[Commonizer] Minor. Reorganize CirClass.supertypes

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/cir/CirClass.kt

@@ -15,9 +15,7 @@ interface CirClass : CirClassifier, CirContainingClass {
     val isValue: Boolean
     val isInner: Boolean
     val isExternal: Boolean
-    val supertypes: Collection<CirType>
-
-    fun setSupertypes(supertypes: Collection<CirType>)
+    var supertypes: List<CirType>
 
     companion object {
         @Suppress("NOTHING_TO_INLINE")
@@ -65,13 +63,12 @@ data class CirClassImpl(
     override val isInner: Boolean,
     override val isExternal: Boolean,
 ) : CirClass {
-    private var _supertypes: Collection<CirType>? = null
+    private var _supertypes: List<CirType>? = null
 
-    override val supertypes: Collection<CirType>
-        get() = _supertypes.orEmpty()
-
-    override fun setSupertypes(supertypes: Collection<CirType>) {
-        check(_supertypes == null)
-        _supertypes = supertypes
-    }
+    override var supertypes: List<CirType>
+        get() = _supertypes ?: error("${::supertypes.name} has not been initialized yet")
+        set(value) {
+            check(_supertypes == null) { "Re-initialization of ${::supertypes.name}" }
+            _supertypes = value
+        }
 }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/cir/RecursionMarkers.kt

@@ -20,8 +20,9 @@ object CirClassRecursionMarker : CirClass, CirRecursionMarker {
     override val isValue get() = unsupported()
     override val isInner get() = unsupported()
     override val isExternal get() = unsupported()
-    override val supertypes get() = unsupported()
-    override fun setSupertypes(supertypes: Collection<CirType>) = unsupported()
+    override var supertypes: List<CirType>
+        get() = unsupported()
+        set(_) = unsupported()
 }
 
 object CirClassifierRecursionMarker : CirClassifier, CirRecursionMarker {

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/core/CommonizationVisitor.kt

@@ -147,6 +147,6 @@ internal class CommonizationVisitor(
             commonize(supertypesGroup, TypeCommonizer(classifiers))
         }.orEmpty()
 
-        setSupertypes(commonSupertypes)
+        supertypes = commonSupertypes
     }
 }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/metadata/CirDeserializers.kt

@@ -264,7 +264,7 @@ object CirDeserializers {
         isInner = Flag.Class.IS_INNER(source.flags),
         isExternal = Flag.Class.IS_EXTERNAL(source.flags)
     ).apply {
-        setSupertypes(source.filteredSupertypes.compactMap { type(it, typeResolver) })
+        supertypes = source.filteredSupertypes.compactMap { type(it, typeResolver) }
     }
 
     fun defaultEnumEntry(
@@ -294,7 +294,7 @@ object CirDeserializers {
             arguments = emptyList(),
             isMarkedNullable = false
         )
-        setSupertypes(listOf(enumClassType))
+        supertypes = listOf(enumClassType)
     }
 
     @Suppress("NOTHING_TO_INLINE")