Check for nots too many in comparison expressions

5 files changed, 86 insertions, 2 deletions

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 8317678..f05e053 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -75,4 +75,4 @@ Order doesn't matter (not that much, at least ;)
 
 * Laura Medioni (Logilab, on behalf of the CNES): misplaced-comparison-constant,
   no-classmethod-decorator, no-staticmethod-decorator, too-many-nested-blocks,
-  too-many-boolean-expressions
\ No newline at end of file
+  too-many-boolean-expressions, unneeded-not
\ No newline at end of file
diff --git a/pylint/checkers/base.py b/pylint/checkers/base.py
index 74a1f64..e8a4396 100644
--- a/pylint/checkers/base.py
+++ b/pylint/checkers/base.py
@@ -1843,6 +1843,36 @@ class ElifChecker(BaseTokenChecker):
                                            (len(self._nested_blocks),
                                             self.config.max_nested_blocks))
 
+class NotChecker(_BasicChecker):
+    """checks for nots too many in comparison expressions
+
+    - "not not" should trigger a warning
+    - "not" followed by a comparison should trigger a warning
+    """
+    msgs = {'W0126': ('One not too many in "%s", should be "%s"',
+                      'unneeded-not',
+                      'Used when a boolean expression contains an unneeded '
+                      'negation.'),
+           }
+
+    @check_messages('unneeded-not')
+    def visit_unaryop(self, node):
+        if node.op != 'not':
+            return
+        operand = node.operand
+        if isinstance(operand, astroid.UnaryOp) and operand.op == 'not':
+            self.add_message('unneeded-not', node=node,
+                             args=(node.as_string(),
+                                   operand.operand.as_string()))
+        elif isinstance(operand, astroid.Compare):
+            operator, _ = operand.ops[0]
+            reverse_op = {'<': '>=', '<=': '>', '>': '<=', '>=': '<',
+                          '==': '!=', '!=': '=='}
+            suggestion = node.as_string().replace('not ', '').replace(
+                operator, reverse_op[operator])
+            self.add_message('unneeded-not', node=node,
+                             args=(node.as_string(), suggestion))
+
 
 def register(linter):
     """required method to auto register this checker"""
@@ -1853,5 +1883,6 @@ def register(linter):
     linter.register_checker(PassChecker(linter))
     linter.register_checker(LambdaForComprehensionChecker(linter))
     linter.register_checker(ComparisonChecker(linter))
+    linter.register_checker(NotChecker(linter))
     linter.register_checker(RecommandationChecker(linter))
     linter.register_checker(ElifChecker(linter))
diff --git a/pylint/test/functional/superfluous_parens.py b/pylint/test/functional/superfluous_parens.py
index 417163e..13418cd 100644
--- a/pylint/test/functional/superfluous_parens.py
+++ b/pylint/test/functional/superfluous_parens.py
@@ -1,6 +1,6 @@
 """Test the superfluous-parens warning."""
 from __future__ import print_function
-
+# pylint: disable=unneeded-not
 i = 3
 if (i == 5):  # [superfluous-parens]
     pass
diff --git a/pylint/test/functional/unneeded_not.py b/pylint/test/functional/unneeded_not.py
new file mode 100644
index 0000000..882a238
--- /dev/null
+++ b/pylint/test/functional/unneeded_not.py
@@ -0,0 +1,41 @@
+"""Check exceeding negations in boolean expressions trigger warnings"""
+
+# pylint: disable=singleton-comparison
+
+def unneeded_not():
+    """This is not ok
+    """
+    bool_var = True
+    someint = 2
+    if not not bool_var:  # [unneeded-not]
+        pass
+    if not someint == 1:  # [unneeded-not]
+        pass
+    if not someint != 1:  # [unneeded-not]
+        pass
+    if not someint < 1:  # [unneeded-not]
+        pass
+    if not someint > 1:  # [unneeded-not]
+        pass
+    if not someint <= 1:  # [unneeded-not]
+        pass
+    if not someint >= 1:  # [unneeded-not]
+        pass
+    if not not someint:  # [unneeded-not]
+        pass
+    if not bool_var == True:  # [unneeded-not]
+        pass
+    if not bool_var == False:  # [unneeded-not]
+        pass
+    if not bool_var != True:  # [unneeded-not]
+        pass
+    if not True == True:  # [unneeded-not]
+        pass
+
+
+def not_checked():
+    """This is ok"""
+    bool_var = True
+    someint = 2
+    if not(bool_var == False and someint == 1):
+        pass
diff --git a/pylint/test/functional/unneeded_not.txt b/pylint/test/functional/unneeded_not.txt
new file mode 100644
index 0000000..83100a4
--- /dev/null
+++ b/pylint/test/functional/unneeded_not.txt
@@ -0,0 +1,12 @@
+unneeded-not:10:unneeded_not:One not too many in "not not bool_var", should be "bool_var"
+unneeded-not:12:unneeded_not:One not too many in "not someint == 1", should be "someint != 1"
+unneeded-not:14:unneeded_not:One not too many in "not someint != 1", should be "someint == 1"
+unneeded-not:16:unneeded_not:One not too many in "not someint < 1", should be "someint >= 1"
+unneeded-not:18:unneeded_not:One not too many in "not someint > 1", should be "someint <= 1"
+unneeded-not:20:unneeded_not:One not too many in "not someint <= 1", should be "someint > 1"
+unneeded-not:22:unneeded_not:One not too many in "not someint >= 1", should be "someint < 1"
+unneeded-not:24:unneeded_not:One not too many in "not not someint", should be "someint"
+unneeded-not:26:unneeded_not:One not too many in "not bool_var == True", should be "bool_var != True"
+unneeded-not:28:unneeded_not:One not too many in "not bool_var == False", should be "bool_var != False"
+unneeded-not:30:unneeded_not:One not too many in "not bool_var != True", should be "bool_var == True"
+unneeded-not:32:unneeded_not:One not too many in "not True == True", should be "True != True"