diff --git a/api/api.base b/api/api.base
index 378fc6a51b..b990727188 100644
--- a/api/api.base
+++ b/api/api.base
@@ -141,7 +141,7 @@ package com.google.devtools.ksp.processing {
     property @NonNull public abstract String targetName;
   }
 
-  public interface PlatformInfo {
+  public sealed interface PlatformInfo {
     method @NonNull public String getPlatformName();
     property @NonNull public abstract String platformName;
   }
@@ -262,7 +262,7 @@ package com.google.devtools.ksp.symbol {
     enum_constant public static final com.google.devtools.ksp.symbol.FunctionKind TOP_LEVEL;
   }
 
-  public interface KSAnnotated extends com.google.devtools.ksp.symbol.KSNode {
+  public sealed interface KSAnnotated extends com.google.devtools.ksp.symbol.KSNode {
     method @NonNull public kotlin.sequences.Sequence<com.google.devtools.ksp.symbol.KSAnnotation> getAnnotations();
     property @NonNull public abstract kotlin.sequences.Sequence<com.google.devtools.ksp.symbol.KSAnnotation> annotations;
   }
@@ -313,7 +313,7 @@ package com.google.devtools.ksp.symbol {
     property @Nullable public abstract com.google.devtools.ksp.symbol.KSClassifierReference qualifier;
   }
 
-  public interface KSDeclaration extends com.google.devtools.ksp.symbol.KSModifierListOwner com.google.devtools.ksp.symbol.KSAnnotated com.google.devtools.ksp.symbol.KSExpectActual {
+  public sealed interface KSDeclaration extends com.google.devtools.ksp.symbol.KSModifierListOwner com.google.devtools.ksp.symbol.KSAnnotated com.google.devtools.ksp.symbol.KSExpectActual {
     method @Nullable public com.google.devtools.ksp.symbol.KSFile getContainingFile();
     method @Nullable public String getDocString();
     method @NonNull public com.google.devtools.ksp.symbol.KSName getPackageName();
@@ -330,7 +330,7 @@ package com.google.devtools.ksp.symbol {
     property @NonNull public abstract java.util.List<com.google.devtools.ksp.symbol.KSTypeParameter> typeParameters;
   }
 
-  public interface KSDeclarationContainer extends com.google.devtools.ksp.symbol.KSNode {
+  public sealed interface KSDeclarationContainer extends com.google.devtools.ksp.symbol.KSNode {
     method @NonNull public kotlin.sequences.Sequence<com.google.devtools.ksp.symbol.KSDeclaration> getDeclarations();
     property @NonNull public abstract kotlin.sequences.Sequence<com.google.devtools.ksp.symbol.KSDeclaration> declarations;
   }
@@ -390,7 +390,7 @@ package com.google.devtools.ksp.symbol {
     property @Nullable public abstract com.google.devtools.ksp.symbol.KSTypeReference returnType;
   }
 
-  public interface KSModifierListOwner extends com.google.devtools.ksp.symbol.KSNode {
+  public sealed interface KSModifierListOwner extends com.google.devtools.ksp.symbol.KSNode {
     method @NonNull public java.util.Set<com.google.devtools.ksp.symbol.Modifier> getModifiers();
     property @NonNull public abstract java.util.Set<com.google.devtools.ksp.symbol.Modifier> modifiers;
   }
@@ -401,7 +401,7 @@ package com.google.devtools.ksp.symbol {
     method @NonNull public String getShortName();
   }
 
-  public interface KSNode {
+  public sealed interface KSNode {
     method public <D, R> R accept(@NonNull com.google.devtools.ksp.symbol.KSVisitor<D,R> visitor, D data);
     method @NonNull public com.google.devtools.ksp.symbol.Location getLocation();
     method @NonNull public com.google.devtools.ksp.symbol.Origin getOrigin();
@@ -416,7 +416,7 @@ package com.google.devtools.ksp.symbol {
     property @NonNull public abstract com.google.devtools.ksp.symbol.KSReferenceElement element;
   }
 
-  public interface KSPropertyAccessor extends com.google.devtools.ksp.symbol.KSDeclarationContainer com.google.devtools.ksp.symbol.KSAnnotated com.google.devtools.ksp.symbol.KSModifierListOwner {
+  public sealed interface KSPropertyAccessor extends com.google.devtools.ksp.symbol.KSDeclarationContainer com.google.devtools.ksp.symbol.KSAnnotated com.google.devtools.ksp.symbol.KSModifierListOwner {
     method @NonNull public com.google.devtools.ksp.symbol.KSPropertyDeclaration getReceiver();
     property @NonNull public abstract com.google.devtools.ksp.symbol.KSPropertyDeclaration receiver;
   }
@@ -449,7 +449,7 @@ package com.google.devtools.ksp.symbol {
     property @NonNull public abstract com.google.devtools.ksp.symbol.KSValueParameter parameter;
   }
 
