[FIR] Never create ConeSubstitutorByMap with empty substitution

Relates to KT-66323

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/components/KtFirSubstitutorFactory.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.analysis.api.components.KtSubstitutorBuilder
 import org.jetbrains.kotlin.analysis.api.components.KtSubstitutorFactory
 import org.jetbrains.kotlin.analysis.api.fir.KtFirAnalysisSession
 import org.jetbrains.kotlin.analysis.api.fir.symbols.KtFirTypeParameterSymbol
+import org.jetbrains.kotlin.analysis.api.fir.types.KtFirGenericSubstitutor
 import org.jetbrains.kotlin.analysis.api.fir.types.KtFirMapBackedSubstitutor
 import org.jetbrains.kotlin.analysis.api.fir.types.KtFirType
 import org.jetbrains.kotlin.analysis.api.types.KtSubstitutor
@@ -29,7 +30,9 @@ internal class KtFirSubstitutorFactory(
             }
         }
 
-        val coneSubstitutor = ConeSubstitutorByMap(firSubstitution, analysisSession.useSiteSession)
-        return KtFirMapBackedSubstitutor(coneSubstitutor, analysisSession.firSymbolBuilder)
+        return when (val coneSubstitutor = ConeSubstitutorByMap.create(firSubstitution, analysisSession.useSiteSession)) {
+            is ConeSubstitutorByMap -> KtFirMapBackedSubstitutor(coneSubstitutor, analysisSession.firSymbolBuilder)
+            else -> KtFirGenericSubstitutor(coneSubstitutor, analysisSession.firSymbolBuilder)
+        }
     }
-}
+}

compiler/fir/checkers/checkers.jvm/src/org/jetbrains/kotlin/fir/analysis/jvm/checkers/expression/FirExpressionJavaNullabilityWarningCheckers.kt

@@ -80,7 +80,7 @@ object FirQualifiedAccessJavaNullabilityWarningChecker : FirQualifiedAccessExpre
             }
         }
 
-        return ConeSubstitutorByMap(substitutionMap, session)
+        return ConeSubstitutorByMap.create(substitutionMap, session)
     }
 }
 

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirCastDiagnosticsHelpers.kt

@@ -279,7 +279,7 @@ fun findStaticallyKnownSubtype(
 
     // At this point we have values for all type parameters of List
     // Let's make a type by substituting them: List<T> -> List<Foo>
-    val substitutor = ConeSubstitutorByMap(resultSubstitution, session)
+    val substitutor = ConeSubstitutorByMap.create(resultSubstitution, session)
     return substitutor.substituteOrSelf(subtypeWithVariablesType)
 }
 

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirInconsistentTypeParameterHelpers.kt

@@ -69,7 +69,7 @@ private fun buildDeepSubstitutionMultimap(
             for (index in 0 until count) {
                 val typeArgument = typeArguments[index]
 
-                val substitutedArgument = ConeSubstitutorByMap(substitution, session)
+                val substitutedArgument = ConeSubstitutorByMap.create(substitution, session)
                     .substituteArgument(typeArgument, index)
                     ?: typeArgument
                 val substitutedType = substitutedArgument.type ?: continue

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

@@ -6,11 +6,13 @@
 package org.jetbrains.kotlin.fir.resolve.substitution
 
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
+import org.jetbrains.kotlin.fir.types.ConeTypeProjection
 import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
 
 abstract class ConeSubstitutor : TypeSubstitutorMarker {
     open fun substituteOrSelf(type: ConeKotlinType): ConeKotlinType = substituteOrNull(type) ?: type
     abstract fun substituteOrNull(type: ConeKotlinType): ConeKotlinType?
+    abstract fun substituteArgument(projection: ConeTypeProjection, index: Int): ConeTypeProjection?
 
     object Empty : ConeSubstitutor() {
         override fun substituteOrSelf(type: ConeKotlinType): ConeKotlinType {
@@ -21,6 +23,10 @@ abstract class ConeSubstitutor : TypeSubstitutorMarker {
             return null
         }
 
+        override fun substituteArgument(projection: ConeTypeProjection, index: Int): ConeTypeProjection? {
+            return null
+        }
+
         override fun toString(): String = "Empty"
     }
 }

