Do not crash when calling unpack_infer. Close #998

ChangeLog

@@ -7,7 +7,9 @@ What's new in Pylint 1.6.3?
 
 Release date: tba
 
+    * Do not crash when inferring uninferable exception types for docparams extension
 
+      Close #998
 
 What's new in Pylint 1.6.2?
 ===========================

pylint/extensions/_check_docs_utils.py

@@ -68,11 +68,14 @@ def possible_exc_types(node):
             handler = handler.parent
 
         if handler and handler.type:
-            excs = astroid.unpack_infer(handler.type)
-            excs = (exc.name for exc in excs if exc is not astroid.YES)
-
-    excs = set(exc for exc in excs if not node_ignores_exception(node, exc))
-    return excs
+            inferred_excs = astroid.unpack_infer(handler.type)
+            excs = (exc.name for exc in inferred_excs
+                    if exc is not astroid.YES)
+
+    try:
+        return set(exc for exc in excs if not node_ignores_exception(node, exc))
+    except astroid.InferenceError:
+        return ()
 
 def docstringify(docstring):
     for docstring_type in [SphinxDocstring, GoogleDocstring, NumpyDocstring]:

pylint/test/extensions/test_check_raise_docs.py

@@ -352,5 +352,40 @@ def my_func(self):
         with self.assertNoMessages():
             self.checker.visit_raise(raise_node)
 
+    def test_no_crash_when_inferring_handlers(self):
+        raise_node = test_utils.extract_node('''
+        import collections
+
+        def test():
+           """raises
+
+           :raise U: pass
+           """
+           try:
+              pass
+           except collections.U as exc:
+              raise #@
+        ''')
+        with self.assertNoMessages():
+            self.checker.visit_raise(raise_node)
+
+    def test_no_crash_when_cant_find_exception(self):
+        raise_node = test_utils.extract_node('''
+        import collections
+
+        def test():
+           """raises
+
+           :raise U: pass
+           """
+           try:
+              pass
+           except U as exc:
+              raise #@
+        ''')
+        with self.assertNoMessages():
+            self.checker.visit_raise(raise_node)
+
+
 if __name__ == '__main__':
     unittest.main()