Add check for unnecessary-default-type-args (#9938)

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>

doc/data/messages/u/unnecessary-default-type-args/bad.py

@@ -0,0 +1,4 @@
+from collections.abc import AsyncGenerator, Generator
+
+a1: AsyncGenerator[int, None]  # [unnecessary-default-type-args]
+b1: Generator[int, None, None]  # [unnecessary-default-type-args]

doc/data/messages/u/unnecessary-default-type-args/details.rst

@@ -0,0 +1,6 @@
+At the moment, this check only works for ``Generator`` and ``AsyncGenerator``.
+
+Starting with Python 3.13, the ``SendType`` and ``ReturnType`` default to ``None``.
+As such it's no longer necessary to specify them. The ``collections.abc`` variants
+don't validate the number of type arguments. Therefore the defaults for these
+can be used in earlier versions as well.

doc/data/messages/u/unnecessary-default-type-args/good.py

@@ -0,0 +1,4 @@
+from collections.abc import AsyncGenerator, Generator
+
+a1: AsyncGenerator[int]
+b1: Generator[int]

doc/data/messages/u/unnecessary-default-type-args/pylintrc

@@ -0,0 +1,2 @@
+[main]
+load-plugins=pylint.extensions.typing

doc/data/messages/u/unnecessary-default-type-args/related.rst

@@ -0,0 +1,2 @@
+- `Python documentation for AsyncGenerator <https://docs.python.org/3.13/library/typing.html#typing.AsyncGenerator>`_
+- `Python documentation for Generator <https://docs.python.org/3.13/library/typing.html#typing.Generator>`_

doc/user_guide/checkers/extensions.rst

@@ -688,6 +688,9 @@ Typing checker Messages
 :consider-alternative-union-syntax (R6003): *Consider using alternative Union syntax instead of '%s'%s*
   Emitted when 'typing.Union' or 'typing.Optional' is used instead of the
   alternative Union syntax 'int | None'.
+:unnecessary-default-type-args (R6007): *Type `%s` has unnecessary default type args. Change it to `%s`.*
+  Emitted when types have default type args which can be omitted. Mainly used
+  for `typing.Generator` and `typing.AsyncGenerator`.
 :redundant-typehint-argument (R6006): *Type `%s` is used more than once in union type annotation. Remove redundant typehints.*
   Duplicated type arguments will be skipped by `mypy` tool, therefore should be
   removed to avoid confusion.

doc/user_guide/messages/messages_overview.rst

@@ -545,6 +545,7 @@ All messages in the refactor category:
    refactor/too-many-statements
    refactor/trailing-comma-tuple
    refactor/unnecessary-comprehension
+   refactor/unnecessary-default-type-args
    refactor/unnecessary-dict-index-lookup
    refactor/unnecessary-list-index-lookup
    refactor/use-a-generator

doc/whatsnew/fragments/9938.new_check

@@ -0,0 +1,4 @@
+Add ``unnecessary-default-type-args`` to the ``typing`` extension to detect the use
+of unnecessary default type args for ``typing.Generator`` and ``typing.AsyncGenerator``.
+
+Refs #9938

pylint/checkers/exceptions.py

@@ -35,7 +35,7 @@ def predicate(obj: Any) -> bool:
 
 def _annotated_unpack_infer(
     stmt: nodes.NodeNG, context: InferenceContext | None = None
-) -> Generator[tuple[nodes.NodeNG, SuccessfulInferenceResult], None, None]:
+) -> Generator[tuple[nodes.NodeNG, SuccessfulInferenceResult]]:
     """Recursively generate nodes inferred by the given statement.
 
     If the inferred value is a list or a tuple, recurse on the elements.

pylint/checkers/symilar.py

@@ -468,7 +468,7 @@ def _get_similarity_report(
     # pylint: disable = too-many-locals
     def _find_common(
         self, lineset1: LineSet, lineset2: LineSet
-    ) -> Generator[Commonality, None, None]:
+    ) -> Generator[Commonality]:
         """Find similarities in the two given linesets.
 
         This the core of the algorithm. The idea is to compute the hashes of a
@@ -541,7 +541,7 @@ def _find_common(
             if eff_cmn_nb > self.namespace.min_similarity_lines:
                 yield com
 
-    def _iter_sims(self) -> Generator[Commonality, None, None]:
+    def _iter_sims(self) -> Generator[Commonality]:
         """Iterate on similarities among all files, by making a Cartesian
         product.
         """

pylint/checkers/variables.py

@@ -249,9 +249,7 @@ class C: ...
     return frame.lineno < defframe.lineno  # type: ignore[no-any-return]
 
 
-def _infer_name_module(
-    node: nodes.Import, name: str
-) -> Generator[InferenceResult, None, None]:
+def _infer_name_module(node: nodes.Import, name: str) -> Generator[InferenceResult]:
     context = astroid.context.InferenceContext()
     context.lookupname = name
     return node.infer(context, asname=False)  # type: ignore[no-any-return]

pylint/extensions/typing.py

@@ -85,6 +85,7 @@ class DeprecatedTypingAliasMsg(NamedTuple):
     parent_subscript: bool = False
 
 
+# pylint: disable-next=too-many-instance-attributes
 class TypingChecker(BaseChecker):
     """Find issue specifically related to type annotations."""
 
