[FIR] Remove unneeded symbol.fir accesses

compiler/fir/checkers/checkers.js/src/org/jetbrains/kotlin/fir/analysis/js/checkers/declaration/FirJsExportDeclarationChecker.kt

@@ -22,8 +22,9 @@ import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.*
 import org.jetbrains.kotlin.fir.expressions.FirConstExpression
 import org.jetbrains.kotlin.fir.isEnumEntries
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
+import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirPropertyAccessorSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.js.common.RESERVED_KEYWORDS
 import org.jetbrains.kotlin.js.common.SPECIAL_KEYWORDS
@@ -73,7 +74,7 @@ object FirJsExportDeclarationChecker : FirBasicDeclarationChecker() {
                     checkTypeParameter(typeParameter)
                 }
 
-                if (declaration.isInlineWithReified) {
+                if (declaration.symbol.isInlineWithReified) {
                     reportWrongExportedDeclaration("inline function with reified type parameters")
                     return
                 }
@@ -153,13 +154,12 @@ object FirJsExportDeclarationChecker : FirBasicDeclarationChecker() {
             return parent != null && parent.isInterface
         }
 
-    private val FirCallableDeclaration.isInlineWithReified: Boolean
+    private val FirCallableSymbol<*>.isInlineWithReified: Boolean
         get() = when (this) {
-            is FirPropertyAccessor -> {
+            is FirPropertyAccessorSymbol -> {
-                @OptIn(SymbolInternals::class)
+                this.propertySymbol.isInlineWithReified
-                this.propertySymbol.fir.isInlineWithReified
             }
-            else -> typeParameters.any { it.symbol.isReified }
+            else -> typeParameterSymbols.any { it.isReified }
         }
 
     private fun ConeKotlinType.isExportableReturn(session: FirSession, currentlyProcessed: MutableSet<ConeKotlinType> = hashSetOf()) =
@@ -208,8 +208,7 @@ object FirJsExportDeclarationChecker : FirBasicDeclarationChecker() {
 
         return when {
             isPrimitiveExportableType -> true
-            @OptIn(SymbolInternals::class)
+            symbol?.isMemberDeclaration != true -> false
-            symbol?.fir !is FirMemberDeclaration -> false
             isEnum -> true
             else -> symbol.isEffectivelyExternal(session) || symbol.isExportedObject(session)
         }

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

@@ -8,8 +8,8 @@ package org.jetbrains.kotlin.fir.analysis.jvm
 import org.jetbrains.kotlin.builtins.jvm.JavaToKotlinClassMap
 import org.jetbrains.kotlin.fir.analysis.FirOverridesBackwardCompatibilityHelper
 import org.jetbrains.kotlin.fir.containingClassLookupTag
-import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
 import org.jetbrains.kotlin.fir.declarations.isJavaOrEnhancement
+import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 
 /**
  * With JVM compilation
@@ -18,7 +18,7 @@ import org.jetbrains.kotlin.fir.declarations.isJavaOrEnhancement
  *    `kotlin.Throwable` does not require `override` keyword.
  */
 object FirJvmOverridesBackwardCompatibilityHelper : FirOverridesBackwardCompatibilityHelper() {
-    override fun additionalCheck(member: FirCallableDeclaration): Boolean? {
+    override fun additionalCheck(member: FirCallableSymbol<*>): Boolean? {
         if (!member.isJavaOrEnhancement) return false
         val containingClassName = member.containingClassLookupTag()?.classId?.asSingleFqName()?.toUnsafe() ?: return false
         // If the super class is mapped to a Kotlin built-in class, then we don't require `override` keyword.

compiler/fir/checkers/checkers.jvm/src/org/jetbrains/kotlin/fir/analysis/jvm/checkers/declaration/FirJvmStaticChecker.kt

