FirTypeIntersectionScope: introduce "intersection" fake overrides

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -447,8 +447,9 @@ class Fir2IrVisitor(
         if (castTypeRef is FirResolvedTypeRef && originalTypeRef is FirResolvedTypeRef) {
             val castType = castTypeRef.type
             if (castType is ConeIntersectionType) {
+                val unwrappedSymbol = (referencedSymbol as? FirCallableSymbol)?.overriddenSymbol ?: referencedSymbol
                 castType.intersectedTypes.forEach {
-                    if (it.doesContainReferencedSymbolInScope(referencedSymbol, calleeReference.name)) {
+                    if (it.doesContainReferencedSymbolInScope(unwrappedSymbol, calleeReference.name)) {
                         return implicitCastOrExpression(value, it)
                     }
                 }

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

@@ -8,10 +8,15 @@ package org.jetbrains.kotlin.fir.scopes.impl
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.declarations.builder.FirSimpleFunctionBuilder
+import org.jetbrains.kotlin.fir.declarations.builder.FirValueParameterBuilder
+import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.scopes.FirTypeScope
 import org.jetbrains.kotlin.fir.scopes.FirOverrideChecker
 import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 
 abstract class AbstractFirOverrideScope(
     val session: FirSession,
@@ -58,4 +63,33 @@ abstract class AbstractFirOverrideScope(
         return override
     }
 
+    protected open fun createFunctionCopy(
+        firSimpleFunction: FirSimpleFunction,
+        newSymbol: FirNamedFunctionSymbol
+    ): FirSimpleFunctionBuilder =
+        FirSimpleFunctionBuilder().apply {
+            source = firSimpleFunction.source
+            session = firSimpleFunction.session
+            origin = FirDeclarationOrigin.FakeOverride
+            returnTypeRef = firSimpleFunction.returnTypeRef
+            receiverTypeRef = firSimpleFunction.receiverTypeRef
+            name = firSimpleFunction.name
+            status = firSimpleFunction.status
+            symbol = newSymbol
+        }
+
+    protected open fun createValueParameterCopy(parameter: FirValueParameter, newDefaultValue: FirExpression?): FirValueParameterBuilder =
+        FirValueParameterBuilder().apply {
+            source = parameter.source
+            session = parameter.session
+            origin = FirDeclarationOrigin.FakeOverride
+            returnTypeRef = parameter.returnTypeRef
+            name = parameter.name
+            symbol = FirVariableSymbol(parameter.symbol.callableId)
+            defaultValue = newDefaultValue
+            isCrossinline = parameter.isCrossinline
+            isNoinline = parameter.isNoinline
+            isVararg = parameter.isVararg
+        }
+
 }

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

@@ -6,13 +6,8 @@
 package org.jetbrains.kotlin.fir.scopes.impl
 
 import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.declarations.FirDeclarationOrigin
 import org.jetbrains.kotlin.fir.declarations.FirFunction
 import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
-import org.jetbrains.kotlin.fir.declarations.FirValueParameter
-import org.jetbrains.kotlin.fir.declarations.builder.FirSimpleFunctionBuilder
-import org.jetbrains.kotlin.fir.declarations.builder.FirValueParameterBuilder
-import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
 import org.jetbrains.kotlin.fir.scopes.FirOverrideChecker
 import org.jetbrains.kotlin.fir.scopes.FirScope
@@ -108,35 +103,6 @@ abstract class AbstractFirUseSiteMemberScope(
         return newSymbol
     }
 
-    protected open fun createFunctionCopy(
-        firSimpleFunction: FirSimpleFunction,
-        newSymbol: FirNamedFunctionSymbol
-    ): FirSimpleFunctionBuilder =
-        FirSimpleFunctionBuilder().apply {
-            source = firSimpleFunction.source
-            session = firSimpleFunction.session
-            origin = FirDeclarationOrigin.FakeOverride
-            returnTypeRef = firSimpleFunction.returnTypeRef
-            receiverTypeRef = firSimpleFunction.receiverTypeRef
-            name = firSimpleFunction.name
-            status = firSimpleFunction.status
-            symbol = newSymbol
-        }
-
-    protected open fun createValueParameterCopy(parameter: FirValueParameter, newDefaultValue: FirExpression?): FirValueParameterBuilder =
-        FirValueParameterBuilder().apply {
-            source = parameter.source
-            session = parameter.session
-            origin = FirDeclarationOrigin.FakeOverride
-            returnTypeRef = parameter.returnTypeRef
-            name = parameter.name
-            symbol = FirVariableSymbol(parameter.symbol.callableId)
-            defaultValue = newDefaultValue
-            isCrossinline = parameter.isCrossinline
-            isNoinline = parameter.isNoinline
-            isVararg = parameter.isVararg
-        }
-
     override fun processOverriddenFunctionsWithDepth(
         functionSymbol: FirFunctionSymbol<*>,
         processor: (FirFunctionSymbol<*>, Int) -> ProcessorAction

