Improve and fix bugs in Lending Protocol - XLS-66 (#6156)

- Fix overpayment asserts (#6084)

- MPTTester::operator() parameter should be std::int64_t
	- Originally defined as uint64_t, but the testIssuerLoan() test called
	  it with a negative number, causing an overflow to a very large number
	  that in some circumstances could be silently cast back to an int64_t,
	  but might not be. I believe this is UB, and we don't want to rely on
	  that.

- Fix Overpayment Calculation  (#6087)
	- Adds additional unit tests to cover math calculations.
	- Removes unused methods.
- Fix LoanBrokerSet debtMaximum limits (#6116)
- Fix some minor bugs in Lending Protocol (#6101)
	- add nodiscard to unimpairLoan, and check result in LoanPay
	- add a check to verify that issuer exists
	- improve LoanManage error code for dust amounts

- In overpayment results, the management fee was being calculated twice:
  once as part of the value change, and as part of the fees paid.
  Exclude it from the value change.

- Round the initial total value computation upward, unless there is
  0-interest.
- Rename getVaultScale to getAssetsTotalScale, and convert one incorrect
  computation to use it.
- Use adjustImpreciseNumber for LossUnrealized.
- Add some logging to computeLoanProperties.

- Check permissions in LoanSet and LoanPay (#6108)

- Disallow pseudo accounts to be Destination for LoanBrokerCoverWithdraw (#6106)

- Ensure vault asset cap is not exceeded (#6124)

- Fix Overpayment ValueChange calculation in Lending Protocol (#6114)
	- Adds loan state to LoanProperties.
	- Cleans up computeLoanProperties.
	- Fixes missing management fee from overpayment.

- fix: Enable LP Deposits when the broker is the asset issuer (#6119)

- Add a few minor changes (#6158)
	- Updates or fixes a couple of things I noticed while reviewing changes
	  to the spec.
	- Rename sfPreviousPaymentDate to sfPreviousPaymentDueDate.
	- Make the vault asset cap check added in #6124 a little more robust:
	  1. Check in preflight if the vault is _already_ over the limit.
	  2. Prevent overflow when checking with the loan value. (Subtract
	     instead of adding, in case the values are near maxint. Both return
	     the same result. Also add a unit test so each case is covered.

- Add minimum grace period validation (#6133)

- Fix bugs: frozen pseudo-account, and FLC cutoff (#6170)
	- Fixes LoanManage tfBAD_LEDGER case by capping the amount of FLC to use to cover a loss at the amount of cover available.
	- Check if the Vault pseudo-account is frozen in LoanBrokerSet

- refactor: Rename raw state to theoretical state (#6187)

- Check if a withdrawal amount exceeds any applicable receiving limit. (#6117)
	- Check the trust line limit is not exceeded for a withdraw to a third party Destination account.

- Fix test failures from interaction between #6120 and #6133
	- LoanSet transaction added in #6120 failed the minimum grace period
	  added by #6133.

- Fix overpayment result calculation (#6195)

- Address review feedback from Lending Protocol re-review (#6161)
	- Reduce code duplication in LoanBrokerDelete
	- Reorder "canWithdraw" parameters to put "view" first
	- Combine accountSpendable into accountHolds
	- Avoid copies by taking a reference for the claw amount
	- Return function results directly
	- Fix typo for "parseLoan" in ledger_entry RPC
	- Improve some comments and unused variables
	- No need for late payment components lambda
	- Add explanatory comment for computeLoanProperties
	- Add comment linking computeRawLoanState to spec
	- Fix typo: TrueTotalPrincipalOutstanding
	- Fix missed ripple -> xrpl update
	- Remove unnecessary "else"s.
	- Clean up std::visit in accountHolds.
	
