Review feedback from @gregtatcam: LoanDeltas

- Renamed to LoanStateDeltas, and document what it's for

src/test/app/Loan_test.cpp

@@ -1024,7 +1024,8 @@ protected:
                 periodicRate,
                 state.paymentRemaining - 1,
                 broker.params.managementFeeRate);
-            detail::LoanDeltas const deltas = currentTrueState - nextTrueState;
+            detail::LoanStateDeltas const deltas =
+                currentTrueState - nextTrueState;
             BEAST_EXPECT(
                 deltas.total() ==
                 deltas.principal + deltas.interest + deltas.managementFee);
@@ -2735,7 +2736,7 @@ protected:
                             periodicRate,
                             state.paymentRemaining - 1,
                             broker.params.managementFeeRate);
-                    detail::LoanDeltas const deltas =
+                    detail::LoanStateDeltas const deltas =
                         currentTrueState - nextTrueState;
 
                     testcase

src/xrpld/app/misc/LendingHelpers.h

@@ -220,7 +220,10 @@ struct PaymentComponents
     trackedInterestPart() const;
 };
 
-struct LoanDeltas
+// This structure describes the difference between two LoanState objects so that
+// the differences between components don't have to be tracked individually,
+// risking more errors. How that difference is used depends on the context.
+struct LoanStateDeltas
 {
     Number principal;
     Number interest;
@@ -250,14 +253,14 @@ computePaymentComponents(
 
 }  // namespace detail
 
-detail::LoanDeltas
+detail::LoanStateDeltas
 operator-(LoanState const& lhs, LoanState const& rhs);
 
 LoanState
-operator-(LoanState const& lhs, detail::LoanDeltas const& rhs);
+operator-(LoanState const& lhs, detail::LoanStateDeltas const& rhs);
 
 LoanState
-operator+(LoanState const& lhs, detail::LoanDeltas const& rhs);
+operator+(LoanState const& lhs, detail::LoanStateDeltas const& rhs);
 
 LoanProperties
 computeLoanProperties(

src/xrpld/app/misc/detail/LendingHelpers.cpp

@@ -835,7 +835,7 @@ PaymentComponents::trackedInterestPart() const
 }
 
 void
-LoanDeltas::nonNegative()
+LoanStateDeltas::nonNegative()
 {
     if (principal < beast::zero)
         principal = numZero;
@@ -899,7 +899,7 @@ computePaymentComponents(
     LoanState const currentLedgerState = constructLoanState(
         totalValueOutstanding, principalOutstanding, managementFeeOutstanding);
 
-    LoanDeltas deltas = currentLedgerState - roundedTarget;
+    LoanStateDeltas deltas = currentLedgerState - roundedTarget;
     deltas.nonNegative();
 
     // Adjust the deltas if necessary for data integrity
@@ -951,7 +951,7 @@ computePaymentComponents(
             "ripple::detail::computePaymentComponents",
             "excess non-negative");
     };
-    auto addressExcess = [&takeFrom](LoanDeltas& deltas, Number& excess) {
+    auto addressExcess = [&takeFrom](LoanStateDeltas& deltas, Number& excess) {
         // This order is based on where errors are the least problematic
         takeFrom(deltas.interest, excess);
         takeFrom(deltas.managementFee, excess);
@@ -1081,10 +1081,10 @@ computeOverpaymentComponents(
 
 }  // namespace detail
 
-detail::LoanDeltas
+detail::LoanStateDeltas
 operator-(LoanState const& lhs, LoanState const& rhs)
 {
-    detail::LoanDeltas result{
+    detail::LoanStateDeltas result{
         .principal = lhs.principalOutstanding - rhs.principalOutstanding,
         .interest = lhs.interestDue - rhs.interestDue,
         .managementFee = lhs.managementFeeDue - rhs.managementFeeDue,
@@ -1094,7 +1094,7 @@ operator-(LoanState const& lhs, LoanState const& rhs)
 }
 
 LoanState
-operator-(LoanState const& lhs, detail::LoanDeltas const& rhs)
+operator-(LoanState const& lhs, detail::LoanStateDeltas const& rhs)
 {
     LoanState result{
         .valueOutstanding = lhs.valueOutstanding - rhs.total(),
@@ -1107,7 +1107,7 @@ operator-(LoanState const& lhs, detail::LoanDeltas const& rhs)
 }
 
 LoanState
-operator+(LoanState const& lhs, detail::LoanDeltas const& rhs)
+operator+(LoanState const& lhs, detail::LoanStateDeltas const& rhs)
 {
     LoanState result{
         .valueOutstanding = lhs.valueOutstanding + rhs.total(),