feat(python): support Ruff formatting and config directories (#1573)

Ruff is now an external formatter for Python next to the Ruff language server: Settings › Languages & Frameworks › Ruff has the executable path, a configuration directory (or file), the provider preference, enabled languages, run-on-save, and Reformat with Ruff. Formatting runs on the unsaved document through stdin (with Ruff's --range for selections, in 1-based code-point columns) and never writes the file first. The configuration directory is shared with Ruff LSP, which can then start without a root marker. Tools that can't format a language are rejected even when requested.

Co-authored-by: muutot <92625353+muutot@users.noreply.github.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ide-core/src/settings.rs

@@ -601,7 +601,7 @@ impl Default for FileSettings {
     }
 }
 
-#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize, Type)]
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Type)]
 #[serde(default, rename_all = "camelCase")]
 pub struct LanguagesSettings {
     pub python: PythonSettings,
@@ -612,11 +612,34 @@ pub struct LanguagesSettings {
     pub typescript: TypeScriptSettings,
     pub prettier: ExternalFormatterSettings,
     pub oxfmt: ExternalFormatterSettings,
+    pub ruff: ExternalFormatterSettings,
     pub java: JavaSettings,
     pub ruby: RubySettings,
     pub markdown: MarkdownSettings,
 }
 
+impl Default for LanguagesSettings {
+    fn default() -> Self {
+        Self {
+            python: PythonSettings::default(),
+            node: NodeSettings::default(),
+            php: PhpSettings::default(),
+            rust: RustSettings::default(),
+            go: GoSettings::default(),
+            typescript: TypeScriptSettings::default(),
+            prettier: ExternalFormatterSettings::default(),
+            oxfmt: ExternalFormatterSettings::default(),
+            ruff: ExternalFormatterSettings {
+                languages: vec!["python".into()],
+                ..ExternalFormatterSettings::default()
+            },
+            java: JavaSettings::default(),
+            ruby: RubySettings::default(),
+            markdown: MarkdownSettings::default(),
+        }
+    }
+}
+
 /// Languages & Frameworks › Markdown. Like IDEA's, it is application-level only.
 #[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize, Type)]
 #[serde(default, rename_all = "camelCase")]
@@ -630,6 +653,7 @@ impl LanguagesSettings {
         match tool {
             ExternalFormatter::Prettier => &self.prettier,
             ExternalFormatter::Oxfmt => &self.oxfmt,
+            ExternalFormatter::Ruff => &self.ruff,
         }
     }
 }
@@ -640,6 +664,7 @@ impl LanguagesSettings {
 pub enum ExternalFormatter {
     Prettier,
     Oxfmt,
+    Ruff,
 }
 
 impl ExternalFormatter {
@@ -648,16 +673,19 @@ impl ExternalFormatter {
         match self {
             Self::Prettier => "prettier",
             Self::Oxfmt => "oxfmt",
+            Self::Ruff => "ruff",
         }
     }
 }
 
-/// An external formatter (Prettier, oxfmt) and the languages it formats.
+/// An external formatter (Prettier, oxfmt, Ruff) and the languages it formats.
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Type)]
 #[serde(default, rename_all = "camelCase")]
 pub struct ExternalFormatterSettings {
-    /// Empty path: project node_modules, managed installation, then PATH.
+    /// Empty path: project node_modules (Prettier/oxfmt), managed installation, then PATH.
     pub path: String,
+    /// Ruff only: directory containing its configuration, or a configuration file.
+    pub configuration_directory: String,
     pub languages: Vec<String>,
     /// Prefer this formatter even when a language server offers formatting.
     pub prefer: bool,
@@ -668,6 +696,7 @@ impl Default for ExternalFormatterSettings {
     fn default() -> Self {
         Self {
             path: String::new(),
+            configuration_directory: String::new(),
             languages: [
                 "markdown",
                 "yaml",

crates/ide-host/src/formatter.rs

@@ -3,7 +3,7 @@
 use crate::Host;
 use ide_core::event::NotifyLevel;
 use ide_core::settings::{ExternalFormatter, LanguagesSettings};
-use ide_core::{DocId, IdeError, IdeEvent, IdeResult, Range, TextEdit};
+use ide_core::{DocId, IdeError, IdeEvent, IdeResult, Pos, Range, TextEdit};
 use ide_language::LanguageConfig;
 use ide_lsp::types::FormatOptions;
 use ide_tools::{Tools, formatter};
@@ -11,20 +11,27 @@ use std::path::Path;
 
 const OXFMT_CONFIGS: [&str; 4] = [".oxfmtrc.json", ".oxfmtrc.jsonc", "oxfmt.config.ts", "oxfmt.config.mts"];
 
+fn supports_external_format(language: &LanguageConfig, tool: ExternalFormatter) -> bool {
+    match language.formatter.as_ref().map(|f| f.tool.as_str()) {
+        Some("prettier") => matches!(tool, ExternalFormatter::Prettier | ExternalFormatter::Oxfmt),
+        Some("ruff") => tool == ExternalFormatter::Ruff,
+        _ => false,
+    }
+}
+
 /// The external formatter of a file, for a language with an external formatter.
-/// `forced` names the tool (Reformat with Prettier/oxfmt). Otherwise oxfmt
-/// applies when it is enabled for the language and either an oxfmt
-/// configuration is found above the file or oxfmt is the selected provider;
-/// else Prettier, when it is enabled. Turning Prettier off for a language
-/// leaves it to the language server, not to oxfmt.
+/// `forced` names the tool (Reformat with Prettier, oxfmt, or Ruff). Ruff is
+/// the base formatter for Python; oxfmt can replace Prettier for its languages
+/// when configured or selected. A tool that cannot format the language is
+/// rejected even when explicitly requested.
 fn external_tool(
     forced: Option<ExternalFormatter>,
     language: Option<&LanguageConfig>,
     file: &Path,
     settings: &LanguagesSettings,
 ) -> IdeResult<Option<ExternalFormatter>> {
-    use ExternalFormatter::{Oxfmt, Prettier};
-    let Some(language) = language.filter(|l| l.formatter.as_ref().is_some_and(|f| f.tool == "prettier")) else {
+    use ExternalFormatter::{Oxfmt, Prettier, Ruff};
+    let Some(language) = language.filter(|l| l.formatter.is_some()) else {
         return match forced {
             Some(tool) => Err(IdeError::invalid(format!(
                 "{} cannot format {} files",
@@ -34,10 +41,21 @@ fn external_tool(
             None => Ok(None),
         };
     };
-    if forced.is_some() {
-        return Ok(forced);
+    if let Some(tool) = forced {
+        return if supports_external_format(language, tool) {
+            Ok(Some(tool))
+        } else {
+            Err(IdeError::invalid(format!(
+                "{} cannot format {} files",
+                formatter::display_name(tool.name()),
+                language.name
+            )))
+        };
     }
     let enabled = |tool| settings.formatter(tool).languages.iter().any(|l| l == language.id.as_str());
+    if language.formatter.as_ref().is_some_and(|f| f.tool == "ruff") {
+        return Ok(enabled(Ruff).then_some(Ruff));
+    }
     let oxfmt_config = || OXFMT_CONFIGS.iter().any(|name| formatter::find_up(file, Path::new(name)).is_some());
     Ok(if enabled(Oxfmt) && (settings.oxfmt.prefer || oxfmt_config()) {
         Some(Oxfmt)
@@ -46,6 +64,34 @@ fn external_tool(
     })
 }
 
