Shkarko Ruff 0.9.0

Check out the blog post for a migration guide and overview of the changes!

Breaking changes
Ruff now formats your code according to the 2025 style guide. As a result, your code might now get formatted differently. See the formatter section for a detailed list of changes.

This release doesn’t remove or remap any existing stable rules.

Stabilization
The following rules have been stabilized and are no longer in preview:

- `stdlib-module-shadowing` (A005).
This rule has also been renamed: previously, it was called `builtin-module-shadowing`.
- `builtin-lambda-argument-shadowing` (A006)
- `slice-to-remove-prefix-or-suffix` (FURB188)
- `boolean-chained-comparison` (PLR1716)
- `decimal-from-float-literal` (RUF032)
- `post-init-default` (RUF033)
- `useless-if-else` (RUF034)

The following behaviors have been stabilized:

- `pytest-parametrize-names-wrong-type` (PT006): Detect `pytest.parametrize` calls outside decorators and calls with keyword arguments.
- `module-import-not-at-top-of-file` (E402): Ignore `pytest.importorskip` calls between import statements.
- `mutable-dataclass-default` (RUF008) and `function-call-in-dataclass-default-argument` (RUF009): Add support for `attrs`.
- `bad-version-info-comparison` (PYI006): Extend the rule to check non-stub files.

The following fixes or improvements to fixes have been stabilized:

- `redundant-numeric-union` (PYI041)
- `duplicate-union-members` (PYI016)

Formatter
This release introduces the new 2025 stable style (#13371), stabilizing the following changes:

- Format expressions in f-string elements (#7594)
- Alternate quotes for strings inside f-strings (#13860)
- Preserve the casing of hex codes in f-string debug expressions (#14766)
- Choose the quote style for each string literal in an implicitly concatenated f-string rather than for the entire string (#13539)
- Automatically join an implicitly concatenated string into a single string literal if it fits on a single line (#9457)
- Remove the ISC001 incompatibility warning (#15123)
- Prefer parenthesizing the `assert` message over breaking the assertion expression (#9457)
- Automatically parenthesize over-long `if` guards in `match` `case` clauses (#13513)
- More consistent formatting for `match` `case` patterns (#6933)
- Avoid unnecessary parentheses around return type annotations (#13381)
- Keep the opening parentheses on the same line as the `if` keyword for comprehensions where the condition has a leading comment (#12282)
- More consistent formatting for `with` statements with a single context manager for Python 3.8 or older (#10276)
- Correctly calculate the line-width for code blocks in docstrings when using `max-doc-code-line-length = "dynamic"` (#13523)

Preview features
- [flake8-bugbear] Implement `class-as-data-structure` (B903) (#9601)
- [flake8-type-checking] Apply `quoted-type-alias` more eagerly in `TYPE_CHECKING` blocks and ignore it in stubs (TC008) (#15180)
- [pylint] Ignore `eq-without-hash` in stub files (PLW1641) (#15310)
- [pyupgrade] Split UP007 into two individual rules: UP007 for `Union` and UP045 for `Optional` (UP007, UP045) (#15313)
- [ruff] New rule that detects classes that are both an enum and a `dataclass` (RUF049) (#15299)
- [ruff] Recode RUF025 to RUF037 (RUF037) (#15258)

Rule changes
- [flake8-builtins] Ignore `stdlib-module-shadowing` in stub files(A005) (#15350)
- [flake8-return] Add support for functions returning `typing.Never` (RET503) (#15298)

Server
- Improve the observability by removing the need for the "trace" value to turn on or off logging. The server logging is solely controlled using the `logLevel` server setting
which defaults to `info`. This addresses the issue where users were notified about an error and told to consult the log, but it didn’t contain any messages. (#15232)
- Ignore diagnostics from other sources for code action requests (#15373)

CLI
- Improve the error message for `--config key=value` when the `key` is for a table and it’s a simple `value`

Bug fixes
- [eradicate] Ignore metadata blocks directly followed by normal blocks (ERA001) (#15330)
- [flake8-django] Recognize other magic methods (DJ012) (#15365)
- [pycodestyle] Avoid false positives related to type aliases (E252) (#15356)
- [pydocstyle] Avoid treating newline-separated sections as sub-sections (D405) (#15311)
- [pyflakes] Remove call when removing final argument from `format` (F523) (#15309)
- [refurb] Mark fix as unsafe when the right-hand side is a string (FURB171) (#15273)
- [ruff] Treat `)` as a regex metacharacter (RUF043, RUF055) (#15318)
- [ruff] Parenthesize the `int`-call argument when removing the `int` call would change semantics (RUF046) (#15277)