lint: Enable flake8-annotations

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

pyproject.toml

@@ -83,6 +83,7 @@ line-length=80
 [tool.ruff.lint]
 select = [
     "A",   # flake8-builtins
+    "ANN", # flake8-annotations
     "ARG", # flake8-unused-arguments
     "B",   # flake8-bugbear
     "C4",  # flake8-comprehensions
@@ -107,6 +108,7 @@ select = [
     "W",   # pycodestyle-warning
 ] 
 ignore = [
+    "ANN101", "ANN102", # nonsense, deprecated in ruff
     "D400", "D415", "D213", "D205", "D202", "D107", "D407", "D413", "D212", "D104", "D406", "D105", "D411", "D401", "D200", "D203",
     "PLR0913", "PLR2004",
     "ISC001", # incompatible with ruff formatter
@@ -127,6 +129,9 @@ ignore = [
     "S603", # bandit: this flags all uses of subprocess.run as vulnerable
 ]
 
+[tool.ruff.lint.flake8-annotations]
+mypy-init-return = true
+
 # mypy section
 # Read more here: https://mypy.readthedocs.io/en/stable/config_file.html#using-a-pyproject-toml-file
 [tool.mypy]

tests/test_fetcher_ng.py

@@ -105,7 +105,7 @@ def test_http_error(self) -> None:
 
     # Response read timeout error
     @patch.object(requests.Session, "get")
-    def test_response_read_timeout(self, mock_session_get: Any) -> None:
+    def test_response_read_timeout(self, mock_session_get: Mock) -> None:
         mock_response = Mock()
         attr = {
             "iter_content.side_effect": requests.exceptions.ConnectionError(
@@ -125,7 +125,7 @@ def test_response_read_timeout(self, mock_session_get: Any) -> None:
         "get",
         side_effect=requests.exceptions.Timeout("Simulated timeout"),
     )
-    def test_session_get_timeout(self, mock_session_get: Any) -> None:
+    def test_session_get_timeout(self, mock_session_get: Mock) -> None:
         with self.assertRaises(exceptions.SlowRetrievalError):
             self.fetcher.fetch(self.url)
         mock_session_get.assert_called_once()

tuf/api/_payload.py

@@ -1491,7 +1491,7 @@ def __init__(
         self.unrecognized_fields = unrecognized_fields
 
     @property
-    def custom(self) -> Any:
+    def custom(self) -> Any:  # noqa: ANN401
         """Get implementation specific data related to the target.
 
         python-tuf does not use or validate this data.