fix function execution mutable list issue

jedi/evaluate/compiled/fake/_functools.pym

@@ -5,5 +5,5 @@ class partial():
         self.__keywords = keywords
 
     def __call__(self, *args, **kwargs):
-        # I know this doesn't work in Python, but Jedi can this ;-)
+        # I know this doesn't work in Python, but in Jedi it does ;-)
         return self.__func(*self.__args, *args, **self.keywords, **kwargs)

jedi/evaluate/representation.py

@@ -444,7 +444,7 @@ class FunctionExecution(Executable):
         if func.is_generator and not evaluate_generator:
             return [iterable.Generator(self._evaluator, func, self.var_args)]
         else:
-            stmts = docstrings.find_return_types(self._evaluator, func)
+            stmts = list(docstrings.find_return_types(self._evaluator, func))
             for r in self.returns:
                 if r is not None:
                     stmts += self._evaluator.eval_statement(r)

test/test_evaluate/test_representation.py

@@ -0,0 +1,20 @@
+from jedi import Script
+
+
+def test_function_execution():
+    """
+    We've been having an issue of a mutable list that was changed inside the
+    function execution. Test if an execution always returns the same result.
+    """
+
+    s = """
+    def x():
+        return str()
+    x"""
+    d = Script(s).goto_definitions()[0]
+    # Now just use the internals of the result (easiest way to get a fully
+    # usable function).
+    func, evaluator = d._definition, d._evaluator
+    # Should return the same result both times.
+    assert len(evaluator.execute(func)) == 1
+    assert len(evaluator.execute(func)) == 1