Add B015: Pointless comparison.

README.rst

@@ -117,6 +117,9 @@ instead of ``except (SomeError,):``.
 **B014**: Redundant exception types in ``except (Exception, TypeError):``.
 Write ``except Exception:``, which catches exactly the same exceptions.
 
+**B015**: Pointless comparison. This comparison does nothing but
+wastes CPU instructions. Remove it.
+
 
 Python 3 compatibility warnings
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

bugbear.py

@@ -1,17 +1,16 @@
 import ast
 import builtins
+import itertools
+import logging
+import re
 from collections import namedtuple
 from contextlib import suppress
 from functools import lru_cache, partial
-import itertools
 from keyword import iskeyword
-import logging
-import re
 
 import attr
 import pycodestyle
 
-
 __version__ = "20.1.4"
 
 LOG = logging.getLogger("flake8.bugbear")
@@ -300,6 +299,9 @@ def visit_Try(self, node):
         self.check_for_b012(node)
         self.generic_visit(node)
 
+    def visit_Compare(self, node):
+        self.check_for_b015(node)
+
     def compose_call_path(self, node):
         if isinstance(node, ast.Attribute):
             yield from self.compose_call_path(node.value)
@@ -371,6 +373,10 @@ def _loop(node, bad_node_types):
         for child in node.finalbody:
             _loop(child, (ast.Return, ast.Continue, ast.Break))
 
+    def check_for_b015(self, node):
+        if isinstance(self.node_stack[-2], ast.Expr):
+            self.errors.append(B015(node.lineno, node.col_offset))
+
     def walk_function_body(self, node):
         def _loop(parent, node):
             if isinstance(node, (ast.AsyncFunctionDef, ast.FunctionDef)):
@@ -658,6 +664,12 @@ def visit(self, node):
         "select.error",
     }
 }
+B015 = Error(
+    message=(
+        "B015 Pointless comparison. This comparison does nothing but wastes "
+        "CPU instructions. Remove it."
+    )
+)
 
 # Those could be false positives but it's more dangerous to let them slip
 # through if they're not.

tests/b015.py

@@ -0,0 +1,29 @@
+"""
+Should emit:
+B015 - on lines 8, 12, 22, 29
+"""
+
+assert 1 == 1
+
+1 == 1
+
+assert 1 in (1, 2)
+
+1 in (1, 2)
+
+
+if 1 == 2:
+    pass
+
+
+def test():
+    assert 1 in (1, 2)
+
+    1 in (1, 2)
+
+
+data = [x for x in [1, 2, 3] if x in (1, 2)]
+
+
+class TestClass:
+    1 == 1

tests/test_bugbear.py

@@ -24,6 +24,7 @@
     B012,
     B013,
     B014,
+    B015,
     B301,
     B302,
     B303,
@@ -182,6 +183,13 @@ def test_b014(self):
         )
         self.assertEqual(errors, expected)
 
+    def test_b015(self):
+        filename = Path(__file__).absolute().parent / "b015.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        expected = self.errors(B015(8, 0), B015(12, 0), B015(22, 4), B015(29, 4))
+        self.assertEqual(errors, expected)
+
     def test_b301_b302_b305(self):
         filename = Path(__file__).absolute().parent / "b301_b302_b305.py"
         bbc = BugBearChecker(filename=str(filename))