-  public interface KSReferenceElement extends com.google.devtools.ksp.symbol.KSNode {
+  public sealed interface KSReferenceElement extends com.google.devtools.ksp.symbol.KSNode {
     method @NonNull public java.util.List<com.google.devtools.ksp.symbol.KSTypeArgument> getTypeArguments();
     property @NonNull public abstract java.util.List<com.google.devtools.ksp.symbol.KSTypeArgument> typeArguments;
   }
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/processing/PlatformInfo.kt b/api/src/main/kotlin/com/google/devtools/ksp/processing/PlatformInfo.kt
index fcefe55fd7..6f05680d0e 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/processing/PlatformInfo.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/processing/PlatformInfo.kt
@@ -20,7 +20,7 @@ package com.google.devtools.ksp.processing
 /**
  * Platform specific information
  */
-interface PlatformInfo {
+sealed interface PlatformInfo {
     val platformName: String
 }
 
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSAnnotated.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSAnnotated.kt
index 3cfd551f8a..a06aee8951 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSAnnotated.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSAnnotated.kt
@@ -19,7 +19,7 @@ package com.google.devtools.ksp.symbol
 /**
  * A symbol that can be annotated with annotations.
  */
-interface KSAnnotated : KSNode {
+sealed interface KSAnnotated : KSNode {
 
     /**
      * All annotations on this symbol.
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclaration.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclaration.kt
index 6d71e13266..7c6322b726 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclaration.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclaration.kt
@@ -19,7 +19,7 @@ package com.google.devtools.ksp.symbol
 /**
  * A declaration, can be function declaration, class declaration and property declaration, or a type alias.
  */
-interface KSDeclaration : KSModifierListOwner, KSAnnotated, KSExpectActual {
+sealed interface KSDeclaration : KSModifierListOwner, KSAnnotated, KSExpectActual {
     /**
      * Simple name of this declaration, usually the name identifier at the declaration site.
      */
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclarationContainer.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclarationContainer.kt
index e9844df31b..3e7edb9e7b 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclarationContainer.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSDeclarationContainer.kt
@@ -19,7 +19,7 @@ package com.google.devtools.ksp.symbol
 /**
  * A declaration container can have a list of declarations declared in it.
  */
-interface KSDeclarationContainer : KSNode {
+sealed interface KSDeclarationContainer : KSNode {
     /**
      * Declarations that are lexically declared inside the current container.
      */
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSModifierListOwner.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSModifierListOwner.kt
index 8d8b20134b..ac9d2e9c8f 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSModifierListOwner.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSModifierListOwner.kt
@@ -19,7 +19,7 @@ package com.google.devtools.ksp.symbol
 /**
  * A [KSModifierListOwner] can have zero or more modifiers.
  */
-interface KSModifierListOwner : KSNode {
+sealed interface KSModifierListOwner : KSNode {
     /**
      * The set of modifiers on this element.
      */
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSNode.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSNode.kt
index 08e2d7df2e..89e7b56ed7 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSNode.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSNode.kt
@@ -19,7 +19,7 @@ package com.google.devtools.ksp.symbol
 /**
  * Base class of every visitable program elements.
  */
-interface KSNode {
+sealed interface KSNode {
     val origin: Origin
     val location: Location
     val parent: KSNode?
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSPropertyAccessor.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSPropertyAccessor.kt
index 3a2405d6f8..0f2af96563 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSPropertyAccessor.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSPropertyAccessor.kt
@@ -21,7 +21,7 @@ package com.google.devtools.ksp.symbol
  * Note that annotation use-site targets such as @get: @set: is not copied to accessor's annotations attribute.
  * Use KSAnnotated.findAnnotationFromUseSiteTarget() to ensure annotations from parent is obtained.
  */
-interface KSPropertyAccessor : KSDeclarationContainer, KSAnnotated, KSModifierListOwner {
+sealed interface KSPropertyAccessor : KSDeclarationContainer, KSAnnotated, KSModifierListOwner {
     /**
      * The owner of the property accessor.
      */
diff --git a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSReferenceElement.kt b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSReferenceElement.kt
index 425036dcba..2ef24569e9 100644
--- a/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSReferenceElement.kt
+++ b/api/src/main/kotlin/com/google/devtools/ksp/symbol/KSReferenceElement.kt
@@ -21,7 +21,7 @@ package com.google.devtools.ksp.symbol
  *
  * KSReferenceElement can specify, for example, a class, interface, or function, etc.
  */
-interface KSReferenceElement : KSNode {
+sealed interface KSReferenceElement : KSNode {
     /**
      * Type arguments in the type reference.
      */
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/Incremental.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/Incremental.kt
index fc184e199c..b78003a426 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/Incremental.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/Incremental.kt
@@ -657,6 +657,8 @@ class IncrementalContext(
         when (declaration) {
             is KSPropertyDeclarationJavaImpl -> recordLookupForJavaField(declaration.psi)
             is KSFunctionDeclarationJavaImpl -> recordLookupForJavaMethod(declaration.psi)
+            is KSClassDeclaration, is KSFunctionDeclaration, is KSPropertyDeclaration, is KSTypeAlias,
+            is KSTypeParameter -> Unit
         }
     }
 
