Use no-op substitutor instead of substitutor with empty map

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/scopes/JavaClassUseSiteScope.kt

@@ -12,7 +12,7 @@ import org.jetbrains.kotlin.fir.java.JavaTypeParameterStack
 import org.jetbrains.kotlin.fir.java.declarations.FirJavaClass
 import org.jetbrains.kotlin.fir.java.toNotNullConeKotlinType
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
-import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
 import org.jetbrains.kotlin.fir.scopes.FirScope
 import org.jetbrains.kotlin.fir.scopes.ProcessorAction
 import org.jetbrains.kotlin.fir.scopes.ProcessorAction.*
@@ -68,7 +68,7 @@ class JavaClassUseSiteScope(
         val types = base.typeParameters.map {
             ConeTypeParameterTypeImpl(it.symbol.toLookupTag(), false)
         }
-        val substitution = ConeSubstitutorByMap(overriddenInJava.typeParameters.map { it.symbol }.zip(types).toMap())
+        val substitution = substitutorByMap(overriddenInJava.typeParameters.map { it.symbol }.zip(types).toMap())
         if (!overriddenInJava.typeParameters.zip(base.typeParameters).all { (a, b) ->
                 a.bounds.size == b.bounds.size && a.bounds.zip(b.bounds).all { (aBound, bBound) ->
                     isEqualTypes(aBound, bBound, substitution)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/ConeInferenceContext.kt

@@ -248,6 +248,7 @@ interface ConeInferenceContext : TypeSystemInferenceExtensionContext,
     }
 
     override fun typeSubstitutorByTypeConstructor(map: Map<TypeConstructorMarker, KotlinTypeMarker>): TypeSubstitutorMarker {
+        if (map.isEmpty()) return ConeSubstitutor.Empty
         return object : AbstractConeSubstitutor(),
             TypeSubstitutorMarker {
             override fun substituteType(type: ConeKotlinType): ConeKotlinType? {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/CreateFreshTypeVariableSubstitutorStage.kt

@@ -9,7 +9,7 @@ import org.jetbrains.kotlin.fir.declarations.FirCallableMemberDeclaration
 import org.jetbrains.kotlin.fir.renderWithType
 import org.jetbrains.kotlin.fir.resolve.constructType
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
-import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
 import org.jetbrains.kotlin.fir.service
 import org.jetbrains.kotlin.fir.symbols.StandardClassIds
 import org.jetbrains.kotlin.fir.symbols.invoke
@@ -92,7 +92,7 @@ fun createToFreshVariableSubstitutorAndAddInitialConstraints(
 
     val freshTypeVariables = typeParameters.map { TypeParameterBasedTypeVariable(it.symbol) }
 
-    val toFreshVariables = ConeSubstitutorByMap(freshTypeVariables.associate { it.typeParameterSymbol to it.defaultType })
+    val toFreshVariables = substitutorByMap(freshTypeVariables.associate { it.typeParameterSymbol to it.defaultType })
 
     for (freshVariable in freshTypeVariables) {
         csBuilder.registerVariable(freshVariable)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/OverloadConflictResolver.kt

@@ -7,7 +7,7 @@ package org.jetbrains.kotlin.fir.resolve.calls
 
 import org.jetbrains.kotlin.fir.declarations.FirConstructor
 import org.jetbrains.kotlin.fir.declarations.FirNamedFunction
-import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.coneTypeUnsafe
@@ -211,7 +211,7 @@ class ConeSimpleConstraintSystemImpl(val system: NewConstraintSystemImpl) : Simp
 
             it to variable.defaultType
         }
-        val substitutor = ConeSubstitutorByMap(substitutionMap.cast())
+        val substitutor = substitutorByMap(substitutionMap.cast())
         for (typeParameter in typeParameters) {
             require(typeParameter is FirTypeParameterSymbol)
             for (upperBound in typeParameter.fir.bounds) {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/substitution/ConeSubstitutor.kt

@@ -13,11 +13,11 @@ import org.jetbrains.kotlin.fir.types.impl.ConeClassTypeImpl
 import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
 
 
-interface ConeSubstitutor : TypeSubstitutorMarker {
-    fun substituteOrSelf(type: ConeKotlinType): ConeKotlinType
-    fun substituteOrNull(type: ConeKotlinType): ConeKotlinType?
+abstract class ConeSubstitutor : TypeSubstitutorMarker {
+    abstract fun substituteOrSelf(type: ConeKotlinType): ConeKotlinType
+    abstract fun substituteOrNull(type: ConeKotlinType): ConeKotlinType?
 
