[FIR] Never create ConeSubstitutorByMap with empty substitution

Relates to KT-66323

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/SupertypeUtils.kt

@@ -307,7 +307,7 @@ fun createSubstitutionForSupertype(superType: ConeLookupTagBasedType, session: F
         it as? ConeKotlinType ?: ConeErrorType(ConeSimpleDiagnostic("illegal projection usage", DiagnosticKind.IllegalProjectionUsage))
     }
     val mapping = klass.typeParameters.map { it.symbol }.zip(arguments).toMap()
-    return ConeSubstitutorByMap(mapping, session)
+    return ConeSubstitutorByMap.create(mapping, session)
 }
 
 fun FirRegularClassSymbol.getSuperClassSymbolOrAny(session: FirSession): FirRegularClassSymbol {

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/substitution/Substitutors.kt

@@ -67,7 +67,7 @@ fun wrapProjection(old: ConeTypeProjection, newType: ConeKotlinType): ConeTypePr
 
 abstract class AbstractConeSubstitutor(protected val typeContext: ConeTypeContext) : ConeSubstitutor() {
     abstract fun substituteType(type: ConeKotlinType): ConeKotlinType?
-    open fun substituteArgument(projection: ConeTypeProjection, index: Int): ConeTypeProjection? {
+    override fun substituteArgument(projection: ConeTypeProjection, index: Int): ConeTypeProjection? {
         val type = (projection as? ConeKotlinTypeProjection)?.type ?: return null
         val newType = substituteOrNull(type) ?: return null
         return wrapProjection(projection, newType)
@@ -212,12 +212,7 @@ abstract class AbstractConeSubstitutor(protected val typeContext: ConeTypeContex
 }
 
 fun substitutorByMap(substitution: Map<FirTypeParameterSymbol, ConeKotlinType>, useSiteSession: FirSession): ConeSubstitutor {
-    // If all arguments match parameters, then substitutor isn't needed
-    if (substitution.all { (parameterSymbol, argumentType) ->
-            (argumentType as? ConeTypeParameterType)?.lookupTag?.typeParameterSymbol == parameterSymbol && !argumentType.isMarkedNullable
-        }
-    ) return ConeSubstitutor.Empty
-    return ConeSubstitutorByMap(substitution, useSiteSession)
+    return ConeSubstitutorByMap.create(substitution, useSiteSession, allowIdenticalSubstitution = false)
 }
 
 data class ChainedSubstitutor(val first: ConeSubstitutor, val second: ConeSubstitutor) : ConeSubstitutor() {
@@ -226,6 +221,11 @@ data class ChainedSubstitutor(val first: ConeSubstitutor, val second: ConeSubsti
         return second.substituteOrNull(type)
     }
 
+    override fun substituteArgument(projection: ConeTypeProjection, index: Int): ConeTypeProjection? {
+        first.substituteArgument(projection, index)?.let { return second.substituteArgument(projection, index) }
+        return second.substituteArgument(projection, index)
+    }
+
     override fun toString(): String {
         return "$first then $second"
     }
@@ -237,11 +237,31 @@ fun ConeSubstitutor.chain(other: ConeSubstitutor): ConeSubstitutor {
     return ChainedSubstitutor(this, other)
 }
 
-class ConeSubstitutorByMap(
+class ConeSubstitutorByMap private constructor(
     // Used only for sake of optimizations at org.jetbrains.kotlin.analysis.api.fir.types.KtFirMapBackedSubstitutor
     val substitution: Map<FirTypeParameterSymbol, ConeKotlinType>,
     private val useSiteSession: FirSession
 ) : AbstractConeSubstitutor(useSiteSession.typeContext) {
+    companion object {
+        fun create(
+            substitution: Map<FirTypeParameterSymbol, ConeKotlinType>,
+            useSiteSession: FirSession,
+            allowIdenticalSubstitution: Boolean = true,
+        ): ConeSubstitutor {
+            if (substitution.isEmpty()) return Empty
+
+            if (!allowIdenticalSubstitution) {
+                // If all arguments match parameters, then substitutor isn't needed
+                val substitutionIsIdentical = substitution.all { (parameterSymbol, argumentType) ->
+                    (argumentType as? ConeTypeParameterType)?.lookupTag?.typeParameterSymbol == parameterSymbol && !argumentType.isMarkedNullable
+                }
+                if (substitutionIsIdentical) {
+                    return Empty
+                }
+            }
+            return ConeSubstitutorByMap(substitution, useSiteSession)
+        }
+    }
 
     private val hashCode by lazy(LazyThreadSafetyMode.PUBLICATION) {
         substitution.hashCode()

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirLocalScope.kt

@@ -79,7 +79,7 @@ class FirLocalScope private constructor(
         val klass = classes[name]
         if (klass != null) {
             val substitution = klass.typeParameterSymbols.associateWith { it.toConeType() }
-            processor(klass, ConeSubstitutorByMap(substitution, useSiteSession))
+            processor(klass, ConeSubstitutorByMap.create(substitution, useSiteSession))
         }
     }
 

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirNestedClassifierScope.kt

@@ -37,7 +37,7 @@ abstract class FirNestedClassifierScope(val klass: FirClass, val useSiteSession:
             val substitution = klass.typeParameters.associate {
                 it.symbol to it.toConeType()
             }
-            ConeSubstitutorByMap(substitution, useSiteSession)
+            ConeSubstitutorByMap.create(substitution, useSiteSession)
         }
         processor(matchedClass, substitutor)
     }

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirScriptDeclarationsScope.kt

@@ -77,8 +77,8 @@ class FirScriptDeclarationsScope(
     ) {
         val matchedClass = classIndex[name] ?: return
         val substitution = matchedClass.typeParameterSymbols.associateWith { it.toConeType() }
-        processor(matchedClass, ConeSubstitutorByMap(substitution, useSiteSession))
+        processor(matchedClass, ConeSubstitutorByMap.create(substitution, useSiteSession))
     }
 
     override fun getClassifierNames(): Set<Name> = classIndex.keys
-}
+}

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/ConeInferenceContext.kt

@@ -424,7 +424,7 @@ interface ConeInferenceContext : TypeSystemInferenceExtensionContext, ConeTypeCo
         val typeParameterErasureMap = this.extractTypeParameters()
             .map { (it as ConeTypeParameterLookupTag).typeParameterSymbol }
             .eraseToUpperBoundsAssociated(session)
-        val substitutor by lazy { ConeSubstitutorByMap(typeParameterErasureMap, session) }
+        val substitutor by lazy { ConeSubstitutorByMap.create(typeParameterErasureMap, session) }
         val typeWithErasedTypeParameters = if (argumentsCount() != 0) {
             replaceArgumentsDeeply {
                 val type = it.getType()

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/ExpectActualUtils.kt

@@ -19,7 +19,7 @@ fun createExpectActualTypeParameterSubstitutor(
     val substitution = expectActualTypeParameters.associate { (expectedParameterSymbol, actualParameterSymbol) ->
         expectedParameterSymbol to actualParameterSymbol.toLookupTag().constructType(emptyArray(), isNullable = false)
     }
-    val substitutor = ConeSubstitutorByMap(
+    val substitutor = ConeSubstitutorByMap.create(
         substitution,
         useSiteSession
     )