Self review

include/xrpl/tx/invariants/LoanInvariant.h

@@ -15,9 +15,25 @@ namespace xrpl {
 /**
  * @brief Invariants: Loans are internally consistent
  *
- * 1. If `Loan.PaymentRemaining = 0` then `Loan.PrincipalOutstanding = 0`
+ * 1. If `Loan.PaymentRemaining = 0` then `Loan.PrincipalOutstanding = 0`.
  * 2. A newly-created Loan against a closed-ended vault must satisfy
  *    `StartDate + PaymentInterval * PaymentRemaining < Vault.RedemptionDate`.
+ * 3. An `ltLOAN` may only be created by a `ttLOAN_SET` transaction.
+ * 4. Prior to `featureLendingProtocolV1_1`, the `lsfLoanOverpayment` flag on a
+ *    Loan must not change. From `featureLendingProtocolV1_1` onward this check
+ *    is enforced in `InvariantChecks.cpp`.
+ * 5. Under `featureLendingProtocolV1_1`:
+ *    a. An `ltLOAN` may only be deleted by a `ttLOAN_DELETE` transaction.
+ *    b. If `Loan.PaymentRemaining = 0` then `Loan.NextPaymentDueDate = 0`.
+ *    c. The `lsfLoanImpaired` flag may only change through a `ttLOAN_MANAGE`
+ *       or `ttLOAN_PAY` transaction.
+ *    d. The `lsfLoanDefault` flag may only change through a `ttLOAN_MANAGE`
+ *       transaction.
+ *    e. Interest due, computed as `TotalValueOutstanding -
+ *       PrincipalOutstanding - ManagementFeeOutstanding`, must not be
+ *       negative.
+ *    f. A Loan must reference a live `ltLOAN_BROKER`, and that broker must
+ *       reference a live `ltVAULT`.
  *
  */
 class ValidLoan

include/xrpl/tx/invariants/VaultInvariant.h

@@ -48,7 +48,10 @@ namespace xrpl {
  *   vault phase is Investment
  *
  * Immutability of VaultKind, SubscriptionDate and RedemptionDate is enforced
- * by NoModifiedUnmodifiableFields (see InvariantCheck.cpp).
+ * by NoModifiedUnmodifiableFields (see InvariantCheck.cpp). From
+ * featureLendingProtocolV1_1 onwards, immutability of the vault's Asset,
+ * pseudo-account and ShareMPTID is likewise enforced by
+ * NoModifiedUnmodifiableFields; prior to that amendment it is checked here.
  */
 class ValidVault
 {