private val CallableId.isStringPlus: Boolean
        get() = classId == StandardClassIds.String && callableName.identifierOrNullIfSpecial == "plus"

    ////// KINDS

    private fun ConeKotlinType.toConstantValueKind(): ConstantValueKind<*>? =
        when (this) {
            is ConeErrorType -> null

        ?.firstOrNull { selection in it.textRange }

/**
 * How a symbol is imported. The order of the enum entry represents the priority of imports. If a symbol is available from multiple kinds of
 * imports, the symbol from "smaller" kind is used. For example, an explicitly imported symbol can overwrite a star-imported symbol.
 */
private enum class ImportKind {

    token: KtLifetimeToken,
) : KtAbstractFirDiagnostic<PsiElement>(firDiagnostic, token), KtFirDiagnostic.NextAmbiguity

internal class AmbiguousFunctionTypeKindImpl(
    override val kinds: List<FunctionTypeKind>,
    firDiagnostic: KtPsiDiagnostic,
    token: KtLifetimeToken,
) : KtAbstractFirDiagnostic<PsiElement>(firDiagnostic, token), KtFirDiagnostic.AmbiguousFunctionTypeKind

        return false
    }

    private class FirElementPathSearcher(statements: Collection<FirElement>) : FirDefaultVisitorVoid() {
        private companion object {
            val FORBIDDEN_FAKE_SOURCE_KINDS: Set<KtFakeSourceElementKind> = setOf(
                KtFakeSourceElementKind.WhenCondition,
                KtFakeSourceElementKind.SingleExpressionBlock
            )
        }

        val candidates: List<KtSymbol>
    }

    interface AmbiguousFunctionTypeKind : KtFirDiagnostic<PsiElement> {
        override val diagnosticClass get() = AmbiguousFunctionTypeKind::class
        val kinds: List<FunctionTypeKind>
    }

    interface NoContextReceiver : KtFirDiagnostic<KtElement> {
        override val diagnosticClass get() = NoContextReceiver::class
        val contextReceiverRepresentation: KtType

        MixingSuspendAndNonSuspendSupertypesImpl(
            firDiagnostic as KtPsiDiagnostic,
            token,
        )
    }
    add(FirErrors.MIXING_FUNCTIONAL_KINDS_IN_SUPERTYPES) { firDiagnostic ->
        MixingFunctionalKindsInSupertypesImpl(
            firDiagnostic.a.map { functionTypeKind ->
                functionTypeKind
            },

### Tools. Compiler plugins. Serialization

- [`KT-58501`](https://youtrack.jetbrains.com/issue/KT-58501) K2/MPP/serialization: several classifier kinds seem to miss generated serializer functions when compiled to K/JS and K/Native targets