+fn codepoint_col(line: &str, utf16_col: u32) -> u32 {
+    let mut units = 0;
+    for (index, ch) in line.chars().enumerate() {
+        if units >= utf16_col {
+            return index as u32;
+        }
+        units += ch.len_utf16() as u32;
+    }
+    line.chars().count() as u32
+}
+
+fn format_range(text: &ide_text::Document, range: Range) -> formatter::FormatRange {
+    let position = |pos: Pos| {
+        let line = text.line(pos.line).unwrap_or_default();
+        (pos.line + 1, codepoint_col(&line, pos.col) + 1)
+    };
+    let (start_line, start_col) = position(range.start);
+    let (end_line, end_col) = position(range.end);
+    formatter::FormatRange {
+        start_offset: text.pos_to_offset(range.start),
+        end_offset: text.pos_to_offset(range.end),
+        start_line,
+        start_col,
+        end_line,
+        end_col,
+    }
+}
+
 pub async fn format(
     host: &Host,
     window: &str,
@@ -85,13 +131,28 @@ pub async fn format(
     let custom = ide_sdk::apply::setting_path(&project.root, &tool_settings.path);
     let tools = Tools::new(&host.local_data_dir);
     let whole_selection = range.is_some() && !formatter::supports_range(tool, &config);
+    let project_root = project.root.clone();
+    let configuration_directory = settings.languages.ruff.configuration_directory.clone();
     let edits: IdeResult<Vec<TextEdit>> = tokio::task::spawn_blocking(move || {
         let text = ide_text::Document::new(&snap.text);
-        let offsets = range.map(|r| (text.pos_to_offset(r.start), text.pos_to_offset(r.end)));
+        let range = range.map(|range| format_range(&text, range));
+        let config_file = if tool == "ruff" {
+            ide_sdk::apply::ruff_configuration(&project_root, &configuration_directory)?
+        } else {
+            None
+        };
         let mut command = tools.formatter_command(tool, &snap.path, custom.as_deref())?;
         let dir = snap.path.parent().ok_or_else(|| IdeError::invalid(format!("{name}: file has no directory")))?;
         command.current_dir(dir);
-        command.args(formatter::arguments(tool, &config, &snap.path, options.tab_size, options.insert_spaces, offsets));
+        command.args(formatter::arguments(
+            tool,
+            &config,
+            &snap.path,
+            options.tab_size,
+            options.insert_spaces,
+            range,
+            config_file.as_deref(),
+        ));
         let formatted = formatter::run(tool, command, &snap.text, &Default::default())?;
         Ok(text
             .diff(&formatted)
@@ -120,7 +181,7 @@ pub async fn format(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use ExternalFormatter::{Oxfmt, Prettier};
+    use ExternalFormatter::{Oxfmt, Prettier, Ruff};
     use ide_core::LanguageId;
     use ide_language::LanguageRegistry;
 
@@ -135,17 +196,36 @@ mod tests {
     }
 
     #[test]
-    fn default_settings_give_every_external_formatter_language_to_prettier() {
+    fn default_settings_use_ruff_for_python_and_prettier_for_the_web() {
         let settings = LanguagesSettings::default();
         let file = Path::new("/project/file");
         for lang in LanguageRegistry::load(None).unwrap().all() {
-            let configured = lang.formatter.as_ref().is_some_and(|f| f.tool == "prettier");
+            let configured = match lang.formatter.as_ref().map(|f| f.tool.as_str()) {
+                Some("prettier") => Some(Prettier),
+                Some("ruff") => Some(Ruff),
+                _ => None,
+            };
             let selected = external_tool(None, Some(&lang), file, &settings).unwrap();
-            assert_eq!(selected, configured.then_some(Prettier), "{}", lang.id);
+            assert_eq!(selected, configured, "{}", lang.id);
         }
         assert_eq!(external_tool(None, None, file, &settings).unwrap(), None);
     }
 
+    #[test]
+    fn ruff_is_the_python_external_formatter_and_is_opt_out() {
+        let file = Path::new("/project/src/example.py");
+        let mut settings = LanguagesSettings::default();
+        assert_eq!(tool(None, "python", file, &settings).unwrap(), Some(Ruff));
+        assert_eq!(tool(Some(Ruff), "python", file, &settings).unwrap(), Some(Ruff));
+        settings.ruff.languages.clear();
+        assert_eq!(tool(None, "python", file, &settings).unwrap(), None);
+        assert_eq!(tool(Some(Ruff), "python", file, &settings).unwrap(), Some(Ruff));
+        let prettier = tool(Some(Prettier), "python", file, &settings).unwrap_err();
+        assert_eq!(prettier.message, "Prettier cannot format Python files");
+        let oxfmt = tool(Some(Oxfmt), "python", file, &settings).unwrap_err();
+        assert_eq!(oxfmt.message, "oxfmt cannot format Python files");
+    }
+
     #[test]
     fn oxfmt_config_selects_oxfmt_for_its_enabled_languages() {
         let dir = tempfile::tempdir().unwrap();
@@ -192,4 +272,21 @@ mod tests {
         let rust = tool(Some(Oxfmt), "rust", &dir.path().join("main.rs"), &settings).unwrap_err();
         assert_eq!(rust.message, "oxfmt cannot format Rust files");
     }
+
+    #[test]
+    fn ruff_ranges_are_one_based_unicode_columns() {
+        let text = ide_text::Document::new("😀x = 1\ny  =  2\n");
+        let range = Range::new(Pos::new(0, 2), Pos::new(1, 2));
+        assert_eq!(
+            format_range(&text, range),
+            formatter::FormatRange {
+                start_offset: 2,
+                end_offset: 10,
+                start_line: 1,
+                start_col: 2,
+                end_line: 2,
+                end_col: 3,
+            }
+        );
+    }
 }

crates/ide-sdk/src/apply.rs

@@ -7,6 +7,7 @@ use crate::{angular, godot, pinned, vue};
 use crate::{bin_dir, exe, venv_of};
 use ide_core::settings::{InspectionLevel, InspectionSettings, LanguageServerSettings, Settings};
 use ide_core::version_managers::Tool;
+use ide_core::{IdeError, IdeResult};
 use ide_language::{LanguageConfig, LanguageServerConfig};
 use ide_run::RunConfig;
 use serde_json::{Value, json};
@@ -28,6 +29,39 @@ pub fn setting_path(root: &Path, s: &str) -> Option<PathBuf> {
     Some(if p.is_absolute() { p } else { root.join(p) })
 }
 
