feat(b038): Change B038 to B909 and make it optional (#456)

B038 lead to some false positives that stem from methods defined in the
standard library that have the same name as mutating functions for
container types like lists and dicts.
Thus we decided to make this rule optional.
See #455 for the related
discussion.

bugbear.py

@@ -524,7 +524,7 @@ def visit_For(self, node):
         self.check_for_b020(node)
         self.check_for_b023(node)
         self.check_for_b031(node)
-        self.check_for_b038(node)
+        self.check_for_b909(node)
         self.generic_visit(node)
 
     def visit_AsyncFor(self, node):
@@ -1574,17 +1574,17 @@ def check(num_args, param_name):
         elif node.func.attr == "split":
             check(2, "maxsplit")
 
-    def check_for_b038(self, node: ast.For):
+    def check_for_b909(self, node: ast.For):
         if isinstance(node.iter, ast.Name):
             name = _to_name_str(node.iter)
         elif isinstance(node.iter, ast.Attribute):
             name = _to_name_str(node.iter)
         else:
             return
-        checker = B038Checker(name)
+        checker = B909Checker(name)
         checker.visit(node.body)
         for mutation in checker.mutations:
-            self.errors.append(B038(mutation.lineno, mutation.col_offset))
+            self.errors.append(B909(mutation.lineno, mutation.col_offset))
 
 
 def compose_call_path(node):
@@ -1597,7 +1597,7 @@ def compose_call_path(node):
         yield node.id
 
 
-class B038Checker(ast.NodeVisitor):
+class B909Checker(ast.NodeVisitor):
     # https://docs.python.org/3/library/stdtypes.html#mutable-sequence-types
     MUTATING_FUNCTIONS = (
         "append",
@@ -2146,12 +2146,22 @@ def visit_Lambda(self, node):
         " statement."
     )
 )
-
-B950 = Error(message="B950 line too long ({} > {} characters)")
-
-B038 = Error(
+B909 = Error(
     message=(
-        "B038 editing a loop's mutable iterable often leads to unexpected results/bugs"
+        "B909 editing a loop's mutable iterable often leads to unexpected results/bugs"
     )
 )
-disabled_by_default = ["B901", "B902", "B903", "B904", "B905", "B906", "B908", "B950"]
+B950 = Error(message="B950 line too long ({} > {} characters)")
+
+
+disabled_by_default = [
+    "B901",
+    "B902",
+    "B903",
+    "B904",
+    "B905",
+    "B906",
+    "B908",
+    "B909",
+    "B950",
+]

tests/test_bugbear.py

@@ -46,7 +46,6 @@
     B035,
     B036,
     B037,
-    B038,
     B901,
     B902,
     B903,
@@ -55,6 +54,7 @@
     B906,
     B907,
     B908,
+    B909,
     B950,
     BugBearChecker,
     BugBearVisitor,
@@ -969,27 +969,27 @@ def test_selfclean_test_bugbear(self):
         self.assertEqual(proc.stdout, b"")
         self.assertEqual(proc.stderr, b"")
 
-    def test_b038(self):
-        filename = Path(__file__).absolute().parent / "b038.py"
-        mock_options = Namespace(select=[], extend_select=["B038"])
+    def test_b909(self):
+        filename = Path(__file__).absolute().parent / "b909.py"
+        mock_options = Namespace(select=[], extend_select=["B909"])
         bbc = BugBearChecker(filename=str(filename), options=mock_options)
         errors = list(bbc.run())
         print(errors)
         expected = [
-            B038(11, 8),
-            B038(26, 8),
-            B038(27, 8),
-            B038(41, 8),
-            B038(47, 8),
-            B038(56, 8),
-            B038(57, 8),
-            B038(58, 8),
-            B038(59, 8),
-            B038(60, 8),
-            B038(61, 8),
-            B038(62, 8),
-            B038(63, 8),
-            B038(74, 8),
+            B909(11, 8),
+            B909(26, 8),
+            B909(27, 8),
+            B909(41, 8),
+            B909(47, 8),
+            B909(56, 8),
+            B909(57, 8),
+            B909(58, 8),
+            B909(59, 8),
+            B909(60, 8),
+            B909(61, 8),
+            B909(62, 8),
+            B909(63, 8),
+            B909(74, 8),
         ]
         self.assertEqual(errors, self.errors(*expected))