override val diagnosticClass get() = ErrorInContractDescription::class
        val reason: String
    }

    interface ContractNotAllowed : KtFirDiagnostic<KtElement> {
        override val diagnosticClass get() = ContractNotAllowed::class
        val reason: String
    }

    interface NoGetMethod : KtFirDiagnostic<KtArrayAccessExpression> {

internal class ErrorInContractDescriptionImpl(
    override val reason: String,
    firDiagnostic: KtPsiDiagnostic,
    token: KtLifetimeToken,
) : KtAbstractFirDiagnostic<KtElement>(firDiagnostic, token), KtFirDiagnostic.ErrorInContractDescription

internal class ContractNotAllowedImpl(
    override val reason: String,
    firDiagnostic: KtPsiDiagnostic,
    token: KtLifetimeToken,

         * guarantee behavior in that case, anyway, and the current behavior is likely undesirable.
         * So that's either a reason to feel free to change it or a reason to not bother thinking
         * further about this.
         */
        V rightValue = uncheckedCastNullableTToT(onlyOnRight.remove(leftKey));