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/processing/impl/ResolverImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/processing/impl/ResolverImpl.kt
index f07b68e633..9d8c24a28f 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/processing/impl/ResolverImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/processing/impl/ResolverImpl.kt
@@ -627,6 +627,11 @@ class ResolverImpl(
                     resolverContext = resolverContext
                         .childForClassOrPackage(resolveJavaDeclaration(e.psi) as ClassDescriptor, JavaClassImpl(e.psi))
                 }
+                is KSClassDeclaration, is KSFunctionDeclaration, is KSPropertyDeclaration, is KSTypeAlias,
+                is KSTypeParameter, is KSFile, is KSPropertyGetter, is KSPropertySetter, is KSTypeArgument,
+                is KSTypeReference, is KSValueArgument, is KSValueParameter, is KSAnnotation, is KSCallableReference,
+                is KSClassifierReference, is KSDefNonNullReference, is KSDynamicReference, is KSParenthesizedReference,
+                -> Unit
             }
         }
         return if (javaType is JavaArrayTypeImpl)
@@ -1192,6 +1197,7 @@ class ResolverImpl(
                         if (declaration.isAbstract)
                             modifiers.add(Modifier.ABSTRACT)
                     }
+                    is KSTypeAlias, is KSTypeParameter -> Unit
                 }
             }
             Origin.KOTLIN_LIB, Origin.JAVA_LIB -> {
@@ -1208,6 +1214,7 @@ class ResolverImpl(
                         if (declaration.jvmAccessFlag and Opcodes.ACC_SYNCHRONIZED != 0)
                             modifiers.add(Modifier.JAVA_SYNCHRONIZED)
                     }
+                    is KSClassDeclaration, is KSTypeAlias, is KSTypeParameter -> Unit
                 }
             }
             else -> Unit
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSDeclarationDescriptorImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSDeclarationDescriptorImpl.kt
index db041b2668..e0e5d6ee17 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSDeclarationDescriptorImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSDeclarationDescriptorImpl.kt
@@ -30,21 +30,22 @@ import org.jetbrains.kotlin.resolve.descriptorUtil.parents
 import org.jetbrains.kotlin.resolve.descriptorUtil.parentsWithSelf
 import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstanceOrNull
 
-abstract class KSDeclarationDescriptorImpl(private val descriptor: DeclarationDescriptor) : KSDeclaration {
+abstract class KSDeclarationDescriptorImpl(private val descriptor: DeclarationDescriptor) /*: KSDeclaration*/ {
 
-    override val origin by lazy {
+    open /*override*/ val origin by lazy {
         descriptor.origin
     }
 
-    override val containingFile: KSFile? = null
+    open /*override*/ val containingFile: KSFile? = null
 
-    override val location: Location = NonExistLocation
+    open /*override*/ val location: Location = NonExistLocation
 
-    override val annotations: Sequence<KSAnnotation> by lazy {
-        descriptor.annotations.asSequence().map { KSAnnotationDescriptorImpl.getCached(it, this) }.memoized()
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
+        descriptor.annotations.asSequence().map { KSAnnotationDescriptorImpl.getCached(it, this as KSDeclaration) }
+            .memoized()
     }
 
-    override val parentDeclaration: KSDeclaration? by lazy {
+    open /*override*/ val parentDeclaration: KSDeclaration? by lazy {
         val containingDescriptor = descriptor.parents.first()
         when (containingDescriptor) {
             is ClassDescriptor -> KSClassDeclarationDescriptorImpl.getCached(containingDescriptor)
@@ -53,19 +54,19 @@ abstract class KSDeclarationDescriptorImpl(private val descriptor: DeclarationDe
         } as KSDeclaration?
     }
 
-    override val parent: KSNode? by lazy {
+    open /*override*/ val parent: KSNode? by lazy {
         parentDeclaration
     }
 
-    override val packageName: KSName by lazy {
+    open /*override*/ val packageName: KSName by lazy {
         KSNameImpl.getCached(descriptor.findPackage().fqName.asString())
     }
 
-    override val qualifiedName: KSName by lazy {
+    open /*override*/ val qualifiedName: KSName by lazy {
         KSNameImpl.getCached(descriptor.fqNameSafe.asString())
     }
 
-    override val simpleName: KSName by lazy {
+    open /*override*/ val simpleName: KSName by lazy {
         KSNameImpl.getCached(descriptor.name.asString())
     }
 
@@ -73,7 +74,7 @@ abstract class KSDeclarationDescriptorImpl(private val descriptor: DeclarationDe
         return this.simpleName.asString()
     }
 