@@ -130,6 +131,12 @@ class TypingChecker(BaseChecker):
             "Duplicated type arguments will be skipped by `mypy` tool, therefore should be "
             "removed to avoid confusion.",
         ),
+        "R6007": (
+            "Type `%s` has unnecessary default type args. Change it to `%s`.",
+            "unnecessary-default-type-args",
+            "Emitted when types have default type args which can be omitted. "
+            "Mainly used for `typing.Generator` and `typing.AsyncGenerator`.",
+        ),
     }
     options = (
         (
@@ -174,6 +181,7 @@ def open(self) -> None:
         self._py37_plus = py_version >= (3, 7)
         self._py39_plus = py_version >= (3, 9)
         self._py310_plus = py_version >= (3, 10)
+        self._py313_plus = py_version >= (3, 13)
 
         self._should_check_typing_alias = self._py39_plus or (
             self._py37_plus and self.linter.config.runtime_typing is False
@@ -248,6 +256,33 @@ def visit_annassign(self, node: nodes.AnnAssign) -> None:
 
         self._check_union_types(types, node)
 
+    @only_required_for_messages("unnecessary-default-type-args")
+    def visit_subscript(self, node: nodes.Subscript) -> None:
+        inferred = safe_infer(node.value)
+        if (  # pylint: disable=too-many-boolean-expressions
+            isinstance(inferred, nodes.ClassDef)
+            and (
+                inferred.qname() in {"typing.Generator", "typing.AsyncGenerator"}
+                and self._py313_plus
+                or inferred.qname()
+                in {"_collections_abc.Generator", "_collections_abc.AsyncGenerator"}
+            )
+            and isinstance(node.slice, nodes.Tuple)
+            and all(
+                (isinstance(el, nodes.Const) and el.value is None)
+                for el in node.slice.elts[1:]
+            )
+        ):
+            suggested_str = (
+                f"{node.value.as_string()}[{node.slice.elts[0].as_string()}]"
+            )
+            self.add_message(
+                "unnecessary-default-type-args",
+                args=(node.as_string(), suggested_str),
+                node=node,
+                confidence=HIGH,
+            )
+
     @staticmethod
     def _is_deprecated_union_annotation(
         annotation: nodes.NodeNG, union_name: str

pylint/pyreverse/diadefslib.py

@@ -84,7 +84,7 @@ def add_class(self, node: nodes.ClassDef) -> None:
 
     def get_ancestors(
         self, node: nodes.ClassDef, level: int
-    ) -> Generator[nodes.ClassDef, None, None]:
+    ) -> Generator[nodes.ClassDef]:
         """Return ancestor nodes of a class node."""
         if level == 0:
             return
@@ -95,7 +95,7 @@ def get_ancestors(
 
     def get_associated(
         self, klass_node: nodes.ClassDef, level: int
-    ) -> Generator[nodes.ClassDef, None, None]:
+    ) -> Generator[nodes.ClassDef]:
         """Return associated nodes of a class node."""
         if level == 0:
             return

pylint/testutils/checker_test_case.py

@@ -40,7 +40,7 @@ def assertNoMessages(self) -> Iterator[None]:
     @contextlib.contextmanager
     def assertAddsMessages(
         self, *messages: MessageTest, ignore_position: bool = False
-    ) -> Generator[None, None, None]:
+    ) -> Generator[None]:
         """Assert that exactly the given method adds the given messages.
 
         The list of messages must exactly match *all* the messages added by the

pylint/testutils/utils.py

@@ -27,7 +27,7 @@ def _patch_streams(out: TextIO) -> Iterator[None]:
 @contextlib.contextmanager
 def _test_sys_path(
     replacement_sys_path: list[str] | None = None,
-) -> Generator[None, None, None]:
+) -> Generator[None]:
     original_path = sys.path
     try:
         if replacement_sys_path is not None:
@@ -40,7 +40,7 @@ def _test_sys_path(
 @contextlib.contextmanager
 def _test_cwd(
     current_working_directory: str | Path | None = None,
-) -> Generator[None, None, None]:
+) -> Generator[None]:
     original_dir = os.getcwd()
     try:
         if current_working_directory is not None:
@@ -53,7 +53,7 @@ def _test_cwd(
 @contextlib.contextmanager
 def _test_environ_pythonpath(
     new_pythonpath: str | None = None,
-) -> Generator[None, None, None]:
+) -> Generator[None]:
     original_pythonpath = os.environ.get("PYTHONPATH")
     if new_pythonpath:
         os.environ["PYTHONPATH"] = new_pythonpath

pylint/utils/pragma_parser.py

@@ -86,7 +86,7 @@ class InvalidPragmaError(PragmaParserError):
     """Thrown in case the pragma is invalid."""
 
