Don't allow DCA trades to go beyond max order size

closes  #7924

freqtrade/freqtradebot.py

@@ -912,6 +912,7 @@ class FreqtradeBot(LoggingMixin):
             stake_amount=stake_amount,
             min_stake_amount=min_stake_amount,
             max_stake_amount=max_stake_amount,
+            trade_amount=trade.stake_amount if trade else None,
         )
 
         return enter_limit_requested, stake_amount, leverage

freqtrade/optimize/backtesting.py

@@ -769,6 +769,7 @@ class Backtesting:
             stake_amount=stake_amount,
             min_stake_amount=min_stake_amount,
             max_stake_amount=max_stake_amount,
+            trade_amount=trade.stake_amount if trade else None
         )
 
         return propose_rate, stake_amount_val, leverage, min_stake_amount

freqtrade/wallets.py

@@ -291,12 +291,17 @@ class Wallets:
         return self._check_available_stake_amount(stake_amount, available_amount)
 
     def validate_stake_amount(self, pair: str, stake_amount: Optional[float],
-                              min_stake_amount: Optional[float], max_stake_amount: float):
+                              min_stake_amount: Optional[float], max_stake_amount: float,
+                              trade_amount: Optional[float]):
         if not stake_amount:
             logger.debug(f"Stake amount is {stake_amount}, ignoring possible trade for {pair}.")
             return 0
 
         max_stake_amount = min(max_stake_amount, self.get_available_stake_amount())
+        if trade_amount:
+            # if in a trade, then the resulting trade size cannot go beyond the max stake
+            # Otherwise we could no longer exit.
+            max_stake_amount = min(max_stake_amount, max_stake_amount - trade_amount)
 
         if min_stake_amount is not None and min_stake_amount > max_stake_amount:
             if self._log:

tests/test_wallets.py

@@ -180,17 +180,17 @@ def test_get_trade_stake_amount_unlimited_amount(default_conf, ticker, balance_r
     assert result == 0
 
 
-@pytest.mark.parametrize('stake_amount,min_stake,stake_available,max_stake,expected', [
-    (22, 11, 50, 10000, 22),
-    (100, 11, 500, 10000, 100),
-    (1000, 11, 500, 10000, 500),  # Above stake_available
-    (700, 11, 1000, 400, 400),  # Above max_stake, below stake available
-    (20, 15, 10, 10000, 0),  # Minimum stake > stake_available
-    (9, 11, 100, 10000, 11),  # Below min stake
-    (1, 15, 10, 10000, 0),  # Below min stake and min_stake > stake_available
-    (20, 50, 100, 10000, 0),  # Below min stake and stake * 1.3 > min_stake
-    (1000, None, 1000, 10000, 1000),  # No min-stake-amount could be determined
-
+@pytest.mark.parametrize('stake_amount,min_stake,stake_available,max_stake,trade_amount,expected', [
+    (22, 11, 50, 10000, None, 22),
+    (100, 11, 500, 10000, None, 100),
+    (1000, 11, 500, 10000, None, 500),  # Above stake_available
+    (700, 11, 1000, 400, None, 400),  # Above max_stake, below stake available
+    (20, 15, 10, 10000, None, 0),  # Minimum stake > stake_available
+    (9, 11, 100, 10000, None, 11),  # Below min stake
+    (1, 15, 10, 10000, None, 0),  # Below min stake and min_stake > stake_available
+    (20, 50, 100, 10000, None, 0),  # Below min stake and stake * 1.3 > min_stake
+    (1000, None, 1000, 10000, None, 1000),  # No min-stake-amount could be determined
+    (2000, 15, 2000, 3000, 1500, 500),  # Rebuy - resulting in too high stake amount. Adjusting.
 ])
 def test_validate_stake_amount(
     mocker,
@@ -199,13 +199,15 @@ def test_validate_stake_amount(
     min_stake,
     stake_available,
     max_stake,
+    trade_amount,
     expected,
 ):
     freqtrade = get_patched_freqtradebot(mocker, default_conf)
 
     mocker.patch("freqtrade.wallets.Wallets.get_available_stake_amount",
                  return_value=stake_available)
-    res = freqtrade.wallets.validate_stake_amount('XRP/USDT', stake_amount, min_stake, max_stake)
+    res = freqtrade.wallets.validate_stake_amount(
+        'XRP/USDT', stake_amount, min_stake, max_stake, trade_amount)
     assert res == expected