-    override val docString = null
+    open /*override*/ val docString: String? = null
 }
 
 val DeclarationDescriptor.origin: Origin
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSNodeDescriptorImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSNodeDescriptorImpl.kt
deleted file mode 100644
index 0c82f750fd..0000000000
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSNodeDescriptorImpl.kt
+++ /dev/null
@@ -1,9 +0,0 @@
-package com.google.devtools.ksp.symbol.impl.binary
-
-import com.google.devtools.ksp.symbol.KSNode
-import com.google.devtools.ksp.symbol.Location
-import com.google.devtools.ksp.symbol.NonExistLocation
-
-abstract class KSNodeDescriptorImpl(override val parent: KSNode?) : KSNode {
-    override val location: Location = NonExistLocation
-}
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSPropertyAccessorDescriptorImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSPropertyAccessorDescriptorImpl.kt
index 99ad99dc06..e51a5d541b 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSPropertyAccessorDescriptorImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSPropertyAccessorDescriptorImpl.kt
@@ -25,8 +25,8 @@ import com.google.devtools.ksp.symbol.impl.toKSPropertyDeclaration
 import com.google.devtools.ksp.toKSModifiers
 import org.jetbrains.kotlin.descriptors.PropertyAccessorDescriptor
 
-abstract class KSPropertyAccessorDescriptorImpl(val descriptor: PropertyAccessorDescriptor) : KSPropertyAccessor {
-    override val origin: Origin by lazy {
+abstract class KSPropertyAccessorDescriptorImpl(val descriptor: PropertyAccessorDescriptor) /*: KSPropertyAccessor*/ {
+    open /*override*/ val origin: Origin by lazy {
         when (receiver.origin) {
             // if receiver is kotlin source, that means we are a synthetic where developer
             // didn't declare an explicit accessor so we used the descriptor instead
@@ -35,26 +35,27 @@ abstract class KSPropertyAccessorDescriptorImpl(val descriptor: PropertyAccessor
         }
     }
 
-    override val receiver: KSPropertyDeclaration by lazy {
+    open /*override*/ val receiver: KSPropertyDeclaration by lazy {
         descriptor.correspondingProperty.toKSPropertyDeclaration()
     }
 
-    override val parent: KSNode? by lazy {
+    open /*override*/ val parent: KSNode? by lazy {
         receiver
     }
 
-    override val location: Location
+    open /*override*/ val location: Location
         get() {
             // if receiver is kotlin source, that means `this` is synthetic hence we want the property's location
             // Otherwise, receiver is also from a .class file where the location will be NoLocation
             return receiver.location
         }
 
-    override val annotations: Sequence<KSAnnotation> by lazy {
-        descriptor.annotations.asSequence().map { KSAnnotationDescriptorImpl.getCached(it, this) }.memoized()
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
+        descriptor.annotations.asSequence().map { KSAnnotationDescriptorImpl.getCached(it, this as KSPropertyAccessor) }
+            .memoized()
     }
 
-    override val modifiers: Set<Modifier> by lazy {
+    open /*override*/ val modifiers: Set<Modifier> by lazy {
         val modifiers = mutableSetOf<Modifier>()
         modifiers.addAll(descriptor.toKSModifiers())
         modifiers.addAll(descriptor.toFunctionKSModifiers())
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSDeclarationJavaImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSDeclarationJavaImpl.kt
index ebdffaccd7..dd23e85afb 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSDeclarationJavaImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSDeclarationJavaImpl.kt
@@ -25,24 +25,24 @@ import com.google.devtools.ksp.symbol.impl.findParentDeclaration
 import com.google.devtools.ksp.symbol.impl.getDocString
 import com.intellij.psi.PsiElement
 
-abstract class KSDeclarationJavaImpl(private val psi: PsiElement) : KSDeclaration {
-    override val packageName: KSName by lazy {
-        this.containingFile!!.packageName
+abstract class KSDeclarationJavaImpl(private val psi: PsiElement) /*: KSDeclaration*/ {
+    open /*override*/ val packageName: KSName by lazy {
+        (this as KSDeclaration).containingFile!!.packageName
     }
 
     override fun toString(): String {
-        return this.simpleName.asString()
+        return (this as KSDeclaration).simpleName.asString()
     }
 
-    override val docString by lazy {
+    open /*override*/ val docString by lazy {
         psi.getDocString()
     }
 
-    override val parentDeclaration: KSDeclaration? by lazy {
+    open /*override*/ val parentDeclaration: KSDeclaration? by lazy {
         psi.findParentDeclaration()
     }
 
-    override val parent: KSNode? by lazy {
+    open /*override*/ val parent: KSNode? by lazy {
         psi.findParentAnnotated()
     }
 }
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSNodeJavaImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSNodeJavaImpl.kt
deleted file mode 100644
index 860fb5fa04..0000000000
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSNodeJavaImpl.kt
+++ /dev/null
@@ -1,12 +0,0 @@
-package com.google.devtools.ksp.symbol.impl.java
-
-import com.google.devtools.ksp.symbol.KSNode
-import com.google.devtools.ksp.symbol.Location
-import com.google.devtools.ksp.symbol.impl.toLocation
-import com.intellij.psi.PsiElement
-
-abstract class KSNodeJavaImpl(private val psi: PsiElement, override val parent: KSNode?) : KSNode {
-    override val location: Location by lazy {
-        psi.toLocation()
-    }
-}
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSDeclarationImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSDeclarationImpl.kt
index b1f2a8499f..c01defae32 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSDeclarationImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSDeclarationImpl.kt
@@ -24,26 +24,26 @@ import com.google.devtools.ksp.symbol.*
 import com.google.devtools.ksp.symbol.impl.*
 import org.jetbrains.kotlin.psi.*
 