+fn toml_has_table(file: &Path, table: &str) -> bool {
+    let Ok(text) = std::fs::read_to_string(file) else { return false };
+    let Ok(value) = toml::from_str::<toml::Value>(&text) else { return false };
+    table.split('.').try_fold(&value, |value, key| value.get(key)).is_some_and(toml::Value::is_table)
+}
+
+/// The Ruff configuration file selected by `languages.ruff.configurationDirectory`.
+/// A file can be chosen directly; a directory resolves `ruff.toml`, `.ruff.toml`,
+/// then a `pyproject.toml` containing `[tool.ruff]`.
+pub fn ruff_configuration(root: &Path, configured: &str) -> IdeResult<Option<PathBuf>> {
+    let Some(path) = setting_path(root, configured) else { return Ok(None) };
+    if path.is_file() {
+        return Ok(Some(path));
+    }
+    if !path.is_dir() {
+        return Err(IdeError::invalid(format!("Ruff configuration path does not exist: {}", path.display())));
+    }
+    for name in ["ruff.toml", ".ruff.toml"] {
+        let file = path.join(name);
+        if file.is_file() {
+            return Ok(Some(file));
+        }
+    }
+    let pyproject = path.join("pyproject.toml");
+    if toml_has_table(&pyproject, "tool.ruff") {
+        return Ok(Some(pyproject));
+    }
+    Err(IdeError::invalid(format!(
+        "Ruff configuration directory has no ruff.toml, .ruff.toml, or pyproject.toml with [tool.ruff]: {}",
+        path.display()
+    )))
+}
+
 /// The project interpreter: the configured one, else a project virtualenv
 /// (`.venv`, `venv`, …) in the project root, else the Python the project pins for mise / asdf.
 pub fn python_interpreter(root: &Path, s: &Settings) -> Option<PathBuf> {
@@ -575,6 +609,18 @@ pub fn configure_server(cfg: &mut LanguageServerConfig, root: &Path, server_root
         }
     }
 
+    if name == "ruff" {
+        match ruff_configuration(root, &s.languages.ruff.configuration_directory) {
+            Ok(Some(path)) => {
+                let mut settings = cfg.settings.take().filter(Value::is_object).unwrap_or_else(|| json!({}));
+                settings["configuration"] = json!(path.to_string_lossy());
+                cfg.settings = Some(settings);
+            }
+            Ok(None) => {}
+            Err(e) => cfg.launch_error = Some(e.message),
+        }
+    }
+
     if name == "rust-analyzer" {
         let r = &s.languages.rust;
         let extra_args: Vec<&str> = r.rustfmt_args.split_whitespace().collect();
@@ -719,6 +765,11 @@ pub fn language_servers(language: &str, defined: &[LanguageServerConfig], s: &Se
             out.push(custom_server(name, ls));
         }
     }
+    if non_empty(&s.languages.ruff.configuration_directory).is_some() {
+        for cfg in out.iter_mut().filter(|cfg| cfg.name == "ruff") {
+            cfg.require_root_marker = false;
+        }
+    }
     out
 }
 

crates/ide-sdk/src/tests.rs

@@ -1,6 +1,6 @@
 use crate::apply::{
     apply_to_run_configs, configure_server, jdtls_jdk, maven_command, maven_options, project_jdk, python_interpreter,
-    terminal_activation, tsdk, without_derived,
+    ruff_configuration, terminal_activation, tsdk, without_derived,
 };
 use crate::python::parse_pip_list;
 use crate::{bin_dir, exe, venv_of};
@@ -481,6 +481,9 @@ fn language_server_settings_disable_add_and_override() {
         (ruff.command.as_str(), ruff.args.as_slice()),
         ("/opt/ruff", &["server".to_string(), "--preview".to_string()][..])
     );
+    s.languages.ruff.configuration_directory = "ruff-config".into();
+    let defined = [server("ruff")];
+    assert!(!language_servers("python", &defined, &s)[0].require_root_marker);
 
     s.language_servers.insert(
         "rust-analyzer".into(),
@@ -523,6 +526,38 @@ fn language_server_settings_disable_add_and_override() {
     assert_eq!(parsed.code_action_kinds, Some(vec!["refactor".to_string()]));
 }
 
+#[test]
+fn ruff_configuration_directory_resolves_files_and_validates_pyproject() {
+    let tmp = tempfile::tempdir().unwrap();
+    let root = tmp.path();
+    let dir = root.join("shared ruff");
+    std::fs::create_dir_all(&dir).unwrap();
+    assert_eq!(ruff_configuration(root, "").unwrap(), None);
+    assert!(ruff_configuration(root, &dir.to_string_lossy()).unwrap_err().message.contains("has no"));
+
+    let ruff = dir.join("ruff.toml");
+    std::fs::write(&ruff, "line-length = 100\n").unwrap();
+    assert_eq!(ruff_configuration(root, &dir.to_string_lossy()).unwrap(), Some(ruff.clone()));
+    assert_eq!(ruff_configuration(root, &ruff.to_string_lossy()).unwrap(), Some(ruff));
+
+    std::fs::remove_file(dir.join("ruff.toml")).unwrap();
+    let pyproject = dir.join("pyproject.toml");
+    std::fs::write(&pyproject, "[project]\nname = \"x\"\n").unwrap();
+    assert!(ruff_configuration(root, &dir.to_string_lossy()).unwrap_err().message.contains("has no"));
+    std::fs::write(&pyproject, "[tool.ruff]\nline-length = 100\n").unwrap();
+    assert_eq!(ruff_configuration(root, &dir.to_string_lossy()).unwrap(), Some(pyproject.clone()));
+
+    let mut settings = Settings::default();
+    settings.languages.ruff.configuration_directory = dir.to_string_lossy().into_owned();
+    let mut cfg = server("ruff");
+    configure_server(&mut cfg, root, root, &settings);
+    let configured = dir.join("pyproject.toml").to_string_lossy().into_owned();
+    assert_eq!(
+        cfg.settings.as_ref().and_then(|s| s.get("configuration")).and_then(|v| v.as_str()),
+        Some(configured.as_str())
+    );
+}
+
 #[test]
 fn jdtls_jdk_setting() {
     if cfg!(windows) {

crates/ide-tools/src/formatter.rs

@@ -8,6 +8,18 @@ use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::time::Duration;
 
