Enable flake8-future-annotations (#2932)

* Enable ruff rules for `flake8-future-annotations`

* Fix new errors introduced by `flake8-future-annotations`

---------

Co-authored-by: John Litborn <[email protected]>

pyproject.toml

@@ -96,6 +96,7 @@ select = [
     "C4",    # flake8-comprehensions
     "E",     # Error
     "F",     # pyflakes
+    "FA",    # flake8-future-annotations
     "I",     # isort
     "PT",    # flake8-pytest-style
     "PYI",   # flake8-pyi

src/trio/_subprocess_platform/__init__.py

@@ -1,16 +1,17 @@
 # Platform-specific subprocess bits'n'pieces.
+from __future__ import annotations
 
 import os
 import sys
-from typing import TYPE_CHECKING, Optional, Tuple
+from typing import TYPE_CHECKING
 
 import trio
 
 from .. import _core, _subprocess
 from .._abc import ReceiveStream, SendStream  # noqa: TCH001
 
-_wait_child_exiting_error: Optional[ImportError] = None
-_create_child_pipe_error: Optional[ImportError] = None
+_wait_child_exiting_error: ImportError | None = None
+_create_child_pipe_error: ImportError | None = None
 
 
 if TYPE_CHECKING:
@@ -26,7 +27,7 @@ def close(self) -> None:
 
 # Fallback versions of the functions provided -- implementations
 # per OS are imported atop these at the bottom of the module.
-async def wait_child_exiting(process: "_subprocess.Process") -> None:
+async def wait_child_exiting(process: _subprocess.Process) -> None:
     """Block until the child process managed by ``process`` is exiting.
 
     It is invalid to call this function if the process has already
@@ -41,7 +42,7 @@ async def wait_child_exiting(process: "_subprocess.Process") -> None:
     raise NotImplementedError from _wait_child_exiting_error  # pragma: no cover
 
 
-def create_pipe_to_child_stdin() -> Tuple["ClosableSendStream", int]:
+def create_pipe_to_child_stdin() -> tuple[ClosableSendStream, int]:
     """Create a new pipe suitable for sending data from this
     process to the standard input of a child we're about to spawn.
 
@@ -54,7 +55,7 @@ def create_pipe_to_child_stdin() -> Tuple["ClosableSendStream", int]:
     raise NotImplementedError from _create_child_pipe_error  # pragma: no cover
 
 
-def create_pipe_from_child_output() -> Tuple["ClosableReceiveStream", int]:
+def create_pipe_from_child_output() -> tuple[ClosableReceiveStream, int]:
     """Create a new pipe suitable for receiving data into this
     process from the standard output or error stream of a child
     we're about to spawn.

src/trio/_tests/test_file_io.py

@@ -1,9 +1,10 @@
+from __future__ import annotations
+
 import importlib
 import io
 import os
-import pathlib
 import re
-from typing import List, Tuple
+from typing import TYPE_CHECKING
 from unittest import mock
 from unittest.mock import sentinel
 
@@ -13,6 +14,9 @@
 from trio import _core, _file_io
 from trio._file_io import _FILE_ASYNC_METHODS, _FILE_SYNC_ATTRS, AsyncIOWrapper
 
+if TYPE_CHECKING:
+    import pathlib
+
 
 @pytest.fixture
 def path(tmp_path: pathlib.Path) -> str:
@@ -109,7 +113,7 @@ def test_type_stubs_match_lists() -> None:
         pytest.fail("No TYPE CHECKING line?")
 
     # Now we should be at the type checking block.
-    found: List[Tuple[str, str]] = []
+    found: list[tuple[str, str]] = []
     for line in source:  # pragma: no branch - expected to break early
         if line.strip() and not line.startswith(" " * 8):
             break  # Dedented out of the if TYPE_CHECKING block.

src/trio/socket.py

@@ -1,14 +1,14 @@
+from __future__ import annotations
+
 # This is a public namespace, so we don't want to expose any non-underscored
 # attributes that aren't actually part of our public API. But it's very
 # annoying to carefully always use underscored names for module-level
 # temporaries, imports, etc. when implementing the module. So we put the
 # implementation in an underscored module, and then re-export the public parts
 # here.
 # We still have some underscore names though but only a few.
-
-
 # Uses `from x import y as y` for compatibility with `pyright --verifytypes` (#2625)
-
+#
 # Dynamically re-export whatever constants this particular Python happens to
 # have:
 import socket as _stdlib_socket
@@ -17,7 +17,7 @@
 
 from . import _socket
 
-_bad_symbols: _t.Set[str] = set()
+_bad_symbols: set[str] = set()
 if sys.platform == "win32":
     # See https://github.com/python-trio/trio/issues/39
     # Do not import for windows platform