Add regression test for m_limit mutation

test/functional/mempool_limit.py

@@ -78,6 +78,56 @@ class MempoolLimitTest(BitcoinTestFramework):
         assert_equal(node.getmempoolinfo()['minrelaytxfee'], Decimal('0.00001000'))
         assert_greater_than(node.getmempoolinfo()['mempoolminfee'], Decimal('0.00001000'))
 
+    def test_rbf_carveout_disallowed(self):
+        node = self.nodes[0]
+
+        self.log.info("Check that individually-evaluated transactions in a package don't increase package limits for other subpackage parts")
+
+        # We set chain limits to 2 ancestors, 1 descendant, then try to get a parents-and-child chain of 2 in mempool
+        #
+        # A: Solo transaction to be RBF'd (to bump descendant limit for package later)
+        # B: First transaction in package, RBFs A by itself under individual evaluation, which would give it +1 descendant limit
+        # C: Second transaction in package, spends B. If the +1 descendant limit persisted, would make it into mempool
+
+        self.restart_node(0, extra_args=self.extra_args[0] + ["-limitancestorcount=2", "-limitdescendantcount=1"])
+
+        # Generate a confirmed utxo we will double-spend
+        rbf_utxo = self.wallet.send_self_transfer(
+            from_node=node,
+            confirmed_only=True
+        )["new_utxo"]
+        self.generate(node, 1)
+
+        # tx_A needs to be RBF'd, set minfee at set size
+        A_weight = 1000
+        mempoolmin_feerate = node.getmempoolinfo()["mempoolminfee"]
+        tx_A = self.wallet.send_self_transfer(
+            from_node=node,
+            fee=(mempoolmin_feerate / 1000) * (A_weight // 4) + Decimal('0.000001'),
+            target_weight=A_weight,
+            utxo_to_spend=rbf_utxo,
+            confirmed_only=True
+        )
+
+        # RBF's tx_A, is not yet submitted
+        tx_B = self.wallet.create_self_transfer(
+            fee=tx_A["fee"] * 4,
+            target_weight=A_weight,
+            utxo_to_spend=rbf_utxo,
+            confirmed_only=True
+        )
+
+        # Spends tx_B's output, too big for cpfp carveout (because that would also increase the descendant limit by 1)
+        non_cpfp_carveout_weight = 40001 # EXTRA_DESCENDANT_TX_SIZE_LIMIT + 1
+        tx_C = self.wallet.create_self_transfer(
+            target_weight=non_cpfp_carveout_weight,
+            fee = (mempoolmin_feerate / 1000) * (non_cpfp_carveout_weight // 4) + Decimal('0.000001'),
+            utxo_to_spend=tx_B["new_utxo"],
+            confirmed_only=True
+        )
+
+        assert_raises_rpc_error(-26, "too-long-mempool-chain", node.submitpackage, [tx_B["hex"], tx_C["hex"]])
+
     def test_mid_package_eviction(self):
         node = self.nodes[0]
         self.log.info("Check a package where each parent passes the current mempoolminfee but would cause eviction before package submission terminates")
@@ -324,6 +374,7 @@ class MempoolLimitTest(BitcoinTestFramework):
 
         self.test_mid_package_replacement()
         self.test_mid_package_eviction()
+        self.test_rbf_carveout_disallowed()
 
 
 if __name__ == '__main__':