[F402] Warn on loop variable shadowing module name

src/fixit/rules/pyflakes/no_shadowing_module_name_in_loop.py

@@ -0,0 +1,122 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from typing import Set, Union
+
+import libcst as cst
+
+from fixit import CstLintRule, InvalidTestCase as Invalid, ValidTestCase as Valid
+
+
+class NoShadowingModuleNameInLoopRule(CstLintRule):
+    """
+    A loop variable name should not shadow an imported module's name.
+
+    Autofix: N/A
+    """
+
+    MESSAGE = "A loop variable name should not shadow an imported module's name."
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.import_names: Set[str] = set()
+
+    def get_import_name(self, node: Union[cst.Import, cst.ImportFrom]) -> None:
+        if isinstance(node.names, cst.ImportStar):
+            return
+        for import_alias in node.names:
+            name = import_alias.asname.name if import_alias.asname is not None else import_alias.name
+            assert isinstance(name, cst.Name)
+            self.import_names.add(name.value)
+
+    def visit_Import(self, node: cst.Import) -> None:
+        self.get_import_name(node)
+
+    def visit_ImportFrom(self, node: cst.ImportFrom) -> None:
+        self.get_import_name(node)
+
+    def visit_For(self, node: cst.For) -> None:
+        assert isinstance(node.target, cst.Name)
+        target = node.target.value
+        if target in self.import_names:
+            self.report(node)
+
+    VALID = [
+        Valid(
+            """
+            import a
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+        Valid(
+            """
+            for i in [1, 2, 3]:
+                print(i)
+
+            import i
+            """
+        ),
+        Valid(
+            """
+            import i as a
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+        Valid(
+            """
+            from i import a
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+        Valid(
+            """
+            from a import i as b
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+    ]
+
+    INVALID = [
+        Invalid(
+            """
+            import i
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+        Invalid(
+            """
+            from a import i
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+        Invalid(
+            """
+            import a as i
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+        Invalid(
+            """
+            from a import b as i
+
+            for i in [1, 2, 3]:
+                print(i)
+            """
+        ),
+    ]