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refactor: Extract FixedPrecision LoanPay deltas and tighten coverage

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Move interest-first AssetsTotal, DebtTotal, and vault-credit rounding into fixed_precision::loanPaymentDeltas, warn before clamping YieldUnrealized, and cover management fees plus early full payoff.
This commit is contained in:
Vito
2026-09-23 18:04:05 +02:00
parent 4e83215457
commit 19519c6b19
6 changed files with 140 additions and 34 deletions
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16
include/xrpl/ledger/helpers/LendingHelpers.h
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@@ -414,6 +414,22 @@ loanPaymentDeltas(LoanPaymentParts const& parts);
} // namespace cash_basis
// FixedPrecision payment accounting records interest into AssetsTotal before
// deriving the cash credit sent to the Vault pseudo-account.
namespace fixed_precision {
struct PaymentDeltas
{
Number assetsTotalDelta;
Number debtTotalDelta;
Number vaultCredit;
};
PaymentDeltas
loanPaymentDeltas(SLE::const_ref vaultSle, LoanPaymentParts const& parts);
} // namespace fixed_precision
// Public dispatchers: pick cash_basis:: if featureLendingProtocolV1_1 is
// enabled AND the Vault's LEVersion (VaultHelpers::getVaultVersion) is
// VaultVersion::CashBasis, else instant_recognition::. These are the only entry points

3
include/xrpl/ledger/helpers/VaultHelpers.h
View File

@@ -60,7 +60,8 @@ roundToPosteriorVaultScale(
Number::RoundingMode roundingMode);
/**
* Round an amount at the posterior live exponent of AssetsAvailable.
* Round the LoanPay cash-credit delta at the posterior live exponent of
* AssetsAvailable. The reference is AssetsAvailable, not AssetsTotal.
*/
[[nodiscard]] STAmount
roundToPosteriorAvailableScale(

34
src/libxrpl/ledger/helpers/LendingHelpers.cpp
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@@ -378,6 +378,40 @@ loanPaymentDeltas(LoanPaymentParts const& parts)
} // namespace cash_basis
namespace fixed_precision {
PaymentDeltas
loanPaymentDeltas(SLE::const_ref vaultSle, LoanPaymentParts const& parts)
{
XRPL_ASSERT(
vaultSle && vaultSle->getType() == ltVAULT,
"xrpl::fixed_precision::loanPaymentDeltas : valid Vault sle");
XRPL_ASSERT(
getVaultVersion(vaultSle) == VaultVersion::FixedPrecision,
"xrpl::fixed_precision::loanPaymentDeltas : FixedPrecision Vault");
Asset const asset = vaultSle->at(sfAsset);
Number const assetsTotalBefore = vaultSle->at(sfAssetsTotal);
Number const assetsTotalAfter = [&] {
NumberRoundModeGuard const rg(Number::RoundingMode::Downward);
// Floor the posterior rather than the interest delta because a prior
// AssetsTotal may be off the posterior grid when this payment coarsens
// the Vault. The STAmount conversion also clamps integral assets.
return Number{STAmount{asset, assetsTotalBefore + parts.interestPaid}};
}();
Number const assetsTotalDelta = assetsTotalAfter - assetsTotalBefore;
Number const creditRaw = parts.principalPaid + assetsTotalDelta;
Number const vaultCredit = roundToPosteriorAvailableScale(
vaultSle, STAmount{asset, creditRaw}, Number::RoundingMode::Downward);
return {
.assetsTotalDelta = assetsTotalDelta,
.debtTotalDelta = parts.principalPaid,
.vaultCredit = vaultCredit};
}
} // namespace fixed_precision
namespace {
// Cash-basis accounting applies to Vaults created under

