v
 }
 
-private fun acceptVersionRequirementVisitor(id: Int, v: KmVersionRequirementVisitor, c: ReadContext) {
+private fun readVersionRequirement(id: Int, c: ReadContext): KmVersionRequirement {
+    val v = KmVersionRequirement()
     val message = VersionRequirement.create(id, c.strings, c.versionRequirements)
         ?: throw InconsistentKotlinMetadataException("No VersionRequirement with the given id in the table")
 
@@ -437,16 +337,19 @@ private fun acceptVersionRequirementVisitor(id: Int, v: KmVersionRequirementVisi
         DeprecationLevel.HIDDEN -> KmVersionRequirementLevel.HIDDEN
     }
 
-    v.visit(kind, level, message.errorCode, message.message)
+    v.kind = kind
+    v.level = level
+    v.errorCode = message.errorCode
+    v.message = message.message
 
     val (major, minor, patch) = message.version
-    v.visitVersion(major, minor, patch)
-
-    v.visitEnd()
+    v.version = KmVersion(major, minor, patch)
+    return v
 }
 
 @ExperimentalContracts
-private fun ProtoBuf.Contract.accept(v: KmContractVisitor, c: ReadContext) {
+private fun ProtoBuf.Contract.toKmContract(c: ReadContext): KmContract {
+    val v = KmContract()
     for (effect in effectList) {
         if (!effect.hasEffectType()) continue
 
@@ -462,34 +365,32 @@ private fun ProtoBuf.Contract.accept(v: KmContractVisitor, c: ReadContext) {
             ProtoBuf.Effect.InvocationKind.AT_LEAST_ONCE -> KmEffectInvocationKind.AT_LEAST_ONCE
         }
 
-        v.visitEffect(effectType, effectKind)?.let { effect.accept(it, c) }
+        v.effects.add(effect.toKmEffect(effectType, effectKind, c))
     }
 
-    v.visitEnd()
+    return v
 }
 
 @ExperimentalContracts
-private fun ProtoBuf.Effect.accept(v: KmEffectVisitor, c: ReadContext) {
-    for (constructorArgument in effectConstructorArgumentList) {
-        v.visitConstructorArgument()?.let { constructorArgument.accept(it, c) }
-    }
+private fun ProtoBuf.Effect.toKmEffect(type: KmEffectType, kind: KmEffectInvocationKind?, c: ReadContext): KmEffect {
+    val v = KmEffect(type, kind)
+    effectConstructorArgumentList.mapTo(v.constructorArguments) { it.toKmEffectExpression(c) }
 
     if (hasConclusionOfConditionalEffect()) {
-        v.visitConclusionOfConditionalEffect()?.let { conclusionOfConditionalEffect.accept(it, c) }
+        v.conclusion = conclusionOfConditionalEffect.toKmEffectExpression(c)
     }
 
-    v.visitEnd()
+    return v
 }
 
 @ExperimentalContracts
-private fun ProtoBuf.Expression.accept(v: KmEffectExpressionVisitor, c: ReadContext) {
-    v.visit(
-        flags,
-        if (hasValueParameterReference()) valueParameterReference else null
-    )
+private fun ProtoBuf.Expression.toKmEffectExpression(c: ReadContext): KmEffectExpression {
+    val v = KmEffectExpression()
+    v.flags = flags
+    v.parameterIndex = if (hasValueParameterReference()) valueParameterReference else null
 
     if (hasConstantValue()) {
-        v.visitConstantValue(
+        v.constantValue = KmConstantValue(
             when (requireNotNull(constantValue)) {
                 ProtoBuf.Expression.ConstantValue.TRUE -> true
                 ProtoBuf.Expression.ConstantValue.FALSE -> false
@@ -498,19 +399,12 @@ private fun ProtoBuf.Expression.accept(v: KmEffectExpressionVisitor, c: ReadCont
         )
     }
 
-    isInstanceType(c.types)?.let { type ->
-        v.visitIsInstanceType(type.typeFlags)?.let { type.accept(it, c) }
-    }
+    v.isInstanceType = isInstanceType(c.types)?.toKmType(c)
 
-    for (andArgument in andArgumentList) {
-        v.visitAndArgument()?.let { andArgument.accept(it, c) }
-    }
+    andArgumentList.mapTo(v.andArguments) { it.toKmEffectExpression(c) }
+    orArgumentList.mapTo(v.orArguments) { it.toKmEffectExpression(c) }
 
-    for (orArgument in orArgumentList) {
-        v.visitOrArgument()?.let { orArgument.accept(it, c) }
-    }
-
-    v.visitEnd()
+    return v
 }
 
 private val ProtoBuf.Type.typeFlags: Int
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/WriteUtils.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/WriteUtils.kt
index aaad129206b..8818f8283e8 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/WriteUtils.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/WriteUtils.kt
@@ -5,10 +5,10 @@
 
 package kotlinx.metadata.internal
 
-import kotlinx.metadata.ClassName
-import kotlinx.metadata.KmAnnotation
-import kotlinx.metadata.KmAnnotationArgument
-import kotlinx.metadata.isLocalClassName
+import kotlinx.metadata.*
+import kotlinx.metadata.internal.extensions.KmExtension
+import kotlinx.metadata.internal.extensions.MetadataExtensions
+import kotlinx.metadata.internal.extensions.applySingleExtension
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.deserialization.Flags
 import org.jetbrains.kotlin.metadata.serialization.StringTable
@@ -115,3 +115,9 @@ internal fun StringTable.getClassNameIndex(name: ClassName): Int =
         getQualifiedClassNameIndex(name.substring(1), true)
     else
         getQualifiedClassNameIndex(name, false)
+
+@Suppress("DEPRECATION_ERROR")
+internal fun <V : KmExtensionVisitor, E : KmExtension<V>> List<E>.writeExtensions(writer: MetadataExtensions.(KmExtensionType) -> V?) =
+    forEach { ext ->
+        applySingleExtension(ext.type) { writer(ext.type) }?.let { ext.accept(it) }
+    }
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Writers.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Writers.kt
index fca22ece5fa..2407a485e9d 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Writers.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/Writers.kt
@@ -2,13 +2,13 @@
  * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION") // flags
 package kotlinx.metadata.internal
 
 import kotlinx.metadata.*
-import kotlinx.metadata.internal.common.KmModuleFragmentExtensionVisitor
-import kotlinx.metadata.internal.common.KmModuleFragmentVisitor
-import kotlinx.metadata.internal.extensions.applySingleExtension
+import kotlinx.metadata.internal.common.KmModuleFragment
+import kotlinx.metadata.internal.extensions.MetadataExtensions
+import kotlinx.metadata.internal.extensions.matchExtensions
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.deserialization.VersionRequirement
 import org.jetbrains.kotlin.metadata.serialization.MutableVersionRequirementTable
@@ -31,526 +31,348 @@ public open class WriteContext(public val strings: StringTable, public val conte
         strings.getClassNameIndex(name)
 }
 
-private fun writeTypeParameter(
-    c: WriteContext, flags: Int, name: String, id: Int, variance: KmVariance,
-    output: (ProtoBuf.TypeParameter.Builder) -> Unit
-): KmTypeParameterVisitor =
-    object : KmTypeParameterVisitor() {
-        private val t = ProtoBuf.TypeParameter.newBuilder()
+private fun WriteContext.writeTypeParameter(kmTypeParameter: KmTypeParameter): ProtoBuf.TypeParameter.Builder {
+    val t = ProtoBuf.TypeParameter.newBuilder()
+    kmTypeParameter.upperBounds.forEach { ub ->
+        t.addUpperBound(writeType(ub).build())
+    }
+    kmTypeParameter.extensions.writeExtensions {
+        writeTypeParameterExtensions(it, t, this@writeTypeParameter)
+    }
+    t.name = this[kmTypeParameter.name]
+    t.id = kmTypeParameter.id
+    val reified = kmTypeParameter.isReified
+    if (reified != ProtoBuf.TypeParameter.getDefaultInstance().reified) {
+        t.reified = reified
+    }
+    if (kmTypeParameter.variance == KmVariance.IN) {
+        t.variance = ProtoBuf.TypeParameter.Variance.IN
+    } else if (kmTypeParameter.variance == KmVariance.OUT) {
+        t.variance = ProtoBuf.TypeParameter.Variance.OUT
+    }
+    return t
+}
 