+/// A selection to format. Offsets are UTF-16 code units for Prettier; the
+/// one-based line and column values are Unicode code points for Ruff.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct FormatRange {
+    pub start_offset: u32,
+    pub end_offset: u32,
+    pub start_line: u32,
+    pub start_col: u32,
+    pub end_line: u32,
+    pub end_col: u32,
+}
+
 /// Walk from the file's directory upward, including workspace parents (monorepos).
 pub fn find_up(file: &Path, relative: &Path) -> Option<PathBuf> {
     file.parent()?.ancestors().map(|dir| dir.join(relative)).find(|p| p.is_file())
@@ -32,9 +44,13 @@ fn package_bin(package: &Path, tool: &str) -> IdeResult<PathBuf> {
     Ok(path)
 }
 
-/// Prettier formats a range for some languages (`config.range`); oxfmt formats whole files only.
+/// Prettier and Ruff format ranges for some languages (`config.range`); oxfmt formats whole files only.
 pub fn supports_range(tool: &str, config: &FormatterConfig) -> bool {
-    tool == "prettier" && config.range
+    matches!(tool, "prettier" | "ruff") && config.range
+}
+
+fn is_formatter(tool: &str) -> bool {
+    crate::registry::find(tool).is_some_and(|t| t.kind == crate::ToolKind::Formatter || t.name == "ruff")
 }
 
 impl Tools {
@@ -44,7 +60,7 @@ impl Tools {
     }
 
     fn resolve_formatter_command(&self, tool: &str, file: &Path, custom: Option<&Path>) -> IdeResult<Command> {
-        if crate::registry::find(tool).is_none_or(|t| t.kind != crate::ToolKind::Formatter) {
+        if !is_formatter(tool) {
             return Err(IdeError::unavailable(format!("Unknown external formatter: {tool}")));
         }
         let package = Path::new("node_modules").join(tool);
@@ -73,18 +89,36 @@ impl Tools {
     }
 }
 
-/// Both tools resolve their configuration and plugins themselves. Prettier's
-/// project configuration overrides the editor indentation passed here; oxfmt has
-/// no such flags and reads its configuration and `.editorconfig` only.
+/// Every tool resolves its configuration itself. Prettier's project configuration
+/// overrides the editor indentation passed here; oxfmt and Ruff read their own
+/// configuration files. Ruff also discovers the nearest `pyproject.toml`,
+/// `ruff.toml`, or `.ruff.toml` from the stdin filename.
 pub fn arguments(
     tool: &str,
     config: &FormatterConfig,
     file: &Path,
     tab_size: u32,
     insert_spaces: bool,
-    range: Option<(u32, u32)>,
+    range: Option<FormatRange>,
+    config_file: Option<&Path>,
 ) -> Vec<OsString> {
     let mut args: Vec<OsString> = Vec::new();
+    if tool == "ruff" {
+        args.push("format".into());
+        if let Some(config_file) = config_file {
+            args.extend(["--config".into(), config_file.as_os_str().to_owned()]);
+        }
+        args.extend(["--stdin-filename".into(), file.as_os_str().to_owned(), "-".into()]);
+        if supports_range(tool, config)
+            && let Some(range) = range
+        {
+            args.extend([
+                "--range".into(),
+                format!("{}:{}-{}:{}", range.start_line, range.start_col, range.end_line, range.end_col).into(),
+            ]);
+        }
+        return args;
+    }
     if tool == "prettier" {
         let parser = if config.parser == "markdown" && file.extension().is_some_and(|s| s == "mdx") {
             "mdx"
@@ -107,9 +141,14 @@ pub fn arguments(
     }
     args.extend(["--stdin-filepath".into(), file.as_os_str().to_owned()]);
     if supports_range(tool, config)
-        && let Some((start, end)) = range
+        && let Some(range) = range
     {
-        args.extend(["--range-start".into(), start.to_string().into(), "--range-end".into(), end.to_string().into()]);
+        args.extend([
+            "--range-start".into(),
+            range.start_offset.to_string().into(),
+            "--range-end".into(),
+            range.end_offset.to_string().into(),
+        ]);
     }
     // CLI defaults only find ignores in cwd; explicitly pass the nearest ancestor's files.
     for name in [".prettierignore", ".gitignore"] {
@@ -181,8 +220,15 @@ mod tests {
             ("vue", true),
         ] {
             let config = FormatterConfig { tool: "prettier".into(), parser: parser.into(), range: supports_range };
-            let args =
-                arguments("prettier", &config, Path::new("/project with spaces/file.md"), 4, false, Some((3, 9)));
+            let range = Some(FormatRange {
+                start_offset: 3,
+                end_offset: 9,
+                start_line: 1,
+                start_col: 1,
+                end_line: 1,
+                end_col: 7,
+            });
+            let args = arguments("prettier", &config, Path::new("/project with spaces/file.md"), 4, false, range, None);
             let args: Vec<_> = args.iter().map(|a| a.to_string_lossy()).collect();
             assert!(args.windows(2).any(|a| a == ["--config-precedence", "file-override"]));
             assert!(args.windows(2).any(|a| a == ["--stdin-filepath", "/project with spaces/file.md"]));
@@ -217,7 +263,9 @@ mod tests {
         );
 
         let config = FormatterConfig { tool: "prettier".into(), parser: "typescript".into(), range: true };
-        let args = arguments("oxfmt", &config, &file, 4, false, Some((3, 9)));
+        let range =
+            Some(FormatRange { start_offset: 3, end_offset: 9, start_line: 1, start_col: 1, end_line: 1, end_col: 7 });
+        let args = arguments("oxfmt", &config, &file, 4, false, range, None);
         let ignore = root.join(".prettierignore").into_os_string();
         assert_eq!(
             args[..4],
@@ -229,4 +277,38 @@ mod tests {
         let unknown = tools.formatter_command("rust-analyzer", &file, None).unwrap_err();
         assert!(unknown.message.contains("Unknown external formatter"), "{}", unknown.message);
     }
+
+    #[test]
+    fn ruff_formats_stdin_and_uses_its_config_and_range_flags() {
+        let config = FormatterConfig { tool: "ruff".into(), parser: "python".into(), range: true };
+        let file = Path::new("/project with spaces/src/example.py");
+        let range = Some(FormatRange {
+            start_offset: 10,
+            end_offset: 20,
+            start_line: 2,
+            start_col: 5,
+            end_line: 4,
+            end_col: 1,
+        });
+        let config_file = Path::new("/shared/config/ruff.toml");
+        let args: Vec<_> = arguments("ruff", &config, file, 4, true, range, Some(config_file))
+            .into_iter()
+            .map(|arg| arg.to_string_lossy().into_owned())
+            .collect();
+        assert_eq!(
+            args,
+            [
+                "format",
+                "--config",
+                "/shared/config/ruff.toml",
+                "--stdin-filename",
+                "/project with spaces/src/example.py",
+                "-",
+                "--range",
+                "2:5-4:1",
+            ]
+        );
+        assert!(supports_range("ruff", &config));
+        assert!(!args.iter().any(|arg| arg == "--stdin-filepath"));
+    }
 }