53
src/libxrpl/tx/transactors/lending/LoanPay.cpp
View File

@@ -491,30 +491,24 @@ LoanPay::doApply()
Number const assetsTotalBefore = *assetsTotalProxy;
auto const totalPaidToVaultRaw = paymentParts->principalPaid + paymentParts->interestPaid;
auto const [assetsTotalDelta, debtTotalDelta] = [&] {
if (!fixedPrecision)
return loanPaymentDeltas(vaultSle, *paymentParts);
Number const assetsTotalAfter = [&] {
NumberRoundModeGuard const rg(Number::RoundingMode::Downward);
// The STAmount conversion also clamps integral assets.
return Number{STAmount{asset, assetsTotalBefore + paymentParts->interestPaid}};
}();
return AccountingDeltas{
.assetsTotalDelta = assetsTotalAfter - assetsTotalBefore,
.debtTotalDelta = paymentParts->principalPaid};
}();
Number const totalPaidToVaultRounded = [&] {
if (!fixedPrecision)
{
return roundToAsset(
asset, totalPaidToVaultRaw, vaultScale, Number::RoundingMode::Downward);
}
Number const creditRaw = paymentParts->principalPaid + assetsTotalDelta;
return Number{roundToPosteriorAvailableScale(
vaultSle, STAmount{asset, creditRaw}, Number::RoundingMode::Downward)};
}();
Number assetsTotalDelta;
Number debtTotalDelta;
Number totalPaidToVaultRounded;
if (fixedPrecision)
{
auto const deltas = fixed_precision::loanPaymentDeltas(vaultSle, *paymentParts);
assetsTotalDelta = deltas.assetsTotalDelta;
debtTotalDelta = deltas.debtTotalDelta;
totalPaidToVaultRounded = deltas.vaultCredit;
}
else
{
auto const deltas = loanPaymentDeltas(vaultSle, *paymentParts);
assetsTotalDelta = deltas.assetsTotalDelta;
debtTotalDelta = deltas.debtTotalDelta;
totalPaidToVaultRounded =
roundToAsset(asset, totalPaidToVaultRaw, vaultScale, Number::RoundingMode::Downward);
}
XRPL_ASSERT_PARTS(
!asset.integral() || totalPaidToVaultRaw == totalPaidToVaultRounded,
"xrpl::LoanPay::doApply",
@@ -588,7 +582,11 @@ LoanPay::doApply()
auto yieldUnrealizedProxy = vaultSle->at(sfYieldUnrealized);
yieldUnrealizedProxy += scheduledInterestDelta;
if (*yieldUnrealizedProxy < beast::kZero)
{
JLOG(j_.warn()) << "LoanPay: YieldUnrealized became negative before clamping: "
<< *yieldUnrealizedProxy;
yieldUnrealizedProxy = kNumZero;
}
}
XRPL_ASSERT_PARTS(
@@ -632,9 +630,10 @@ LoanPay::doApply()
if (assetsAvailableAfter == assetsAvailableBefore)
{
// An unchanged assetsAvailable indicates that the amount paid to the
// vault was zero, or rounded to zero. That should be impossible, but I
// can't rule it out for extreme edge cases, so fail gracefully if it
// happens.
// vault was zero, or rounded to zero. FixedPrecision LoanSet requires
// positive first-payment principal, and no transaction-generated
// schedule currently produces a non-terminal zero-credit payment.
// Fail gracefully if an extreme edge case still reaches this branch.
//
// LCOV_EXCL_START
JLOG(j_.warn()) << "LoanPay: Vault assets available unchanged after rounding: " //

27
src/test/app/lending/LendingHelpers_test.cpp
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@@ -1667,6 +1667,32 @@ class LendingHelpers_test : public beast::unit_test::Suite
}
}
void
testFixedPrecisionLoanPaymentDeltas()
{
testcase("fixed_precision::loanPaymentDeltas floors posterior AssetsTotal");
using namespace jtx;
Env const env{*this};
Account const issuer{"issuer"};
PrettyAsset const asset = issuer["USD"];
auto vault = std::make_shared<SLE>(ltVAULT, uint256{2u});
vault->setFieldIssue(sfAsset, STIssue{sfAsset, asset});
vault->at(sfAssetsTotal) = Number{9'999'999'999'999'999, -6};
vault->at(sfAssetsAvailable) = Number{9'999'999'999'999'999, -6};
vault->at(sfScale) = 6;
vault->at(sfLEVersion) = std::to_underlying(VaultVersion::FixedPrecision);
associateAsset(*vault, asset);
LoanPaymentParts const parts{.principalPaid = Number{1, -5}, .interestPaid = Number{5, -6}};
auto const deltas = fixed_precision::loanPaymentDeltas(vault, parts);
BEAST_EXPECT((deltas.assetsTotalDelta == Number{1, -6}));
BEAST_EXPECT(deltas.debtTotalDelta == parts.principalPaid);
BEAST_EXPECT((deltas.vaultCredit == Number{1, -5}));
}
void
testLoanOriginationDeltasDispatcher()
{
@@ -2050,6 +2076,7 @@ public:
testInstantRecognitionLoanVaultExposure();
testCashBasisLoanVaultExposure();
testLoanPaymentDeltas();
testFixedPrecisionLoanPaymentDeltas();
testLoanOriginationDeltasDispatcher();
testLoanOriginationExceedsVaultMaximumDispatcher();
testLoanVaultExposureDispatcher();