-        override fun visitUpperBound(flags: Int): KmTypeVisitor? =
-            writeType(c, flags) { t.addUpperBound(it) }
-
-        override fun visitExtensions(type: KmExtensionType): KmTypeParameterExtensionVisitor? =
-            applySingleExtension(type) {
-                writeTypeParameterExtensions(type, t, c)
-            }
-
-        override fun visitEnd() {
-            t.name = c[name]
-            t.id = id
-            val reified = Flag.TypeParameter.IS_REIFIED(flags)
-            if (reified != ProtoBuf.TypeParameter.getDefaultInstance().reified) {
-                t.reified = reified
-            }
-            if (variance == KmVariance.IN) {
-                t.variance = ProtoBuf.TypeParameter.Variance.IN
-            } else if (variance == KmVariance.OUT) {
-                t.variance = ProtoBuf.TypeParameter.Variance.OUT
-            }
-            output(t)
+private fun WriteContext.writeTypeProjection(argument: KmTypeProjection): ProtoBuf.Type.Argument.Builder {
+    val t = ProtoBuf.Type.Argument.newBuilder()
+    if (argument == KmTypeProjection.STAR) {
+        t.projection = ProtoBuf.Type.Argument.Projection.STAR
+    } else {
+        val (variance, argType) = argument
+        if (variance == null || argType == null)
+            throw InconsistentKotlinMetadataException("Variance and type must be set for non-star type projection")
+        if (variance == KmVariance.IN) {
+            t.projection = ProtoBuf.Type.Argument.Projection.IN
+        } else if (variance == KmVariance.OUT) {
+            t.projection = ProtoBuf.Type.Argument.Projection.OUT
         }
+        t.type = writeType(argType).build()
     }
 
-private fun writeType(c: WriteContext, flags: Int, output: (ProtoBuf.Type.Builder) -> Unit): KmTypeVisitor =
-    object : KmTypeVisitor() {
-        private val t = ProtoBuf.Type.newBuilder()
+    return t
+}
 
-        override fun visitClass(name: ClassName) {
-            t.className = c.getClassName(name)
+private fun WriteContext.writeType(kmType: KmType): ProtoBuf.Type.Builder {
+    val t = ProtoBuf.Type.newBuilder()
+    when (val cls = kmType.classifier) {
+        is KmClassifier.Class -> t.className = getClassName(cls.name)
+        is KmClassifier.TypeAlias -> t.typeAliasName = getClassName(cls.name)
+        is KmClassifier.TypeParameter -> t.typeParameter = cls.id
+    }
+    kmType.arguments.forEach { argument ->
+        t.addArgument(writeTypeProjection(argument))
+    }
+
+    kmType.abbreviatedType?.let { t.abbreviatedType = writeType(it).build() }
+    kmType.outerType?.let { t.outerType = writeType(it).build() }
+    kmType.flexibleTypeUpperBound?.let { fub ->
+        val fubType = writeType(fub.type)
+        fub.typeFlexibilityId?.let { t.flexibleTypeCapabilitiesId = this[it] }
+        t.flexibleUpperBound = fubType.build()
+    }
+
+    kmType.extensions.writeExtensions {
+        writeTypeExtensions(it, t, this@writeType)
+    }
+
+    if (kmType.isNullable) {
+        t.nullable = true
+    }
+    val flagsToWrite = kmType.flags shr 1
+    if (flagsToWrite != ProtoBuf.Type.getDefaultInstance().flags) {
+        t.flags = flagsToWrite
+    }
+    return t
+}
+
+private fun WriteContext.writeConstructor(kmConstructor: KmConstructor): ProtoBuf.Constructor.Builder {
+    val t = ProtoBuf.Constructor.newBuilder()
+
+    kmConstructor.valueParameters.forEach {
+        t.addValueParameter(writeValueParameter(it).build())
+    }
+    kmConstructor.versionRequirements.forEach { t.addVersionRequirement(writeVersionRequirement(it)) }
+    kmConstructor.extensions.writeExtensions {
+        writeConstructorExtensions(it, t, this@writeConstructor)
+    }
+    if (kmConstructor.flags != ProtoBuf.Constructor.getDefaultInstance().flags) {
+        t.flags = kmConstructor.flags
+    }
+    return t
+}
+
+private fun WriteContext.writeFunction(kmFunction: KmFunction): ProtoBuf.Function.Builder {
+    val t = ProtoBuf.Function.newBuilder()
+    t.addAllTypeParameter(kmFunction.typeParameters.map { writeTypeParameter(it).build() })
+    kmFunction.receiverParameterType?.let { t.receiverType = writeType(it).build() }
+    @OptIn(ExperimentalContextReceivers::class)
+    t.addAllContextReceiverType(kmFunction.contextReceiverTypes.map { writeType(it).build() })
+    t.addAllValueParameter(kmFunction.valueParameters.map { writeValueParameter(it).build() })
+    t.returnType = writeType(kmFunction.returnType).build()
+    t.addAllVersionRequirement(kmFunction.versionRequirements.map(::writeVersionRequirement))
+    @OptIn(ExperimentalContracts::class)
+    kmFunction.contract?.let { t.contract = writeContract(it) }
+    kmFunction.extensions.writeExtensions { writeFunctionExtensions(it, t, this@writeFunction) }
+    t.name = this[kmFunction.name]
+    if (kmFunction.flags != ProtoBuf.Function.getDefaultInstance().flags) {
+        t.flags = kmFunction.flags
+    }
+    return t
+}
+
+
+public fun WriteContext.writeProperty(kmProperty: KmProperty): ProtoBuf.Property.Builder {
+    val t = ProtoBuf.Property.newBuilder()
+
+    kmProperty.typeParameters.forEach { tp ->
+        t.addTypeParameter(writeTypeParameter(tp).build())
+    }
+    kmProperty.receiverParameterType?.let { t.receiverType = writeType(it).build() }
+    @OptIn(ExperimentalContextReceivers::class)
+    t.addAllContextReceiverType(kmProperty.contextReceiverTypes.map { writeType(it).build() })
+    kmProperty.setterParameter?.let { t.setterValueParameter = writeValueParameter(it).build() }
+    t.returnType = writeType(kmProperty.returnType).build()
+    t.addAllVersionRequirement(kmProperty.versionRequirements.map { writeVersionRequirement(it) })
+    kmProperty.extensions.writeExtensions { writePropertyExtensions(it, t, this@writeProperty) }
+    t.name = this[kmProperty.name]
+    if (kmProperty.flags != ProtoBuf.Property.getDefaultInstance().flags) {
+        t.flags = kmProperty.flags
+    }
+    // TODO: do not write getterFlags/setterFlags if not needed
+    if (kmProperty.hasGetter) t.getterFlags = kmProperty.getterFlags
+    if (kmProperty.hasSetter) t.setterFlags = kmProperty.setterFlags
+    return t
+}
+
+private fun WriteContext.writeValueParameter(
+    kmValueParameter: KmValueParameter,
+): ProtoBuf.ValueParameter.Builder {
+    val t = ProtoBuf.ValueParameter.newBuilder()
+    t.type = writeType(kmValueParameter.type).build()
+    kmValueParameter.varargElementType?.let { t.varargElementType = writeType(it).build() }
+    kmValueParameter.extensions.writeExtensions { writeValueParameterExtensions(it, t, this@writeValueParameter) }
+    if (kmValueParameter.flags != ProtoBuf.ValueParameter.getDefaultInstance().flags) {
+        t.flags = kmValueParameter.flags
+    }
+    t.name = this[kmValueParameter.name]
+    return t
+}
+
+private fun WriteContext.writeTypeAlias(
+    typeAlias: KmTypeAlias,
+): ProtoBuf.TypeAlias.Builder {
+    val t = ProtoBuf.TypeAlias.newBuilder()
+    t.addAllTypeParameter(typeAlias.typeParameters.map { writeTypeParameter(it).build() })
+    t.underlyingType = writeType(typeAlias.underlyingType).build()
+    t.expandedType = writeType(typeAlias.expandedType).build()
+    t.addAllAnnotation(typeAlias.annotations.map { it.writeAnnotation(strings).build() })
+    t.addAllVersionRequirement(typeAlias.versionRequirements.map(::writeVersionRequirement))
+    typeAlias.extensions.writeExtensions { writeTypeAliasExtensions(it, t, this@writeTypeAlias) }
+
+    if (typeAlias.flags != ProtoBuf.TypeAlias.getDefaultInstance().flags) {
+        t.flags = typeAlias.flags
+    }
+    t.name = this[typeAlias.name]
+    return t
+}
+
+private fun WriteContext.writeVersionRequirement(kmVersionRequirement: KmVersionRequirement): Int {
+    val kind = kmVersionRequirement.kind
+    val level = kmVersionRequirement.level
+    val errorCode = kmVersionRequirement.errorCode
+    val message = kmVersionRequirement.message
+    val t = ProtoBuf.VersionRequirement.newBuilder().apply {
+        val versionKind = when (kind) {
+            KmVersionRequirementVersionKind.LANGUAGE_VERSION -> ProtoBuf.VersionRequirement.VersionKind.LANGUAGE_VERSION
+            KmVersionRequirementVersionKind.COMPILER_VERSION -> ProtoBuf.VersionRequirement.VersionKind.COMPILER_VERSION
+            KmVersionRequirementVersionKind.API_VERSION -> ProtoBuf.VersionRequirement.VersionKind.API_VERSION
         }
-
-        override fun visitTypeAlias(name: ClassName) {
-            t.typeAliasName = c.getClassName(name)
+        if (versionKind != defaultInstanceForType.versionKind) {
+            this.versionKind = versionKind
         }
+        val requirementLevel = when (level) {
+            KmVersionRequirementLevel.WARNING -> ProtoBuf.VersionRequirement.Level.WARNING
+            KmVersionRequirementLevel.ERROR -> ProtoBuf.VersionRequirement.Level.ERROR
+            KmVersionRequirementLevel.HIDDEN -> ProtoBuf.VersionRequirement.Level.HIDDEN
+        }
+        if (requirementLevel != defaultInstanceForType.level) {
+            this.level = requirementLevel
+        }
+        if (errorCode != null) {
+            this.errorCode = errorCode
+        }
+        if (message != null) {
+            this.message = this@writeVersionRequirement[message]
+        }
+    }
+    val (major, minor, patch) = kmVersionRequirement.version
 