@@ -23,7 +23,6 @@ import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.*
 import org.jetbrains.kotlin.fir.expressions.FirAnnotation
 import org.jetbrains.kotlin.fir.languageVersionSettings
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
 import org.jetbrains.kotlin.fir.types.coneType
@@ -212,10 +211,7 @@ object FirJvmStaticChecker : FirBasicDeclarationChecker() {
 
     private fun CheckerContext.containerIsNonCompanionObject(outerLevel: Int): Boolean {
         val containingClassSymbol = this.getContainerAt(outerLevel) ?: return false
-
+        val containingClass = (containingClassSymbol as? FirRegularClassSymbol) ?: return false
-        @OptIn(SymbolInternals::class)
-        val containingClass = (containingClassSymbol.fir as? FirRegularClass) ?: return false
-
         return containingClass.classKind == ClassKind.OBJECT && !containingClass.isCompanion
     }
 

compiler/fir/checkers/checkers.jvm/src/org/jetbrains/kotlin/fir/analysis/jvm/checkers/declaration/FirOverrideJavaNullabilityWarningChecker.kt

@@ -7,18 +7,17 @@ package org.jetbrains.kotlin.fir.analysis.jvm.checkers.declaration
 
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.diagnostics.reportOn
-import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirAbstractOverrideChecker
 import org.jetbrains.kotlin.fir.analysis.checkers.unsubstitutedScope
 import org.jetbrains.kotlin.fir.analysis.diagnostics.jvm.FirJvmErrors
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.java.enhancement.EnhancedForWarningConeSubstitutor
-import org.jetbrains.kotlin.fir.scopes.firOverrideChecker
+import org.jetbrains.kotlin.fir.scopes.*
-import org.jetbrains.kotlin.fir.scopes.getDirectOverriddenFunctions
-import org.jetbrains.kotlin.fir.scopes.getDirectOverriddenProperties
 import org.jetbrains.kotlin.fir.scopes.impl.FirFakeOverrideGenerator
 import org.jetbrains.kotlin.fir.symbols.SymbolInternals
+import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhase
 import org.jetbrains.kotlin.fir.types.coneType
 import org.jetbrains.kotlin.fir.types.typeContext
@@ -41,22 +40,21 @@ object FirOverrideJavaNullabilityWarningChecker : FirAbstractOverrideChecker() {
                 val enhancedOverrides = scope
                     .getDirectOverriddenFunctions(member.symbol)
                     .map {
-                        @OptIn(SymbolInternals::class)
+                        val substitutedBase = it.substituteOrNull(substitutor, context) ?: return@map it
-                        val substitutedBase = it.fir.substituteOrNull(substitutor, context) ?: return@map it
                         anyBaseEnhanced = true
 
-                        if (!anyReported && !context.session.firOverrideChecker.isOverriddenFunction(member, substitutedBase)) {
+                        if (!anyReported && !context.session.firOverrideChecker.isOverriddenFunction(member.symbol, substitutedBase)) {
                             anyReported = true
                             reporter.reportOn(
                                 member.source,
                                 FirJvmErrors.WRONG_NULLABILITY_FOR_JAVA_OVERRIDE,
                                 member.symbol,
-                                substitutedBase.symbol,
+                                substitutedBase,
                                 context
                             )
                         }
 
-                        substitutedBase.symbol
+                        substitutedBase
                     }
 
                 if (anyBaseEnhanced && !anyReported) {
@@ -70,22 +68,21 @@ object FirOverrideJavaNullabilityWarningChecker : FirAbstractOverrideChecker() {
                 val enhancedOverrides = scope
                     .getDirectOverriddenProperties(member.symbol)
                     .map {
-                        @OptIn(SymbolInternals::class)
+                        val substitutedBase = it.substituteOrNull(substitutor, context) ?: return@map it
-                        val substitutedBase = it.fir.substituteOrNull(substitutor, context) ?: return@map it
                         anyBaseEnhanced = true
 
-                        if (!anyReported && !context.session.firOverrideChecker.isOverriddenProperty(member, substitutedBase)) {
+                        if (!anyReported && !context.session.firOverrideChecker.isOverriddenProperty(member.symbol, substitutedBase)) {
                             anyReported = true
                             reporter.reportOn(
                                 member.source,
                                 FirJvmErrors.WRONG_NULLABILITY_FOR_JAVA_OVERRIDE,
                                 member.symbol,
-                                substitutedBase.symbol,
+                                substitutedBase,
                                 context
                             )
                         }
 
-                        substitutedBase.symbol
+                        substitutedBase
                     }
 
                 if (anyBaseEnhanced && !anyReported) {
@@ -133,6 +130,15 @@ private fun FirSimpleFunction.substituteOrNull(
     }
 }
 
