Several improvements in tuples and abi.decode support

abi.decode:
- Better IR output
- Propagate types (fix #529 third cases)
- Correct parsing in abi.decode parameters in case of arrays

Tuples:
- Improve support of tuple singleton (the generated IR was missing an
Unpack operation)

slither/core/expressions/elementary_type_name_expression.py

@@ -15,5 +15,10 @@ class ElementaryTypeNameExpression(Expression):
     def type(self) -> Type:
         return self._type
 
+    @type.setter
+    def type(self, new_type: Type):
+        assert isinstance(new_type, Type)
+        self._type = new_type
+
     def __str__(self):
         return str(self._type)

slither/slithir/convert.py

@@ -803,6 +803,12 @@ def convert_to_solidity_func(ir):
     new_ir.set_node(ir.node)
     if isinstance(call.return_type, list) and len(call.return_type) == 1:
         new_ir.lvalue.set_type(call.return_type[0])
+    elif (isinstance(new_ir.lvalue, TupleVariable) and
+                call == SolidityFunction("abi.decode()") and
+                len(new_ir.arguments) == 2 and
+                isinstance(new_ir.arguments[1], list)):
+        types = [x for x in new_ir.arguments[1]]
+        new_ir.lvalue.set_type(types)
     else:
         new_ir.lvalue.set_type(call.return_type)
     return new_ir

slither/slithir/operations/solidity_call.py

@@ -30,8 +30,17 @@ class SolidityCall(Call, OperationWithLValue):
         return self._type_call
 
     def __str__(self):
-        args = [str(a) for a in self.arguments]
-        return str(self.lvalue) +' = SOLIDITY_CALL {}({})'.format(self.function.full_name, ','.join(args))
-   #     return str(self.lvalue) +' = INTERNALCALL {} (arg {})'.format(self.function,
-   #                                                                   self.nbr_arguments)
-
+        if (self.function == SolidityFunction("abi.decode()") and
+                len(self.arguments) == 2 and
+                isinstance(self.arguments[1], list)):
+            args = str(self.arguments[0]) + '(' + ','.join([str(a) for a in self.arguments[1]]) + ')'
+        else:
+            args = ','.join([str(a) for a in self.arguments])
+
+        lvalue = ''
+        if self.lvalue:
+            if isinstance(self.lvalue.type, (list,)):
+                lvalue = '{}({}) = '.format(self.lvalue, ','.join(str(x) for x in self.lvalue.type))
+            else:
+                lvalue = '{}({}) = '.format(self.lvalue, self.lvalue.type)
+        return lvalue + 'SOLIDITY_CALL {}({})'.format(self.function.full_name, args)

slither/solc_parsing/declarations/function.py

@@ -631,6 +631,8 @@ class FunctionSolc:
                     i = 0
                     new_node = node
                     for variable in variables:
+                        if variable is None:
+                            continue
                         init = inits[i]
                         src = variable["src"]
                         i = i + 1

slither/solc_parsing/expressions/expression_parsing.py

@@ -421,7 +421,6 @@ def parse_expression(expression: Dict, caller_context: CallerContext) -> "Expres
     #    | Expression '?' Expression ':' Expression
     #    | Expression ('=' | '|=' | '^=' | '&=' | '<<=' | '>>=' | '+=' | '-=' | '*=' | '/=' | '%=') Expression
     #    | PrimaryExpression
-
     # The AST naming does not follow the spec
     name = expression[caller_context.get_key()]
     is_compact_ast = caller_context.is_compact_ast
@@ -646,7 +645,12 @@ def parse_expression(expression: Dict, caller_context: CallerContext) -> "Expres
         # if abi.decode is used
         # For example, abi.decode(data, ...(uint[]) )
         if right is None:
-            return parse_expression(left, caller_context)
+            ret = parse_expression(left, caller_context)
+            # Nested array are not yet available in abi.decode
+            if isinstance(ret, ElementaryTypeNameExpression):
+                old_type = ret.type
+                ret.type = ArrayType(old_type, None)
+            return ret
 
         left_expression = parse_expression(left, caller_context)
         right_expression = parse_expression(right, caller_context)

slither/visitors/slithir/expression_to_slithir.py

@@ -5,6 +5,7 @@ from slither.core.expressions import (AssignmentOperationType,
                                       UnaryOperationType, BinaryOperationType)
 from slither.core.solidity_types import ArrayType, ElementaryType
 from slither.core.solidity_types.type import Type
+from slither.core.variables.local_variable_init_from_tuple import LocalVariableInitFromTuple
 from slither.slithir.operations import (Assignment, Binary, BinaryType, Delete,
                                         Index, InitArray, InternalCall, Member,
                                         NewArray, NewContract,
@@ -130,6 +131,14 @@ class ExpressionToSlithIR(ExpressionVisitor):
                         operation.set_expression(expression)
                         self._result.append(operation)
                 set_val(expression, None)
+        # Tuple with only one element. We need to convert the assignment to a Unpack
+        # Ex:
+        # (uint a,,) = g()
+        elif isinstance(left, LocalVariableInitFromTuple) and left.tuple_index:
+            operation = Unpack(left, right, left.tuple_index)
+            operation.set_expression(expression)
+            self._result.append(operation)
+            set_val(expression, None)
         else:
             # Init of array, like
             # uint8[2] var = [1,2];