-        override fun visitStarProjection() {
-            t.addArgument(ProtoBuf.Type.Argument.newBuilder().apply {
-                projection = ProtoBuf.Type.Argument.Projection.STAR
+    VersionRequirement.Version(major, minor, patch).encode(
+        writeVersion = { t!!.version = it },
+        writeVersionFull = { t!!.versionFull = it }
+    )
+
+    return this.versionRequirements[t] //??
+}
+
+@ExperimentalContracts
+private fun WriteContext.writeContract(contract: KmContract): ProtoBuf.Contract {
+    val t = ProtoBuf.Contract.newBuilder()
+
+    t.addAllEffect(contract.effects.map(::writeEffect))
+    return t.build()
+}
+
+@ExperimentalContracts
+private fun WriteContext.writeEffect(
+    effect: KmEffect,
+): ProtoBuf.Effect {
+    val t = ProtoBuf.Effect.newBuilder()
+
+    t.addAllEffectConstructorArgument(effect.constructorArguments.map(::writeEffectExpression))
+    effect.conclusion?.let { t.conclusionOfConditionalEffect = writeEffectExpression(it) }
+
+    when (effect.type) {
+        KmEffectType.RETURNS_CONSTANT -> t.effectType = ProtoBuf.Effect.EffectType.RETURNS_CONSTANT
+        KmEffectType.CALLS -> t.effectType = ProtoBuf.Effect.EffectType.CALLS
+        KmEffectType.RETURNS_NOT_NULL -> t.effectType = ProtoBuf.Effect.EffectType.RETURNS_NOT_NULL
+    }
+    when (effect.invocationKind) {
+        KmEffectInvocationKind.AT_MOST_ONCE -> t.kind = ProtoBuf.Effect.InvocationKind.AT_MOST_ONCE
+        KmEffectInvocationKind.EXACTLY_ONCE -> t.kind = ProtoBuf.Effect.InvocationKind.EXACTLY_ONCE
+        KmEffectInvocationKind.AT_LEAST_ONCE -> t.kind = ProtoBuf.Effect.InvocationKind.AT_LEAST_ONCE
+        null -> {} // nop
+    }
+    return t.build()
+}
+
+@ExperimentalContracts
+private fun WriteContext.writeEffectExpression(effectExpression: KmEffectExpression): ProtoBuf.Expression {
+    val t = ProtoBuf.Expression.newBuilder()
+
+    if (effectExpression.flags != ProtoBuf.Expression.getDefaultInstance().flags) {
+        t.flags = effectExpression.flags
+    }
+    effectExpression.parameterIndex?.let { t.valueParameterReference = it }
+    val cv = effectExpression.constantValue
+    if (cv != null) {
+        when (val value = cv.value) {
+            true -> t.constantValue = ProtoBuf.Expression.ConstantValue.TRUE
+            false -> t.constantValue = ProtoBuf.Expression.ConstantValue.FALSE
+            null -> t.constantValue = ProtoBuf.Expression.ConstantValue.NULL
+            else -> throw IllegalArgumentException("Only true, false or null constant values are allowed for effects (was=$value)")
+        }
+    }
+    effectExpression.isInstanceType?.let { t.isInstanceType = writeType(it).build() }
+    t.addAllAndArgument(effectExpression.andArguments.map(::writeEffectExpression))
+    t.addAllOrArgument(effectExpression.orArguments.map(::writeEffectExpression))
+    return t.build()
+}
+
+public open class ClassWriter(stringTable: StringTable, contextExtensions: List<WriteContextExtension> = emptyList()) {
+    public val t: ProtoBuf.Class.Builder = ProtoBuf.Class.newBuilder()!!
+    public val c: WriteContext = WriteContext(stringTable, contextExtensions)
+
+    public fun writeClass(kmClass: KmClass) {
+        if (kmClass.flags != ProtoBuf.Class.getDefaultInstance().flags) {
+            t.flags = kmClass.flags
+        }
+        t.fqName = c.getClassName(kmClass.name)
+
+        t.addAllTypeParameter(kmClass.typeParameters.map { c.writeTypeParameter(it).build() })
+        t.addAllSupertype(kmClass.supertypes.map { c.writeType(it).build() })
+        t.addAllConstructor(kmClass.constructors.map { c.writeConstructor(it).build() })
+        t.addAllFunction(kmClass.functions.map { c.writeFunction(it).build() })
+        t.addAllProperty(kmClass.properties.map { c.writeProperty(it).build() })
+        t.addAllTypeAlias(kmClass.typeAliases.map { c.writeTypeAlias(it).build() })
+
+        kmClass.companionObject?.let { t.companionObjectName = c[it] }
+        kmClass.nestedClasses.forEach { t.addNestedClassName(c[it]) }
+
+        kmClass.enumEntries.forEach { name ->
+            t.addEnumEntry(ProtoBuf.EnumEntry.newBuilder().also { enumEntry ->
+                enumEntry.name = c[name]
             })
         }
 
