Support partially cancelled orders for fee calculation

freqtrade/exchange/exchange.py

@@ -1095,7 +1095,8 @@ class Exchange:
         # Calculate fee based on order details
         if fee_curr in self.get_pair_base_currency(order['symbol']):
             # Base currency - divide by amount
-            return round(order['fee']['cost'] / order['amount'], 8)
+            return round(
+                order['fee']['cost'] / safe_value_fallback(order, order, 'filled', 'amount'), 8)
         elif fee_curr in self.get_pair_quote_currency(order['symbol']):
             # Quote currency - divide by cost
             return round(order['fee']['cost'] / order['cost'], 8)

freqtrade/freqtradebot.py

@@ -1144,8 +1144,6 @@ class FreqtradeBot:
                 if not isclose(order['amount'], new_amount, abs_tol=constants.MATH_CLOSE_PREC):
                     order['amount'] = new_amount
                     order.pop('filled', None)
-                    # Fee was applied, so set to 0
-                    trade.fee_open = 0
                     trade.recalc_open_trade_price()
             except DependencyException as exception:
                 logger.warning("Could not update trade amount: %s", exception)

freqtrade/persistence.py

@@ -377,7 +377,7 @@ class Trade(_DECL_BASE):
         )
 
     def update_fee(self, fee_cost: float, fee_currency: Optional[str], fee_rate: Optional[float],
-                   side: str) -> None:
+                   side) -> None:
         """
         Update Fee parameters. Only acts once per side
         """