Merge bitcoin/bitcoin#26203: wallet: Use correct effective value when checking target

d0d9cf7 test: Check external coin effective value is used in CoinSelection (Aurèle Oulès)
76b79c1 wallet: Use correct effective value when checking target (Aurèle Oulès)

Pull request description:

  Fixes #26185. The following assert failed because it was not checked in the parent function.

  https://github.com/bitcoin/bitcoin/blob/2bd9aa5a44b88c866c4d98f8a7bf7154049cba31/src/wallet/coinselection.cpp#L391

ACKs for top commit:
  glozow:
    reACK d0d9cf7
  furszy:
    ACK d0d9cf7

Tree-SHA512: e126daba1115e9d143f2a582c6953e7ea55e96853b6e819c7744fd7a23668f7d9854681d43ef55d8774655bc54e7e87c1c9fccd746d9e30fbf3caa82ef808ae9

Author: glozow

src/wallet/spend.cpp

@@ -582,7 +582,13 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& a
     if (coin_control.HasSelected() && !coin_control.m_allow_other_inputs) {
         SelectionResult result(nTargetValue, SelectionAlgorithm::MANUAL);
         result.AddInput(preset_inputs);
-        if (result.GetSelectedValue() < nTargetValue) return std::nullopt;
+
+        if (!coin_selection_params.m_subtract_fee_outputs && result.GetSelectedEffectiveValue() < nTargetValue) {
+            return std::nullopt;
+        } else if (result.GetSelectedValue() < nTargetValue) {
+            return std::nullopt;
+        }
+
         result.ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
         return result;
     }

src/wallet/test/coinselector_tests.cpp

@@ -922,5 +922,52 @@ BOOST_AUTO_TEST_CASE(effective_value_test)
     BOOST_CHECK_EQUAL(output5.GetEffectiveValue(), nValue); // The effective value should be equal to the absolute value if input_bytes is -1
 }
 
+BOOST_AUTO_TEST_CASE(SelectCoins_effective_value_test)
+{
+    // Test that the effective value is used to check whether preset inputs provide sufficient funds when subtract_fee_outputs is not used.
+    // This test creates a coin whose value is higher than the target but whose effective value is lower than the target.
+    // The coin is selected using coin control, with m_allow_other_inputs = false. SelectCoins should fail due to insufficient funds.
+
+    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", m_args, CreateMockWalletDatabase());
+    wallet->LoadWallet();
+    LOCK(wallet->cs_wallet);
+    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
+    wallet->SetupDescriptorScriptPubKeyMans();
+
+    CoinsResult available_coins;
+    {
+        std::unique_ptr<CWallet> dummyWallet = std::make_unique<CWallet>(m_node.chain.get(), "dummy", m_args, CreateMockWalletDatabase());
+        dummyWallet->LoadWallet();
+        LOCK(dummyWallet->cs_wallet);
+        dummyWallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
+        dummyWallet->SetupDescriptorScriptPubKeyMans();
+
+        add_coin(available_coins, *dummyWallet, 100000); // 0.001 BTC
+    }
+
+    CAmount target{99900}; // 0.000999 BTC
+
+    FastRandomContext rand;
+    CoinSelectionParams cs_params{
+        rand,
+        /*change_output_size=*/34,
+        /*change_spend_size=*/148,
+        /*min_change_target=*/1000,
+        /*effective_feerate=*/CFeeRate(3000),
+        /*long_term_feerate=*/CFeeRate(1000),
+        /*discard_feerate=*/CFeeRate(1000),
+        /*tx_noinputs_size=*/0,
+        /*avoid_partial=*/false,
+    };
+    CCoinControl cc;
+    cc.m_allow_other_inputs = false;
+    COutput output = available_coins.All().at(0);
+    cc.SetInputWeight(output.outpoint, 148);
+    cc.SelectExternal(output.outpoint, output.txout);
+
+    const auto result = SelectCoins(*wallet, available_coins, target, cc, cs_params);
+    BOOST_CHECK(!result);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 } // namespace wallet