-        override fun visitArgument(flags: Int, variance: KmVariance): KmTypeVisitor? =
-            writeType(c, flags) { argument ->
-                t.addArgument(ProtoBuf.Type.Argument.newBuilder().apply {
-                    if (variance == KmVariance.IN) {
-                        projection = ProtoBuf.Type.Argument.Projection.IN
-                    } else if (variance == KmVariance.OUT) {
-                        projection = ProtoBuf.Type.Argument.Projection.OUT
-                    }
-                    type = argument.build()
-                })
-            }
+        t.addAllSealedSubclassFqName(kmClass.sealedSubclasses.map { c.getClassName(it) })
 
-        override fun visitTypeParameter(id: Int) {
-            t.typeParameter = id
-        }
+        kmClass.inlineClassUnderlyingPropertyName?.let { t.inlineClassUnderlyingPropertyName = c[it] }
+        kmClass.inlineClassUnderlyingType?.let { t.inlineClassUnderlyingType = c.writeType(it).build() }
 
-        override fun visitAbbreviatedType(flags: Int): KmTypeVisitor? =
-            writeType(c, flags) { t.abbreviatedType = it.build() }
+        @OptIn(ExperimentalContextReceivers::class)
+        t.addAllContextReceiverType(kmClass.contextReceiverTypes.map { c.writeType(it).build() })
 
-        override fun visitOuterType(flags: Int): KmTypeVisitor? =
-            writeType(c, flags) { t.outerType = it.build() }
+        t.addAllVersionRequirement(kmClass.versionRequirements.map { c.writeVersionRequirement(it) })
+        kmClass.extensions.matchExtensions { writeClassExtensions(it, t, c) }
 
