Merge #11882: Disable default fallbackfee on mainnet

3f592b8 [QA] add wallet-rbf test (Jonas Schnelli)
8222e05 Disable wallet fallbackfee by default on mainnet (Jonas Schnelli)

Pull request description:

  Removes the default fallback fee on mainnet (but keeps it on testnet/regtest).

  Transactions using the fallbackfee in case the fallback fee has not been set are getting rejected.

Tree-SHA512: e54d2594b7f954e640cc513a18b0bfbe189f15e15bdeed4fe02b7677f939bca1731fef781b073127ffd4ce08a595fb118259b8826cdaa077ff7d5ae9495810db

src/wallet/wallet.cpp

@@ -43,6 +43,7 @@ bool bSpendZeroConfChange = DEFAULT_SPEND_ZEROCONF_CHANGE;
 bool fWalletRbf = DEFAULT_WALLET_RBF;
 OutputType g_address_type = OUTPUT_TYPE_NONE;
 OutputType g_change_type = OUTPUT_TYPE_NONE;
+bool g_wallet_allow_fallback_fee = false; //<! will be defined via chainparams
 
 const char * DEFAULT_WALLET_DAT = "wallet.dat";
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
@@ -2918,6 +2919,11 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                 }
 
                 nFeeNeeded = GetMinimumFee(nBytes, coin_control, ::mempool, ::feeEstimator, &feeCalc);
+                if (feeCalc.reason == FeeReason::FALLBACK && !g_wallet_allow_fallback_fee) {
+                    // eventually allow a fallback fee
+                    strFailReason = _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
+                    return false;
+                }
 
                 // If we made it here and we aren't even able to meet the relay fee on the next pass, give up
                 // because we must be at the maximum allowed fee.