Add unpopulated option to additional components qty multiplier

docs/syntax.md

@@ -408,6 +408,7 @@ Parts can be added to a connector or cable in the section `<additional-component
                   # when used in a connector:
                   # pincount         number of pins of connector
                   # populated        number of populated positions in a connector
+                  # unpopulated      number of unpopulated positions
                   # when used in a cable:
                   # wirecount        number of wires of cable/bundle
                   # terminations     number of terminations on a cable/bundle

src/wireviz/DataClasses.py

@@ -18,7 +18,7 @@ MultilineHypertext = (
 Designator = PlainText  # Case insensitive unique name of connector or cable
 
 # Literal type aliases below are commented to avoid requiring python 3.8
-ConnectorMultiplier = PlainText  # = Literal['pincount', 'populated']
+ConnectorMultiplier = PlainText  # = Literal['pincount', 'populated', 'unpopulated']
 CableMultiplier = (
     PlainText  # = Literal['wirecount', 'terminations', 'length', 'total_length']
 )
@@ -232,6 +232,8 @@ class Connector:
             return self.pincount
         elif qty_multiplier == "populated":
             return sum(self.visible_pins.values())
+        elif qty_multiplier == 'unpopulated':
+            return (self.pincount - sum(self.visible_pins.values()))
         else:
             raise ValueError(
                 f"invalid qty multiplier parameter for connector {qty_multiplier}"