crates/ide-tools/tests/prettier.rs

@@ -19,7 +19,15 @@ fn format(
     };
     let mut cmd = tools.formatter_command("prettier", path, None)?;
     cmd.current_dir(path.parent().unwrap());
-    cmd.args(formatter::arguments("prettier", &config, path, 4, true, range));
+    let range = range.map(|(start_offset, end_offset)| formatter::FormatRange {
+        start_offset,
+        end_offset,
+        start_line: 1,
+        start_col: 1,
+        end_line: 1,
+        end_col: 1,
+    });
+    cmd.args(formatter::arguments("prettier", &config, path, 4, true, range, None));
     formatter::run("prettier", cmd, text, &CancellationToken::new())
 }
 

crates/ide-tools/tests/ruff.rs

@@ -0,0 +1,67 @@
+//! `cargo test -p ide-tools --test ruff -- --ignored --nocapture`
+
+use ide_core::CancellationToken;
+use ide_language::FormatterConfig;
+use ide_tools::{Tools, formatter};
+use std::path::Path;
+
+fn format(
+    tools: &Tools,
+    path: &Path,
+    text: &str,
+    range: Option<formatter::FormatRange>,
+    config_file: Option<&Path>,
+) -> ide_core::IdeResult<String> {
+    let config = FormatterConfig { tool: "ruff".into(), parser: "python".into(), range: true };
+    let mut cmd = tools.formatter_command("ruff", path, None)?;
+    cmd.current_dir(path.parent().unwrap());
+    cmd.args(formatter::arguments("ruff", &config, path, 4, true, range, config_file));
+    formatter::run("ruff", cmd, text, &CancellationToken::new())
+}
+
+#[test]
+#[ignore = "requires ruff on PATH"]
+fn real_ruff_reads_project_config_formats_stdin_and_supports_ranges() {
+    let temp = tempfile::tempdir().unwrap();
+    let tools = Tools::new(&temp.path().join("app-data"));
+    if tools.info("ruff", &[]).unwrap().status == ide_tools::ToolStatus::Missing {
+        eprintln!("SKIP real Ruff: not on PATH");
+        return;
+    }
+    let project = temp.path().join("project with spaces");
+    std::fs::create_dir_all(&project).unwrap();
+    std::fs::write(project.join("pyproject.toml"), "[tool.ruff.format]\nquote-style = \"single\"\n").unwrap();
+    let path = project.join("example.py");
+    let input = "def greet(name):\n    return {\"message\": name}\n";
+    let output = format(&tools, &path, input, None, None).unwrap();
+    assert_eq!(output, "def greet(name):\n    return {'message': name}\n");
+    assert!(!path.exists(), "formatting must never write the file");
+
+    let range = formatter::FormatRange {
+        start_offset: 0,
+        end_offset: 0,
+        start_line: 2,
+        start_col: 1,
+        end_line: 2,
+        end_col: 100,
+    };
+    let mixed = "def untouched( a,b ):\n    return {\"message\": name}\n";
+    let output = format(&tools, &path, mixed, Some(range), None).unwrap();
+    assert!(output.starts_with("def untouched( a,b ):"), "{output}");
+    assert!(output.contains("return {'message': name}"), "{output}");
+
+    let shared = temp.path().join("shared config");
+    std::fs::create_dir_all(&shared).unwrap();
+    let shared_config = shared.join("ruff.toml");
+    std::fs::write(&shared_config, "[format]\nquote-style = \"double\"\n").unwrap();
+    std::fs::remove_file(project.join("pyproject.toml")).unwrap();
+    let output = format(&tools, &path, input, None, Some(&shared_config)).unwrap();
+    assert_eq!(output, "def greet(name):\n    return {\"message\": name}\n");
+
+    let invalid = "def broken(:\n    pass\n";
+    let error = format(&tools, &path, invalid, None, Some(&shared_config)).unwrap_err();
+    assert!(error.message.contains("Failed to parse"), "{}", error.message);
+    eprintln!(
+        "PASS: real Ruff config discovery, custom config file, stdin formatting, quote style, range, invalid syntax diagnostics, no disk writes"
+    );
+}

crates/ide-workspace/src/settings.rs

@@ -479,6 +479,10 @@ mod tests {
         let text = std::fs::read_to_string(added.join("settings.toml")).unwrap();
         assert_eq!(text, "[languageServers.ruff]\nargs = [\"server\"]\ncommand = \"ruff\"\nlanguages = [\"python\"]\n");
 
+        let s =
+            store.set(SettingsScope::Global, "languages.ruff.configurationDirectory", json!("shared/ruff")).unwrap();
+        assert_eq!(s.languages.ruff.configuration_directory, "shared/ruff");
+
         // Project layer is created on demand and wins.
         let s = store.set(SettingsScope::Project, "editor.fontSize", json!(12)).unwrap();
         assert_eq!(s.editor.font_size, 12.0);

languages/python.toml

@@ -1,5 +1,6 @@
 id = "python"
 name = "Python"
+formatter = { tool = "ruff", parser = "python", range = true }
 extensions = ["py", "pyi", "pyw"]
 filenames = ["SConstruct", "SConscript"]
 first-line = "^#!.*\\bpython[0-9.]*\\b"

src/bindings.ts

@@ -3489,12 +3489,14 @@ export type ExtensionCount = {
 };
 
 /**  A formatter that runs outside the language servers, with its own settings group. */
-export type ExternalFormatter = "prettier" | "oxfmt";
+export type ExternalFormatter = "prettier" | "oxfmt" | "ruff";
 
-/**  An external formatter (Prettier, oxfmt) and the languages it formats. */
+/**  An external formatter (Prettier, oxfmt, Ruff) and the languages it formats. */
 export type ExternalFormatterSettings = {
-	/**  Empty path: project node_modules, managed installation, then PATH. */
+	/**  Empty path: project node_modules (Prettier/oxfmt), managed installation, then PATH. */
 	path?: string,
+	/**  Ruff only: directory containing its configuration, or a configuration file. */
+	configurationDirectory?: string,
 	languages?: string[],
 	/**  Prefer this formatter even when a language server offers formatting. */
 	prefer?: boolean,
@@ -4815,6 +4817,7 @@ export type LanguagesSettings = {
 	typescript?: TypeScriptSettings,
 	prettier?: ExternalFormatterSettings,
 	oxfmt?: ExternalFormatterSettings,
+	ruff?: ExternalFormatterSettings,
 	java?: JavaSettings,
 	ruby?: RubySettings,
 	markdown?: MarkdownSettings,

src/editor/lsp/actions.ts

@@ -124,12 +124,12 @@ function editorAction(
   return { id, title, category, when: EDITOR_WHEN, run: withEditor(run), ...extra };
 }
 