-        override fun visitFlexibleTypeUpperBound(flags: Int, typeFlexibilityId: String?): KmTypeVisitor? =
-            writeType(c, flags) {
-                if (typeFlexibilityId != null) {
-                    t.flexibleTypeCapabilitiesId = c[typeFlexibilityId]
-                }
-                t.flexibleUpperBound = it.build()
-            }
-
-        override fun visitExtensions(type: KmExtensionType): KmTypeExtensionVisitor? =
-            applySingleExtension(type) {
-                writeTypeExtensions(type, t, c)
-            }
-
-        override fun visitEnd() {
-            if (Flag.Type.IS_NULLABLE(flags)) {
-                t.nullable = true
-            }
-            val flagsToWrite = flags shr 1
-            if (flagsToWrite != ProtoBuf.Type.getDefaultInstance().flags) {
-                t.flags = flagsToWrite
-            }
-            output(t)
-        }
-    }
-
-private fun writeConstructor(c: WriteContext, flags: Int, output: (ProtoBuf.Constructor.Builder) -> Unit): KmConstructorVisitor =
-    object : KmConstructorVisitor() {
-        val t = ProtoBuf.Constructor.newBuilder()
-
-        override fun visitValueParameter(flags: Int, name: String): KmValueParameterVisitor? =
-            writeValueParameter(c, flags, name) { t.addValueParameter(it.build()) }
-
-        override fun visitVersionRequirement(): KmVersionRequirementVisitor? =
-            writeVersionRequirement(c) { t.addVersionRequirement(it) }
-
-        override fun visitExtensions(type: KmExtensionType): KmConstructorExtensionVisitor? =
-            applySingleExtension(type) {
-                writeConstructorExtensions(type, t, c)
-            }
-
-        override fun visitEnd() {
-            if (flags != ProtoBuf.Constructor.getDefaultInstance().flags) {
-                t.flags = flags
-            }
-            output(t)
-        }
-    }
-
-private fun writeFunction(c: WriteContext, flags: Int, name: String, output: (ProtoBuf.Function.Builder) -> Unit): KmFunctionVisitor =
-    object : KmFunctionVisitor() {
-        val t = ProtoBuf.Function.newBuilder()
-
-        override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor? =
-            writeTypeParameter(c, flags, name, id, variance) { t.addTypeParameter(it) }
-
-        override fun visitReceiverParameterType(flags: Int): KmTypeVisitor? =
-            writeType(c, flags) { t.receiverType = it.build() }
-
-        @ExperimentalContextReceivers
-        override fun visitContextReceiverType(flags: Int): KmTypeVisitor =
-            writeType(c, flags) { t.addContextReceiverType(it) }
-
-        override fun visitValueParameter(flags: Int, name: String): KmValueParameterVisitor? =
-            writeValueParameter(c, flags, name) { t.addValueParameter(it) }
-
-        override fun visitReturnType(flags: Int): KmTypeVisitor? =
-            writeType(c, flags) { t.returnType = it.build() }
-
-        override fun visitVersionRequirement(): KmVersionRequirementVisitor? =
-            writeVersionRequirement(c) { t.addVersionRequirement(it) }
-
-        @OptIn(ExperimentalContracts::class)
-        override fun visitContract(): KmContractVisitor? =
-            writeContract(c) { t.contract = it.build() }
-
-        override fun visitExtensions(type: KmExtensionType): KmFunctionExtensionVisitor? =
-            applySingleExtension(type) {
-                writeFunctionExtensions(type, t, c)
-            }
-
-        override fun visitEnd() {
-            t.name = c[name]
-            if (flags != ProtoBuf.Function.getDefaultInstance().flags) {
-                t.flags = flags
-            }
-            output(t)
-        }
-    }
-
-public fun writeProperty(
-    c: WriteContext, flags: Int, name: String, getterFlags: Int, setterFlags: Int, output: (ProtoBuf.Property.Builder) -> Unit
-): KmPropertyVisitor = object : KmPropertyVisitor() {
-    val t = ProtoBuf.Property.newBuilder()
-
-    override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor? =
-        writeTypeParameter(c, flags, name, id, variance) { t.addTypeParameter(it) }
-
-    override fun visitReceiverParameterType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.receiverType = it.build() }
-
-    @ExperimentalContextReceivers
-    override fun visitContextReceiverType(flags: Int): KmTypeVisitor =
-        writeType(c, flags) { t.addContextReceiverType(it) }
-
-    override fun visitSetterParameter(flags: Int, name: String): KmValueParameterVisitor? =
-        writeValueParameter(c, flags, name) { t.setterValueParameter = it.build() }
-
-    override fun visitReturnType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.returnType = it.build() }
-
-    override fun visitVersionRequirement(): KmVersionRequirementVisitor? =
-        writeVersionRequirement(c) { t.addVersionRequirement(it) }
-
-    override fun visitExtensions(type: KmExtensionType): KmPropertyExtensionVisitor? =
-        applySingleExtension(type) {
-            writePropertyExtensions(type, t, c)
-        }
-
-    override fun visitEnd() {
-        t.name = c[name]
-        if (flags != ProtoBuf.Property.getDefaultInstance().flags) {
-            t.flags = flags
-        }
-        // TODO: do not write getterFlags/setterFlags if not needed
-        if (Flag.Property.HAS_GETTER(flags)) t.getterFlags = getterFlags
-        if (Flag.Property.HAS_SETTER(flags)) t.setterFlags = setterFlags
-        output(t)
-    }
-}
-
-private fun writeValueParameter(
-    c: WriteContext, flags: Int, name: String,
-    output: (ProtoBuf.ValueParameter.Builder) -> Unit
-): KmValueParameterVisitor = object : KmValueParameterVisitor() {
-    val t = ProtoBuf.ValueParameter.newBuilder()
-
-    override fun visitType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.type = it.build() }
-
-    override fun visitVarargElementType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.varargElementType = it.build() }
-
-    override fun visitExtensions(type: KmExtensionType): KmValueParameterExtensionVisitor? =
-        applySingleExtension(type) {
-            writeValueParameterExtensions(type, t, c)
-        }
-
-    override fun visitEnd() {
-        if (flags != ProtoBuf.ValueParameter.getDefaultInstance().flags) {
-            t.flags = flags
-        }
-        t.name = c[name]
-        output(t)
-    }
-}
-
-private fun writeTypeAlias(
-    c: WriteContext, flags: Int, name: String,
-    output: (ProtoBuf.TypeAlias.Builder) -> Unit
-): KmTypeAliasVisitor = object : KmTypeAliasVisitor() {
-    val t = ProtoBuf.TypeAlias.newBuilder()
-
-    override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor? =
-        writeTypeParameter(c, flags, name, id, variance) { t.addTypeParameter(it) }
-
-    override fun visitUnderlyingType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.underlyingType = it.build() }
-
-    override fun visitExpandedType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.expandedType = it.build() }
-
-    override fun visitAnnotation(annotation: KmAnnotation) {
-        t.addAnnotation(annotation.writeAnnotation(c.strings))
-    }
-
-    override fun visitVersionRequirement(): KmVersionRequirementVisitor? =
-        writeVersionRequirement(c) { t.addVersionRequirement(it) }
-
-    override fun visitExtensions(type: KmExtensionType): KmTypeAliasExtensionVisitor? =
-        applySingleExtension(type) {
-            writeTypeAliasExtensions(type, t, c)
-        }
-
-    override fun visitEnd() {
-        if (flags != ProtoBuf.TypeAlias.getDefaultInstance().flags) {
-            t.flags = flags
-        }
-        t.name = c[name]
-        output(t)
-    }
-}
-
-private fun writeVersionRequirement(
-    c: WriteContext, output: (Int) -> Unit
-): KmVersionRequirementVisitor = object : KmVersionRequirementVisitor() {
-    var t: ProtoBuf.VersionRequirement.Builder? = null
-
-    override fun visit(kind: KmVersionRequirementVersionKind, level: KmVersionRequirementLevel, errorCode: Int?, message: String?) {
-        t = ProtoBuf.VersionRequirement.newBuilder().apply {
-            val versionKind = when (kind) {
-                KmVersionRequirementVersionKind.LANGUAGE_VERSION -> ProtoBuf.VersionRequirement.VersionKind.LANGUAGE_VERSION
-                KmVersionRequirementVersionKind.COMPILER_VERSION -> ProtoBuf.VersionRequirement.VersionKind.COMPILER_VERSION
-                KmVersionRequirementVersionKind.API_VERSION -> ProtoBuf.VersionRequirement.VersionKind.API_VERSION
-            }
-            if (versionKind != defaultInstanceForType.versionKind) {
-                this.versionKind = versionKind
-            }
-            val requirementLevel = when (level) {
-                KmVersionRequirementLevel.WARNING -> ProtoBuf.VersionRequirement.Level.WARNING
-                KmVersionRequirementLevel.ERROR -> ProtoBuf.VersionRequirement.Level.ERROR
-                KmVersionRequirementLevel.HIDDEN -> ProtoBuf.VersionRequirement.Level.HIDDEN
-            }
-            if (requirementLevel != defaultInstanceForType.level) {
-                this.level = requirementLevel
-            }
-            if (errorCode != null) {
-                this.errorCode = errorCode
-            }
-            if (message != null) {
-                this.message = c[message]
-            }
-        }
-    }
-
-    override fun visitVersion(major: Int, minor: Int, patch: Int) {
-        if (t == null) {
-            throw IllegalStateException("KmVersionRequirementVisitor.visit has not been called")
-        }
-        VersionRequirement.Version(major, minor, patch).encode(
-            writeVersion = { t!!.version = it },
-            writeVersionFull = { t!!.versionFull = it }
-        )
-    }
-
-    override fun visitEnd() {
-        if (t == null) {
-            throw IllegalStateException("KmVersionRequirementVisitor.visit has not been called")
-        }
-        output(c.versionRequirements[t!!])
-    }
-}
-
-@ExperimentalContracts
-private fun writeContract(c: WriteContext, output: (ProtoBuf.Contract.Builder) -> Unit): KmContractVisitor =
-    object : KmContractVisitor() {
-        val t = ProtoBuf.Contract.newBuilder()
-
-        override fun visitEffect(type: KmEffectType, invocationKind: KmEffectInvocationKind?): KmEffectVisitor? =
-            writeEffect(c, type, invocationKind) { t.addEffect(it) }
-
-        override fun visitEnd() {
-            output(t)
-        }
-    }
-
-@ExperimentalContracts
-private fun writeEffect(
-    c: WriteContext, type: KmEffectType, invocationKind: KmEffectInvocationKind?,
-    output: (ProtoBuf.Effect.Builder) -> Unit
-): KmEffectVisitor = object : KmEffectVisitor() {
-    val t = ProtoBuf.Effect.newBuilder()
-
-    override fun visitConstructorArgument(): KmEffectExpressionVisitor? =
-        writeEffectExpression(c) { t.addEffectConstructorArgument(it) }
-
-    override fun visitConclusionOfConditionalEffect(): KmEffectExpressionVisitor? =
-        writeEffectExpression(c) { t.conclusionOfConditionalEffect = it.build() }
-
-    @Suppress("UNUSED_VARIABLE") // force exhaustive whens
-    override fun visitEnd() {
-        val unused = when (type) {
-            KmEffectType.RETURNS_CONSTANT -> t.effectType = ProtoBuf.Effect.EffectType.RETURNS_CONSTANT
-            KmEffectType.CALLS -> t.effectType = ProtoBuf.Effect.EffectType.CALLS
-            KmEffectType.RETURNS_NOT_NULL -> t.effectType = ProtoBuf.Effect.EffectType.RETURNS_NOT_NULL
-        }
-        val unused2 = when (invocationKind) {
-            KmEffectInvocationKind.AT_MOST_ONCE -> t.kind = ProtoBuf.Effect.InvocationKind.AT_MOST_ONCE
-            KmEffectInvocationKind.EXACTLY_ONCE -> t.kind = ProtoBuf.Effect.InvocationKind.EXACTLY_ONCE
-            KmEffectInvocationKind.AT_LEAST_ONCE -> t.kind = ProtoBuf.Effect.InvocationKind.AT_LEAST_ONCE
-            null -> null
-        }
-        output(t)
-    }
-}
-
-@ExperimentalContracts
-private fun writeEffectExpression(c: WriteContext, output: (ProtoBuf.Expression.Builder) -> Unit): KmEffectExpressionVisitor =
-    object : KmEffectExpressionVisitor() {
-        val t = ProtoBuf.Expression.newBuilder()
-
-        override fun visit(flags: Int, parameterIndex: Int?) {
-            if (flags != ProtoBuf.Expression.getDefaultInstance().flags) {
-                t.flags = flags
-            }
-            if (parameterIndex != null) {
-                t.valueParameterReference = parameterIndex
-            }
-        }
-
-        override fun visitConstantValue(value: Any?) {
-            when (value) {
-                true -> t.constantValue = ProtoBuf.Expression.ConstantValue.TRUE
-                false -> t.constantValue = ProtoBuf.Expression.ConstantValue.FALSE
-                null -> t.constantValue = ProtoBuf.Expression.ConstantValue.NULL
-                else -> throw IllegalArgumentException("Only true, false or null constant values are allowed for effects (was=$value)")
-            }
-        }
-
-        override fun visitIsInstanceType(flags: Int): KmTypeVisitor? =
-            writeType(c, flags) { t.isInstanceType = it.build() }
-
-        override fun visitAndArgument(): KmEffectExpressionVisitor? =
-            writeEffectExpression(c) { t.addAndArgument(it) }
-
-        override fun visitOrArgument(): KmEffectExpressionVisitor? =
-            writeEffectExpression(c) { t.addOrArgument(it) }
-
-        override fun visitEnd() {
-            output(t)
-        }
-    }
-
-public open class ClassWriter(stringTable: StringTable, contextExtensions: List<WriteContextExtension> = emptyList()) : KmClassVisitor() {
-    protected val t: ProtoBuf.Class.Builder = ProtoBuf.Class.newBuilder()!!
-    protected val c: WriteContext = WriteContext(stringTable, contextExtensions)
-
-    override fun visit(flags: Int, name: ClassName) {
-        if (flags != ProtoBuf.Class.getDefaultInstance().flags) {
-            t.flags = flags
-        }
-        t.fqName = c.getClassName(name)
-    }
-
-    override fun visitTypeParameter(flags: Int, name: String, id: Int, variance: KmVariance): KmTypeParameterVisitor? =
-        writeTypeParameter(c, flags, name, id, variance) { t.addTypeParameter(it) }
-
-    override fun visitSupertype(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.addSupertype(it) }
-
-    override fun visitConstructor(flags: Int): KmConstructorVisitor? =
-        writeConstructor(c, flags) { t.addConstructor(it) }
-
-    override fun visitFunction(flags: Int, name: String): KmFunctionVisitor? =
-        writeFunction(c, flags, name) { t.addFunction(it) }
-
-    override fun visitProperty(flags: Int, name: String, getterFlags: Int, setterFlags: Int): KmPropertyVisitor? =
-        writeProperty(c, flags, name, getterFlags, setterFlags) { t.addProperty(it) }
-
-    override fun visitTypeAlias(flags: Int, name: String): KmTypeAliasVisitor? =
-        writeTypeAlias(c, flags, name) { t.addTypeAlias(it) }
-
-    override fun visitCompanionObject(name: String) {
-        t.companionObjectName = c[name]
-    }
-
-    override fun visitNestedClass(name: String) {
-        t.addNestedClassName(c[name])
-    }
-
-    override fun visitEnumEntry(name: String) {
-        t.addEnumEntry(ProtoBuf.EnumEntry.newBuilder().also { enumEntry ->
-            enumEntry.name = c[name]
-        })
-    }
-
-    override fun visitSealedSubclass(name: ClassName) {
-        t.addSealedSubclassFqName(c.getClassName(name))
-    }
-
-    override fun visitInlineClassUnderlyingPropertyName(name: String) {
-        t.inlineClassUnderlyingPropertyName = c[name]
-    }
-
-    override fun visitInlineClassUnderlyingType(flags: Int): KmTypeVisitor? =
-        writeType(c, flags) { t.inlineClassUnderlyingType = it.build() }
-
-    @ExperimentalContextReceivers
-    override fun visitContextReceiverType(flags: Int): KmTypeVisitor =
-        writeType(c, flags) { t.addContextReceiverType(it) }
-
-    override fun visitVersionRequirement(): KmVersionRequirementVisitor? =
-        writeVersionRequirement(c) { t.addVersionRequirement(it) }
-
-    override fun visitExtensions(type: KmExtensionType): KmClassExtensionVisitor? =
-        applySingleExtension(type) {
-            writeClassExtensions(type, t, c)
-        }
-
-    override fun visitEnd() {
         c.versionRequirements.serialize()?.let {
             t.versionRequirementTable = it
         }
     }
 }
 
