Add ruff linting

Configure ruff in pyproject.toml and apply its fixes: modern annotations
(X | None, builtin generics, collections.abc), sorted imports, explicit
stacklevel in test warnings.

tests/test_cli.py

@@ -2,8 +2,9 @@
 
 import os
 import pwd
+from collections.abc import Callable
 from pathlib import Path
-from typing import Any, Callable, Optional
+from typing import Any
 
 import pytest
 
@@ -25,8 +26,8 @@ class FakeBackup:
     check_code = 0
 
     def __init__(self, inputs: Any, output: Any, exclude: Any, keep: Any, options: str,
-                 ssh_host: Optional[str] = None, ssh_user: Optional[str] = None,
-                 ssh_keyfile: Optional[str] = None, remote_sudo: bool = False,
+                 ssh_host: str | None = None, ssh_user: str | None = None,
+                 ssh_keyfile: str | None = None, remote_sudo: bool = False,
                  remove_before: bool = False, verbose: bool = False, progress: bool = False) -> None:
         self.inputs = inputs
         self.output = output
@@ -40,7 +41,7 @@ class FakeBackup:
         self.remove_before = remove_before
         self.verbose = verbose
         self.progress = progress
-        self.homedir: Optional[str] = None
+        self.homedir: str | None = None
         self.ran = False
         self.closed = False
         FakeBackup.instances.append(self)
@@ -86,13 +87,13 @@ def as_root(monkeypatch: pytest.MonkeyPatch) -> None:
 
 
 @pytest.fixture
-def config_calls(monkeypatch: pytest.MonkeyPatch) -> list[tuple[str, Optional[str]]]:
+def config_calls(monkeypatch: pytest.MonkeyPatch) -> list[tuple[str, str | None]]:
     """Record the config file path and user instead of reading the file"""
 
-    calls: list[tuple[str, Optional[str]]] = []
+    calls: list[tuple[str, str | None]] = []
     read_config = sb._read_config
 
-    def record(config_file: str, user: Optional[str] = None) -> sb.ConfigArgs:
+    def record(config_file: str, user: str | None = None) -> sb.ConfigArgs:
         calls.append((config_file, user))
 
         return read_config('/nonexistent/simple_backup.conf', user)
@@ -249,20 +250,20 @@ ssh_keyfile=/keys/id
 
 class TestUser:
     @pytest.mark.usefixtures('as_user')
-    def test_current_user(self, run_cli: RunCli, config_calls: list[tuple[str, Optional[str]]]) -> None:
+    def test_current_user(self, run_cli: RunCli, config_calls: list[tuple[str, str | None]]) -> None:
         assert run_cli() == 0
         assert config_calls == [(f'{HOME}/.config/simple_backup/simple_backup.conf', USER)]
         assert last_backup().homedir == HOME
 
     @pytest.mark.usefixtures('as_root')
-    def test_explicit_user(self, run_cli: RunCli, config_calls: list[tuple[str, Optional[str]]]) -> None:
+    def test_explicit_user(self, run_cli: RunCli, config_calls: list[tuple[str, str | None]]) -> None:
         assert run_cli('-u', USER, '-c', '~/other.conf') == 0
         assert config_calls == [(f'{HOME}/other.conf', USER)]
         assert last_backup().homedir == HOME
 
     @pytest.mark.usefixtures('as_root')
     @pytest.mark.parametrize('var', ['SUDO_USER', 'DOAS_USER'])
-    def test_sudo_or_doas_user(self, run_cli: RunCli, config_calls: list[tuple[str, Optional[str]]],
+    def test_sudo_or_doas_user(self, run_cli: RunCli, config_calls: list[tuple[str, str | None]],
                                monkeypatch: pytest.MonkeyPatch, var: str) -> None:
         monkeypatch.setenv(var, USER)
 
@@ -271,7 +272,7 @@ class TestUser:
         assert last_backup().homedir == HOME
 
     @pytest.mark.usefixtures('as_root')
-    def test_root_without_user(self, run_cli: RunCli, config_calls: list[tuple[str, Optional[str]]],
+    def test_root_without_user(self, run_cli: RunCli, config_calls: list[tuple[str, str | None]],
                                caplog: pytest.LogCaptureFixture) -> None:
         assert run_cli() == 0
         # '~' is left to expanduser, i.e. $HOME