-abstract class KSDeclarationImpl(val ktDeclaration: KtDeclaration) : KSDeclaration {
-    override val origin: Origin = Origin.KOTLIN
+abstract class KSDeclarationImpl(val ktDeclaration: KtDeclaration) /*: KSDeclaration*/ {
+    open /*override*/ val origin: Origin = Origin.KOTLIN
 
-    override val location: Location by lazy {
+    open /*override*/ val location: Location by lazy {
         ktDeclaration.toLocation()
     }
 
-    override val simpleName: KSName by lazy {
+    open /*override*/ val simpleName: KSName by lazy {
         KSNameImpl.getCached(ktDeclaration.name!!)
     }
 
-    override val qualifiedName: KSName? by lazy {
+    open /*override*/ val qualifiedName: KSName? by lazy {
         (ktDeclaration as? KtNamedDeclaration)?.fqName?.let { KSNameImpl.getCached(it.asString()) }
     }
 
-    override val annotations: Sequence<KSAnnotation> by lazy {
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
         ktDeclaration.annotationEntries.asSequence().map { KSAnnotationImpl.getCached(it) }.memoized()
     }
 
-    override val modifiers: Set<Modifier> by lazy {
+    open /*override*/ val modifiers: Set<Modifier> by lazy {
         // we do not check for JVM_STATIC here intentionally as it actually means static in parent class,
         // not in this class.
         // see: https://github.com/google/ksp/issues/378
@@ -56,25 +56,25 @@ abstract class KSDeclarationImpl(val ktDeclaration: KtDeclaration) : KSDeclarati
         }
     }
 
-    override val containingFile: KSFile? by lazy {
+    open /*override*/ val containingFile: KSFile? by lazy {
         KSFileImpl.getCached(ktDeclaration.containingKtFile)
     }
 
-    override val packageName: KSName by lazy {
+    open /*override*/ val packageName: KSName by lazy {
         this.containingFile!!.packageName
     }
 
-    override val typeParameters: List<KSTypeParameter> by lazy {
+    open /*override*/ val typeParameters: List<KSTypeParameter> by lazy {
         (ktDeclaration as? KtTypeParameterListOwner)?.let {
             it.typeParameters.map { KSTypeParameterImpl.getCached(it) }
         } ?: emptyList()
     }
 
-    override val parentDeclaration: KSDeclaration? by lazy {
+    open /*override*/ val parentDeclaration: KSDeclaration? by lazy {
         ktDeclaration.findParentDeclaration()
     }
 
-    override val parent: KSNode? by lazy {
+    open /*override*/ val parent: KSNode? by lazy {
         ktDeclaration.findParentAnnotated()
     }
 
@@ -86,7 +86,7 @@ abstract class KSDeclarationImpl(val ktDeclaration: KtDeclaration) : KSDeclarati
         ktDeclaration.annotationEntries.map { KSAnnotationImpl.getCached(it) }
     }
 
-    override val docString by lazy {
+    open /*override*/ val docString by lazy {
         ktDeclaration.getDocString()
     }
 }
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSNodeKtImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSNodeKtImpl.kt
deleted file mode 100644
index 8c44b1453f..0000000000
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSNodeKtImpl.kt
+++ /dev/null
@@ -1,12 +0,0 @@
-package com.google.devtools.ksp.symbol.impl.kotlin
-
-import com.google.devtools.ksp.symbol.KSNode
-import com.google.devtools.ksp.symbol.Location
-import com.google.devtools.ksp.symbol.impl.toLocation
-import org.jetbrains.kotlin.psi.KtElement
-
-abstract class KSNodeKtImpl(private val element: KtElement) : KSNode {
-    override val location: Location by lazy {
-        element.toLocation()
-    }
-}
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSPropertyAccessorImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSPropertyAccessorImpl.kt
index 9d57b25d27..79a12a6d0f 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSPropertyAccessorImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSPropertyAccessorImpl.kt
@@ -26,7 +26,7 @@ import com.google.devtools.ksp.symbol.impl.toLocation
 import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.psi.KtPropertyAccessor
 