-public open class PackageWriter(stringTable: StringTable, contextExtensions: List<WriteContextExtension> = emptyList()) : KmPackageVisitor() {
-    protected val t: ProtoBuf.Package.Builder = ProtoBuf.Package.newBuilder()!!
-    protected val c: WriteContext = WriteContext(stringTable, contextExtensions)
+public open class PackageWriter(stringTable: StringTable, contextExtensions: List<WriteContextExtension> = emptyList()) {
+    public val t: ProtoBuf.Package.Builder = ProtoBuf.Package.newBuilder()
+    public val c: WriteContext = WriteContext(stringTable, contextExtensions)
 
-    override fun visitFunction(flags: Int, name: String): KmFunctionVisitor? =
-        writeFunction(c, flags, name) { t.addFunction(it) }
-
-    override fun visitProperty(flags: Int, name: String, getterFlags: Int, setterFlags: Int): KmPropertyVisitor? =
-        writeProperty(c, flags, name, getterFlags, setterFlags) { t.addProperty(it) }
-
-    override fun visitTypeAlias(flags: Int, name: String): KmTypeAliasVisitor? =
-        writeTypeAlias(c, flags, name) { t.addTypeAlias(it) }
-
-    override fun visitExtensions(type: KmExtensionType): KmPackageExtensionVisitor? =
-        applySingleExtension(type) {
-            writePackageExtensions(type, t, c)
-        }
-
-    override fun visitEnd() {
+    public fun writePackage(kmPackage: KmPackage) {
+        t.addAllFunction(kmPackage.functions.map { c.writeFunction(it).build() })
+        t.addAllProperty(kmPackage.properties.map { c.writeProperty(it).build() })
+        t.addAllTypeAlias(kmPackage.typeAliases.map { c.writeTypeAlias(it).build() })
+        kmPackage.extensions.matchExtensions { writePackageExtensions(it, t, c) }
         c.versionRequirements.serialize()?.let {
             t.versionRequirementTable = it
         }
     }
 }
 
-public open class ModuleFragmentWriter(stringTable: StringTable, contextExtensions: List<WriteContextExtension> = emptyList()) :
-    KmModuleFragmentVisitor() {
+public open class ModuleFragmentWriter(stringTable: StringTable, contextExtensions: List<WriteContextExtension> = emptyList()) {
     protected val t: ProtoBuf.PackageFragment.Builder = ProtoBuf.PackageFragment.newBuilder()!!
     protected val c: WriteContext = WriteContext(stringTable, contextExtensions)
 
-    override fun visitPackage(): KmPackageVisitor? = object : PackageWriter(c.strings, c.contextExtensions) {
-        override fun visitEnd() {
-            super.visitEnd()
-            this@ModuleFragmentWriter.t.setPackage(t)
+    public open fun writeModuleFragment(kmPackageFragment: KmModuleFragment) {
+        kmPackageFragment.pkg?.let {
+            val pkgWriter = PackageWriter(c.strings, c.contextExtensions)
+            pkgWriter.writePackage(it)
+            t.setPackage(pkgWriter.t)
         }
-    }
 
-    override fun visitClass(): KmClassVisitor? = object : ClassWriter(c.strings, c.contextExtensions) {
-        override fun visitEnd() {
-            super.visitEnd()
-            this@ModuleFragmentWriter.t.addClass_(t)
+        kmPackageFragment.classes.forEach {
+            val classWriter = ClassWriter(c.strings, c.contextExtensions)
+            classWriter.writeClass(it)
+            t.addClass_(classWriter.t)
         }
-    }
 
