Ruff's new parser is **>2x faster**, which translates to a **20-40% speedup** for all linting and formatting invocations.
There's a lot to say about this exciting change, so check out the [blog post](https://astral.sh/blog/ruff-v0.4.0) for more details!
See [#10036](https://github.com/astral-sh/ruff/pull/10036) for implementation details.
### A new language server in Rust
With this release, we also want to highlight our new language server. `ruff server` is a Rust-powered language
server that comes built-in with Ruff. It can be used with any editor that supports the [Language Server Protocol](https://microsoft.github.io/language-server-protocol/) (LSP).
It uses a multi-threaded, lock-free architecture inspired by `rust-analyzer` and it will open the door for a lot
of exciting features. It’s also faster than our previous [Python-based language server](https://github.com/astral-sh/ruff-lsp)
-- but you probably guessed that already.
`ruff server` is only in alpha, but it has a lot of features that you can try out today:
- Lints Python files automatically and shows quick-fixes when available
- Formats Python files, with support for range formatting
- Comes with commands for quickly performing actions: `ruff.applyAutofix`, `ruff.applyFormat`, and `ruff.applyOrganizeImports`
- Supports `source.fixAll` and `source.organizeImports` source actions
- Automatically reloads your project configuration when you change it
To setup `ruff server` with your editor, refer to the [README.md](https://github.com/astral-sh/ruff/blob/main/crates/ruff_server/README.md).
### Preview features
- \[`pycodestyle`\] Do not trigger `E3` rules on `def`s following a function/method with a dummy body ([#10704](https://github.com/astral-sh/ruff/pull/10704))
- \[`pylint`\] Omit stubs from `invalid-bool` and `invalid-str-return-type` ([#11008](https://github.com/astral-sh/ruff/pull/11008))
- \[`ruff`\] New rule `unused-async` (`RUF029`) to detect unneeded `async` keywords on functions ([#9966](https://github.com/astral-sh/ruff/pull/9966))