Remove F821 monkey patch (#530)

Author: srittau

.flake8

@@ -30,4 +30,4 @@ max-complexity = 12
 noqa-require-code = true
 per-file-ignores =
   *.py: B905, B907, B950, E203, E501, W503, W291, W293
-  *.pyi: B, E301, E302, E305, E501, E701, E704, W503
+  *.pyi: B, E301, E302, E305, E501, E701, E704, F821, W503

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Change Log
 
+## Unreleased
+
+* **Breaking change:** Previously, flake8-pyi monkey patched flake8's F821
+  (undefined name) check to avoid false positives in stub files. This monkey
+  patch has been removed. Instead, we now recommend to disable F821 when running flake8
+  on stub files.
+* Remove the now unnecessary `--no-pyi-aware-file-checker` option.
+
 New error codes:
 * Introduce Y068: Don't use `@override` in stub files.
 

flake8_pyi/checker.py

@@ -1,106 +1,18 @@
 from __future__ import annotations
 
-import argparse
 import ast
 import logging
 import re
 from dataclasses import dataclass
-from typing import Any, ClassVar, Iterator, Literal
+from typing import ClassVar, Iterator
 
-from flake8 import checker
 from flake8.options.manager import OptionManager
-from flake8.plugins.finder import LoadedPlugin
-from flake8.plugins.pyflakes import FlakesChecker
-from pyflakes.checker import ModuleScope
 
 from . import errors, visitor
 
 LOG = logging.getLogger("flake8.pyi")
 
 
-class PyflakesPreProcessor(ast.NodeTransformer):
-    """Transform AST prior to passing it to pyflakes.
-
-    This reduces false positives on recursive class definitions.
-    """
-
-    def visit_ClassDef(self, node: ast.ClassDef) -> ast.ClassDef:
-        self.generic_visit(node)
-        node.bases = [
-            # Remove the subscript to prevent F821 errors from being emitted
-            # for (valid) recursive definitions: Foo[Bar] --> Foo
-            base.value if isinstance(base, ast.Subscript) else base
-            for base in node.bases
-        ]
-        return node
-
-
-class PyiAwareFlakesChecker(FlakesChecker):
-    def __init__(self, tree: ast.AST, *args: Any, **kwargs: Any) -> None:
-        super().__init__(PyflakesPreProcessor().visit(tree), *args, **kwargs)
-
-    @property
-    def annotationsFutureEnabled(self) -> Literal[True]:
-        """Always allow forward references in `.pyi` files.
-
-        Pyflakes can already handle forward refs for annotations,
-        but only via `from __future__ import annotations`.
-        In a stub file, `from __future__ import annotations` is unnecessary,
-        so we pretend to pyflakes that it's always present when linting a `.pyi` file.
-        """
-        return True
-
-    @annotationsFutureEnabled.setter
-    def annotationsFutureEnabled(self, value: bool) -> None:
-        """Does nothing, as we always want this property to be `True`."""
-
-    def ASSIGN(
-        self, tree: ast.Assign, omit: str | tuple[str, ...] | None = None
-    ) -> None:
-        """Defer evaluation of assignments in the module scope.
-
-        This is a custom implementation of ASSIGN, originally derived from
-        handleChildren() in pyflakes 1.3.0.
-
-        This reduces false positives for:
-          - TypeVars bound or constrained to forward references
-          - Assignments to forward references that are not explicitly
-            demarcated as type aliases.
-        """
-        if not isinstance(self.scope, ModuleScope):
-            super().ASSIGN(tree)
-            return
-
-        for target in tree.targets:
-            self.handleNode(target, tree)
-
-        self.deferFunction(lambda: self.handleNode(tree.value, tree))
-
-    def handleNodeDelete(self, node: ast.AST) -> None:
-        """Null implementation.
-
-        Lets users use `del` in stubs to denote private names.
-        """
-        return
-
-
-class PyiAwareFileChecker(checker.FileChecker):
-    def run_check(self, plugin: LoadedPlugin, **kwargs: Any) -> Any:
-        if plugin.obj is FlakesChecker:
-            if self.filename == "-":
-                filename = self.options.stdin_display_name
-            else:
-                filename = self.filename
-
-            if filename.endswith(".pyi"):
-                LOG.info(
-                    f"Replacing FlakesChecker with PyiAwareFlakesChecker while "
-                    f"checking {filename!r}"
-                )
-                plugin = plugin._replace(obj=PyiAwareFlakesChecker)
-        return super().run_check(plugin, **kwargs)
-
-
 _TYPE_COMMENT_REGEX = re.compile(r"#\s*type:\s*(?!\s?ignore)([^#]+)(\s*#.*?)?$")
 
 
@@ -136,18 +48,5 @@ def run(self) -> Iterator[errors.Error]:
 
     @staticmethod
     def add_options(parser: OptionManager) -> None:
-        """This is brittle, there's multiple levels of caching of defaults."""
         parser.parser.set_defaults(filename="*.py,*.pyi")
         parser.extend_default_ignore(errors.DISABLED_BY_DEFAULT)
-        parser.add_option(
-            "--no-pyi-aware-file-checker",
-            default=False,
-            action="store_true",
-            parse_from_config=True,
-            help="don't patch flake8 with .pyi-aware file checker",
-        )
-
-    @staticmethod
-    def parse_options(options: argparse.Namespace) -> None:
-        if not options.no_pyi_aware_file_checker:
-            checker.FileChecker = PyiAwareFileChecker

tests/forward_refs.pyi

@@ -1,6 +1,3 @@
-# Temporary workaround until pyflakes supports PEP 695:
-# flags: --extend-ignore=F821
-
 import typing
 from collections.abc import Iterator
 from typing import (