-    override fun visitExtensions(type: KmExtensionType): KmModuleFragmentExtensionVisitor? =
-        applySingleExtension(type) {
-            writeModuleFragmentExtensions(type, t, c)
-        }
+        kmPackageFragment.extensions.writeExtensions { writeModuleFragmentExtensions(it, t, c) }
+    }
 }
 
-public open class LambdaWriter(stringTable: StringTable) : KmLambdaVisitor() {
-    protected var t: ProtoBuf.Function.Builder? = null
-    protected val c: WriteContext = WriteContext(stringTable)
+public open class LambdaWriter(stringTable: StringTable) {
+    public var t: ProtoBuf.Function.Builder? = null
+    public val c: WriteContext = WriteContext(stringTable)
 
-    override fun visitFunction(flags: Int, name: String): KmFunctionVisitor? =
-        writeFunction(c, flags, name) { t = it }
+    public fun writeLambda(kmLambda: KmLambda) {
+        t = c.writeFunction(kmLambda.function)
+    }
 }
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/common/KotlinCommonMetadata.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/common/KotlinCommonMetadata.kt
index 291fd2f677e..ee2a519cf2d 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/common/KotlinCommonMetadata.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/common/KotlinCommonMetadata.kt
@@ -2,13 +2,14 @@
  * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata.internal.common
 
 import kotlinx.metadata.*
 import kotlinx.metadata.VISITOR_API_MESSAGE
-import kotlinx.metadata.internal.accept
+import kotlinx.metadata.internal.toKmPackage
+import kotlinx.metadata.internal.toKmClass
 import kotlinx.metadata.internal.extensions.KmModuleFragmentExtension
 import kotlinx.metadata.internal.extensions.MetadataExtensions
 import kotlinx.metadata.internal.extensions.singleOfType
@@ -23,23 +24,33 @@ import java.io.ByteArrayInputStream
  * distribution can also be read with this reader.
  */
 public class KotlinCommonMetadata private constructor(private val proto: ProtoBuf.PackageFragment) {
+
+    public val kmModuleFragment: KmModuleFragment = readImpl()
+
+    @Deprecated(
+        "To avoid excessive copying, use .kmModuleFragment property instead. Note that it returns a view and not a copy.",
+        ReplaceWith("kmModuleFragment"),
+        DeprecationLevel.WARNING
+    )
     public fun toKmModuleFragment(): KmModuleFragment =
-        KmModuleFragment().apply(this::accept)
+        KmModuleFragment().apply { kmModuleFragment.accept(this) }
 
     // private because there are no use-cases and it is not finished
     private class Writer : KmModuleFragmentVisitor() {
         // TODO
     }
 
-    public fun accept(v: KmModuleFragmentVisitor) {
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
+    public fun accept(v: KmModuleFragmentVisitor): Unit = kmModuleFragment.accept(v)
+
+    private fun readImpl(): KmModuleFragment {
+        val v = KmModuleFragment()
         val strings = NameResolverImpl(proto.strings, proto.qualifiedNames)
         if (proto.hasPackage()) {
-            v.visitPackage()?.let { proto.`package`.accept(it, strings) }
+           v.pkg = proto.`package`.toKmPackage(strings)
         }
-        for (klass in proto.class_List) {
-            v.visitClass()?.let { klass.accept(it, strings) }
-        }
-        v.visitEnd()
+        proto.class_List.mapTo(v.classes) { it.toKmClass(strings) }
+        return v
     }
 
     public companion object {
@@ -62,7 +73,6 @@ public class KotlinCommonMetadata private constructor(private val proto: ProtoBu
  *
  * Can be read with [KotlinCommonMetadata.read].
  */
-@Suppress("DEPRECATION")
 public class KmModuleFragment : KmModuleFragmentVisitor() {
 
     /**
@@ -75,18 +85,18 @@ public class KmModuleFragment : KmModuleFragmentVisitor() {
      */
     public val classes: MutableList<KmClass> = ArrayList()
 
-    private val extensions: List<KmModuleFragmentExtension> =
+    internal val extensions: List<KmModuleFragmentExtension> =
         MetadataExtensions.INSTANCES.map(MetadataExtensions::createModuleFragmentExtensions)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitPackage(): KmPackageVisitor? =
         KmPackage().also { pkg = it }
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitExtensions(type: KmExtensionType): KmModuleFragmentExtensionVisitor? =
         extensions.singleOfType(type)
 
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     override fun visitClass(): KmClassVisitor? =
         KmClass().addTo(classes)
 
@@ -95,7 +105,7 @@ public class KmModuleFragment : KmModuleFragmentVisitor() {
      *
      * @param visitor the visitor which will visit data in the module fragment.
      */
-    @Deprecated(VISITOR_API_MESSAGE)
+    @Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
     public fun accept(visitor: KmModuleFragmentVisitor) {
         pkg?.let { visitor.visitPackage()?.let(it::accept) }
         classes.forEach { visitor.visitClass()?.let(it::accept) }
@@ -110,8 +120,7 @@ public class KmModuleFragment : KmModuleFragmentVisitor() {
  *
  * When using this class, [visitEnd] must be called exactly once and after calls to all other visit* methods.
  */
-@Deprecated(VISITOR_API_MESSAGE)
-@Suppress("DEPRECATION")
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public abstract class KmModuleFragmentVisitor @JvmOverloads constructor(private val delegate: KmModuleFragmentVisitor? = null) {
 
     /**
@@ -145,5 +154,5 @@ public abstract class KmModuleFragmentVisitor @JvmOverloads constructor(private
 /**
  * A visitor to visit platform-specific extensions for a module fragment.
  */
-@Deprecated(VISITOR_API_MESSAGE)
+@Deprecated(VISITOR_API_MESSAGE, level = DeprecationLevel.ERROR)
 public interface KmModuleFragmentExtensionVisitor : KmExtensionVisitor
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionNodes.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionNodes.kt
index 7ba40334022..7c6812c199b 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionNodes.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionNodes.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 
 package kotlinx.metadata.internal.extensions
 
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionUtils.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionUtils.kt
index 4944ee26c08..5f4b38709c5 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionUtils.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/ExtensionUtils.kt
@@ -2,7 +2,7 @@
  * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
-@file:Suppress("DEPRECATION")
+@file:Suppress("DEPRECATION_ERROR")
 package kotlinx.metadata.internal.extensions
 
 import kotlinx.metadata.KmExtensionType
@@ -20,6 +20,17 @@ internal fun <T : KmExtensionVisitor> applySingleExtension(type: KmExtensionType
     return result
 }
 
+internal fun <E : KmExtension<*>> List<E>.matchExtensions(block: MetadataExtensions.(E) -> Boolean) {
+    forEach { ext ->
+        var processed = false
+        for (extesion in MetadataExtensions.INSTANCES) {
+            val current = extesion.block(ext)
+            if (processed && current) throw IllegalStateException("Multiple extensions handle the same extension type: ${ext.type}")
+            processed = current
+        }
+    }
+}
+
 internal fun <N : KmExtension<*>> Collection<N>.singleOfType(type: KmExtensionType): N {
     var result: N? = null
     for (node in this) {
diff --git a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/MetadataExtensions.kt b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/MetadataExtensions.kt
index c867e278d90..e238d75b51d 100644
--- a/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/MetadataExtensions.kt
+++ b/libraries/kotlinx-metadata/src/kotlinx/metadata/internal/extensions/MetadataExtensions.kt
@@ -11,7 +11,7 @@ import kotlinx.metadata.internal.common.*
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import java.util.*
 
