Fix tokens comparison in Payment for temREDUNDANT error

include/xrpl/protocol/Asset.h

@@ -97,6 +97,13 @@ class Asset
 
     friend constexpr bool
     operator==(Currency const& lhs, Asset const& rhs);
+
+    /** Return true if both asset's issue (Issue or MPTIssue)
+     * are the same and hold the same token (currency or MPTID).
+     * Otherwise return false.
+     */
+    friend constexpr bool
+    equalTokens(Asset const& lhs, Asset const& rhs);
 };
 
 template <ValidIssueType TIss>
@@ -157,6 +164,26 @@ operator==(Currency const& lhs, Asset const& rhs)
     return rhs.holds<Issue>() && rhs.get<Issue>().currency == lhs;
 }
 
+constexpr bool
+equalTokens(Asset const& lhs, Asset const& rhs)
+{
+    return std::visit(
+        [&]<typename TLhs, typename TRhs>(
+            TLhs const& issLhs, TRhs const& issRhs) {
+            if constexpr (
+                std::is_same_v<TLhs, Issue> && std::is_same_v<TRhs, Issue>)
+                return issLhs.currency == issRhs.currency;
+            else if constexpr (
+                std::is_same_v<TLhs, MPTIssue> &&
+                std::is_same_v<TRhs, MPTIssue>)
+                return issLhs.getMptID() == issRhs.getMptID();
+            else
+                return false;
+        },
+        lhs.issue_,
+        rhs.issue_);
+}
+
 inline bool
 isXRP(Asset const& asset)
 {

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

@@ -145,7 +145,7 @@ Payment::preflight(PreflightContext const& ctx)
         JLOG(j.trace()) << "Malformed transaction: " << "Bad currency.";
         return temBAD_CURRENCY;
     }
-    if (account == dstAccountID && srcAsset == dstAsset && !hasPaths)
+    if (account == dstAccountID && equalTokens(srcAsset, dstAsset) && !hasPaths)
     {
         // You're signing yourself a payment.
         // If hasPaths is true, you might be trying some arbitrage.