Fix an inference for trying to unpack Uninferable value in context manager (#429)

Closes PyCQA/pylint#1463

3 files changed, 23 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index a1deca0a..5146d4e3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,8 @@ TBD -- 1.5.3
     - https://bitbucket.org/ambv/singledispatch/issues/8/inconsistent-hierarchy-with-enum
     - https://bitbucket.org/stoneleaf/enum34/commits/da50803651ab644e6fce66ebc85562f1117c344b
 
+    * Do not raise an exception when uninferable value is unpacked in ``with`` statement.
+
     * Lock objects from ``threading`` module are now correctly recognised
       as context managers.
 
diff --git a/astroid/protocols.py b/astroid/protocols.py
index c3abc819..f19a9f41 100644
--- a/astroid/protocols.py
+++ b/astroid/protocols.py
@@ -514,6 +514,11 @@ def with_assigned_stmts(self, node=None, context=None, asspath=None):
                         'Tried to infer a nonexistent target with index {index} '
                         'in {node!r}.', node=self, targets=node,
                         assign_path=asspath, context=context))
+                except TypeError:
+                    util.reraise(exceptions.InferenceError(
+                        'Tried to unpack an non-iterable value '
+                        'in {node!r}.', node=self, targets=node,
+                        assign_path=asspath, context=context))
             yield obj
     # Explicit StopIteration to return error information, see comment
     # in raise_if_nothing_inferred.
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index d1ffc899..9a12e322 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -2098,6 +2098,22 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ''')
         self.assertRaises(InferenceError, next, module['a'].infer())
 
+    def test_inferring_context_manager_unpacking_inference_error(self):
+        # https://github.com/PyCQA/pylint/issues/1463
+        module = parse('''
+        import contextlib
+
+        @contextlib.contextmanager
+        def _select_source(a=None):
+            with _select_source() as result:
+                yield result
+
+        result = _select_source()
+        with result as (a, b, c):
+            pass
+        ''')
+        self.assertRaises(InferenceError, next, module['a'].infer())
+
     def test_inferring_with_contextlib_contextmanager_failures(self):
         module = parse('''
         from contextlib import contextmanager