Support unary operation, MINUS_PRE, on constants

slither/visitors/expression/constants_folding.py

@@ -1,4 +1,4 @@
-from slither.core.expressions import BinaryOperationType, Literal
+from slither.core.expressions import BinaryOperationType, Literal, UnaryOperationType
 from slither.utils.integer_conversion import convert_string_to_int
 from slither.visitors.expression.expression import ExpressionVisitor
 
@@ -65,7 +65,16 @@ class ConstantFolding(ExpressionVisitor):
             raise NotConstant
 
     def _post_unary_operation(self, expression):
-        raise NotConstant
+        # Case of uint a = -7; uint[-a] arr;
+        if expression.type == UnaryOperationType.MINUS_PRE:
+            expr = expression.expression
+            if not isinstance(expr, Literal):
+                cf = ConstantFolding(expr, self._type)
+                expr = cf.result()
+            assert isinstance(expr, Literal)
+            set_val(expression, int(expr.value))
+        else:
+            raise NotConstant
 
     def _post_literal(self, expression):
         if expression.value.isdigit():

tests/constant_folding_unary.sol

@@ -0,0 +1,7 @@
+contract C {
+    int8 constant a = -7;
+    function f() public pure {
+        uint[-a] memory x;
+        x[0] = 2;
+    }
+}

tests/test_constant_folding_unary.py

@@ -0,0 +1,5 @@
+from slither import Slither
+
+
+def test_constant_folding_unary():
+    Slither("./tests/constant_folding_unary.sol")