Implement most pessimistic handling of trailing stoploss.

freqtrade/optimize/backtesting.py

@@ -225,6 +225,22 @@ class Backtesting:
                 # sell at open price.
                 return sell_row[OPEN_IDX]
 
+            # Special case: trailing triggers within same candle as trade opened. Assume most
+            # pessimistic price movement, which is moving just enough to arm stoploss and
+            # immediately going down to stop price.
+            if sell.sell_type == SellType.TRAILING_STOP_LOSS and trade_dur == 0 and \
+               self.strategy.trailing_stop_positive:
+                if self.strategy.trailing_only_offset_is_reached:
+                    # Worst case: price reaches stop_positive_offset and dives down.
+                    stop_rate = sell_row[OPEN_IDX] * \
+                                (1 + abs(self.strategy.trailing_stop_positive_offset) -
+                                 abs(self.strategy.trailing_stop_positive))
+                else:
+                    # Worst case: price ticks tiny bit above open and dives down.
+                    stop_rate = sell_row[OPEN_IDX] * (1 - abs(self.strategy.trailing_stop_positive))
+                    assert stop_rate < sell_row[HIGH_IDX]
+                return stop_rate
+
             # Set close_rate to stoploss
             return trade.stop_loss
         elif sell.sell_type == (SellType.ROI):

freqtrade/strategy/interface.py

@@ -610,7 +610,7 @@ class IStrategy(ABC, HyperStrategyMixin):
         # Initiate stoploss with open_rate. Does nothing if stoploss is already set.
         trade.adjust_stop_loss(trade.open_rate, stop_loss_value, initial=True)
 
-        if self.use_custom_stoploss:
+        if self.use_custom_stoploss and trade.stop_loss < current_rate:
             stop_loss_value = strategy_safe_wrapper(self.custom_stoploss, default_retval=None
                                                     )(pair=trade.pair, trade=trade,
                                                       current_time=current_time,
@@ -623,7 +623,7 @@ class IStrategy(ABC, HyperStrategyMixin):
             else:
                 logger.warning("CustomStoploss function did not return valid stoploss")
 
-        if self.trailing_stop:
+        if self.trailing_stop and trade.stop_loss < current_rate:
             # trailing stoploss handling
             sl_offset = self.trailing_stop_positive_offset