Unused variable: Check for array length expressions (fix #167)

slither/detectors/variables/unused_state_variables.py

@@ -3,6 +3,9 @@
 """
 
 from slither.detectors.abstract_detector import AbstractDetector, DetectorClassification
+from slither.core.solidity_types import ArrayType
+from slither.visitors.expression.export_values import ExportValues
+from slither.core.variables.state_variable import StateVariable
 
 class UnusedStateVars(AbstractDetector):
     """
@@ -26,10 +29,21 @@ def detect_unused(self, contract):
         if contract.is_signature_only():
             return None
         # Get all the variables read in all the functions and modifiers
+
+        all_functions = (contract.all_functions_called + contract.modifiers)
         variables_used = [x.state_variables_read + x.state_variables_written for x in
-                          (contract.all_functions_called + contract.modifiers)]
+                          all_functions]
+
+        array_candidates = [x.variables for x in all_functions]
+        array_candidates = [i for sl in array_candidates for i in sl] + contract.state_variables
+        array_candidates = [x.type.length for x in array_candidates if isinstance(x.type, ArrayType) and x.type.length]
+        array_candidates = [ExportValues(x).result() for x in array_candidates]
+        array_candidates = [i for sl in array_candidates for i in sl]
+        array_candidates = [v for v in array_candidates if isinstance(v, StateVariable)]
+
         # Flat list
         variables_used = [item for sublist in variables_used for item in sublist]
+        variables_used = list(set(variables_used + array_candidates))
         # Return the variables unused that are not public
         return [x for x in contract.variables if
                 x not in variables_used and x.visibility != 'public']