Merge remote-tracking branch 'upstream/main' into fix/b005-message

# Conflicts:
#	README.rst

Author: LuisFigueroaG

README.rst

@@ -316,6 +316,15 @@ There is no additional safety in using ``delattr`` if you know the attribute nam
 
 **B044**: `assert <generator_expression>` is always true. Did you forget `all()`?
 
+.. _B045:
+
+**B045**: A loop control variable overrides a variable in an enclosing loop.
+Python loops do not create a new scope, so the inner loop overwrites the outer
+loop's value. Use different names for nested ``for`` and ``async for`` targets.
+Names beginning with an underscore are ignored to allow intentional discards.
+Separate function/class/comprehension scopes and a loop's ``else`` suite do not
+count as active enclosing loops.
+
 
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~
@@ -518,6 +527,8 @@ Change Log
 UNRELEASED
 ~~~~~~~~~~
 
+* B045: detect reuse of an enclosing loop's control variable in a nested loop
+  in the same scope (#360).
 * B005: say in the message that only strings with repeated characters are
   reported, since ``.strip("abc")`` style character sets are fine (#91)
 * B031: only treat a bare ``groupby()`` call as ``itertools.groupby`` when the

bugbear.py

@@ -810,6 +810,7 @@ def visit_Assign(self, node: ast.Assign) -> None:
         self.generic_visit(node)
 
     def visit_For(self, node: ast.For) -> None:
+        self.check_for_b045(node)
         self.check_for_b007(node)
         self.check_for_b020(node)
         self.check_for_b023(node)
@@ -819,6 +820,7 @@ def visit_For(self, node: ast.For) -> None:
         self.generic_visit(node)
 
     def visit_AsyncFor(self, node: ast.AsyncFor) -> None:
+        self.check_for_b045(node)
         self.check_for_b023(node)
         self.generic_visit(node)
 
@@ -2598,6 +2600,17 @@ def is_exception(s: str):
                 return
         # no `def __init__` found, which is fine
 
+    def check_for_b045(self, node: ast.For | ast.AsyncFor) -> None:
+        # The stack belongs to the current scope: nested functions, classes,
+        # and comprehensions cannot overwrite an enclosing loop's binding.
+        outer_names = set()
+        for ancestor, child in zip(self.node_stack, self.node_stack[1:], strict=False):
+            if isinstance(ancestor, (ast.For, ast.AsyncFor)) and child in ancestor.body:
+                outer_names.update(names_from_assignments(ancestor.target))
+        for name in names_from_assignments(node.target):
+            if name in outer_names and not name.startswith("_"):
+                self.add_error("B045", node.target, name)
+
     def check_for_b044(self, node: ast.Assert) -> None:
         if isinstance(node.test, ast.GeneratorExp):
             self.add_error("B044", node)
@@ -3400,6 +3413,12 @@ def __call__(self, lineno: int, col: int, vars: tuple[object, ...] = ()) -> erro
             "B044 `assert <generator_expression>` is always true. Did you forget `all()`?"
         )
     ),
+    "B045": Error(
+        message=(
+            "B045 Loop control variable {} overrides a variable in an enclosing loop. "
+            "Use a different name for the inner loop variable."
+        )
+    ),
     # Warnings disabled by default.
     "B901": Error(
         message=(

tests/eval_files/b045.py

@@ -0,0 +1,11 @@
+for i in xs:
+    for i in ys:  # B045: 8, "i"
+        print(i)
+    print(i)
+
+
+async def check():
+    async for value in xs:
+        async for value in ys:  # B045: 18, "value"
+            print(value)
+        print(value)

tests/test_bugbear.py

@@ -102,6 +102,66 @@ def _parse_eval_file(test: str, content: str) -> tuple[list[error], Namespace |
     return expected, options
 
 
+@pytest.mark.parametrize(
+    "source, expected",
+    [
+        ("for i in xs:\n    for i in ys:\n        print(i)\n    print(i)", ["i"]),
+        (
+            "for i in xs:\n    for j in ys:\n        for i in zs:\n            print(i)",
+            ["i"],
+        ),
+        ("for i, j in xs:\n    for j, i in ys:\n        print(i, j)", ["j", "i"]),
+        ("for i in xs:\n    for first, (*i,) in ys:\n        print(i)", ["i"]),
+        (
+            "for i in xs:\n    if flag:\n        for i in ys:\n            print(i)",
+            ["i"],
+        ),
+        (
+            "async def f():\n    async for i in xs:\n"
+            "        for i in ys:\n            print(i)",
+            ["i"],
+        ),
+        (
+            "async def f():\n    for i in xs:\n"
+            "        async for i in ys:\n            print(i)",
+            ["i"],
+        ),
+        (
+            "for i in xs:\n    for i in ys:\n        for i in zs:\n            print(i)",
+            ["i", "i"],
+        ),
+        ("for i in xs:\n    for j in ys:\n        print(i, j)", []),
+        ("for i in xs:\n    print(i)\nfor i in ys:\n    print(i)", []),
+        ("for _ in xs:\n    for _ in ys:\n        pass", []),
+        ("for _unused in xs:\n    for _unused in ys:\n        pass", []),
+        ("for obj in xs:\n    for obj.attr in ys:\n        pass", []),
+        ("for i in xs:\n    for values[i] in ys:\n        pass", []),
+        ("for i in xs:\n    for values[[i for i in zs][0]] in ys:\n        pass", []),
+        ("for values[[i for i in zs][0]] in xs:\n    for i in ys:\n        pass", []),
+        ("for obj.attr in xs:\n    for obj in ys:\n        pass", []),
+        ("for i in xs:\n    values = [i for i in ys]", []),
+        ("for i in xs:\n    def f():\n        for i in ys:\n            print(i)", []),
+        (
+            "for i in xs:\n    async def f():\n"
+            "        async for i in ys:\n            print(i)",
+            [],
+        ),
+        ("for i in xs:\n    class C:\n        for i in ys:\n            print(i)", []),
+        ("for i in xs:\n    print(i)\nelse:\n    for i in ys:\n        print(i)", []),
+        (
+            "for i in xs:\n    for j in ys:\n        pass\n"
+            "    else:\n        for i in zs:\n            print(i)",
+            ["i"],
+        ),
+    ],
+)
+def test_nested_loop_bindings(source, expected):
+    visitor = BugBearVisitor(filename="example.py", lines=source.splitlines())
+    visitor.visit(ast.parse(source))
+    errors = [error for error in visitor.errors if error.message.startswith("B045")]
+    assert [error.vars[0] for error in errors] == expected
+
+
 class BugbearTestCase(unittest.TestCase):
     maxDiff = None