-abstract class KSPropertyAccessorImpl(val ktPropertyAccessor: KtPropertyAccessor) : KSPropertyAccessor {
+abstract class KSPropertyAccessorImpl(val ktPropertyAccessor: KtPropertyAccessor) /*: KSPropertyAccessor*/ {
     companion object {
         fun getCached(ktPropertyAccessor: KtPropertyAccessor): KSPropertyAccessor {
             return if (ktPropertyAccessor.isGetter) {
@@ -36,27 +36,27 @@ abstract class KSPropertyAccessorImpl(val ktPropertyAccessor: KtPropertyAccessor
             }
         }
     }
-    override val receiver: KSPropertyDeclaration by lazy {
+    open /*override*/ val receiver: KSPropertyDeclaration by lazy {
         KSPropertyDeclarationImpl.getCached(ktPropertyAccessor.property as KtProperty)
     }
-    override val annotations: Sequence<KSAnnotation> by lazy {
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
         ktPropertyAccessor.filterUseSiteTargetAnnotations().map { KSAnnotationImpl.getCached(it) }
-            .plus(this.findAnnotationFromUseSiteTarget())
+            .plus((this as KSPropertyAccessor).findAnnotationFromUseSiteTarget())
     }
 
-    override val parent: KSNode? by lazy {
+    open /*override*/ val parent: KSNode? by lazy {
         receiver
     }
 
-    override val location: Location by lazy {
+    open /*override*/ val location: Location by lazy {
         ktPropertyAccessor.toLocation()
     }
 
-    override val modifiers: Set<Modifier> by lazy {
+    open /*override*/ val modifiers: Set<Modifier> by lazy {
         ktPropertyAccessor.toKSModifiers()
     }
 
-    override val declarations: Sequence<KSDeclaration> by lazy {
+    open /*override*/ val declarations: Sequence<KSDeclaration> by lazy {
         if (!ktPropertyAccessor.hasBlockBody()) {
             emptySequence()
         } else {
@@ -65,10 +65,10 @@ abstract class KSPropertyAccessorImpl(val ktPropertyAccessor: KtPropertyAccessor
         }
     }
 
-    override val origin: Origin = Origin.KOTLIN
+    open /*override*/ val origin: Origin = Origin.KOTLIN
 
-    override fun <D, R> accept(visitor: KSVisitor<D, R>, data: D): R {
-        return visitor.visitPropertyAccessor(this, data)
+    open /*override*/ fun <D, R> accept(visitor: KSVisitor<D, R>, data: D): R {
+        return visitor.visitPropertyAccessor(this as KSPropertyAccessor, data)
     }
 
     internal val originalAnnotations: List<KSAnnotation> by lazy {
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSConstructorSyntheticImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSConstructorSyntheticImpl.kt
index 8f2efd36f7..dc0bd3a47a 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSConstructorSyntheticImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSConstructorSyntheticImpl.kt
@@ -25,9 +25,7 @@ import com.google.devtools.ksp.processing.impl.ResolverImpl
 import com.google.devtools.ksp.symbol.*
 
 class KSConstructorSyntheticImpl private constructor(val ksClassDeclaration: KSClassDeclaration) :
-    KSFunctionDeclaration,
-    KSDeclaration
-    by ksClassDeclaration {
+    KSFunctionDeclaration {
     companion object : KSObjectCache<KSClassDeclaration, KSConstructorSyntheticImpl>() {
         fun getCached(ksClassDeclaration: KSClassDeclaration) =
             KSConstructorSyntheticImpl.cache.getOrPut(ksClassDeclaration) {
@@ -43,6 +41,10 @@ class KSConstructorSyntheticImpl private constructor(val ksClassDeclaration: KSC
 
     override val functionKind: FunctionKind = FunctionKind.MEMBER
 
+    override val docString: String? get() = ksClassDeclaration.docString
+
+    override val packageName: KSName get() = ksClassDeclaration.packageName
+
     override val qualifiedName: KSName? by lazy {
         KSNameImpl.getCached(ksClassDeclaration.qualifiedName?.asString()?.plus(".<init>") ?: "")
     }
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSPropertyAccessorSyntheticImpl.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSPropertyAccessorSyntheticImpl.kt
index f6f0ad9fc6..98d5fe5f4a 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSPropertyAccessorSyntheticImpl.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/synthetic/KSPropertyAccessorSyntheticImpl.kt
@@ -20,22 +20,22 @@ package com.google.devtools.ksp.symbol.impl.synthetic
 import com.google.devtools.ksp.processing.impl.findAnnotationFromUseSiteTarget
 import com.google.devtools.ksp.symbol.*
 
-abstract class KSPropertyAccessorSyntheticImpl(ksPropertyDeclaration: KSPropertyDeclaration) : KSPropertyAccessor {
-    override val annotations: Sequence<KSAnnotation> by lazy {
-        this.findAnnotationFromUseSiteTarget()
+abstract class KSPropertyAccessorSyntheticImpl(ksPropertyDeclaration: KSPropertyDeclaration) /*: KSPropertyAccessor*/ {
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
+        (this as KSPropertyAccessor).findAnnotationFromUseSiteTarget()
     }
 
-    override val location: Location by lazy {
+    open /*override*/ val location: Location by lazy {
         ksPropertyDeclaration.location
     }
 
-    override val modifiers: Set<Modifier> = emptySet()
+    open /*override*/ val modifiers: Set<Modifier> = emptySet()
 
-    override val origin: Origin = Origin.SYNTHETIC
+    open /*override*/ val origin: Origin = Origin.SYNTHETIC
 