 
-def parse_pragma(pylint_pragma: str) -> Generator[PragmaRepresenter, None, None]:
+def parse_pragma(pylint_pragma: str) -> Generator[PragmaRepresenter]:
     action: str | None = None
     messages: list[str] = []
     assignment_required = False

tests/functional/ext/typing/unnecessary_default_type_args.py

@@ -0,0 +1,17 @@
+# pylint: disable=missing-docstring,deprecated-typing-alias
+import collections.abc as ca
+import typing as t
+
+a1: t.Generator[int, str, str]
+a2: t.Generator[int, None, None]
+a3: t.Generator[int]
+b1: t.AsyncGenerator[int, str]
+b2: t.AsyncGenerator[int, None]
+b3: t.AsyncGenerator[int]
+
+c1: ca.Generator[int, str, str]
+c2: ca.Generator[int, None, None]  # [unnecessary-default-type-args]
+c3: ca.Generator[int]
+d1: ca.AsyncGenerator[int, str]
+d2: ca.AsyncGenerator[int, None]  # [unnecessary-default-type-args]
+d3: ca.AsyncGenerator[int]

tests/functional/ext/typing/unnecessary_default_type_args.rc

@@ -0,0 +1,3 @@
+[main]
+py-version=3.10
+load-plugins=pylint.extensions.typing

tests/functional/ext/typing/unnecessary_default_type_args.txt

@@ -0,0 +1,2 @@
+unnecessary-default-type-args:13:4:13:33::Type `ca.Generator[int, None, None]` has unnecessary default type args. Change it to `ca.Generator[int]`.:HIGH
+unnecessary-default-type-args:16:4:16:32::Type `ca.AsyncGenerator[int, None]` has unnecessary default type args. Change it to `ca.AsyncGenerator[int]`.:HIGH

tests/functional/ext/typing/unnecessary_default_type_args_py313.py

@@ -0,0 +1,17 @@
+# pylint: disable=missing-docstring,deprecated-typing-alias
+import collections.abc as ca
+import typing as t
+
+a1: t.Generator[int, str, str]
+a2: t.Generator[int, None, None]  # [unnecessary-default-type-args]
+a3: t.Generator[int]
+b1: t.AsyncGenerator[int, str]
+b2: t.AsyncGenerator[int, None]  # [unnecessary-default-type-args]
+b3: t.AsyncGenerator[int]
+
+c1: ca.Generator[int, str, str]
+c2: ca.Generator[int, None, None]  # [unnecessary-default-type-args]
+c3: ca.Generator[int]
+d1: ca.AsyncGenerator[int, str]
+d2: ca.AsyncGenerator[int, None]  # [unnecessary-default-type-args]
+d3: ca.AsyncGenerator[int]

tests/functional/ext/typing/unnecessary_default_type_args_py313.rc

@@ -0,0 +1,3 @@
+[main]
+py-version=3.13
+load-plugins=pylint.extensions.typing

tests/functional/ext/typing/unnecessary_default_type_args_py313.txt

@@ -0,0 +1,4 @@
+unnecessary-default-type-args:6:4:6:32::Type `t.Generator[int, None, None]` has unnecessary default type args. Change it to `t.Generator[int]`.:HIGH
+unnecessary-default-type-args:9:4:9:31::Type `t.AsyncGenerator[int, None]` has unnecessary default type args. Change it to `t.AsyncGenerator[int]`.:HIGH
+unnecessary-default-type-args:13:4:13:33::Type `ca.Generator[int, None, None]` has unnecessary default type args. Change it to `ca.Generator[int]`.:HIGH
+unnecessary-default-type-args:16:4:16:32::Type `ca.AsyncGenerator[int, None]` has unnecessary default type args. Change it to `ca.AsyncGenerator[int]`.:HIGH

tests/pyreverse/test_inspector.py

@@ -26,7 +26,7 @@
 
 
 @pytest.fixture
-def project(get_project: GetProjectCallable) -> Generator[Project, None, None]:
+def project(get_project: GetProjectCallable) -> Generator[Project]:
     with _test_cwd(TESTS):
         project = get_project("data", "data")
         linker = inspector.Linker(project)