wallet: refactor eight consecutive 'AttemptSelection' calls into a loop

and remove 'CoinEligibilityFilter' default constructor to prevent
mistakes.

src/wallet/coinselection.h

@@ -186,6 +186,7 @@ struct CoinEligibilityFilter
     /** When avoid_reuse=true and there are full groups (OUTPUT_GROUP_MAX_ENTRIES), whether or not to use any partial groups.*/
     const bool m_include_partial_groups{false};
 
+    CoinEligibilityFilter() = delete;
     CoinEligibilityFilter(int conf_mine, int conf_theirs, uint64_t max_ancestors) : conf_mine(conf_mine), conf_theirs(conf_theirs), max_ancestors(max_ancestors), max_descendants(max_ancestors) {}
     CoinEligibilityFilter(int conf_mine, int conf_theirs, uint64_t max_ancestors, uint64_t max_descendants) : conf_mine(conf_mine), conf_theirs(conf_theirs), max_ancestors(max_ancestors), max_descendants(max_descendants) {}
     CoinEligibilityFilter(int conf_mine, int conf_theirs, uint64_t max_ancestors, uint64_t max_descendants, bool include_partial) : conf_mine(conf_mine), conf_theirs(conf_theirs), max_ancestors(max_ancestors), max_descendants(max_descendants), m_include_partial_groups(include_partial) {}

src/wallet/spend.cpp

@@ -622,6 +622,11 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& a
     return op_selection_result;
 }
 
+struct SelectionFilter {
+    CoinEligibilityFilter filter;
+    bool allow_mixed_output_types{true};
+};
+
 std::optional<SelectionResult> AutomaticCoinSelection(const CWallet& wallet, CoinsResult& available_coins, const CAmount& value_to_select, const CCoinControl& coin_control, const CoinSelectionParams& coin_selection_params)
 {
     unsigned int limit_ancestor_count = 0;
@@ -644,50 +649,42 @@ std::optional<SelectionResult> AutomaticCoinSelection(const CWallet& wallet, Coi
     // transaction at a target feerate. If an attempt fails, more attempts may be made using a more
     // permissive CoinEligibilityFilter.
     std::optional<SelectionResult> res = [&] {
+        // Place coins eligibility filters on a scope increasing order.
+        std::vector<SelectionFilter> ordered_filters{
                 // 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.
-        if (auto r1{AttemptSelection(wallet, value_to_select, CoinEligibilityFilter(1, 6, 0), available_coins, coin_selection_params, /*allow_mixed_output_types=*/false)}) return r1;
+                {CoinEligibilityFilter(1, 6, 0), /*allow_mixed_output_types=*/false},
-        // Allow mixing only if no solution from any single output type can be found
+                {CoinEligibilityFilter(1, 1, 0)},
-        if (auto r2{AttemptSelection(wallet, value_to_select, CoinEligibilityFilter(1, 1, 0), available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) return r2;
+        };
-
         // Fall back to using zero confirmation change (but with as few ancestors in the mempool as
         // possible) if we cannot fund the transaction otherwise.
         if (wallet.m_spend_zero_conf_change) {
-            if (auto r3{AttemptSelection(wallet, value_to_select, CoinEligibilityFilter(0, 1, 2), available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) return r3;
+            ordered_filters.push_back({CoinEligibilityFilter(0, 1, 2)});
-            if (auto r4{AttemptSelection(wallet, value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)),
+            ordered_filters.push_back({CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3))});
-                                   available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) {
+            ordered_filters.push_back({CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2)});
-                return r4;
-            }
-            if (auto r5{AttemptSelection(wallet, value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2),
-                                   available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) {
-                return r5;
-            }
             // If partial groups are allowed, relax the requirement of spending OutputGroups (groups
             // of UTXOs sent to the same address, which are obviously controlled by a single wallet)
             // in their entirety.
-            if (auto r6{AttemptSelection(wallet, value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, /*include_partial=*/true),
+            ordered_filters.push_back({CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, /*include_partial=*/true)});
-                                   available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) {
-                return r6;
-            }
             // Try with unsafe inputs if they are allowed. This may spend unconfirmed outputs
             // received from other wallets.
             if (coin_control.m_include_unsafe_inputs) {
-                if (auto r7{AttemptSelection(wallet, value_to_select,
+                ordered_filters.push_back({CoinEligibilityFilter(/*conf_mine=*/0, /*conf_theirs*/0, max_ancestors-1, max_descendants-1, /*include_partial=*/true)});
-                    CoinEligibilityFilter(/*conf_mine=*/0, /*conf_theirs=*/0, max_ancestors-1, max_descendants-1, /*include_partial=*/true),
-                    available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) {
-                    return r7;
-                }
             }
             // Try with unlimited ancestors/descendants. The transaction will still need to meet
             // mempool ancestor/descendant policy to be accepted to mempool and broadcasted, but
             // OutputGroups use heuristics that may overestimate ancestor/descendant counts.
             if (!fRejectLongChains) {
-                if (auto r8{AttemptSelection(wallet, value_to_select,
+                ordered_filters.push_back({CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(),
-                                      CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(), std::numeric_limits<uint64_t>::max(), /*include_partial=*/true),
+                                                                   std::numeric_limits<uint64_t>::max(),
-                                      available_coins, coin_selection_params, /*allow_mixed_output_types=*/true)}) {
+                                                                   /*include_partial=*/true)});
-                    return r8;
             }
         }
+
+        // Walk-through the filters until the solution gets found
+        for (const auto& select_filter : ordered_filters) {
+            if (auto res{AttemptSelection(wallet, value_to_select, select_filter.filter, available_coins,
+                                          coin_selection_params, select_filter.allow_mixed_output_types)}) return res;
         }
         // Coin Selection failed.
         return std::optional<SelectionResult>();