Fix a false positive on Python 2 for raising-bad-type and tuples.

Raising tuples in the form 'raise (ZeroDivisionError, None)' is not
an error on Python 2, but it is an error on Python 3.

3 files changed, 86 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 5ebb6ca88..bb4410e92 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -22,6 +22,9 @@ ChangeLog for Pylint
     * Fix a false negative with raising-non-exception, when the raise used
       an uninferrable exception context.
 
+    * Fix a false positive on Python 2 for raising-bad-type, when
+      raising tuples in the form 'raise (ZeroDivisionError, None)'.
+
 
 2014-11-23 -- 1.4.0
 
diff --git a/checkers/exceptions.py b/checkers/exceptions.py
index 8a1c98a4a..88a8f225e 100644
--- a/checkers/exceptions.py
+++ b/checkers/exceptions.py
@@ -180,9 +180,28 @@ class ExceptionsChecker(BaseChecker):
                expr.name in ('None', 'True', 'False')) or
               isinstance(expr, (astroid.List, astroid.Dict, astroid.Tuple,
                                 astroid.Module, astroid.Function))):
-            self.add_message('raising-bad-type',
-                             node=node,
-                             args=expr.name)
+            emit = True
+            if not PY3K and isinstance(expr, astroid.Tuple):
+                # On Python 2, using the following is not an error:
+                #    raise (ZeroDivisionError, None)
+                #    raise (ZeroDivisionError, )
+                # What's left to do is to check that the first
+                # argument is indeed an exception.
+                # Verifying the other arguments is not
+                # the scope of this check.
+                first = expr.elts[0]
+                inferred = safe_infer(first)
+                if isinstance(inferred, Instance):
+                    # pylint: disable=protected-access
+                    inferred = inferred._proxied
+                if (inferred is YES or
+                        isinstance(inferred, astroid.Class)
+                        and inherit_from_std_ex(inferred)):
+                    emit = False
+            if emit:
+                self.add_message('raising-bad-type',
+                                 node=node,
+                                 args=expr.name)
         elif ((isinstance(expr, astroid.Name) and expr.name == 'NotImplemented')
               or (isinstance(expr, astroid.CallFunc) and
                   isinstance(expr.func, astroid.Name) and
diff --git a/test/unittest_checker_exceptions.py b/test/unittest_checker_exceptions.py
new file mode 100644
index 000000000..544e1790b
--- /dev/null
+++ b/test/unittest_checker_exceptions.py
@@ -0,0 +1,61 @@
+# Copyright (c) 2003-2015 LOGILAB S.A. (Paris, FRANCE).
+# http://www.logilab.fr/ -- mailto:contact@logilab.fr
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+"""Tests for pylint.checkers.exceptions."""
+
+import sys
+import unittest
+
+from astroid import test_utils
+from pylint.checkers import exceptions
+from pylint.testutils import CheckerTestCase, Message
+
+
+class ExceptionsCheckerTest(CheckerTestCase):
+    """Tests for pylint.checkers.exceptions."""
+
+    CHECKER_CLASS = exceptions.ExceptionsChecker
+
+    # These tests aren't in the functional test suite,
+    # since they will be converted with 2to3 for Python 3
+    # and `raise (Error, ...)` will be converted to
+    # `raise Error(...)`, so it beats the purpose of the test.
+
+    @unittest.skipUnless(sys.version_info[0] == 3,
+                         "The test should emit an error on Python 3.")
+    def test_raising_bad_type_python3(self):
+        node = test_utils.extract_node('raise (ZeroDivisionError, None)  #@')
+        message = Message('raising-bad-type', node=node, args='tuple')
+        with self.assertAddsMessages(message):
+            self.checker.visit_raise(node)
+
+    @unittest.skipUnless(sys.version_info[0] == 2,
+                         "The test is valid only on Python 2.")
+    def test_raising_bad_type_python2(self):
+        nodes = test_utils.extract_node('''
+        raise (ZeroDivisionError, None)  #@
+        from something import something
+        raise (something, None) #@
+
+        raise (4, None) #@
+        ''')
+        with self.assertNoMessages():
+            self.checker.visit_raise(nodes[0])
+        with self.assertNoMessages():
+            self.checker.visit_raise(nodes[1])
+
+        message = Message('raising-bad-type', node=nodes[2], args='tuple')
+        with self.assertAddsMessages(message):
+            self.checker.visit_raise(nodes[2])