Merge bitcoin/bitcoin#27969: bumpfee: ignore WALLET_INCREMENTAL_RELAY_FEE when user specifies fee_rate

f58beabe754363cb7d5b24032fd392654b9514ac test: bumpfee with user specified fee_rate ignores walletIncrementalRelayFee (ismaelsadeeq)
436e88f4336199998184cbfa5d1c889ffaefbfb5 bumpfee: ignore WALLET_INCREMENTAL_RELAY_FEE when user specifies fee rate (ismaelsadeeq)

Pull request description:

  Fixes #26973

  When using the `bumpfee` RPC and manually specifying `fee_rate`, there should be no requirement that the new fee must be at least the sum of the original fee and `incrementalFee` (maximum of `relayIncrementalFee` and `WALLET_INCREMENTAL_RELAY_FEE`).

  This restriction should only apply when user did not specify `fee_rate`.
  > because the GUI doesn't let the user specify the new fee rate yet (https://github.com/bitcoin-core/gui/issues/647), it would be very annoying to have to bump 20 times to increment by 20 sat/vbyte.

  The restriction should instead be the new fee must be at least the sum of the original fee and `incrementalFee` (`relayIncrementalFee`)

ACKs for top commit:
  achow101:
    ACK f58beabe754363cb7d5b24032fd392654b9514ac
  murchandamus:
    ACK f58beabe754363cb7d5b24032fd392654b9514ac

Tree-SHA512: 193259f87173b7d5a8e68e0e29f2ca7e75c550e3cf0dee3d6d822b5b1e07c2e6dec0bfc8fb435855736ebced97a10dbdbfef72e8c5abde06fdefcba122f2e7f1

2 files changed, 25 insertions, 2 deletions

diff --git a/src/wallet/feebumper.cpp b/src/wallet/feebumper.cpp
index 1288d3b418..3184d0f3b0 100644
--- a/src/wallet/feebumper.cpp
+++ b/src/wallet/feebumper.cpp
@@ -93,7 +93,7 @@ static feebumper::Result CheckFeeRate(const CWallet& wallet, const CMutableTrans
     }
     CAmount new_total_fee = newFeerate.GetFee(maxTxSize) + combined_bump_fee.value();
 
-    CFeeRate incrementalRelayFee = std::max(wallet.chain().relayIncrementalFee(), CFeeRate(WALLET_INCREMENTAL_RELAY_FEE));
+    CFeeRate incrementalRelayFee = wallet.chain().relayIncrementalFee();
 
     // Min total fee is old fee + relay fee
     CAmount minTotalFee = old_fee + incrementalRelayFee.GetFee(maxTxSize);
diff --git a/test/functional/wallet_bumpfee.py b/test/functional/wallet_bumpfee.py
index 5b7db55f45..6d45adc823 100755
--- a/test/functional/wallet_bumpfee.py
+++ b/test/functional/wallet_bumpfee.py
@@ -117,6 +117,7 @@ class BumpFeeTest(BitcoinTestFramework):
 
         # Context independent tests
         test_feerate_checks_replaced_outputs(self, rbf_node, peer_node)
+        test_bumpfee_with_feerate_ignores_walletincrementalrelayfee(self, rbf_node, peer_node)
 
     def test_invalid_parameters(self, rbf_node, peer_node, dest_address):
         self.log.info('Test invalid parameters')
@@ -816,7 +817,7 @@ def test_feerate_checks_replaced_outputs(self, rbf_node, peer_node):
     # Since the bumped tx will replace all of the outputs with a single output, we can estimate that its size will 31 * (len(outputs) - 1) bytes smaller
     tx_size = tx_details["decoded"]["vsize"]
     est_bumped_size = tx_size - (len(tx_details["decoded"]["vout"]) - 1) * 31
-    inc_fee_rate = max(rbf_node.getmempoolinfo()["incrementalrelayfee"], Decimal(0.00005000)) # Wallet has a fixed incremental relay fee of 5 sat/vb
+    inc_fee_rate = rbf_node.getmempoolinfo()["incrementalrelayfee"]
     # RPC gives us fee as negative
     min_fee = (-tx_details["fee"] + get_fee(est_bumped_size, inc_fee_rate)) * Decimal(1e8)
     min_fee_rate = (min_fee / est_bumped_size).quantize(Decimal("1.000"))
@@ -830,5 +831,27 @@ def test_feerate_checks_replaced_outputs(self, rbf_node, peer_node):
     self.clear_mempool()
 
 
+def test_bumpfee_with_feerate_ignores_walletincrementalrelayfee(self, rbf_node, peer_node):
+    self.log.info('Test that bumpfee with fee_rate ignores walletincrementalrelayfee')
+    # Make sure there is enough balance
+    peer_node.sendtoaddress(rbf_node.getnewaddress(), 2)
+    self.generate(peer_node, 1)
+
+    dest_address = peer_node.getnewaddress(address_type="bech32")
+    tx = rbf_node.send(outputs=[{dest_address: 1}], fee_rate=2)
+
+    # Ensure you can not fee bump with a fee_rate below or equal to the original fee_rate
+    assert_raises_rpc_error(-8, "Insufficient total fee", rbf_node.bumpfee, tx["txid"], {"fee_rate": 1})
+    assert_raises_rpc_error(-8, "Insufficient total fee", rbf_node.bumpfee, tx["txid"], {"fee_rate": 2})
+
+    # Ensure you can not fee bump if the fee_rate is more than original fee_rate but the total fee from new fee_rate is
+    # less than (original fee + incrementalrelayfee)
+    assert_raises_rpc_error(-8, "Insufficient total fee", rbf_node.bumpfee, tx["txid"], {"fee_rate": 2.8})
+
+    # You can fee bump as long as the new fee set from fee_rate is atleast (original fee + incrementalrelayfee)
+    rbf_node.bumpfee(tx["txid"], {"fee_rate": 3})
+    self.clear_mempool()
+
+
 if __name__ == "__main__":
     BumpFeeTest().main()