-    object Empty : ConeSubstitutor {
+    object Empty : ConeSubstitutor() {
         override fun substituteOrSelf(type: ConeKotlinType): ConeKotlinType {
             return type
         }
@@ -33,7 +33,7 @@ fun ConeSubstitutor.substituteOrNull(type: ConeKotlinType?): ConeKotlinType? {
     return type?.let { substituteOrNull(it) }
 }
 
-abstract class AbstractConeSubstitutor : ConeSubstitutor {
+abstract class AbstractConeSubstitutor : ConeSubstitutor() {
     private fun wrapProjection(old: ConeKotlinTypeProjection, newType: ConeKotlinType): ConeKotlinTypeProjection {
         return when (old) {
             is ConeStarProjection -> old
@@ -130,6 +130,11 @@ abstract class AbstractConeSubstitutor : ConeSubstitutor {
 }
 
 
+fun substitutorByMap(substitution: Map<ConeTypeParameterSymbol, ConeKotlinType>): ConeSubstitutor {
+    if (substitution.isEmpty()) return ConeSubstitutor.Empty
+    return ConeSubstitutorByMap(substitution)
+}
+
 class ConeSubstitutorByMap(val substitution: Map<ConeTypeParameterSymbol, ConeKotlinType>) : AbstractConeSubstitutor() {
 
     override fun substituteType(type: ConeKotlinType): ConeKotlinType? {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/AbstractFirOverrideScope.kt

@@ -9,7 +9,7 @@ import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
-import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
 import org.jetbrains.kotlin.fir.scopes.FirScope
 import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.ConeCallableSymbol
@@ -38,7 +38,7 @@ abstract class AbstractFirOverrideScope(val session: FirSession) : FirScope() {
         val types = self.typeParameters.map {
             ConeTypeParameterTypeImpl(it.symbol.toLookupTag(), false)
         }
-        val substitution = ConeSubstitutorByMap(member.typeParameters.map { it.symbol }.zip(types).toMap())
+        val substitution = substitutorByMap(member.typeParameters.map { it.symbol }.zip(types).toMap())
         if (!member.typeParameters.zip(self.typeParameters).all { (a, b) ->
                 a.bounds.size == b.bounds.size &&
                         a.bounds.zip(b.bounds).all { (aBound, bBound) -> isEqualTypes(aBound, bBound, substitution) }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirClassSubstitutionScope.kt

@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.fir.declarations.impl.FirDeclarationStatusImpl
 import org.jetbrains.kotlin.fir.declarations.impl.FirMemberFunctionImpl
 import org.jetbrains.kotlin.fir.declarations.impl.FirValueParameterImpl
 import org.jetbrains.kotlin.fir.resolve.ScopeSession
-import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
 import org.jetbrains.kotlin.fir.resolve.transformers.ReturnTypeCalculatorWithJump
 import org.jetbrains.kotlin.fir.scopes.FirScope
 import org.jetbrains.kotlin.fir.scopes.ProcessorAction
@@ -33,7 +33,7 @@ class FirClassSubstitutionScope(
 
     private val fakeOverrides = mutableMapOf<FirFunctionSymbol<*>, FirFunctionSymbol<*>>()
 
-    private val substitutor = ConeSubstitutorByMap(substitution)
+    private val substitutor = substitutorByMap(substitution)
 
     override fun processFunctionsByName(name: Name, processor: (FirFunctionSymbol<*>) -> ProcessorAction): ProcessorAction {
         useSiteScope.processFunctionsByName(name) process@{ original ->

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/ConeTypeContext.kt

@@ -15,7 +15,7 @@ import org.jetbrains.kotlin.fir.resolve.*
 import org.jetbrains.kotlin.fir.resolve.calls.ConeTypeVariableTypeConstructor
 import org.jetbrains.kotlin.fir.resolve.calls.hasNullableSuperType
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
-import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
+import org.jetbrains.kotlin.fir.resolve.substitution.substitutorByMap
 import org.jetbrains.kotlin.fir.resolve.transformers.firUnsafe
 import org.jetbrains.kotlin.fir.service
 import org.jetbrains.kotlin.fir.symbols.*
@@ -435,7 +435,7 @@ class ConeTypeCheckerContext(override val isErrorTypeEqualsToAnything: Boolean,
                     parameter.symbol as ConeTypeParameterSymbol to ((argument as? ConeTypedProjection)?.type
                         ?: StandardClassIds.Any(session.firSymbolProvider).constructType(emptyArray(), isNullable = true))
                 }
-            ConeSubstitutorByMap(substitution)
+            substitutorByMap(substitution)
         } else {
             ConeSubstitutor.Empty
         }