Add support for explicit overpayment flag in LoanPay

- Uses the same name and value as for LoanSet: tfLoanOverpayment.
- Untested.
- Also create several placeholders for missing test cases.

include/xrpl/protocol/TxFlags.h

@@ -285,10 +285,14 @@ constexpr std::uint32_t tfIndependent                  = 0x00080000;
 constexpr std::uint32_t const tfBatchMask =
     ~(tfUniversal | tfAllOrNothing | tfOnlyOne | tfUntilFailure | tfIndependent) | tfInnerBatchTxn;
 
-// LoanSet flags:
-// True, indicates the loan supports overpayments
+// LoanSet and LoanPay flags:
+// LoanSet: True, indicates the loan supports overpayments
+// LoanPay: True, indicates any excess in this payment can be used
+// as an overpayment. False, no overpayments will be taken.
 constexpr std::uint32_t const tfLoanOverpayment = 0x00010000;
+// Use two separate mask variables in case the set of flags diverges
 constexpr std::uint32_t const tfLoanSetMask = ~(tfUniversal | tfLoanOverpayment);
+constexpr std::uint32_t const tfLoanPayMask = ~(tfUniversal | tfLoanOverpayment);
 
 // LoanManage flags:
 constexpr std::uint32_t const tfLoanDefault = 0x00010000;

src/test/app/Loan_test.cpp

@@ -1330,6 +1330,19 @@ class Loan_test : public beast::unit_test::suite
             env(pay(evan, loanKeylet.key, broker.asset(500)),
                 ter(tecNO_PERMISSION));
 
+            // TODO: Write a general "isFlag" function? See STObject::isFlag.
+            // Maybe add a static overloaded member?
+            if (!(state.flags & lsfLoanOverpayment))
+            {
+                // If the loan does not allow overpayments, send a payment that
+                // tries to make an overpayment
+                env(pay(borrower,
+                        loanKeylet.key,
+                        broker.asset(state.periodicPayment * 2),
+                        tfLoanOverpayment),
+                    ter(temINVALID_FLAG));
+            }
+
             {
                 auto const otherAsset = broker.asset.raw() == assets[0].raw()
                     ? assets[1]
@@ -1845,6 +1858,71 @@ class Loan_test : public beast::unit_test::suite
                 env(manage(lender, loanKeylet.key, tfLoanDefault),
                     ter(tecNO_PERMISSION));
             });
+
+#if LOANCOMPLETE
+        // TODO
+
+        lifecycle(
+            caseLabel,
+            "Loan overpayment allowed - Explicit overpayment",
+            env,
+            loanAmount,
+            interestExponent,
+            lender,
+            borrower,
+            evan,
+            broker,
+            pseudoAcct,
+            tfLoanOverpayment,
+            [&](Keylet const& loanKeylet,
+                VerifyLoanStatus const& verifyLoanStatus) { throw 0; });
+
+        lifecycle(
+            caseLabel,
+            "Loan overpayment prohibited - Late payment",
+            env,
+            loanAmount,
+            interestExponent,
+            lender,
+            borrower,
+            evan,
+            broker,
+            pseudoAcct,
+            tfLoanOverpayment,
+            [&](Keylet const& loanKeylet,
+                VerifyLoanStatus const& verifyLoanStatus) { throw 0; });
+
+        lifecycle(
+            caseLabel,
+            "Loan overpayment allowed - Late payment",
+            env,
+            loanAmount,
+            interestExponent,
+            lender,
+            borrower,
+            evan,
+            broker,
+            pseudoAcct,
+            tfLoanOverpayment,
+            [&](Keylet const& loanKeylet,
+                VerifyLoanStatus const& verifyLoanStatus) { throw 0; });
+
+        lifecycle(
+            caseLabel,
+            "Loan overpayment allowed - Late payment and overpayment",
+            env,
+            loanAmount,
+            interestExponent,
+            lender,
+            borrower,
+            evan,
+            broker,
+            pseudoAcct,
+            tfLoanOverpayment,
+            [&](Keylet const& loanKeylet,
+                VerifyLoanStatus const& verifyLoanStatus) { throw 0; });
+
+#endif
     }
 
     void

src/xrpld/app/misc/LendingHelpers.h

@@ -1410,6 +1410,7 @@ loanMakePayment(
     SLE::ref loan,
     SLE::const_ref brokerSle,
     STAmount const& amount,
+    bool const overpaymentAllowed,
     beast::Journal j)
 {
     /*
@@ -1648,8 +1649,8 @@ loanMakePayment(
 
     // -------------------------------------------------------------
     // overpayment handling
-    if (loan->isFlag(lsfLoanOverpayment) && paymentRemainingProxy > 0 &&
-        nextDueDateProxy && totalPaid < amount)
+    if (overpaymentAllowed && loan->isFlag(lsfLoanOverpayment) &&
+        paymentRemainingProxy > 0 && nextDueDateProxy && totalPaid < amount)
     {
         TenthBips32 const overpaymentInterestRate{
             loan->at(sfOverpaymentInterestRate)};

src/xrpld/app/tx/detail/LoanPay.cpp

@@ -30,6 +30,12 @@ LoanPay::checkExtraFeatures(PreflightContext const& ctx)
     return checkLendingProtocolDependencies(ctx);
 }
 
+std::uint32_t
+LoanPay::getFlagsMask(PreflightContext const& ctx)
+{
+    return tfLoanPayMask;
+}
+
 NotTEC
 LoanPay::preflight(PreflightContext const& ctx)
 {
@@ -139,6 +145,13 @@ LoanPay::preclaim(PreclaimContext const& ctx)
         return tecNO_PERMISSION;
     }
 
+    if (tx.isFlag(tfLoanOverpayment) && !loanSle->isFlag(lsfLoanOverpayment))
+    {
+        JLOG(ctx.j.warn())
+            << "Requested overpayment on a loan that doesn't allow it";
+        return temINVALID_FLAG;
+    }
+
     auto const principalOutstanding = loanSle->at(sfPrincipalOutstanding);
     TenthBips32 const interestRate{loanSle->at(sfInterestRate)};
     auto const paymentRemaining = loanSle->at(sfPaymentRemaining);
@@ -267,8 +280,14 @@ LoanPay::doApply()
         LoanManage::unimpairLoan(view, loanSle, vaultSle, j_);
     }
 
-    Expected<LoanPaymentParts, TER> paymentParts =
-        loanMakePayment(asset, view, loanSle, brokerSle, amount, j_);
+    Expected<LoanPaymentParts, TER> paymentParts = loanMakePayment(
+        asset,
+        view,
+        loanSle,
+        brokerSle,
+        amount,
+        tx.isFlag(tfLoanOverpayment),
+        j_);
 
     if (!paymentParts)
     {

src/xrpld/app/tx/detail/LoanPay.h

@@ -36,6 +36,9 @@ public:
     static bool
     checkExtraFeatures(PreflightContext const& ctx);
 
+    static std::uint32_t
+    getFlagsMask(PreflightContext const& ctx);
+
     static NotTEC
     preflight(PreflightContext const& ctx);