+private fun FirNamedFunctionSymbol.substituteOrNull(
+    substitutor: EnhancedForWarningConeSubstitutor,
+    context: CheckerContext,
+): FirNamedFunctionSymbol? {
+    // Ok, because `substituteOrNull` calls lazyResolveToPhase
+    @OptIn(SymbolInternals::class)
+    return fir.substituteOrNull(substitutor, context)?.symbol
+}
+
 /**
  * @see org.jetbrains.kotlin.fir.scopes.impl.FirClassSubstitutionScope.createSubstitutionOverrideProperty
  * @see org.jetbrains.kotlin.fir.scopes.impl.FirClassSubstitutionScope.createSubstitutedData
@@ -163,4 +169,13 @@ private fun FirProperty.substituteOrNull(
             newReceiverType = newExtensionReceiverType,
         )
     }
-}
+}
+
+private fun FirPropertySymbol.substituteOrNull(
+    substitutor: EnhancedForWarningConeSubstitutor,
+    context: CheckerContext,
+): FirPropertySymbol? {
+    // Ok, because `substituteOrNull` calls `lazyResolveToPhase`
+    @OptIn(SymbolInternals::class)
+    return fir.substituteOrNull(substitutor, context)?.symbol
+}

compiler/fir/checkers/checkers.wasm/src/org/jetbrains/kotlin/fir/analysis/wasm/checkers/FirWasmWebCheckerUtils.kt

@@ -7,14 +7,12 @@ package org.jetbrains.kotlin.fir.analysis.wasm.checkers
 
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.web.common.checkers.FirAbstractWebCheckerUtils
-import org.jetbrains.kotlin.fir.declarations.FirClass
 import org.jetbrains.kotlin.fir.declarations.utils.isEffectivelyExternal
 import org.jetbrains.kotlin.fir.declarations.utils.isInterface
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 
 object FirWasmWebCheckerUtils : FirAbstractWebCheckerUtils() {
-    @OptIn(SymbolInternals::class)
     override fun isNativeOrExternalInterface(symbol: FirBasedSymbol<*>, session: FirSession): Boolean =
-        symbol.isEffectivelyExternal(session) && (symbol.fir as? FirClass)?.isInterface == true
+        symbol.isEffectivelyExternal(session) && (symbol as? FirClassSymbol<*>)?.isInterface == true
 }

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

@@ -15,8 +15,9 @@ import org.jetbrains.kotlin.fir.declarations.utils.isInterface
 import org.jetbrains.kotlin.fir.resolve.toFirRegularClassSymbol
 import org.jetbrains.kotlin.fir.scopes.getDirectOverriddenFunctions
 import org.jetbrains.kotlin.fir.scopes.getDirectOverriddenProperties
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhase
 import org.jetbrains.kotlin.fir.types.toRegularClassSymbol
 import org.jetbrains.kotlin.name.ClassId
@@ -54,16 +55,14 @@ abstract class FirOverridesBackwardCompatibilityHelper : FirSessionComponent {
 
         val originalMemberSymbol = symbol.originalOrSelf()
         originalMemberSymbol.lazyResolveToPhase(FirResolvePhase.BODY_RESOLVE)
-        @OptIn(SymbolInternals::class)
+        if (originalMemberSymbol.hasAnnotation(platformDependentAnnotation, context.session)) {
-        val originalMember = originalMemberSymbol.fir
-        if (originalMember.hasAnnotation(platformDependentAnnotation, context.session)) {
             return true
         }
 
-        additionalCheck(originalMember)?.let { return it }
+        additionalCheck(originalMemberSymbol)?.let { return it }
 
-        if (!originalMember.isAbstract) {
+        if (!originalMemberSymbol.isAbstract) {
-            val containingClass = originalMember.containingClassLookupTag()?.toFirRegularClassSymbol(context.session)
+            val containingClass = originalMemberSymbol.containingClassLookupTag()?.toFirRegularClassSymbol(context.session)
             if (containingClass?.isInterface == false) {
                 return false
             }
@@ -71,16 +70,16 @@ abstract class FirOverridesBackwardCompatibilityHelper : FirSessionComponent {
 