---------

Co-authored-by: Vito Tumas <5780819+Tapanito@users.noreply.github.com>
Co-authored-by: Shawn Xie <35279399+shawnxie999@users.noreply.github.com>
Co-authored-by: Jingchen <a1q123456@users.noreply.github.com>
Co-authored-by: Gregory Tsipenyuk <gregtatcam@users.noreply.github.com>

Author: 5 people

src/xrpld/app/paths/Credit.h include/xrpl/ledger/Credit.hsrc/xrpld/app/paths/Credit.h renamed to include/xrpl/ledger/Credit.h

@@ -17,8 +17,8 @@
 */
 //==============================================================================
 
-#ifndef RIPPLE_APP_PATHS_CREDIT_H_INCLUDED
-#define RIPPLE_APP_PATHS_CREDIT_H_INCLUDED
+#ifndef RIPPLE_LEDGER_CREDIT_H_INCLUDED
+#define RIPPLE_LEDGER_CREDIT_H_INCLUDED
 
 #include <xrpl/ledger/View.h>
 #include <xrpl/protocol/IOUAmount.h>

include/xrpl/ledger/View.h

@@ -80,6 +80,9 @@ enum FreezeHandling { fhIGNORE_FREEZE, fhZERO_IF_FROZEN };
 /** Controls the treatment of unauthorized MPT balances */
 enum AuthHandling { ahIGNORE_AUTH, ahZERO_IF_UNAUTHORIZED };
 
+/** Controls whether to include the account's full spendable balance */
+enum SpendableHandling { shSIMPLE_BALANCE, shFULL_BALANCE };
+
 [[nodiscard]] bool
 isGlobalFrozen(ReadView const& view, AccountID const& issuer);
 
@@ -324,7 +327,17 @@ isLPTokenFrozen(
     Issue const& asset,
     Issue const& asset2);
 
-// Returns the amount an account can spend without going into debt.
+// Returns the amount an account can spend.
+//
+// If shSIMPLE_BALANCE is specified, this is the amount the account can spend
+// without going into debt.
+//
+// If shFULL_BALANCE is specified, this is the amount the account can spend
+// total. Specifically:
+// * The account can go into debt if using a trust line, and the other side has
+// a non-zero limit.
+// * If the account is the asset issuer the limit is defined by the asset /
+//   issuance.
 //
 // <-- saAmount: amount of currency held by account. May be negative.
 [[nodiscard]] STAmount
@@ -334,15 +347,17 @@ accountHolds(
     Currency const& currency,
     AccountID const& issuer,
     FreezeHandling zeroIfFrozen,
-    beast::Journal j);
+    beast::Journal j,
+    SpendableHandling includeFullBalance = shSIMPLE_BALANCE);
 
 [[nodiscard]] STAmount
 accountHolds(
     ReadView const& view,
     AccountID const& account,
     Issue const& issue,
     FreezeHandling zeroIfFrozen,
-    beast::Journal j);
+    beast::Journal j,
+    SpendableHandling includeFullBalance = shSIMPLE_BALANCE);
 
 [[nodiscard]] STAmount
 accountHolds(
@@ -351,7 +366,8 @@ accountHolds(
     MPTIssue const& mptIssue,
     FreezeHandling zeroIfFrozen,
     AuthHandling zeroIfUnauthorized,
-    beast::Journal j);
+    beast::Journal j,
+    SpendableHandling includeFullBalance = shSIMPLE_BALANCE);
 
 [[nodiscard]] STAmount
 accountHolds(
@@ -360,50 +376,8 @@ accountHolds(
     Asset const& asset,
     FreezeHandling zeroIfFrozen,
     AuthHandling zeroIfUnauthorized,
-    beast::Journal j);
-
-// Returns the amount an account can spend total.
-//
-// These functions use accountHolds, but unlike accountHolds:
-// * The account can go into debt.
-// * If the account is the asset issuer the only limit is defined by the asset /
-//   issuance.
-//
-// <-- saAmount: amount of currency held by account. May be negative.
-[[nodiscard]] STAmount
-accountSpendable(
-    ReadView const& view,
-    AccountID const& account,
-    Currency const& currency,
-    AccountID const& issuer,
-    FreezeHandling zeroIfFrozen,
-    beast::Journal j);
-
-[[nodiscard]] STAmount
-accountSpendable(
-    ReadView const& view,
-    AccountID const& account,
-    Issue const& issue,
-    FreezeHandling zeroIfFrozen,
-    beast::Journal j);
-
-[[nodiscard]] STAmount
-accountSpendable(
-    ReadView const& view,
-    AccountID const& account,
-    MPTIssue const& mptIssue,
-    FreezeHandling zeroIfFrozen,
-    AuthHandling zeroIfUnauthorized,
-    beast::Journal j);
-
-[[nodiscard]] STAmount
-accountSpendable(
-    ReadView const& view,
-    AccountID const& account,
-    Asset const& asset,
-    FreezeHandling zeroIfFrozen,
-    AuthHandling zeroIfUnauthorized,
-    beast::Journal j);
+    beast::Journal j,
+    SpendableHandling includeFullBalance = shSIMPLE_BALANCE);
 
