Fix object_len infererence without context causing RecursionError (#660)

The dropped context was causing RecursionErrors
in self referential assignment

Example:

    self.a = len(self.a)

There is a bigger problem of inference not understanding control flow
that this fix does not solve.

Close pylint-dev/pylint#2736
Close pylint-dev/pylint#2734
Close pylint-dev/pylint#2740

ChangeLog

@@ -25,6 +25,13 @@ Release Date: TBA
   Close PyCQA/pylint#2791
 
 
+* Fix recursion error involving ``len`` and self referential attributes
+
+  Close PyCQA/pylint#2736
+  Close PyCQA/pylint#2734
+  Close PyCQA/pylint#2740
+
+
 What's New in astroid 2.2.0?
 ============================
 Release Date: 2019-02-27

astroid/brain/brain_builtin_inference.py

@@ -679,7 +679,7 @@ def infer_len(node, context=None):
         )
     [argument_node] = call.positional_arguments
     try:
-        return nodes.Const(helpers.object_len(argument_node))
+        return nodes.Const(helpers.object_len(argument_node, context=context))
     except (AstroidTypeError, InferenceError) as exc:
         raise UseInferenceDefault(str(exc)) from exc
 

astroid/tests/unittest_brain.py

@@ -1652,6 +1652,26 @@ def test_len_builtin_inference_attribute_error_str(self):
         except astroid.InferenceError:
             pass
 
+    def test_len_builtin_inference_recursion_error_self_referential_attribute(self):
+        """Make sure len calls do not trigger
+        recursion errors for self referential assignment
+
+        See https://github.com/PyCQA/pylint/issues/2734
+        """
+        code = """
+        class Data:
+            def __init__(self):
+                self.shape = []
+
+        data = Data()
+        data.shape = len(data.shape)
+        data.shape #@
+        """
+        try:
+            astroid.extract_node(code).inferred()
+        except RecursionError:
+            pytest.fail("Inference call should not trigger a recursion error")
+
 
 def test_infer_str():
     ast_nodes = astroid.extract_node(