Fold GetSelectionWaste() into ComputeAndSetWaste()

Both `GetSelectionWaste()` and `ComputeAndSetWaste()` now are part of
`SelectionResult`. Instead of `ComputeAndSetWaste()` being a wrapper for
`GetSelectionWaste()`, we combine them to a new function
`RecalculateWaste()`.

As I was combining the logic of the two functions, I noticed that
`GetSelectionWaste()` was making the odd assumption that the
`change_cost` being set to zero means that no change is created.
However, if we build transactions at a feerate of zero with the
`discard_feerate` also set to zero, we'd organically have a
`change_cost` of zero, even when we create change on a transaction.

This commit cleans up this duplicate meaning of `change_cost` and relies
on `GetChange()` to figure out whether there is change on basis of the
`min_viable_change` and whatever is left after deducting fees.

Since this broke a bunch of tests that relied on the double-meaning of
`change_cost` a bunch of tests had to be fixed.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 5d23ebd35a..89317b7656 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -711,7 +711,7 @@ util::Result<SelectionResult> ChooseSelectionResult(interfaces::Chain& chain, co
 
     if (coin_selection_params.m_effective_feerate > CFeeRate{3 * coin_selection_params.m_long_term_feerate}) { // Minimize input set for feerates of at least 3×LTFRE (default: 30 ṩ/vB+)
         if (auto cg_result{CoinGrinder(groups.positive_group, nTargetValue, coin_selection_params.m_min_change_target, max_inputs_weight)}) {
-            cg_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
+            cg_result->RecalculateWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
             results.push_back(*cg_result);
         } else {
             append_error(cg_result);
@@ -746,7 +746,7 @@ util::Result<SelectionResult> ChooseSelectionResult(interfaces::Chain& chain, co
         if (bump_fee_overestimate) {
             result.SetBumpFeeDiscount(bump_fee_overestimate);
         }
-        result.ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
+        result.RecalculateWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
     }
 
     // Choose the result with the least waste
@@ -771,7 +771,7 @@ util::Result<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& av
     if (selection_target <= 0) {
         SelectionResult result(nTargetValue, SelectionAlgorithm::MANUAL);
         result.AddInputs(pre_set_inputs.coins, coin_selection_params.m_subtract_fee_outputs);
-        result.ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
+        result.RecalculateWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
         return result;
     }
 
@@ -792,7 +792,7 @@ util::Result<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& av
         SelectionResult preselected(pre_set_inputs.total_amount, SelectionAlgorithm::MANUAL);
         preselected.AddInputs(pre_set_inputs.coins, coin_selection_params.m_subtract_fee_outputs);
         op_selection_result->Merge(preselected);
-        op_selection_result->ComputeAndSetWaste(coin_selection_params.min_viable_change,
+        op_selection_result->RecalculateWaste(coin_selection_params.min_viable_change,
                                                 coin_selection_params.m_cost_of_change,
                                                 coin_selection_params.m_change_fee);
     }