-/** Whether saving a `language` file formats it: Format on save, or Run on save of Prettier or oxfmt. */
+/** Whether saving a `language` file formats it: Format on save, or Run on save of an external formatter. */
 export function formatsOnSave(settings: Settings | null, language: string): boolean {
-  const { prettier, oxfmt } = validateLanguages(settings?.languages);
+  const { prettier, oxfmt, ruff } = validateLanguages(settings?.languages);
   return (
     !!settings?.editor?.formatOnSave ||
-    [prettier, oxfmt].some((formatter) => formatter.runOnSave && formatter.languages.includes(language))
+    [prettier, oxfmt, ruff].some((formatter) => formatter.runOnSave && formatter.languages.includes(language))
   );
 }
 
@@ -206,6 +206,13 @@ export function registerLspActions(): () => void {
       (v) => formatDocument(v, { explicit: true, tool: "oxfmt" }),
       { keywords: ["format", "oxfmt", "oxc"] },
     ),
+    editorAction(
+      "code.reformatWithRuff",
+      "Reformat with Ruff",
+      "Code",
+      (v) => formatDocument(v, { explicit: true, tool: "ruff" }),
+      { keywords: ["format", "ruff", "python"] },
+    ),
     editorAction("code.reformatDialog", "Reformat File…", "Code", (v) =>
       reformatDialog(v, (view) => applyKindSilently(view, "source.organizeImports")),
     ),

src/editor/lsp/format.test.ts

@@ -177,6 +177,8 @@ describe("format on save provider isolation", () => {
     expect(formatsOnSave(oxfmt, "typescript")).toBe(true);
     expect(formatsOnSave(oxfmt, "markdown")).toBe(false);
     expect(formatsOnSave(settings({ prettier: { runOnSave: true } }), "markdown")).toBe(true);
+    expect(formatsOnSave(settings({ ruff: { runOnSave: true } }), "python")).toBe(true);
+    expect(formatsOnSave(settings({ ruff: { runOnSave: true } }), "typescript")).toBe(false);
     expect(formatsOnSave(settings({}), "typescript")).toBe(false);
     expect(formatsOnSave(settings({}, true), "rust")).toBe(true);
     expect(formatsOnSave(null, "typescript")).toBe(false);

src/editor/lsp/format.ts

@@ -136,20 +136,26 @@ async function format(view: EditorView, opts: FormatDocumentOptions): Promise<Fo
       commands.lspFormat(doc.doc, range, { ...options, onSave: opts.onSave, tool: opts.tool }),
     );
   } catch (e) {
-    if (e instanceof IpcError && e.data?.type === "tool" && (e.data.tool === "prettier" || e.data.tool === "oxfmt")) {
+    const formatter =
+      e instanceof IpcError && e.data?.type === "tool"
+        ? {
+            prettier: { failed: "Prettier formatting failed", timedOut: "Prettier formatting timed out" },
+            oxfmt: { failed: "oxfmt formatting failed", timedOut: "oxfmt formatting timed out" },
+            ruff: { failed: "Ruff formatting failed", timedOut: "Ruff formatting timed out" },
+          }[e.data.tool]
+        : undefined;
+    if (e instanceof IpcError && e.data?.type === "tool" && formatter) {
       const tool = e.data.tool;
       if (e.kind === "notFound" && e.data.missing) {
-        await executeAction("tools.promptInstall", { name: tool, sticky: !opts.onSave });
+        await executeAction("tools.promptInstall", { name: tool, sticky: !opts.onSave, formatter: true });
       } else if (e.kind !== "cancelled") {
         notifications().notify({
           group: "tools",
           level: "error",
-          title: tool === "oxfmt" ? tx("oxfmt formatting failed") : tx("Prettier formatting failed"),
+          title: tx(formatter.failed),
           body:
             e.kind === "timedOut"
-              ? tool === "oxfmt"
-                ? tx("oxfmt formatting timed out")
-                : tx("Prettier formatting timed out")
+              ? tx(formatter.timedOut)
               : createElement("span", { className: styles.diagnostics }, e.message),
           key: `${tool}-format-error:${doc.path}`,
           sticky: false,

src/editor/lsp/formatErrors.test.tsx

@@ -44,9 +44,9 @@ afterEach(() => {
   _resetI18nForTests();
 });
 
-describe.each(["prettier", "oxfmt"])("%s formatter errors", (name) => {
+describe.each(["prettier", "oxfmt", "ruff"])("%s formatter errors", (name) => {
   const tool = { type: "tool", tool: name, missing: false } as const;
-  const display = name === "prettier" ? "Prettier" : name;
+  const display = name === "prettier" ? "Prettier" : name === "ruff" ? "Ruff" : name;
   it("uses structured missing-tool information to request the shared install prompt", async () => {
     const prompt = vi.fn();
     const dispose = registerAction({
@@ -57,9 +57,9 @@ describe.each(["prettier", "oxfmt"])("%s formatter errors", (name) => {
     try {
       failWith({ kind: "notFound", message: "unrelated diagnostic", data: { ...tool, missing: true } });
       await formatDocument(viewFor());
-      expect(prompt).toHaveBeenCalledWith({ name, sticky: true });
+      expect(prompt).toHaveBeenCalledWith({ name, sticky: true, formatter: true });
       await formatDocument(viewFor(), { explicit: false, onSave: true });
-      expect(prompt).toHaveBeenLastCalledWith({ name, sticky: false });
+      expect(prompt).toHaveBeenLastCalledWith({ name, sticky: false, formatter: true });
       expect(useNotifications.getState().items).toHaveLength(0);
     } finally {
       dispose();
@@ -126,10 +126,11 @@ describe.each(["prettier", "oxfmt"])("%s formatter errors", (name) => {
   });
 });
 
-describe("Reformat with Prettier / oxfmt", () => {
+describe("Reformat with an external formatter", () => {
   it.each([
     ["code.reformatWithPrettier", "prettier"],
     ["code.reformatWithOxfmt", "oxfmt"],
+    ["code.reformatWithRuff", "ruff"],
   ])("%s asks the backend for %s whatever the settings select", async (id, tool) => {
     vi.spyOn(lsp, "lspRequest").mockImplementation(async (request) => {
       await request();

src/features/settings/__tests__/languages.test.ts

@@ -92,7 +92,13 @@ describe("languages settings", () => {
       validateLanguages({
         prettier: { path: " ./bin/prettier ", languages: ["markdown", 4, "markdown"], prefer: true, runOnSave: true },
       }).prettier,
-    ).toEqual({ path: "./bin/prettier", languages: ["markdown"], prefer: true, runOnSave: true });
+    ).toEqual({
+      path: "./bin/prettier",
+      configurationDirectory: "",
+      languages: ["markdown"],
+      prefer: true,
+      runOnSave: true,
+    });
     expect(validateLanguages({ prettier: { languages: [] } }).prettier.languages).toEqual([]);
   });
 
