rewrite TypeVar defaults for Generator / AsyncGenerator

README.md

@@ -754,6 +754,24 @@ Availability:
      ...
 ```
 
+### pep 696 TypeVar defaults
+
+Availability:
+- File imports `from __future__ import annotations`
+    - Unless `--keep-runtime-typing` is passed on the commandline.
+- `--py313-plus` is passed on the commandline.
+
+```diff
+-def f() -> Generator[int, None, None]:
++def f() -> Generator[int]:
+     yield 1
+```
+
+```diff
+-async def f() -> AsyncGenerator[int, None]:
++async def f() -> AsyncGenerator[int]:
+     yield 1
+```
 
 ### remove quoted annotations
 

pyupgrade/_data.py

@@ -40,6 +40,7 @@ class State(NamedTuple):
     '__future__',
     'asyncio',
     'collections',
+    'collections.abc',
     'functools',
     'mmap',
     'os',

pyupgrade/_plugins/legacy.py

@@ -91,7 +91,7 @@ def __init__(self) -> None:
         self.yield_offsets: set[Offset] = set()
 
     @contextlib.contextmanager
-    def _scope(self, node: ast.AST) -> Generator[None, None, None]:
+    def _scope(self, node: ast.AST) -> Generator[None]:
         self._scopes.append(Scope(node))
         try:
             yield

pyupgrade/_plugins/percent_format.py

@@ -46,7 +46,7 @@ def _must_match(regex: Pattern[str], string: str, pos: int) -> Match[str]:
 
 
 def _parse_percent_format(s: str) -> tuple[PercentFormat, ...]:
-    def _parse_inner() -> Generator[PercentFormat, None, None]:
+    def _parse_inner() -> Generator[PercentFormat]:
         string_start = 0
         string_end = 0
         in_fmt = False

pyupgrade/_plugins/typing_pep696_typevar_defaults.py

@@ -0,0 +1,72 @@
+from __future__ import annotations
+
+import ast
+from typing import Iterable
+
+from tokenize_rt import Offset
+from tokenize_rt import Token
+
+from pyupgrade._ast_helpers import ast_to_offset
+from pyupgrade._ast_helpers import is_name_attr
+from pyupgrade._data import register
+from pyupgrade._data import State
+from pyupgrade._data import TokenFunc
+from pyupgrade._token_helpers import find_op
+from pyupgrade._token_helpers import parse_call_args
+
+
+def _fix_typevar_default(i: int, tokens: list[Token]) -> None:
+    j = find_op(tokens, i, '[')
+    args, end = parse_call_args(tokens, j)
+    # remove the trailing `None` arguments
+    del tokens[args[0][1]:args[-1][1]]
+
+
+def _should_rewrite(state: State) -> bool:
+    return (
+        state.settings.min_version >= (3, 13) or (
+            not state.settings.keep_runtime_typing and
+            state.in_annotation and
+            'annotations' in state.from_imports['__future__']
+        )
+    )
+
+
+def _is_none(node: ast.AST) -> bool:
+    return isinstance(node, ast.Constant) and node.value is None
+
+
+@register(ast.Subscript)
+def visit_Subscript(
+        state: State,
+        node: ast.Subscript,
+        parent: ast.AST,
+) -> Iterable[tuple[Offset, TokenFunc]]:
+    if not _should_rewrite(state):
+        return
+
+    if (
+            is_name_attr(
+                node.value,
+                state.from_imports,
+                ('collections.abc', 'typing', 'typing_extensions'),
+                ('Generator',),
+            ) and
+            isinstance(node.slice, ast.Tuple) and
+            len(node.slice.elts) == 3 and
+            _is_none(node.slice.elts[1]) and
+            _is_none(node.slice.elts[2])
+    ):
+        yield ast_to_offset(node), _fix_typevar_default
+    elif (
+            is_name_attr(
+                node.value,
+                state.from_imports,
+                ('collections.abc', 'typing', 'typing_extensions'),
+                ('AsyncGenerator',),
+            ) and
+            isinstance(node.slice, ast.Tuple) and
+            len(node.slice.elts) == 2 and
+            _is_none(node.slice.elts[1])
+    ):
+        yield ast_to_offset(node), _fix_typevar_default

tests/features/typing_pep696_typevar_defaults_test.py

@@ -0,0 +1,126 @@
