[FIR] Fix implementation of primaryConstructorSymbol utility

Originally it used list of declarations, which is incorrect, because
  some constructors may be contributed by compiler plugin. And those
  constructors will be contained only in scope

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

@@ -704,7 +704,7 @@ private fun findDefaultValue(source: KtLightSourceElement): KtLightSourceElement
 
 fun ConeKotlinType.getInlineClassUnderlyingType(session: FirSession): ConeKotlinType {
     require(this.isSingleFieldValueClass(session))
-    return toRegularClassSymbol(session)!!.primaryConstructorSymbol()!!.valueParameterSymbols[0].resolvedReturnTypeRef.coneType
+    return toRegularClassSymbol(session)!!.primaryConstructorSymbol(session)!!.valueParameterSymbols[0].resolvedReturnTypeRef.coneType
 }
 
 fun FirNamedFunctionSymbol.directOverriddenFunctions(session: FirSession, scopeSession: ScopeSession): List<FirNamedFunctionSymbol> {

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

@@ -168,7 +168,7 @@ object FirAnnotationClassDeclarationChecker : FirRegularClassChecker() {
     }
 
     private fun checkCyclesInParameters(annotation: FirRegularClassSymbol, context: CheckerContext, reporter: DiagnosticReporter) {
-        val primaryConstructor = annotation.primaryConstructorSymbol() ?: return
+        val primaryConstructor = annotation.primaryConstructorSymbol(context.session) ?: return
         val checker = CycleChecker(annotation, context.session)
         for (valueParameter in primaryConstructor.valueParameterSymbols) {
             if (checker.parameterHasCycle(annotation, valueParameter)) {
@@ -182,7 +182,7 @@ object FirAnnotationClassDeclarationChecker : FirRegularClassChecker() {
         private val annotationsWithCycle = mutableSetOf(targetAnnotation)
 
         fun annotationHasCycle(annotation: FirRegularClassSymbol): Boolean {
-            val primaryConstructor = annotation.primaryConstructorSymbol() ?: return false
+            val primaryConstructor = annotation.primaryConstructorSymbol(session) ?: return false
             for (valueParameter in primaryConstructor.valueParameterSymbols) {
                 if (parameterHasCycle(annotation, valueParameter)) return true
             }

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

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.modality
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.*
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
+import org.jetbrains.kotlin.fir.symbols.SymbolInternals
 import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.types.coneType
@@ -96,13 +97,9 @@ internal val FirBasedSymbol<*>.isLocalMember: Boolean
 internal val FirCallableSymbol<*>.isExtensionMember: Boolean
     get() = resolvedReceiverTypeRef != null && dispatchReceiverType != null
 
-fun FirClassSymbol<*>.primaryConstructorSymbol(): FirConstructorSymbol? {
+@OptIn(SymbolInternals::class)
-    for (declarationSymbol in this.declarationSymbols) {
+fun FirClassSymbol<*>.primaryConstructorSymbol(session: FirSession): FirConstructorSymbol? {
-        if (declarationSymbol is FirConstructorSymbol && declarationSymbol.isPrimary) {
+    return fir.primaryConstructorIfAny(session)
-            return declarationSymbol
-        }
-    }
-    return null
 }
 
 fun FirTypeRef.needsMultiFieldValueClassFlattening(session: FirSession) = with(session.typeContext) {

plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/services/FirSerializablePropertiesProvider.kt

@@ -89,7 +89,7 @@ class FirSerializablePropertiesProvider(session: FirSession) : FirExtensionSessi
             .let { restoreCorrectOrderFromClassProtoExtension(classSymbol, it) }
 
         val isExternallySerializable = classSymbol.isEnumClass ||
-                primaryConstructorProperties.size == (classSymbol.primaryConstructorSymbol()?.valueParameterSymbols?.size ?: 0)
+                primaryConstructorProperties.size == (classSymbol.primaryConstructorSymbol(session)?.valueParameterSymbols?.size ?: 0)
 
         val (serializableConstructorProperties, serializableStandaloneProperties) = serializableProperties.partition { it.propertySymbol in primaryConstructorProperties }
         return FirSerializableProperties(