 // Returns the amount an account can spend of the currency type saDefault, or
 // returns saDefault if this account is the issuer of the currency in
@@ -674,7 +648,7 @@ createPseudoAccount(
     uint256 const& pseudoOwnerKey,
     SField const& ownerField);
 
-// Returns true iff sleAcct is a pseudo-account or specific
+// Returns true if and only if sleAcct is a pseudo-account or specific
 // pseudo-accounts in pseudoFieldFilter.
 //
 // Returns false if sleAcct is
@@ -729,13 +703,16 @@ checkDestinationAndTag(SLE::const_ref toSle, bool hasDestinationTag);
  *    - If withdrawing to self, succeed.
  *    - If not, checks if the receiver requires deposit authorization, and if
  *      the sender has it.
+ *    - Checks that the receiver will not exceed the limit (IOU trustline limit
+ *      or MPT MaximumAmount).
  */
 [[nodiscard]] TER
 canWithdraw(
-    AccountID const& from,
     ReadView const& view,
+    AccountID const& from,
     AccountID const& to,
     SLE::const_ref toSle,
+    STAmount const& amount,
     bool hasDestinationTag);
 
 /** Checks that can withdraw funds from an object to itself or a destination.
@@ -749,12 +726,15 @@ canWithdraw(
  *    - If withdrawing to self, succeed.
  *    - If not, checks if the receiver requires deposit authorization, and if
  *      the sender has it.
+ *    - Checks that the receiver will not exceed the limit (IOU trustline limit
+ *      or MPT MaximumAmount).
  */
 [[nodiscard]] TER
 canWithdraw(
-    AccountID const& from,
     ReadView const& view,
+    AccountID const& from,
     AccountID const& to,
+    STAmount const& amount,
     bool hasDestinationTag);
 
 /** Checks that can withdraw funds from an object to itself or a destination.
@@ -768,6 +748,8 @@ canWithdraw(
  *    - If withdrawing to self, succeed.
  *    - If not, checks if the receiver requires deposit authorization, and if
  *      the sender has it.
+ *    - Checks that the receiver will not exceed the limit (IOU trustline limit
+ *      or MPT MaximumAmount).
  */
 [[nodiscard]] TER
 canWithdraw(ReadView const& view, STTx const& tx);

include/xrpl/protocol/detail/ledger_entries.macro

@@ -560,7 +560,7 @@ LEDGER_ENTRY(ltLOAN, 0x0089, Loan, loan, ({
     {sfStartDate,            soeREQUIRED},
     {sfPaymentInterval,      soeREQUIRED},
     {sfGracePeriod,          soeDEFAULT},
-    {sfPreviousPaymentDate,  soeDEFAULT},
+    {sfPreviousPaymentDueDate, soeDEFAULT},
     {sfNextPaymentDueDate,   soeDEFAULT},
     // The loan object tracks these values:
     //

include/xrpl/protocol/detail/sfields.macro

@@ -121,7 +121,7 @@ TYPED_SFIELD(sfMutableFlags,             UINT32,    53)
 TYPED_SFIELD(sfStartDate,                UINT32,    54)
 TYPED_SFIELD(sfPaymentInterval,          UINT32,    55)
 TYPED_SFIELD(sfGracePeriod,              UINT32,    56)
-TYPED_SFIELD(sfPreviousPaymentDate,      UINT32,    57)
+TYPED_SFIELD(sfPreviousPaymentDueDate,   UINT32,    57)
 TYPED_SFIELD(sfNextPaymentDueDate,       UINT32,    58)
 TYPED_SFIELD(sfPaymentRemaining,         UINT32,    59)
 TYPED_SFIELD(sfPaymentTotal,             UINT32,    60)