@@ -102,10 +108,43 @@ describe("languages settings", () => {
       prettier: { runOnSave: true },
       oxfmt: { path: " ./bin/oxfmt ", languages: ["typescript", null, "typescript"], prefer: true },
     });
-    expect(v.oxfmt).toEqual({ path: "./bin/oxfmt", languages: ["typescript"], prefer: true, runOnSave: false });
+    expect(v.oxfmt).toEqual({
+      path: "./bin/oxfmt",
+      configurationDirectory: "",
+      languages: ["typescript"],
+      prefer: true,
+      runOnSave: false,
+    });
     expect(v.prettier).toMatchObject({ runOnSave: true, prefer: false, path: "" });
   });
 
+  it("enables Ruff for Python by default and keeps its settings separate", () => {
+    expect(validateLanguages({}).ruff).toMatchObject({
+      path: "",
+      configurationDirectory: "",
+      languages: ["python"],
+      prefer: false,
+      runOnSave: false,
+    });
+    const v = validateLanguages({
+      ruff: {
+        path: " ./bin/ruff ",
+        configurationDirectory: " ./config/ruff ",
+        languages: ["python", null, "python", "pyi"],
+        prefer: true,
+        runOnSave: true,
+      },
+    });
+    expect(v.ruff).toEqual({
+      path: "./bin/ruff",
+      configurationDirectory: "./config/ruff",
+      languages: ["python", "pyi"],
+      prefer: true,
+      runOnSave: true,
+    });
+    expect(v.prettier).toEqual(DEFAULT_LANGUAGES.prettier);
+  });
+
   it("leaves the Markdown preview font size unset (editor font) and keeps a set one in 8..72", () => {
     expect(validateLanguages({}).markdown).toEqual({ previewFontSize: null });
     expect(validateLanguages({ markdown: { previewFontSize: 90 } }).markdown).toEqual({ previewFontSize: 72 });
@@ -143,6 +182,7 @@ describe("language pages", () => {
       "PHP",
       "Prettier",
       "oxfmt",
+      "Ruff",
       "Ruby",
       "Rust",
       "TypeScript",

src/features/settings/languages/FormatterPage.tsx

@@ -1,9 +1,11 @@
 import { useId } from "react";
 import type { ExternalFormatter } from "@/bindings";
-import { Input } from "@/ui";
+import { IconButton, Input } from "@/ui";
 import { Row, Section, Select, Toggle } from "../components/Form";
 import { useSetting } from "../components/context";
 import { DEFAULT_LANGUAGES } from "@/platform/languageSettings";
+import { choosePath } from "./api";
+import styles from "./Sdk.module.css";
 
 const names: Record<string, string> = {
   markdown: "Markdown",
@@ -20,17 +22,28 @@ const names: Record<string, string> = {
   json: "JSON",
   jsonc: "JSON with Comments",
   vue: "Vue",
+  python: "Python",
 };
 
 interface FormatterPageProps {
   tool: ExternalFormatter;
   name: string;
   pathLabel: string;
+  pathHint?: string;
+  configurationDirectory?: boolean;
   providerHint?: string;
   saveHint: string;
 }
 
-function FormatterPage({ tool, name, pathLabel, providerHint, saveHint }: FormatterPageProps) {
+function FormatterPage({
+  tool,
+  name,
+  pathLabel,
+  pathHint = "Auto: nearest project node_modules, managed installation, then PATH. An explicit path overrides auto detection.",
+  configurationDirectory = false,
+  providerHint,
+  saveHint,
+}: FormatterPageProps) {
   const id = useId();
   const [path, setPath] = useSetting<string>(`languages.${tool}.path`);
   const [languages, setLanguages] = useSetting<string[]>(`languages.${tool}.languages`);
@@ -39,13 +52,10 @@ function FormatterPage({ tool, name, pathLabel, providerHint, saveHint }: Format
   return (
     <>
       <Section title={name}>
-        <Row
-          label={pathLabel}
-          htmlFor={id}
-          hint="Auto: nearest project node_modules, managed installation, then PATH. An explicit path overrides auto detection."
-        >
+        <Row label={pathLabel} htmlFor={id} hint={pathHint}>
           <Input id={id} mono value={path} placeholder="Auto" onChange={(e) => setPath(e.target.value)} />
         </Row>
+        {configurationDirectory && <ConfigurationDirectory settingKey={`languages.${tool}.configurationDirectory`} />}
         <Row label="Formatting provider" hint={providerHint}>
           <Select
             value={prefer ? tool : "auto"}
@@ -75,6 +85,43 @@ function FormatterPage({ tool, name, pathLabel, providerHint, saveHint }: Format
   );
 }
 
+function ConfigurationDirectory({ settingKey }: { settingKey: string }) {
+  const id = useId();
+  const [path, setPath] = useSetting<string>(settingKey);
+  return (
+    <Row
+      label="Configuration directory"
+      htmlFor={id}
+      hint="Empty uses the nearest project pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. A configured directory must contain one of them."
+    >
+      <span className={styles.pathRow}>
+        <Input
+          id={id}
+          mono
+          className={styles.pathInput}
+          value={path}
+          placeholder="Project configuration"
+          onChange={(e) => setPath(e.target.value)}
+        />
+        <IconButton
+          icon="folder-open"
+          size="small"
+          title="Browse…"
+          aria-label="Select Ruff Configuration Directory"
+          onClick={async () => {
+            const picked = await choosePath({
+              directory: true,
+              title: "Select Ruff Configuration Directory",
+              defaultPath: path || undefined,
+            });
+            if (picked) setPath(picked);
+          }}
+        />
+      </span>
+    </Row>
+  );
+}
+
 export function PrettierPage() {
   return (
     <FormatterPage
@@ -97,3 +144,17 @@ export function OxfmtPage() {
     />
   );
 }
+
+export function RuffPage() {
+  return (
+    <FormatterPage
+      tool="ruff"
+      name="Ruff"
+      pathLabel="Ruff path"
+      pathHint="Auto: managed installation, then PATH. An explicit path overrides auto detection."
+      configurationDirectory
+      providerHint="Ruff reads the nearest pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. Use it before the language server when preferred."
+      saveHint="Run Ruff on save for enabled languages when it is the selected formatting provider."
+    />
+  );
+}