         val scope =
             symbol.dispatchReceiverClassTypeOrNull()?.toRegularClassSymbol(context.session)?.unsubstitutedScope(context) ?: return false
-        val overriddenSymbols = when (originalMember) {
+        val overriddenSymbols = when (originalMemberSymbol) {
-            is FirSimpleFunction -> scope.getDirectOverriddenFunctions(originalMember.symbol)
+            is FirNamedFunctionSymbol -> scope.getDirectOverriddenFunctions(originalMemberSymbol)
-            is FirProperty -> scope.getDirectOverriddenProperties(originalMember.symbol)
+            is FirPropertySymbol -> scope.getDirectOverriddenProperties(originalMemberSymbol)
             else -> return false
         }
         if (overriddenSymbols.isEmpty()) return false
         return overriddenSymbols.all { isPlatformSpecificSymbolThatCanBeImplicitlyOverridden(it, visitedSymbols, context) }
     }
 
-    protected open fun additionalCheck(member: FirCallableDeclaration): Boolean? = null
+    protected open fun additionalCheck(member: FirCallableSymbol<*>): Boolean? = null
 }
 
 val FirSession.overridesBackwardCompatibilityHelper: FirOverridesBackwardCompatibilityHelper by FirSession.sessionComponentAccessor()

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt

@@ -85,7 +85,6 @@ fun PropertyInitializationInfoData.checkPropertyAccesses(
     )
 }
 
-@OptIn(SymbolInternals::class)
 private fun PropertyInitializationInfoData.checkPropertyAccesses(
     graph: ControlFlowGraph,
     properties: Set<FirPropertySymbol>,
@@ -116,7 +115,7 @@ private fun PropertyInitializationInfoData.checkPropertyAccesses(
 
             node is VariableAssignmentNode -> {
                 val symbol = node.fir.calleeReference?.toResolvedPropertySymbol() ?: continue
-                if (!symbol.fir.isVal || node.fir.unwrapLValue()?.hasCorrectReceiver() != true || symbol !in properties) continue
+                if (!symbol.isVal || node.fir.unwrapLValue()?.hasCorrectReceiver() != true || symbol !in properties) continue
 
                 if (getValue(node).values.any { it[symbol]?.canBeRevisited() == true }) {
                     reporter.reportOn(node.fir.lValue.source, FirErrors.VAL_REASSIGNMENT, symbol, context)

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

@@ -518,15 +518,14 @@ private fun FirDeclarationCollector<*>.areNonConflictingCallables(
     return session.declarationOverloadabilityHelper.isOverloadable(declaration, conflicting)
 }
 
-@OptIn(SymbolInternals::class)
+internal fun FirVariable.getDestructuredParameter(): FirValueParameterSymbol? {
-internal fun FirVariable.getDestructuredParameter(): FirValueParameter? {
     val initializer = initializer
     if (initializer !is FirComponentCall) return null
     if (initializer.source?.kind !is KtFakeSourceElementKind.DesugaredComponentFunctionCall) return null
     val receiver = initializer.dispatchReceiver ?: initializer.extensionReceiver ?: return null
     if (receiver !is FirPropertyAccessExpression) return null
     val calleeReference = receiver.calleeReference as? FirResolvedNamedReference ?: return null
-    return calleeReference.resolvedSymbol.fir as? FirValueParameter
+    return calleeReference.resolvedSymbol as? FirValueParameterSymbol
 }
 
 /** Checks for redeclarations of value and type parameters, and local variables. */

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

@@ -9,7 +9,6 @@ import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.fir.declarations.hasAnnotation
 import org.jetbrains.kotlin.fir.declarations.utils.isConst
 import org.jetbrains.kotlin.fir.declarations.utils.isStatic
@@ -194,19 +193,19 @@ internal fun checkConstantArguments(
 
             val propertySymbol = expressionSymbol as? FirPropertySymbol ?: return ConstantArgumentKind.NOT_CONST
 