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

@@ -91,8 +91,22 @@ class FirTypeIntersectionScope private constructor(
             val extractedOverrides = extractBothWaysOverridable(maxByVisibility, allMembers)
 
             val mostSpecific = selectMostSpecificMember(extractedOverrides)
-            overriddenSymbols[mostSpecific] = extractedOverrides
-            processor(mostSpecific)
+            if (extractedOverrides.size > 1 && mostSpecific is FirNamedFunctionSymbol) {
+                // TODO: same code for properties
+                val newSymbol = FirNamedFunctionSymbol(mostSpecific.callableId, mostSpecific.isFakeOverride, mostSpecific)
+                val mostSpecificFunction = mostSpecific.fir
+                createFunctionCopy(mostSpecific.fir, newSymbol).apply {
+                    resolvePhase = mostSpecificFunction.resolvePhase
+                    typeParameters += mostSpecificFunction.typeParameters
+                    valueParameters += mostSpecificFunction.valueParameters
+                }.build()
+                overriddenSymbols[newSymbol] = extractedOverrides
+                @Suppress("UNCHECKED_CAST")
+                processor(newSymbol as D)
+            } else {
+                overriddenSymbols[mostSpecific] = extractedOverrides
+                processor(mostSpecific)
+            }
         }
 
         return true
@@ -240,12 +254,13 @@ class FirTypeIntersectionScope private constructor(
         functionSymbol: FirFunctionSymbol<*>,
         processor: (FirFunctionSymbol<*>, Int) -> ProcessorAction
     ): ProcessorAction {
-        for (directOverridden in getDirectOverriddenSymbols(functionSymbol)) {
-            if (!processor(directOverridden, 0)) return ProcessorAction.STOP
+        for (overridden in getDirectOverriddenSymbols(functionSymbol)) {
+            val overriddenDepth = if (overridden is FirNamedFunctionSymbol && overridden.overriddenSymbol != null) 0 else 1
+            if (!processor(overridden, overriddenDepth)) return ProcessorAction.STOP
             // TODO: Preserve the scope where directOverridden came from
             for (scope in scopes) {
-                if (!scope.processOverriddenFunctionsWithDepth(directOverridden) { symbol, depth ->
-                        processor(symbol, depth)
+                if (!scope.processOverriddenFunctionsWithDepth(overridden) { symbol, depth ->
+                        processor(symbol, depth + overriddenDepth)
                     }
                 ) return ProcessorAction.STOP
             }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/scopes/FirTypeScope.kt

@@ -49,7 +49,7 @@ abstract class FirTypeScope : FirScope() {
             directOverriddenMap[functionSymbol] ?: return baseScope.processOverriddenFunctionsWithDepth(functionSymbol, processor)
 
         for (overridden in directOverridden) {
-            val overriddenDepth = if (overridden is FirNamedFunctionSymbol && overridden.isFakeOverride) 0 else 1
+            val overriddenDepth = if (overridden is FirNamedFunctionSymbol && overridden.overriddenSymbol != null) 0 else 1
             if (!processor(overridden, overriddenDepth)) return ProcessorAction.STOP
             if (!baseScope.processOverriddenFunctionsWithDepth(overridden) { symbol, depth ->
                     processor(symbol, depth + overriddenDepth)

compiler/testData/ir/irText/classes/implicitNotNullOnDelegatedImplementation.fir.txt

@@ -97,8 +97,8 @@ FILE fqName:<root> fileName:/implicitNotNullOnDelegatedImplementation.kt
         INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:K4 modality:FINAL visibility:public superTypes:[<root>.JUnrelatedFoo; <root>.IFoo]'
     FUN name:foo visibility:public modality:FINAL <> ($this:<root>.K4) returnType:kotlin.String?
       overridden:
-        public abstract fun foo (): kotlin.String declared in <root>.IFoo
         public open fun foo (): kotlin.String? declared in <root>.JUnrelatedFoo
+        public abstract fun foo (): kotlin.String declared in <root>.IFoo
       $this: VALUE_PARAMETER name:<this> type:<root>.K4
       BLOCK_BODY
         RETURN type=kotlin.Nothing from='public final fun foo (): kotlin.String? declared in <root>.K4'