Partial fix for vyperlang#590. Adds check for a minimum of one return…

… statement.

viper/parser/parser.py

@@ -275,13 +275,18 @@ def __init__(self, vars=None, globals=None, sigs=None, forvars=None, return_type
         self.origcode = origcode
         # In Loop status. Whether body is currently evaluating within a for-loop or not.
         self.in_for_loop = set()
+        # Count returns in function
+        self.function_return_count = 0
 
     def set_in_for_loop(self, name_of_list):
         self.in_for_loop.add(name_of_list)
 
     def remove_in_for_loop(self, name_of_list):
         self.in_for_loop.remove(name_of_list)
 
+    def increment_return_counter(self):
+        self.function_return_count += 1
+
     # Add a new variable
     def new_variable(self, name, typ):
         if not is_varname_valid(name):
@@ -470,6 +475,13 @@ def parse_func(code, _globals, sigs, origcode, _vars=None):
                                   ['eq', ['mload', 0], method_id_node],
                                   ['seq'] + clampers + [parse_body(c, context) for c in code.body] + ['stop']
                                ], typ=None, pos=getpos(code))
+
+    # Check for at leasts one return statement if necessary.
+    if context.return_type and context.function_return_count == 0:
+        raise StructureException(
+            "Missing return statement in function '%s' " % sig.name, code
+        )
+
     o.context = context
     o.total_gas = o.gas + calc_mem_gas(o.context.next_mem)
     o.func_name = sig.name

viper/parser/stmt.py

@@ -320,6 +320,7 @@ def parse_return(self):
         if not self.stmt.value:
             raise TypeMismatchException("Expecting to return a value", self.stmt)
         sub = Expr(self.stmt.value, self.context).lll_node
+        self.context.increment_return_counter()
         # Returning a value (most common case)
         if isinstance(sub.typ, BaseType):
             if not isinstance(self.context.return_type, BaseType):