Fix bugs with dependency tracking

scone/head/dependency_tracking.py

@@ -217,7 +217,7 @@ class DependencyVarProxy:
         else:
             return repr(self)
 
-    def raw_(self) -> Dict[str, Any]:
+    def raw_(self) -> Union[Dict[str, Any], List[Any], int, str, bool]:
         if not self._current_path_prefix:
             raw_dict = self._vars.toplevel()
         else:
@@ -238,6 +238,12 @@ class DependencyVarProxy:
             self._tracker.register_variable(dotted_path, raw_value)
             return raw_value
 
+    def __iter__(self):
+        return iter(self.raw_())
+
+    def __contains__(self, item):
+        return item in self.raw_()
+
 
 class DependencyCache:
     def __init__(self):

scone/head/kitchen.py

@@ -247,7 +247,11 @@ class Kitchen:
         sous_vars = recipe.recipe_context.variables
         vars_to_hash = {}
         for var in prev_book.var_list:
-            vars_to_hash[var] = sous_vars.get_dotted(var)
+            try:
+                vars_to_hash[var] = sous_vars.get_dotted(var)
+            except KeyError:
+                # variable missing
+                return prev_book, False
         my_varhash = hash_dict(vars_to_hash)
         if prev_book.varhash != my_varhash:
             return prev_book, False