-            @OptIn(SymbolInternals::class)
-            val property = propertySymbol.fir
             when {
-                property.unwrapFakeOverrides().symbol.canBeEvaluated() || property.isCompileTimeBuiltinProperty(session) -> {
+                propertySymbol.unwrapFakeOverrides().canBeEvaluated() || propertySymbol.isCompileTimeBuiltinProperty(session) -> {
                     val receiver = listOf(expression.dispatchReceiver, expression.extensionReceiver).single { it != null }!!
                     return checkConstantArguments(receiver, session)
                 }
                 propertySymbol.isLocal -> return ConstantArgumentKind.NOT_CONST
                 expressionType.classId == StandardClassIds.KClass -> return ConstantArgumentKind.NOT_KCLASS_LITERAL
             }
-            return when (property.initializer) {
+            // Ok, because we only look at the structure, not resolution-dependent properties.
+            @OptIn(SymbolInternals::class)
+            return when (propertySymbol.fir.initializer) {
                 is FirConstExpression<*> -> when {
-                    property.isVal -> ConstantArgumentKind.NOT_CONST_VAL_IN_CONST_EXPRESSION
+                    propertySymbol.isVal -> ConstantArgumentKind.NOT_CONST_VAL_IN_CONST_EXPRESSION
                     else -> ConstantArgumentKind.NOT_CONST
                 }
                 is FirGetClassCall -> ConstantArgumentKind.NOT_KCLASS_LITERAL
@@ -255,7 +254,7 @@ private fun FirFunctionCall.isCompileTimeBuiltinCall(session: FirSession): Boole
     return false
 }
 
-private fun FirProperty.isCompileTimeBuiltinProperty(session: FirSession): Boolean {
+private fun FirPropertySymbol.isCompileTimeBuiltinProperty(session: FirSession): Boolean {
     val receiverType = dispatchReceiverType ?: receiverParameter?.typeRef?.coneTypeSafe<ConeKotlinType>() ?: return false
     val receiverClassId = receiverType.fullyExpandedClassId(session) ?: return false
     return when (name.asString()) {

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

@@ -345,13 +345,11 @@ fun FirCallableSymbol<*>.getImplementationStatus(
         var hasImplementationVar = false
 
         for (intersection in symbol.intersections) {
-            @OptIn(SymbolInternals::class)
+            val unwrapped = intersection.unwrapFakeOverrides()
-            val fir = intersection.fir
+            val isVar = unwrapped is FirPropertySymbol && unwrapped.isVar
-            val unwrappedFir = fir.unwrapFakeOverrides()
+            val isFromClass = unwrapped.getContainingClassSymbol(sessionHolder.session)?.classKind == ClassKind.CLASS
-            val isVar = unwrappedFir is FirProperty && unwrappedFir.isVar
-            val isFromClass = unwrappedFir.getContainingClassSymbol(sessionHolder.session)?.classKind == ClassKind.CLASS
 
-            if (fir.isAbstract) {
+            if (intersection.isAbstract) {
                 if (isFromClass) {
                     hasAbstractFromClass = true
                 }
@@ -359,7 +357,7 @@ fun FirCallableSymbol<*>.getImplementationStatus(
                     hasAbstractVar = true
                 }
             } else {
-                if (fir.origin == FirDeclarationOrigin.Delegated) {
+                if (intersection.origin == FirDeclarationOrigin.Delegated) {
                     hasInterfaceDelegation = true
                 }
                 if (isFromClass) {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConflictsDeclarationChecker.kt

@@ -53,7 +53,9 @@ object FirConflictsDeclarationChecker : FirBasicDeclarationChecker() {
 
     private fun getDestructuredParameters(function: FirFunction): List<FirVariable> {
         if (function.valueParameters.none { it.name == SpecialNames.DESTRUCT }) return function.valueParameters
-        val destructuredParametersBoxes = function.valueParameters.filterTo(mutableSetOf()) { it.name == SpecialNames.DESTRUCT }
+        val destructuredParametersBoxes = function.valueParameters
+            .filter { it.name == SpecialNames.DESTRUCT }
+            .mapTo(mutableSetOf()) { it.symbol }
 
         return function.body?.statements.orEmpty().mapNotNullTo(function.valueParameters.toMutableList()) {
             val destructuredParameter = (it as? FirVariable)?.getDestructuredParameter() ?: return@mapNotNullTo null

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirFunctionParameterChecker.kt

@@ -23,7 +23,6 @@ import org.jetbrains.kotlin.fir.diagnostics.DiagnosticKind
 import org.jetbrains.kotlin.fir.expressions.FirPropertyAccessExpression
 import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
 import org.jetbrains.kotlin.fir.references.toResolvedValueParameterSymbol
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.visitors.FirVisitorVoid
 
@@ -97,8 +96,7 @@ object FirFunctionParameterChecker : FirFunctionChecker() {
                 override fun visitQualifiedAccessExpression(qualifiedAccessExpression: FirQualifiedAccessExpression) {
                     val referredParameter = qualifiedAccessExpression.calleeReference.toResolvedValueParameterSymbol() ?: return
 