41
src/test/app/lending/LoanPay_test.cpp
View File

@@ -1510,18 +1510,19 @@ private:
env(trust(lender, asset(10'000'000)));
env(trust(borrower, asset(10'000'000)));
env(pay(issuer, lender, asset(2'000'000)));
env(pay(issuer, borrower, asset(100)));
env.close();
BrokerParameters brokerParams;
brokerParams.vaultScale = 6;
brokerParams.managementFeeRate = TenthBips16{0};
brokerParams.managementFeeRate = TenthBips16{100};
auto const broker = createVaultAndBroker(env, asset, lender, brokerParams);
auto const loanKeylet = nextLoanKeylet(env, broker);
env(set(borrower, broker.brokerID, asset(1'000).value()),
Sig(sfCounterpartySignature, lender),
kInterestRate(percentageToTenthBips(12)),
kPaymentTotal(2),
kPaymentTotal(3),
kPaymentInterval(24 * 60 * 60),
Fee(env.current()->fees().base * 2));
env.close();
@@ -1541,8 +1542,11 @@ private:
Number const yieldBefore = vaultBefore->at(sfYieldUnrealized);
Number const debtBefore = brokerBefore->at(sfDebtTotal);
Number const principalBefore = loanBefore->at(sfPrincipalOutstanding);
Number const scheduledInterestBefore = loanBefore->at(sfTotalValueOutstanding) -
principalBefore - loanBefore->at(sfManagementFeeOutstanding);
Number const managementFeeBefore = loanBefore->at(sfManagementFeeOutstanding);
Number const scheduledInterestBefore =
loanBefore->at(sfTotalValueOutstanding) - principalBefore - managementFeeBefore;
Number const lenderBalanceBefore = env.balance(lender, asset).number();
BEAST_EXPECT(managementFeeBefore > beast::kZero);
env(pay(borrower, loanKeylet.key, payment));
env.close();
@@ -1556,8 +1560,9 @@ private:
Number const principalAfter = loanAfter->at(sfPrincipalOutstanding);
Number const principalPaid = principalBefore - principalAfter;
Number const credit = vaultAfter->at(sfAssetsAvailable) - assetsAvailableBefore;
Number const scheduledInterestAfter = loanAfter->at(sfTotalValueOutstanding) -
principalAfter - loanAfter->at(sfManagementFeeOutstanding);
Number const managementFeeAfter = loanAfter->at(sfManagementFeeOutstanding);
Number const scheduledInterestAfter =
loanAfter->at(sfTotalValueOutstanding) - principalAfter - managementFeeAfter;
Number const interestPaid = scheduledInterestBefore - scheduledInterestAfter;
Number const expectedAssetsTotal = [&] {
NumberRoundModeGuard const rg(Number::RoundingMode::Downward);
@@ -1570,7 +1575,11 @@ private:
vaultAfter->at(sfAssetsTotal) == expectedAssetsTotal,
"AssetsTotal expected " + to_string(expectedAssetsTotal) + ", got " +
to_string(vaultAfter->at(sfAssetsTotal)));
BEAST_EXPECT(expectedAssetsTotal == assetsTotalBefore + interestPaid);
BEAST_EXPECT(credit == principalPaid + interestActual);
BEAST_EXPECT(
env.balance(lender, asset).number() - lenderBalanceBefore ==
managementFeeBefore - managementFeeAfter);
BEAST_EXPECT(
vaultAfter->at(sfYieldUnrealized) ==
yieldBefore + scheduledInterestAfter - scheduledInterestBefore);
@@ -1579,6 +1588,24 @@ private:
assetsTotalBefore + yieldBefore,
"capacity before " + to_string(assetsTotalBefore + yieldBefore) + ", after " +
to_string(vaultAfter->at(sfAssetsTotal) + vaultAfter->at(sfYieldUnrealized)));
Number const yieldBeforeFull = vaultAfter->at(sfYieldUnrealized);
BEAST_EXPECT(scheduledInterestAfter > beast::kZero);
BEAST_EXPECT(yieldBeforeFull > beast::kZero);
Number const fullPaymentMaximum = env.balance(borrower, asset).number();
env(pay(borrower, loanKeylet.key, asset(fullPaymentMaximum), tfLoanFullPayment));
env.close();
auto const vaultAfterFull = env.le(broker.vaultKeylet());
auto const loanAfterFull = env.le(loanKeylet);
if (!BEAST_EXPECT(vaultAfterFull && loanAfterFull))
return;
BEAST_EXPECT(loanAfterFull->at(sfPaymentRemaining) == 0);
BEAST_EXPECT(loanAfterFull->at(sfTotalValueOutstanding) == beast::kZero);
BEAST_EXPECT(loanAfterFull->at(sfPrincipalOutstanding) == beast::kZero);
BEAST_EXPECT(loanAfterFull->at(sfManagementFeeOutstanding) == beast::kZero);
BEAST_EXPECT(vaultAfterFull->at(sfYieldUnrealized) == beast::kZero);
}
void
@@ -2262,6 +2289,8 @@ private:
testFixedPrecisionSpecialPayments();
testFixedPrecisionIntegralPayments();
testFixedPrecisionYieldAcrossLoans();
testOverpaymentManagementFee(
all_ | featureLendingProtocolV1_1 | featureLendingProtocolV1_2);
}
// Tests run under each entry in amendmentCombinations().