Add new extension for detecting integer comparisons against zero (#1243)

2 files changed, 84 insertions, 0 deletions

diff --git a/pylint/test/extensions/data/compare_to_zero.py b/pylint/test/extensions/data/compare_to_zero.py
new file mode 100644
index 000000000..06f3475dc
--- /dev/null
+++ b/pylint/test/extensions/data/compare_to_zero.py
@@ -0,0 +1,28 @@
+# pylint: disable=literal-comparison,missing-docstring,misplaced-comparison-constant
+
+X = 123
+Y = len('test')
+
+if X is 0:  # [compare-to-zero]
+    pass
+
+if Y is not 0:  # [compare-to-zero]
+    pass
+
+if X == 0:  # [compare-to-zero]
+    pass
+
+if Y != 0:  # [compare-to-zero]
+    pass
+
+if X > 0:  # [compare-to-zero]
+    pass
+
+if X < 0: #  this is allowed
+    pass
+
+if 0 < X:  # [compare-to-zero]
+    pass
+
+if 0 > X: #  this is allowed
+    pass
diff --git a/pylint/test/extensions/test_comparetozero.py b/pylint/test/extensions/test_comparetozero.py
new file mode 100644
index 000000000..8ae795593
--- /dev/null
+++ b/pylint/test/extensions/test_comparetozero.py
@@ -0,0 +1,56 @@
+# Copyright (c) 2016 Alexander Todorov <atodorov@MrSenko.com>
+
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint/blob/master/COPYING
+
+"""Tests for the pylint checker in :mod:`pylint.extensions.emptystring
+"""
+
+import os
+import os.path as osp
+import unittest
+
+from pylint import checkers
+from pylint.extensions.comparetozero import CompareToZeroChecker
+from pylint.lint import PyLinter
+from pylint.reporters import BaseReporter
+
+
+class CompareToZeroTestReporter(BaseReporter):
+
+    def handle_message(self, msg):
+        self.messages.append(msg)
+
+    def on_set_current_module(self, module, filepath):
+        self.messages = []
+
+
+class CompareToZeroUsedTC(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        cls._linter = PyLinter()
+        cls._linter.set_reporter(CompareToZeroTestReporter())
+        checkers.initialize(cls._linter)
+        cls._linter.register_checker(CompareToZeroChecker(cls._linter))
+        cls._linter.disable('I')
+
+    def test_comparetozero_message(self):
+        elif_test = osp.join(osp.dirname(osp.abspath(__file__)), 'data',
+                             'compare_to_zero.py')
+        self._linter.check([elif_test])
+        msgs = self._linter.reporter.messages
+        self.assertEqual(len(msgs), 6)
+        for msg in msgs:
+            self.assertEqual(msg.symbol, 'compare-to-zero')
+            self.assertEqual(msg.msg, 'Avoid comparisons to zero')
+        self.assertEqual(msgs[0].line, 6)
+        self.assertEqual(msgs[1].line, 9)
+        self.assertEqual(msgs[2].line, 12)
+        self.assertEqual(msgs[3].line, 15)
+        self.assertEqual(msgs[4].line, 18)
+        self.assertEqual(msgs[5].line, 24)
+
+
+if __name__ == '__main__':
+    unittest.main()