Fix a crash which occurred when old visit methods are encountered

 in plugin modules.

If a plugin uses an old visit method (visit_class for instance), this can lead
to a crash in pylint's base checkers, because the logic in the PylintASTWalker
assumes that all checkers have a visit_class / leave_class method. The
patch fixes this by looking for both names.
Closes issue #711.

3 files changed, 29 insertions, 9 deletions

diff --git a/ChangeLog b/ChangeLog
index e53e79c..f97a547 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,6 +10,9 @@ ChangeLog for Pylint
       emitted when item deletion is tried on an object which doesn't
       have this ability. Closes issue #592.
 
+    * Fix a crash which occurred when old visit methods are encountered
+      in plugin modules. Closes issue #711.
+
     * Added multiple warnings related to imports. 'wrong-import-order'
       is emitted when PEP 8 recommendations regarding imports are not
       respected (that is, standard imports should be followed by third-party
diff --git a/pylint/test/unittest_lint.py b/pylint/test/unittest_lint.py
index 3095108..5877d4c 100644
--- a/pylint/test/unittest_lint.py
+++ b/pylint/test/unittest_lint.py
@@ -33,6 +33,7 @@ from pylint.utils import MSG_STATE_SCOPE_CONFIG, MSG_STATE_SCOPE_MODULE, MSG_STA
 from pylint.testutils import TestReporter
 from pylint.reporters import text, html
 from pylint import checkers
+from pylint.checkers.utils import check_messages
 from pylint import interfaces
 
 if os.name == 'java':
@@ -217,6 +218,22 @@ class PyLinterTC(unittest.TestCase):
         linter.file_state = FileState('toto')
         return linter
 
+    def test_pylint_visit_method_taken_in_account(self):
+        class CustomChecker(checkers.BaseChecker):
+            __implements__ = interfaces.IAstroidChecker
+            name = 'custom'
+            msgs = {'W9999': ('', 'custom', '')}
+
+            @check_messages('custom')
+            def visit_class(self, _):
+               pass
+
+        self.linter.register_checker(CustomChecker(self.linter))
+        self.linter.open()
+        out = six.moves.StringIO()
+        self.linter.set_reporter(text.TextReporter(out))
+        self.linter.check('abc')
+
     def test_enable_message(self):
         linter = self.init_linter()
         self.assertTrue(linter.is_message_enabled('W0101'))
@@ -669,6 +686,6 @@ class MessagesStoreTC(unittest.TestCase):
         self.assertEqual('msg-symbol',
                          self.store.check_message_id('old-symbol').symbol)
 
-
+   
 if __name__ == '__main__':
     unittest.main()
diff --git a/pylint/utils.py b/pylint/utils.py
index 090b0a5..d2bca89 100644
--- a/pylint/utils.py
+++ b/pylint/utils.py
@@ -19,6 +19,7 @@ main pylint class
 from __future__ import print_function
 
 import collections
+import itertools
 import os
 from os.path import dirname, basename, splitext, exists, isdir, join, normpath
 import re
@@ -904,15 +905,14 @@ class PyLintASTWalker(object):
         # Detect if the node is a new name for a deprecated alias.
         # In this case, favour the methods for the deprecated
         # alias if any,  in order to maintain backwards
-        # compatibility. If both of them are present,
-        # only the old ones will be called.
+        # compatibility.
         old_cid = DEPRECATED_ALIASES.get(cid)
         visit_events = ()
         leave_events = ()
 
         if old_cid:
-            visit_events = self.visit_events.get(old_cid)
-            leave_events = self.leave_events.get(old_cid)
+            visit_events = self.visit_events.get(old_cid, ())
+            leave_events = self.leave_events.get(old_cid, ())
             if visit_events or leave_events:
                 msg = ("Implemented method {meth}_{old} instead of {meth}_{new}. "
                        "This will be supported until Pylint 2.0.")
@@ -923,10 +923,10 @@ class PyLintASTWalker(object):
                     warnings.warn(msg.format(meth="leave", old=old_cid, new=cid),
                                   PendingDeprecationWarning)
 
-        if not visit_events:
-            visit_events = self.visit_events.get(cid)
-        if not leave_events:
-            leave_events = self.leave_events.get(cid)
+        visit_events = itertools.chain(visit_events,
+                                       self.visit_events.get(cid, ()))
+        leave_events = itertools.chain(leave_events,
+                                       self.leave_events.get(cid, ()))
 
         if astroid.is_statement:
             self.nbstatements += 1