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/ConversionUtils.kt

@@ -900,7 +900,7 @@ internal fun FirQualifiedAccessExpression.buildSubstitutorByCalledCallable(): Co
         val typeProjection = typeArguments.getOrNull(index) as? FirTypeProjectionWithVariance ?: continue
         map[typeParameter.symbol] = typeProjection.typeRef.coneType
     }
-    return ConeSubstitutorByMap(map, session)
+    return ConeSubstitutorByMap.create(map, session)
 }
 
 val augmentedArrayAssignSourceKindToIrStatementOrigin = mapOf(

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/enhancement/SignatureEnhancement.kt

@@ -32,6 +32,7 @@ import org.jetbrains.kotlin.fir.java.resolveIfJavaType
 import org.jetbrains.kotlin.fir.java.symbols.FirJavaOverriddenSyntheticPropertySymbol
 import org.jetbrains.kotlin.fir.java.toConeKotlinTypeProbablyFlexible
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
+import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutorByMap
 import org.jetbrains.kotlin.fir.scopes.jvm.computeJvmDescriptor
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTag
@@ -279,7 +280,7 @@ class FirSignatureEnhancement(
         var isJavaRecordComponent = false
 
         val typeParameterSubstitutionMap = mutableMapOf<FirTypeParameterSymbol, ConeKotlinType>()
-        var typeParameterSubstitutor: ConeSubstitutorByMap? = null
+        var typeParameterSubstitutor: ConeSubstitutor? = null
         val declarationOrigin =
             if (isIntersectionOverride) FirDeclarationOrigin.IntersectionOverride else FirDeclarationOrigin.Enhancement
 
@@ -360,7 +361,7 @@ class FirSignatureEnhancement(
                         newTypeParameter
                     }
                     if (typeParameterSubstitutionMap.isNotEmpty()) {
-                        typeParameterSubstitutor = ConeSubstitutorByMap(typeParameterSubstitutionMap, session)
+                        typeParameterSubstitutor = ConeSubstitutorByMap.create(typeParameterSubstitutionMap, session)
                     }
                     returnTypeRef = newReturnTypeRef.withReplacedConeType(
                         typeParameterSubstitutor?.substituteOrNull(newReturnTypeRef.coneType)

compiler/fir/java/src/org/jetbrains/kotlin/fir/scopes/jvm/JvmMappedScope.kt

@@ -415,7 +415,7 @@ class JvmMappedScope(
          * @returns {T1  -> F1, T2 -> F2} substitution
          */
         private fun createMappingSubstitutor(fromClass: FirRegularClass, toClass: FirRegularClass, session: FirSession): ConeSubstitutor =
-            ConeSubstitutorByMap(
+            ConeSubstitutorByMap.create(
                 fromClass.typeParameters.zip(toClass.typeParameters).associate { (fromTypeParameter, toTypeParameter) ->
                     fromTypeParameter.symbol to ConeTypeParameterTypeImpl(
                         ConeTypeParameterLookupTag(toTypeParameter.symbol),

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
     )

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/dfa/FirDataFlowAnalyzer.kt

@@ -1024,7 +1024,7 @@ abstract class FirDataFlowAnalyzer(
             val substitutionFromArguments = typeParameters.zip(qualifiedAccess.typeArguments).map { (typeParameterRef, typeArgument) ->
                 typeParameterRef.symbol to typeArgument.toConeTypeProjection().type
             }.filter { it.second != null }.toMap() as Map<FirTypeParameterSymbol, ConeKotlinType>
-            ConeSubstitutorByMap(substitutionFromArguments, components.session)
+            ConeSubstitutorByMap.create(substitutionFromArguments, components.session)
         } else {
             ConeSubstitutor.Empty
         }
@@ -1034,7 +1034,7 @@ abstract class FirDataFlowAnalyzer(
             typeArgumentsSubstitutor
         } else {
             val map = originalFunction.symbol.typeParameterSymbols.zip(typeParameters.map { it.symbol.toConeType() }).toMap()
-            ConeSubstitutorByMap(map, components.session).chain(typeArgumentsSubstitutor)
+            ConeSubstitutorByMap.create(map, components.session).chain(typeArgumentsSubstitutor)
         }
 
         for (conditionalEffect in conditionalEffects) {