-@Suppress("DEPRECATION")
+@Suppress("DEPRECATION_ERROR")
 public interface MetadataExtensions {
     public fun readClassExtensions(v: KmClassVisitor, proto: ProtoBuf.Class, c: ReadContext)
 
@@ -33,9 +33,9 @@ public interface MetadataExtensions {
 
     public fun readValueParameterExtensions(v: KmValueParameterVisitor, proto: ProtoBuf.ValueParameter, c: ReadContext)
 
-    public fun writeClassExtensions(type: KmExtensionType, proto: ProtoBuf.Class.Builder, c: WriteContext): KmClassExtensionVisitor?
+    public fun writeClassExtensions(extension: KmClassExtension, proto: ProtoBuf.Class.Builder, c: WriteContext): Boolean
 
-    public fun writePackageExtensions(type: KmExtensionType, proto: ProtoBuf.Package.Builder, c: WriteContext): KmPackageExtensionVisitor?
+    public fun writePackageExtensions(extension: KmPackageExtension, proto: ProtoBuf.Package.Builder, c: WriteContext): Boolean
 
     public fun writeModuleFragmentExtensions(
         type: KmExtensionType, proto: ProtoBuf.PackageFragment.Builder, c: WriteContext
diff --git a/libraries/tools/kotlinp/src/org/jetbrains/kotlin/kotlinp/printers.kt b/libraries/tools/kotlinp/src/org/jetbrains/kotlin/kotlinp/printers.kt
index 490d50f7b6c..ad0575ea1b8 100644
--- a/libraries/tools/kotlinp/src/org/jetbrains/kotlin/kotlinp/printers.kt
+++ b/libraries/tools/kotlinp/src/org/jetbrains/kotlin/kotlinp/printers.kt
@@ -183,7 +183,7 @@ private fun printType(type: KmType): String {
     val abbreviatedType = type.abbreviatedType?.let(::printType)
     val outerType = type.outerType?.let(::printType)
     val platformTypeUpperBound = type.flexibleTypeUpperBound?.let {
-        @Suppress("DEPRECATION")
+        @Suppress("DEPRECATION_ERROR")
         (if (it.typeFlexibilityId == JvmTypeExtensionVisitor.PLATFORM_TYPE_ID) {
             printType(it.type)
         } else null)
diff --git a/libraries/tools/kotlinp/test/org/jetbrains/kotlin/kotlinp/test/KotlinpTestUtils.kt b/libraries/tools/kotlinp/test/org/jetbrains/kotlin/kotlinp/test/KotlinpTestUtils.kt
index 9d5564521a5..8e4b85abfde 100644
--- a/libraries/tools/kotlinp/test/org/jetbrains/kotlin/kotlinp/test/KotlinpTestUtils.kt
+++ b/libraries/tools/kotlinp/test/org/jetbrains/kotlin/kotlinp/test/KotlinpTestUtils.kt
@@ -60,7 +60,6 @@ private fun compileAndPrintAllFiles(
     useK2: Boolean,
 ) {
     val main = StringBuilder()
-    val afterVisitors = StringBuilder()
     val afterNodes = StringBuilder()
 
     val kotlinp = Kotlinp(KotlinpSettings(isVerbose = true, sortDeclarations = true))
@@ -70,11 +69,10 @@ private fun compileAndPrintAllFiles(
         when (outputFile.extension) {
             "kotlin_module" -> {
                 val moduleFile = kotlinp.readModuleFile(outputFile)!!
-                val transformedWithVisitors = KotlinModuleMetadata.read(transformModuleFileWithReadWriteVisitors(moduleFile))
                 val transformedWithNodes = KotlinModuleMetadata.read(transformModuleFileWithNodes(moduleFile))
 
                 for ((sb, moduleFileToRender) in listOf(
-                    main to moduleFile, afterVisitors to transformedWithVisitors, afterNodes to transformedWithNodes
+                    main to moduleFile, afterNodes to transformedWithNodes
                 )) {
                     sb.appendFileName(outputFile.relativeTo(tmpdir))
                     sb.append(kotlinp.renderModuleFile(moduleFileToRender))
@@ -83,11 +81,10 @@ private fun compileAndPrintAllFiles(
             "class" -> {
                 val metadata = kotlinp.readClassFile(outputFile)
                 val classFile = kotlinp.readMetadata(metadata)
-                val classFile2 = transformClassFileWithReadWriteVisitors(classFile)
                 val classFile3 = KotlinClassMetadata.read(transformClassFileWithNodes(metadata, classFile))
 
                 for ((sb, classFileToRender) in listOf(
-                    main to classFile, afterVisitors to classFile2, afterNodes to classFile3
+                    main to classFile, afterNodes to classFile3
                 )) {
                     sb.appendFileName(outputFile.relativeTo(tmpdir))
                     sb.append(kotlinp.renderClassFile(classFileToRender))
@@ -102,7 +99,6 @@ private fun compileAndPrintAllFiles(
     }
 
     if (readWriteAndCompare && InTextDirectivesUtils.findStringWithPrefixes(file.readText(), "// NO_READ_WRITE_COMPARE") == null) {
-        assertEquals("Metadata is different after transformation with visitors.", main.toString(), afterVisitors.toString())
         assertEquals("Metadata is different after transformation with nodes.", main.toString(), afterNodes.toString())
     }
 }
@@ -130,27 +126,6 @@ private fun StringBuilder.appendFileName(file: File) {
     appendLine("// ------------------------------------------")
 }
 
-// Reads the class file and writes it back with *Writer visitors.
-// The resulting class file should be the same from the point of view of any metadata reader, including kotlinp
-// (the exact bytes may differ though, because there are multiple ways to encode the same metadata)
-@Suppress("DEPRECATION")
-private fun transformClassFileWithReadWriteVisitors(classFile: KotlinClassMetadata): KotlinClassMetadata =
-    when (classFile) {
-        is KotlinClassMetadata.Class -> KotlinClassMetadata.Class.Writer().apply(classFile::accept).write()
-        is KotlinClassMetadata.FileFacade -> KotlinClassMetadata.FileFacade.Writer().apply(classFile::accept).write()
-        is KotlinClassMetadata.SyntheticClass -> {
-            val writer = KotlinClassMetadata.SyntheticClass.Writer()
-            if (classFile.isLambda) {
-                classFile.accept(writer)
-            }
-            writer.write()
-        }
-        is KotlinClassMetadata.MultiFileClassFacade -> KotlinClassMetadata.MultiFileClassFacade.Writer().write(classFile.partClassNames)
-        is KotlinClassMetadata.MultiFileClassPart ->
-            KotlinClassMetadata.MultiFileClassPart.Writer().apply(classFile::accept).write(classFile.facadeClassName)
-        else -> classFile
-    }
-
 // Reads the class file and writes it back with KmClass/KmFunction/... elements.
 private fun transformClassFileWithNodes(metadata: Metadata, classFile: KotlinClassMetadata): Metadata =
     when (classFile) {
@@ -166,11 +141,6 @@ private fun transformClassFileWithNodes(metadata: Metadata, classFile: KotlinCla
         is KotlinClassMetadata.Unknown -> metadata
     }
 
-@Suppress("DEPRECATION") // We're testing that reading/writing with KmNodes is identical to direct
-@OptIn(UnstableMetadataApi::class)
-private fun transformModuleFileWithReadWriteVisitors(moduleFile: KotlinModuleMetadata): ByteArray =
-    KotlinModuleMetadata.Writer().apply(moduleFile::accept).write()
-
 @OptIn(UnstableMetadataApi::class)
 private fun transformModuleFileWithNodes(moduleFile: KotlinModuleMetadata): ByteArray =
     KotlinModuleMetadata.write(moduleFile.kmModule)