+from __future__ import annotations
+
+import pytest
+
+from pyupgrade._data import Settings
+from pyupgrade._main import _fix_plugins
+
+
+@pytest.mark.parametrize(
+    ('s', 'version'),
+    (
+        pytest.param(
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int, None, None]: yield 1\n',
+            (3, 12),
+            id='not 3.13+, no __future__.annotations',
+        ),
+        pytest.param(
+            'from __future__ import annotations\n'
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int]: yield 1\n',
+            (3, 12),
+            id='already converted!',
+        ),
+        pytest.param(
+            'from __future__ import annotations\n'
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int, int, None]: yield 1\n'
+            'def g() -> Generator[int, int, int]: yield 1\n',
+            (3, 12),
+            id='non-None send/return type',
+        ),
+    ),
+)
+def test_fix_pep696_noop(s, version):
+    assert _fix_plugins(s, settings=Settings(min_version=version)) == s
+
+
+def test_fix_pep696_noop_keep_runtime_typing():
+    settings = Settings(min_version=(3, 12), keep_runtime_typing=True)
+    s = '''\
+from __future__ import annotations
+from collections.abc import Generator
+def f() -> Generator[int, None, None]: yield 1
+'''
+    assert _fix_plugins(s, settings=settings) == s
+
+
+@pytest.mark.parametrize(
+    ('s', 'expected'),
+    (
+        pytest.param(
+            'from __future__ import annotations\n'
+            'from typing import Generator\n'
+            'def f() -> Generator[int, None, None]: yield 1\n',
+
+            'from __future__ import annotations\n'
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int]: yield 1\n',
+
+            id='typing.Generator',
+        ),
+        pytest.param(
+            'from __future__ import annotations\n'
+            'from typing_extensions import Generator\n'
+            'def f() -> Generator[int, None, None]: yield 1\n',
+
+            'from __future__ import annotations\n'
+            'from typing_extensions import Generator\n'
+            'def f() -> Generator[int]: yield 1\n',
+
+            id='typing_extensions.Generator',
+        ),
+        pytest.param(
+            'from __future__ import annotations\n'
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int, None, None]: yield 1\n',
+
+            'from __future__ import annotations\n'
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int]: yield 1\n',
+
+            id='collections.abc.Generator',
+        ),
+        pytest.param(
+            'from __future__ import annotations\n'
+            'from collections.abc import AsyncGenerator\n'
+            'async def f() -> AsyncGenerator[int, None]: yield 1\n',
+
+            'from __future__ import annotations\n'
+            'from collections.abc import AsyncGenerator\n'
+            'async def f() -> AsyncGenerator[int]: yield 1\n',
+
+            id='collections.abc.AsyncGenerator',
+        ),
+    ),
+)
+def test_fix_pep696_with_future_annotations(s, expected):
+    assert _fix_plugins(s, settings=Settings(min_version=(3, 12))) == expected
+
+
+@pytest.mark.parametrize(
+    ('s', 'expected'),
+    (
+        pytest.param(
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int, None, None]: yield 1\n',
+
+            'from collections.abc import Generator\n'
+            'def f() -> Generator[int]: yield 1\n',
+
+            id='Generator',
+        ),
+        pytest.param(
+            'from collections.abc import AsyncGenerator\n'
+            'async def f() -> AsyncGenerator[int, None]: yield 1\n',
+
+            'from collections.abc import AsyncGenerator\n'
+            'async def f() -> AsyncGenerator[int]: yield 1\n',
+
+            id='AsyncGenerator',
+        ),
+    ),
+)
+def test_fix_pep696_with_3_13(s, expected):
+    assert _fix_plugins(s, settings=Settings(min_version=(3, 13))) == expected