-                    @OptIn(SymbolInternals::class)
+                    val referredParameterIndex = function.valueParameters.indexOfFirst { it.symbol == referredParameter }
-                    val referredParameterIndex = function.valueParameters.indexOf(referredParameter.fir)
                     // Skip if the referred parameter is not declared in the same function.
                     if (referredParameterIndex < 0) return
 

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

@@ -10,7 +10,6 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.declarations.fullyExpandedClass
 import org.jetbrains.kotlin.fir.expressions.FirResolvedQualifier
 import org.jetbrains.kotlin.fir.resolve.diagnostics.ConeDeprecated
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
 
 object FirDeprecatedQualifierChecker : FirResolvedQualifierChecker() {
     override fun check(expression: FirResolvedQualifier, context: CheckerContext, reporter: DiagnosticReporter) {
@@ -27,8 +26,7 @@ object FirDeprecatedQualifierChecker : FirResolvedQualifierChecker() {
             // is handled automatically when getting deprecationInfo
             // for the typealias symbol (in FirDeprecationChecker).
             // Below we check "the last transition".
-            @OptIn(SymbolInternals::class)
+            val companionSymbol = expression.symbol?.fullyExpandedClass(context.session)?.companionObjectSymbol ?: return
-            val companionSymbol = expression.symbol?.fullyExpandedClass(context.session)?.fir?.companionObjectSymbol ?: return
             FirDeprecationChecker.reportApiStatusIfNeeded(expression.source, companionSymbol, context, reporter)
         }
     }

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

@@ -14,7 +14,6 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.utils.sourceElement
 import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
 import org.jetbrains.kotlin.fir.references.toResolvedCallableSymbol
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
 import org.jetbrains.kotlin.fir.symbols.impl.FirFunctionSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.coneType
@@ -34,8 +33,7 @@ object FirIncompatibleClassExpressionChecker : FirQualifiedAccessExpressionCheck
             }
         }
 
-        @OptIn(SymbolInternals::class)
+        checkSourceElement(symbol.containerSource, expression, context, reporter)
-        checkSourceElement(symbol.fir.containerSource, expression, context, reporter)
     }
 
     internal fun checkType(type: ConeKotlinType?, element: FirElement, context: CheckerContext, reporter: DiagnosticReporter) {

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

@@ -10,7 +10,6 @@ import org.jetbrains.kotlin.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.getContainingClassSymbol
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
-import org.jetbrains.kotlin.fir.declarations.FirDeclaration
 import org.jetbrains.kotlin.fir.declarations.FirFunction
 import org.jetbrains.kotlin.fir.declarations.hasAnnotation
 import org.jetbrains.kotlin.fir.declarations.utils.isInline
@@ -19,7 +18,7 @@ import org.jetbrains.kotlin.fir.expressions.FirCallableReferenceAccess
 import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
 import org.jetbrains.kotlin.fir.references.toResolvedPropertySymbol
 import org.jetbrains.kotlin.fir.resolve.providers.firProvider
-import org.jetbrains.kotlin.fir.symbols.SymbolInternals
+import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.name.StandardClassIds.Annotations
 
@@ -51,7 +50,8 @@ object FirLateinitIntrinsicApplicabilityChecker : FirQualifiedAccessExpressionCh
         }
 
         // property must be declared in one of the outer lexical scopes
-        if (calleePropertySymbol.containingClassOrFile(context) !in context.containingDeclarations) {
+        val containingSymbol = calleePropertySymbol.containingClassOrFile(context)
+        if (context.containingDeclarations.none { it.symbol == containingSymbol }) {
             reporter.reportOn(
                 source,
                 FirErrors.LATEINIT_INTRINSIC_CALL_ON_NON_ACCESSIBLE_PROPERTY,
@@ -70,11 +70,10 @@ object FirLateinitIntrinsicApplicabilityChecker : FirQualifiedAccessExpressionCh
     /**
      * Returns the containing class or file if the property is top-level.
      */
-    @OptIn(SymbolInternals::class)
     private fun FirPropertySymbol.containingClassOrFile(
         context: CheckerContext
-    ): FirDeclaration? {
+    ): FirBasedSymbol<*>? {
-        return getContainingClassSymbol(context.session)?.fir
+        return getContainingClassSymbol(context.session)
-            ?: context.session.firProvider.getFirCallableContainerFile(this)
+            ?: context.session.firProvider.getFirCallableContainerFile(this)?.symbol
     }
 }

