refactor: update linting with the latest ruff (#1441)

Update linting rules with the latest ruff version 0.7.0.

After upgrading ruff to the latest version [in this
PR](#1437), some rules can be
removed since they are not hitting any code, and some other rules can be
relatively easily refactored.

ops/_private/harness.py

@@ -39,6 +39,7 @@
     AnyStr,
     BinaryIO,
     Callable,
+    ClassVar,
     Dict,
     Generic,
     Iterable,
@@ -2225,7 +2226,7 @@ def decorator(target_cls: Any):
 class _TestingConfig(Dict[str, Union[str, int, float, bool]]):
     """Represents the Juju Config."""
 
-    _supported_types = {
+    _supported_types: ClassVar[Dict[str, Any]] = {
         'string': str,
         'boolean': bool,
         'int': int,
@@ -2838,9 +2839,7 @@ def _has_secret_owner_permission(self, secret: _Secret) -> bool:
         unit_secret = secret.owner_name == self.unit_name
         app_secret = secret.owner_name == self.app_name
 
-        if unit_secret or (app_secret and self.is_leader()):
-            return True
-        return False
+        return unit_secret or (app_secret and self.is_leader())
 
     def secret_info_get(
         self, *, id: Optional[str] = None, label: Optional[str] = None

ops/charm.py

@@ -22,6 +22,7 @@
 from typing import (
     TYPE_CHECKING,
     Any,
+    ClassVar,
     Dict,
     List,
     Literal,
@@ -1678,7 +1679,7 @@ class RelationMeta:
     ``metadata.yaml`` and used by the charm code if appropriate.
     """
 
-    VALID_SCOPES = ['global', 'container']
+    VALID_SCOPES: ClassVar[List[str]] = ['global', 'container']
 
     def __init__(self, role: RelationRole, relation_name: str, raw: '_RelationMetaDict'):
         assert isinstance(

ops/model.py

@@ -39,6 +39,7 @@
     Any,
     BinaryIO,
     Callable,
+    ClassVar,
     Dict,
     Generator,
     Iterable,
@@ -1963,7 +1964,7 @@ class StatusBase:
     directly use the child class such as :class:`ActiveStatus` to indicate their status.
     """
 
-    _statuses: Dict[StatusName, Type['StatusBase']] = {}
+    _statuses: ClassVar[Dict[StatusName, Type['StatusBase']]] = {}
 
     # Subclasses must provide this attribute
     name: StatusName
@@ -2023,7 +2024,7 @@ def _register(cls, child: Type['StatusBase']) -> None:
             )
         cls._statuses[child.name] = child
 
-    _priorities = {
+    _priorities: ClassVar[Dict[str, Any]] = {
         'error': 5,
         'blocked': 4,
         'maintenance': 3,
@@ -3715,7 +3716,7 @@ def secret_info_get(
             args.extend(['--label', label])
         result = self._run_for_secret('secret-info-get', *args, return_output=True, use_json=True)
         info_dicts = typing.cast(Dict[str, Any], result)
-        id = list(info_dicts)[0]  # Juju returns dict of {secret_id: {info}}
+        id = next(iter(info_dicts))  # Juju returns dict of {secret_id: {info}}
         return SecretInfo.from_dict(
             id, typing.cast(Dict[str, Any], info_dicts[id]), model_uuid=self.model_uuid
         )

pyproject.toml

@@ -146,17 +146,9 @@ ignore = [
     # Missing docstring in `__init__`
     "D107",
 
-    # Manual list comprehension.
-    "PERF401",
     # Manual dict comprehension.
     "PERF403",
 
-    # Convert Dict[X] to dict[x], which we cannot do while we support Python 3.8
-    "UP006",
-
-    # Convert Union[X, Y] to X | Y, which we cannot do while we support Python 3.8
-    "UP007",
-
     # Convert {} from `TypedDict` functional to class syntax
     # Note that since we have some `TypedDict`s that cannot use the class
     # syntax, we're currently choosing to be consistent in syntax even though
@@ -167,14 +159,6 @@ ignore = [
 
     # `subprocess` call: check for execution of untrusted input
     "S603",
-    # Prefer `next(iter(info_dicts))` over single element slice
-    "RUF015",
-    # Mutable class attributes should be annotated with `typing.ClassVar`
-    "RUF012",
-    # Unnecessary `tuple` call (rewrite as a literal)
-    "C408",
-    # Unnecessary dict comprehension for iterable; use `dict.fromkeys` instead
-    "C420",
 ]
 
 [tool.ruff.lint.pyupgrade]
@@ -211,6 +195,7 @@ keep-runtime-typing = true
     "E266",  # Too many leading `#` before block comment
     "I001",  # Import block is un-sorted or un-formatted
     "RUF003",  # Comment contains ambiguous unicode characters (EN DASH, RIGHT SINGLE QUOTATION MARK)
+    "RUF012",  # Mutable class attributes should be annotated with `typing.ClassVar`
     "UP031",  # Use format specifiers instead of percent format
 ]
 

test/test_real_pebble.py

@@ -123,15 +123,15 @@ def test_checks_and_health(self, client: pebble.Client):
         # After two retries the "bad" check should go down
         for _ in range(5):
             checks = client.get_checks()
-            bad_check = [c for c in checks if c.name == 'bad'][0]
+            bad_check = next(c for c in checks if c.name == 'bad')
             if bad_check.status == pebble.CheckStatus.DOWN:
                 break
             time.sleep(0.06)
         else:
             assert False, 'timed out waiting for "bad" check to go down'
         assert bad_check.failures == 2
         assert bad_check.threshold == 2
-        good_check = [c for c in checks if c.name == 'good'][0]
+        good_check = next(c for c in checks if c.name == 'good')
         assert good_check.status == pebble.CheckStatus.UP
 
         # And /v1/health should return "unhealthy" (with status HTTP 502)

test/test_testing.py

@@ -5113,7 +5113,7 @@ def test_push_files_and_list(
         }
 
         # Let's pull the first file again and check its details
-        file = [f for f in files if f.path == f'{pebble_dir}/file1'][0]
+        file = next(f for f in files if f.path == f'{pebble_dir}/file1')
         assert file.name == 'file1'
         assert file.type == pebble.FileType.FILE
         assert file.size == 4
@@ -5275,8 +5275,8 @@ def test_make_dir_with_permission_mask(
         client.make_dir(f'{pebble_dir}/dir2', permissions=0o777)
 
         files = client.list_files(f'{pebble_dir}/', pattern='dir*')
-        assert [f for f in files if f.path == f'{pebble_dir}/dir1'][0].permissions == 0o700
-        assert [f for f in files if f.path == f'{pebble_dir}/dir2'][0].permissions == 0o777
+        assert next(f for f in files if f.path == f'{pebble_dir}/dir1').permissions == 0o700
+        assert next(f for f in files if f.path == f'{pebble_dir}/dir2').permissions == 0o777
 
         # If permissions are outside of the range 0o000 through 0o777, an exception should be
         # raised.
@@ -5432,8 +5432,8 @@ def test_container_storage_mounts(self, request: pytest.FixtureRequest):
         assert not c1.exists(c1_fpath)
 
     def _select_testing_user_group(self):
-        user = [u for u in pwd.getpwall() if u.pw_uid != os.getuid()][0]
-        group = [g for g in grp.getgrall() if g.gr_gid != os.getgid()][0]
+        user = next(u for u in pwd.getpwall() if u.pw_uid != os.getuid())
+        group = next(g for g in grp.getgrall() if g.gr_gid != os.getgid())
         return user, group
 
     def test_push_with_ownership(