wallet: track which coin selection algorithm produced a SelectionResult

src/wallet/coinselection.cpp

@@ -64,7 +64,7 @@ static const size_t TOTAL_TRIES = 100000;
 
 std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change)
 {
-    SelectionResult result(selection_target);
+    SelectionResult result(selection_target, SelectionAlgorithm::BNB);
     CAmount curr_value = 0;
     std::vector<size_t> curr_selection; // selected utxo indexes
 
@@ -167,7 +167,7 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
 
 std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng)
 {
-    SelectionResult result(target_value);
+    SelectionResult result(target_value, SelectionAlgorithm::SRD);
 
     std::vector<size_t> indexes;
     indexes.resize(utxo_pool.size());
@@ -249,7 +249,7 @@ static void ApproximateBestSubset(FastRandomContext& insecure_rand, const std::v
 std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
                                               CAmount change_target, FastRandomContext& rng)
 {
-    SelectionResult result(nTargetValue);
+    SelectionResult result(nTargetValue, SelectionAlgorithm::KNAPSACK);
 
     // List of values less than target
     std::optional<OutputGroup> lowest_larger;
@@ -460,4 +460,17 @@ std::string COutput::ToString() const
 {
     return strprintf("COutput(%s, %d, %d) [%s]", outpoint.hash.ToString(), outpoint.n, depth, FormatMoney(txout.nValue));
 }
+
+std::string GetAlgorithmName(const SelectionAlgorithm algo)
+{
+    switch (algo)
+    {
+    case SelectionAlgorithm::BNB: return "bnb";
+    case SelectionAlgorithm::KNAPSACK: return "knapsack";
+    case SelectionAlgorithm::SRD: return "srd";
+    case SelectionAlgorithm::MANUAL: return "manual";
+    // No default case to allow for compiler to warn
+    }
+    assert(false);
+}
 } // namespace wallet

src/wallet/coinselection.h

@@ -239,6 +239,16 @@ struct OutputGroup
  */
 [[nodiscard]] CAmount GenerateChangeTarget(CAmount payment_value, FastRandomContext& rng);
 
+enum class SelectionAlgorithm : uint8_t
+{
+    BNB = 0,
+    KNAPSACK = 1,
+    SRD = 2,
+    MANUAL = 3,
+};
+
+std::string GetAlgorithmName(const SelectionAlgorithm algo);
+
 struct SelectionResult
 {
 private:
@@ -250,10 +260,12 @@ private:
     bool m_use_effective{false};
     /** The computed waste */
     std::optional<CAmount> m_waste;
+    /** The algorithm used to produce this result */
+    SelectionAlgorithm m_algo;
 
 public:
-    explicit SelectionResult(const CAmount target)
-        : m_target(target) {}
+    explicit SelectionResult(const CAmount target, SelectionAlgorithm algo)
+        : m_target(target), m_algo(algo) {}
 
     SelectionResult() = delete;
 

src/wallet/spend.cpp

@@ -435,7 +435,7 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, const std::vec
              */
             preset_inputs.Insert(out, /*ancestors=*/ 0, /*descendants=*/ 0, /*positive_only=*/ false);
         }
-        SelectionResult result(nTargetValue);
+        SelectionResult result(nTargetValue, SelectionAlgorithm::MANUAL);
         result.AddInput(preset_inputs);
         if (result.GetSelectedValue() < nTargetValue) return std::nullopt;
         return result;
@@ -519,7 +519,7 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, const std::vec
     // permissive CoinEligibilityFilter.
     std::optional<SelectionResult> res = [&] {
         // Pre-selected inputs already cover the target amount.
-        if (value_to_select <= 0) return std::make_optional(SelectionResult(nTargetValue));
+        if (value_to_select <= 0) return std::make_optional(SelectionResult(nTargetValue, SelectionAlgorithm::MANUAL));
 
         // If possible, fund the transaction with confirmed UTXOs only. Prefer at least six
         // confirmations on outputs received from other wallets and only spend confirmed change.

src/wallet/test/coinselector_tests.cpp

@@ -168,7 +168,7 @@ BOOST_AUTO_TEST_CASE(bnb_search_test)
     FastRandomContext rand{};
     // Setup
     std::vector<COutput> utxo_pool;
-    SelectionResult expected_result(CAmount(0));
+    SelectionResult expected_result(CAmount(0), SelectionAlgorithm::BNB);
 
     /////////////////////////
     // Known Outcome tests //