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

@@ -150,9 +150,8 @@ object FirOptInUsageBaseChecker {
         fromSetter = false, dispatchReceiverType = null, fromSupertype = true
     )
 
-    @OptIn(SymbolInternals::class)
     fun FirClassLikeSymbol<*>.isExperimentalMarker(session: FirSession) =
-        this is FirRegularClassSymbol && fir.getAnnotationByClassId(OptInNames.REQUIRES_OPT_IN_CLASS_ID, session) != null
+        this is FirRegularClassSymbol && getAnnotationByClassId(OptInNames.REQUIRES_OPT_IN_CLASS_ID, session) != null
 
     @OptIn(SymbolInternals::class)
     private fun FirBasedSymbol<*>.loadExperimentalities(
@@ -284,7 +283,7 @@ object FirOptInUsageBaseChecker {
             else -> null
         }
 
-        val severity = Experimentality.Severity.values().firstOrNull { it.name == levelName } ?: Experimentality.DEFAULT_SEVERITY
+        val severity = Experimentality.Severity.entries.firstOrNull { it.name == levelName } ?: Experimentality.DEFAULT_SEVERITY
         val message = (experimental.findArgumentByName(MESSAGE) as? FirConstExpression<*>)?.value as? String
         return Experimentality(symbol.classId, severity, message, annotatedOwnerClassName)
     }

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/FirOverrideChecker.kt

@@ -10,7 +10,9 @@ import org.jetbrains.kotlin.fir.FirSessionComponent
 import org.jetbrains.kotlin.fir.declarations.FirCallableDeclaration
 import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
+import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 
 interface FirOverrideChecker : FirSessionComponent {
     fun isOverriddenFunction(
@@ -29,4 +31,9 @@ fun FirOverrideChecker.isOverriddenFunction(
     baseDeclaration: FirNamedFunctionSymbol
 ): Boolean = isOverriddenFunction(overrideCandidate.fir, baseDeclaration.fir)
 
+fun FirOverrideChecker.isOverriddenProperty(
+    overrideCandidate: FirCallableSymbol<*>,
+    baseDeclaration: FirPropertySymbol
+): Boolean = isOverriddenProperty(overrideCandidate.fir, baseDeclaration.fir)
+
 val FirSession.firOverrideChecker: FirOverrideChecker by FirSession.sessionComponentAccessor()

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/FirDeclarationUtil.kt

@@ -50,6 +50,10 @@ val FirDeclaration.isNonLocal
 
 val FirCallableDeclaration.isExtension get() = receiverParameter != null
 
+val FirBasedSymbol<*>.isMemberDeclaration: Boolean
+    // Accessing `fir` is ok, because we don't really use it
+    get() = fir is FirMemberDeclaration
+
 val FirBasedSymbol<*>.memberDeclarationNameOrNull: Name?
     // Accessing `fir` is ok, because `nameOrSpecialName` only accesses names
     get() = (fir as? FirMemberDeclaration)?.nameOrSpecialName

compiler/fir/tree/src/org/jetbrains/kotlin/fir/symbols/impl/FirCallableSymbol.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.mpp.CallableSymbolMarker
 import org.jetbrains.kotlin.name.CallableId
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
 
 abstract class FirCallableSymbol<D : FirCallableDeclaration> : FirBasedSymbol<D>(), CallableSymbolMarker {
     abstract val callableId: CallableId
@@ -76,6 +77,10 @@ abstract class FirCallableSymbol<D : FirCallableDeclaration> : FirBasedSymbol<D>
     val name: Name
         get() = callableId.callableName
 
+    val containerSource: DeserializedContainerSource?
+        // This is ok, because containerSource should be set during fir creation
+        get() = fir.containerSource
+
     fun getDeprecation(languageVersionSettings: LanguageVersionSettings): DeprecationsPerUseSite? {
         lazyResolveToPhase(FirResolvePhase.COMPILER_REQUIRED_ANNOTATIONS)
         return fir.deprecationsProvider.getDeprecationsInfo(languageVersionSettings)