diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt
index 00ba8b05901..9fd89babe5b 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt
@@ -9,10 +9,10 @@ import org.jetbrains.kotlin.builtins.jvm.JavaToKotlinClassMap
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.*
-import org.jetbrains.kotlin.fir.scopes.FirScope
-import org.jetbrains.kotlin.fir.scopes.impl.*
-import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.fir.inferenceContext
+import org.jetbrains.kotlin.fir.scopes.FirScope
+import org.jetbrains.kotlin.fir.scopes.impl.FirClassSubstitutionScope
+import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.fir.types.*
 
 abstract class SupertypeSupplier {
@@ -37,26 +37,13 @@ fun lookupSuperTypes(
     }
 }
 
-class ScopeSession {
-    private val scopes = hashMapOf<Any, HashMap<ScopeSessionKey<*, *>, FirScope>>()
-    fun <ID : Any, FS : FirScope> getOrBuild(id: ID, key: ScopeSessionKey<ID, FS>, build: () -> FS): FS {
-        return scopes.getOrPut(id) {
-            hashMapOf()
-        }.getOrPut(key) {
-            build()
-        } as FS
-    }
-}
-
-abstract class ScopeSessionKey<ID : Any, FS : FirScope>
-
 inline fun <reified ID : Any, reified FS : FirScope> scopeSessionKey(): ScopeSessionKey<ID, FS> {
     return object : ScopeSessionKey<ID, FS>() {}
 }
 
 val USE_SITE = scopeSessionKey<FirClassSymbol<*>, FirScope>()
 
-data class SubstitutionScopeKey(val type: ConeClassLikeType) : ScopeSessionKey<FirClassLikeSymbol<*>, FirClassSubstitutionScope>() {}
+data class SubstitutionScopeKey(val type: ConeClassLikeType) : ScopeSessionKey<FirClassLikeSymbol<*>, FirClassSubstitutionScope>()
 
 fun FirClassSymbol<*>.buildUseSiteMemberScope(useSiteSession: FirSession, builder: ScopeSession): FirScope? {
     return when (this) {
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/resolve/ScopeSession.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/resolve/ScopeSession.kt
new file mode 100644
index 00000000000..402a64f51de
--- /dev/null
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/resolve/ScopeSession.kt
@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+package org.jetbrains.kotlin.fir.resolve
+
+import org.jetbrains.kotlin.fir.scopes.FirScope
+
+class ScopeSession {
+    private val scopes = hashMapOf<Any, HashMap<ScopeSessionKey<*, *>, FirScope>>()
+    fun <ID : Any, FS : FirScope> getOrBuild(id: ID, key: ScopeSessionKey<ID, FS>, build: () -> FS): FS {
+        return scopes.getOrPut(id) {
+            hashMapOf()
+        }.getOrPut(key) {
+            build()
+        } as FS
+    }
+}
+
+abstract class ScopeSessionKey<ID : Any, FS : FirScope>
+