-    override val receiver: KSPropertyDeclaration = ksPropertyDeclaration
+    open /*override*/ val receiver: KSPropertyDeclaration = ksPropertyDeclaration
 
-    override fun <D, R> accept(visitor: KSVisitor<D, R>, data: D): R {
-        return visitor.visitPropertyAccessor(this, data)
+    open /*override*/ fun <D, R> accept(visitor: KSVisitor<D, R>, data: D): R {
+        return visitor.visitPropertyAccessor(this as KSPropertyAccessor, data)
     }
 }
diff --git a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/utils.kt b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/utils.kt
index 66de2f9d6a..a926f0fe0c 100644
--- a/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/utils.kt
+++ b/compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/utils.kt
@@ -319,7 +319,7 @@ internal class DeclarationOrdering(
     }
 
     private fun getOrder(decl: KSDeclarationDescriptorImpl): Int {
-        return declOrdering.getOrPut(decl) {
+        return declOrdering.getOrPut(decl as KSDeclaration) {
             when (decl) {
                 is KSPropertyDeclarationDescriptorImpl -> {
                     fieldOrdering[decl.simpleName.asString()]?.let {
@@ -467,7 +467,8 @@ internal val KSDeclarationContainer.declarationsInSourceOrder: Sequence<KSDeclar
             DeclarationOrdering(it)
         } ?: return declarations
 
-        return (declarations as? Sequence<KSDeclarationDescriptorImpl>)?.sortedWith(declarationOrdering.comparator)
+        return (declarations as? Sequence<KSDeclarationDescriptorImpl>)
+            ?.sortedWith(declarationOrdering.comparator) as Sequence<KSDeclaration>?
             ?: declarations
     }
 
diff --git a/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/ResolverAAImpl.kt b/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/ResolverAAImpl.kt
index d32aa91d98..31dd70be87 100644
--- a/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/ResolverAAImpl.kt
+++ b/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/ResolverAAImpl.kt
@@ -166,6 +166,7 @@ class ResolverAAImpl(
                         if (declaration.isAbstract)
                             modifiers.add(Modifier.ABSTRACT)
                     }
+                    is KSTypeAlias, is KSTypeParameter -> Unit
                 }
             }
             Origin.KOTLIN_LIB, Origin.JAVA_LIB -> {
@@ -186,6 +187,7 @@ class ResolverAAImpl(
                         if (declaration.jvmAccessFlag and Opcodes.ACC_SYNCHRONIZED != 0)
                             modifiers.add(Modifier.JAVA_SYNCHRONIZED)
                     }
+                    is KSClassDeclaration, is KSTypeAlias, is KSTypeParameter -> Unit
                 }
             }
             else -> Unit
diff --git a/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/AbstractKSDeclarationImpl.kt b/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/AbstractKSDeclarationImpl.kt
index f96dae191b..72fe8f6f20 100644
--- a/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/AbstractKSDeclarationImpl.kt
+++ b/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/AbstractKSDeclarationImpl.kt
@@ -38,24 +38,24 @@ import org.jetbrains.kotlin.analysis.utils.printer.parentOfType
 import org.jetbrains.kotlin.psi.KtElement
 import org.jetbrains.kotlin.psi.KtModifierListOwner
 
-abstract class AbstractKSDeclarationImpl(val ktDeclarationSymbol: KtDeclarationSymbol) : KSDeclaration, Deferrable {
-    override val origin: Origin by lazy {
+abstract class AbstractKSDeclarationImpl(val ktDeclarationSymbol: KtDeclarationSymbol) : /*KSDeclaration,*/ Deferrable {
+    open /*override*/ val origin: Origin by lazy {
         mapAAOrigin(ktDeclarationSymbol)
     }
 
-    override val location: Location by lazy {
+    open /*override*/ val location: Location by lazy {
         ktDeclarationSymbol.psi.toLocation()
     }
 
-    override val simpleName: KSName by lazy {
+    open /*override*/ val simpleName: KSName by lazy {
         KSNameImpl.getCached((ktDeclarationSymbol as? KtNamedSymbol)?.name?.asString() ?: "")
     }
 
-    override val annotations: Sequence<KSAnnotation> by lazy {
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
         originalAnnotations
     }
 
-    override val modifiers: Set<Modifier> by lazy {
+    open /*override*/ val modifiers: Set<Modifier> by lazy {
         if (origin == Origin.JAVA_LIB || origin == Origin.KOTLIN_LIB) {
             when (ktDeclarationSymbol) {
                 is KtPropertySymbol -> ktDeclarationSymbol.toModifiers()
@@ -73,24 +73,24 @@ abstract class AbstractKSDeclarationImpl(val ktDeclarationSymbol: KtDeclarationS
         }
     }
 
-    override val containingFile: KSFile? by lazy {
+    open /*override*/ val containingFile: KSFile? by lazy {
         ktDeclarationSymbol.toContainingFile()
     }
 
