Catch when make_forecast=True on a calculated item is not allowing th…

…e plug to flow through to the balance item, and throw an indicative error

finstmt/config_manage/base.py

@@ -83,7 +83,7 @@ def eqs_involving(self, item_key: str, include_self_eq: bool = False) -> List[Eq
 
         return eqs
 
-    def _calculated_item_determinant_keys(self, item_key: str) -> List[str]:
+    def _calculated_item_determinant_keys(self, item_key: str, for_forecast: bool = True) -> List[str]:
         determinant_keys: List[str] = []
         to_process_keys: List[str] = [item_key]
         i = -1
@@ -99,11 +99,21 @@ def _calculated_item_determinant_keys(self, item_key: str) -> List[str]:
                 new_keys = [
                     key for key in all_eq_keys if key != process_key and key not in to_process_keys + determinant_keys
                 ]
+                if for_forecast:
+                    accepted_keys: List[str] = []
+                    for key in new_keys:
+                        if self.get(key).forecast_config.make_forecast:
+                            # As forecast is being made for this item, it is not calculated,
+                            # and so shouldn't be processed. It should still be added to determinants
+                            determinant_keys.append(key)
+                            continue
+                        accepted_keys.append(key)
+                    new_keys = accepted_keys
                 to_process_keys.extend(new_keys)
         return determinant_keys
 
-    def item_determinant_keys(self, item_key: str, include_pct_of: bool = True) -> List[str]:
-        determinant_keys = self._calculated_item_determinant_keys(item_key)
+    def item_determinant_keys(self, item_key: str, include_pct_of: bool = True, for_forecast: bool = True) -> List[str]:
+        determinant_keys = self._calculated_item_determinant_keys(item_key, for_forecast=for_forecast)
         if include_pct_of:
             for item in self.items:
                 # TODO: multiple passes through determinants may be necessary for complicated pct_of structures

finstmt/resolver/forecast.py

@@ -415,11 +415,27 @@ def _adjust_x0_to_initial_balance_guess(
                     plug_key = plug1
 
                 if plug_key is None:
-                    raise InvalidBalancePlugsException(
+                    normally_calculated_but_not_keys: List[str] = []
+                    for item in config.items:
+                        if item.expr_str is not None and item.forecast_config.make_forecast == True:
+                            normally_calculated_but_not_keys.append(item.key)
+                    message = (
                         f'Trying to balance {adjust_side} but no plug affects it. One of the following '
                         f'items must have forecast_config.plug = True so that it can be balanced: '
-                        f'{config.item_determinant_keys(adjust_side)}. Current plugs: {plug_keys}'
+                        f'{config.item_determinant_keys(adjust_side)}. Current plugs: {plug_keys}. '
                     )
+                    if normally_calculated_but_not_keys:
+                        message += (
+                            f'If you expected one of the plugs to affect {adjust_side} but it is not listed '
+                            f'in the possible items, it may be that make_forecast has been set to True for an '
+                            f'item which would normally be calculated from your plug, but as make_forecast is True '
+                            f'it forecasts it rather than calculating and it cannot flow through. Possible items '
+                            f'which are normally calculated but are instead being forecasted due to the config: '
+                            f'{normally_calculated_but_not_keys}. Either change the plug to be that same item '
+                            f'which is normally calculated but instead is forecasted, or set make_forecast=False '
+                            f'for that item.'
+                        )
+                    raise InvalidBalancePlugsException(message)
 
                 # Determine index of array to increment. Array has structure of num plugs * num periods, with
                 # plugs in order of plug_keys and periods in order within the plugs