minor feerate improvements

Summary:
This is a partial backport of [[bitcoin/bitcoin#20220 | core#20220]]

Most of the PR is not applicable because we do not use `estimate_mode` nor `conf_target` for fees.

List of changes and source commits:
- Use a const ref in `FundTransaction` for `options`: bitcoin/bitcoin@1697a40
- Minor rpc_psbt.py refactoring: bitcoin/bitcoin@6e1ea42
- Add a `log.info` in wallet_basic.py: bitcoin/bitcoin@dd341e6
- Improve RPC doc for `subtract_fee_from_outputs`: bitcoin/bitcoin@778b9be

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10716

src/wallet/rpcwallet.cpp

@@ -3799,8 +3799,8 @@ static RPCHelpMan listunspent() {
 }
 
 void FundTransaction(CWallet *const pwallet, CMutableTransaction &tx,
-                     Amount &fee_out, int &change_position, UniValue options,
-                     CCoinControl &coinControl) {
+                     Amount &fee_out, int &change_position,
+                     const UniValue &options, CCoinControl &coinControl) {
     // Make sure the results are valid at least up to the most recent block
     // the user could have gotten from another RPC command prior to now
     pwallet->BlockUntilSyncedToCurrentChain();
@@ -4825,7 +4825,8 @@ static RPCHelpMan send() {
                      "subtract_fee_from_outputs",
                      RPCArg::Type::ARR,
                      /* default */ "empty array",
-                     "A JSON array of integers.\n"
+                     "Outputs to subtract the fee from, specified as integer "
+                     "indices.\n"
                      "The fee will be equally deducted from the amount of each "
                      "specified output.\n"
                      "Those recipients will receive less bitcoins than you "

test/functional/rpc_psbt.py

@@ -118,42 +118,32 @@ def run_test(self):
         self.nodes[1].sendrawtransaction(
             self.nodes[1].finalizepsbt(walletprocesspsbt_out['psbt'])['hex'])
 
-        # feeRate of 100,000 XEC / KB produces a total fee slightly below
-        # -maxtxfee
+        inputs = [{"txid": txid, "vout": p2sh_pos},
+                  {"txid": txid, "vout": p2pkh_pos}]
+        output = {self.nodes[1].getnewaddress(): 29_990_000}
+
+        self.log.info(
+            "Test walletcreatefundedpsbt feeRate of 100,000 XEC/kB produces a "
+            "total fee at or slightly below -maxtxfee")
         res = self.nodes[1].walletcreatefundedpsbt(
-            [
-                {
-                    "txid": txid, "vout": p2sh_pos}, {
-                    "txid": txid, "vout": p2pkh_pos}], {
-                        self.nodes[1].getnewaddress(): 29990000}, 0, {
-                            "feeRate": 100000, "add_inputs": True})
+            inputs, output, 0, {"feeRate": 100_000, "add_inputs": True})
         assert_approx(res["fee"], 65000, 5000)
 
-        # feeRate of 10,000,000 XEC / KB produces a total fee well above -maxtxfee
+        self.log.info(
+            "Test walletcreatefundedpsbt feeRate of 10,000,000 XEC/kB  produces "
+            "a total fee well above -maxtxfee and raises RPC error")
         # previously this was silently capped at -maxtxfee
-        assert_raises_rpc_error(-4,
-                                "Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)",
-                                self.nodes[1].walletcreatefundedpsbt,
-                                [{"txid": txid,
-                                  "vout": p2sh_pos},
-                                 {"txid": txid,
-                                     "vout": p2pkh_pos}],
-                                {self.nodes[1].getnewaddress(): 29990000},
-                                0,
-                                {"feeRate": 10000000,
-                                    "add_inputs": True})
-        assert_raises_rpc_error(-4,
-                                "Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)",
-                                self.nodes[1].walletcreatefundedpsbt,
-                                [{"txid": txid,
-                                  "vout": p2sh_pos},
-                                    {"txid": txid,
-                                     "vout": p2pkh_pos}],
-                                {self.nodes[1].getnewaddress(): 1000000},
-                                0,
-                                {"feeRate": 10000000,
-                                    "add_inputs": False})
-
+        for bool_add, output_ in (
+                (True, output),
+                (False, {self.nodes[1].getnewaddress(): 1_000_000})):
+            assert_raises_rpc_error(
+                -4,
+                "Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)",
+                self.nodes[1].walletcreatefundedpsbt,
+                inputs, output_, 0,
+                {"feeRate": 10_000_000, "add_inputs": bool_add})
+
+        self.log.info("Test various PSBT operations")
         # partially sign multisig things with node 1
         psbtx = self.nodes[1].walletcreatefundedpsbt([{"txid": txid, "vout": p2sh_pos}], {
                                                      self.nodes[1].getnewaddress(): 9990000})['psbt']

test/functional/wallet_basic.py

@@ -228,6 +228,8 @@ def run_test(self):
         node_0_bal = self.check_fee_amount(self.nodes[0].getbalance(), Decimal(
             '20000000'), fee_per_byte, count_bytes(self.nodes[2].gettransaction(txid)['hex']))
 
+        self.log.info("Test sendmany")
+
         # Sendmany 10,000,000 XEC
         txid = self.nodes[2].sendmany('', {address: 10000000}, 0, "", [])
         self.nodes[2].generate(1)