-    override val packageName: KSName by lazy {
+    open /*override*/ val packageName: KSName by lazy {
         ((containingFile?.packageName ?: ktDeclarationSymbol.getContainingKSSymbol()?.packageName)?.asString() ?: "")
             .let { KSNameImpl.getCached(it) }
     }
 
-    override val typeParameters: List<KSTypeParameter> by lazy {
+    open /*override*/ val typeParameters: List<KSTypeParameter> by lazy {
         ktDeclarationSymbol.typeParameters.map { KSTypeParameterImpl.getCached(it) }
     }
 
-    override val parentDeclaration: KSDeclaration? by lazy {
+    open /*override*/ val parentDeclaration: KSDeclaration? by lazy {
         parent as? KSDeclaration
     }
 
-    override val parent: KSNode? by lazy {
+    open /*override*/ val parent: KSNode? by lazy {
         analyze {
             ktDeclarationSymbol.getContainingSymbol()?.let {
                 ktDeclarationSymbol.getContainingKSSymbol()
@@ -104,11 +104,11 @@ abstract class AbstractKSDeclarationImpl(val ktDeclarationSymbol: KtDeclarationS
         return simpleName.asString()
     }
 
-    override val docString: String?
+    open /*override*/ val docString: String?
         get() = ktDeclarationSymbol.toDocString()
 
     internal val originalAnnotations = if (ktDeclarationSymbol.psi is KtElement || ktDeclarationSymbol.psi == null) {
-        ktDeclarationSymbol.annotations(this)
+        ktDeclarationSymbol.annotations(this as KSDeclaration)
     } else {
         (ktDeclarationSymbol.psi as PsiJvmModifiersOwner)
             .annotations.map { KSAnnotationJavaImpl.getCached(it) }.asSequence()
diff --git a/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/KSPropertyAccessorImpl.kt b/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/KSPropertyAccessorImpl.kt
index fb5863c85b..443f74bca8 100644
--- a/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/KSPropertyAccessorImpl.kt
+++ b/kotlin-analysis-api/src/main/kotlin/com/google/devtools/ksp/impl/symbol/kotlin/KSPropertyAccessorImpl.kt
@@ -31,23 +31,23 @@ import org.jetbrains.kotlin.psi.KtPropertyAccessor
 
 abstract class KSPropertyAccessorImpl(
     internal val ktPropertyAccessorSymbol: KtPropertyAccessorSymbol,
-    override val receiver: KSPropertyDeclaration
-) : KSPropertyAccessor, Deferrable {
+    open /*override*/ val receiver: KSPropertyDeclaration
+) : /*KSPropertyAccessor,*/ Deferrable {
 
-    override val annotations: Sequence<KSAnnotation> by lazy {
+    open /*override*/ val annotations: Sequence<KSAnnotation> by lazy {
         ktPropertyAccessorSymbol.annotations.asSequence()
             .filter { it.useSiteTarget != AnnotationUseSiteTarget.SETTER_PARAMETER }
-            .map { KSAnnotationImpl.getCached(it, this) }
-            .plus(findAnnotationFromUseSiteTarget())
+            .map { KSAnnotationImpl.getCached(it, this as KSPropertyAccessor) }
+            .plus((this as KSPropertyAccessor).findAnnotationFromUseSiteTarget())
     }
 
-    internal val originalAnnotations = ktPropertyAccessorSymbol.annotations(this)
+    internal val originalAnnotations = ktPropertyAccessorSymbol.annotations(this as KSPropertyAccessor)
 
-    override val location: Location by lazy {
+    open /*override*/ val location: Location by lazy {
         ktPropertyAccessorSymbol.psi?.toLocation() ?: NonExistLocation
     }
 
-    override val modifiers: Set<Modifier> by lazy {
+    open /*override*/ val modifiers: Set<Modifier> by lazy {
         ((ktPropertyAccessorSymbol.psi as? KtModifierListOwner)?.toKSModifiers() ?: emptySet()).let {
             if (origin == Origin.SYNTHETIC &&
                 (receiver.parentDeclaration as? KSClassDeclaration)?.classKind == ClassKind.INTERFACE
@@ -59,7 +59,7 @@ abstract class KSPropertyAccessorImpl(
         }
     }
 
-    override val origin: Origin by lazy {
+    open /*override*/ val origin: Origin by lazy {
         val symbolOrigin = mapAAOrigin(ktPropertyAccessorSymbol)
         if (symbolOrigin == Origin.KOTLIN && ktPropertyAccessorSymbol.psi == null) {
             Origin.SYNTHETIC
@@ -68,10 +68,10 @@ abstract class KSPropertyAccessorImpl(
         }
     }
 
-    override val parent: KSNode?
+    open /*override*/ val parent: KSNode?
         get() = ktPropertyAccessorSymbol.getContainingKSSymbol()
 
-    override val declarations: Sequence<KSDeclaration> by lazy {
+    open /*override*/ val declarations: Sequence<KSDeclaration> by lazy {
         val psi = ktPropertyAccessorSymbol.psi as? KtPropertyAccessor ?: return@lazy emptySequence()
         if (!psi.hasBlockBody()) {
             emptySequence()