src/features/settings/pages/languages.tsx

@@ -5,7 +5,7 @@
  */
 import { GoPage, JavaPage, NodePage, PhpPage, RubyPage, RustPage, TypeScriptPage } from "../languages/LanguagePages";
 import { MarkdownPage } from "../languages/MarkdownPage";
-import { OxfmtPage, PrettierPage } from "../languages/FormatterPage";
+import { OxfmtPage, PrettierPage, RuffPage } from "../languages/FormatterPage";
 import { ProjectStructurePage } from "../languages/ProjectStructurePage";
 import { PythonInterpreterPage } from "../languages/PythonInterpreterPage";
 import { GoBuildTagsPage, GO_BUILD_TAG_SECTIONS } from "../languages/GoBuildTags";
@@ -138,6 +138,24 @@ export const LANGUAGE_PAGES: PageSpec[] = [
     keywords: ["formatter", "oxfmt", "oxc", ".oxfmtrc.json", "format on save", "node_modules"],
     component: OxfmtPage,
   },
+  {
+    id: "languages.ruff",
+    projectScope: true,
+    defaultScope: "project",
+    title: "Ruff",
+    group: LANGUAGES_GROUP,
+    order: 403.7,
+    keywords: [
+      "formatter",
+      "ruff",
+      "python",
+      "configuration directory",
+      "pyproject.toml",
+      "ruff.toml",
+      "format on save",
+    ],
+    component: RuffPage,
+  },
   {
     id: "languages.php",
     projectScope: true,

src/features/tools/__tests__/tools.test.tsx

@@ -147,6 +147,25 @@ describe("missing language server prompt", () => {
     off();
   });
 
+  it("offers Ruff formatting even when another Python server is installed", async () => {
+    const installed = sampleTools().find((t) => t.name === "basedpyright")!;
+    backend.tools.push({
+      ...installed,
+      name: "ruff",
+      displayName: "Ruff",
+      command: "ruff",
+      installMethod: "uv (virtualenv)",
+      languages: ["Python"],
+      alternatives: [],
+    });
+    await promptInstall("ruff", true, new Set(), true);
+    expect(notes.at(-1)).toMatchObject({
+      title: "Ruff is not installed",
+      body: "Reformat Code needs Ruff. Install it via uv (virtualenv)?",
+      key: missingKey("ruff"),
+    });
+  });
+
   it("stays silent when an installed alternative serves the same languages", async () => {
     const off = installMissingServerPrompts();
     // typescript-language-server (on PATH) covers vtsls' languages.

src/features/tools/index.ts

@@ -46,7 +46,12 @@ export function activate(): () => void {
         hidden: true,
         run: async ({ arg }) => {
           if (arg && typeof arg === "object" && "name" in arg && typeof arg.name === "string") {
-            await promptInstall(arg.name, !("sticky" in arg) || arg.sticky !== false);
+            await promptInstall(
+              arg.name,
+              !("sticky" in arg) || arg.sticky !== false,
+              new Set(),
+              "formatter" in arg && arg.formatter === true,
+            );
           }
         },
       },

src/features/tools/missing.ts

@@ -21,12 +21,14 @@ export async function promptInstall(
   name: string,
   sticky = true,
   offered: ReadonlySet<string> = new Set(),
+  formatter = false,
 ): Promise<boolean> {
   if (!useTools.getState().loaded) await refreshTools();
   const tool = toolByName(name);
   if (!tool || !tool.canInstall || tool.status !== "missing") return false;
   const position = tool.alternatives.indexOf(name);
   if (position > 0 && tool.alternatives.slice(0, position).some((n) => offered.has(n))) return false;
+  formatter ||= tool.kind === "formatter";
   // An installed alternative (typescript-language-server for vtsls) already serves these files.
   const served = useTools
     .getState()
@@ -37,17 +39,16 @@ export async function promptInstall(
         t.status !== "missing" &&
         t.languages.some((l) => tool.languages.includes(l)),
     );
-  if (tool.kind !== "formatter" && served) return false;
+  if (!formatter && served) return false;
   const key = missingKey(name);
   const langs = tool.languages.length ? tool.languages.join(", ") : "these files";
   notifications().notify({
     group: "tools",
     level: "warning",
     title: tx`${tool.displayName} is not installed`,
-    body:
-      tool.kind === "formatter"
-        ? tx`Reformat Code needs ${tool.displayName}. Install it via ${tool.installMethod}?`
-        : tx`Code insight for ${langs} needs ${tool.command}. Install it via ${tool.installMethod}?`,
+    body: formatter
+      ? tx`Reformat Code needs ${tool.displayName}. Install it via ${tool.installMethod}?`
+      : tx`Code insight for ${langs} needs ${tool.command}. Install it via ${tool.installMethod}?`,
     key,
     sticky,
     actions: [

src/platform/languageSettings.ts

@@ -25,9 +25,10 @@ const DEFAULT_GO_BUILD_TAGS: GoBuildTags = {
   experiments: "",
 };
 
-/** An external formatter (Prettier, oxfmt) and the languages it formats. */
+/** An external formatter (Prettier, oxfmt, Ruff) and the languages it formats. */
 interface ExternalFormatterValid {
   path: string;
+  configurationDirectory: string;
   languages: string[];
   prefer: boolean;
   runOnSave: boolean;
@@ -35,6 +36,7 @@ interface ExternalFormatterValid {
 
 const DEFAULT_FORMATTER: ExternalFormatterValid = {
   path: "",
+  configurationDirectory: "",
   languages: [
     "markdown",
     "yaml",
@@ -55,6 +57,11 @@ const DEFAULT_FORMATTER: ExternalFormatterValid = {
   runOnSave: false,
 };
 
+const DEFAULT_RUFF_FORMATTER: ExternalFormatterValid = {
+  ...DEFAULT_FORMATTER,
+  languages: ["python"],
+};
+
 /** `languages.php.languageLevel` values; `""` = Auto (from `composer.json`). */
 export const PHP_LANGUAGE_LEVELS = [
   "",
@@ -99,6 +106,7 @@ export interface LanguagesValid {
   typescript: { version: string };
   prettier: ExternalFormatterValid;
   oxfmt: ExternalFormatterValid;
+  ruff: ExternalFormatterValid;
   java: {
     jdk: string;
     jdtlsJdk: string;
@@ -159,6 +167,7 @@ export const DEFAULT_LANGUAGES: LanguagesValid = {
   typescript: { version: "bundled" },
   prettier: DEFAULT_FORMATTER,
   oxfmt: DEFAULT_FORMATTER,
+  ruff: DEFAULT_RUFF_FORMATTER,
   java: {
     jdk: "",
     jdtlsJdk: "",
@@ -228,11 +237,11 @@ const folders = (v: unknown): string[] =>
 const folderKey = (stored: string) => (stored === "." ? "" : stored);
 const storedFolder = (rel: string) => normalizeFolder(rel) || ".";
 
-function validateFormatter(raw: unknown): ExternalFormatterValid {
-  const d = DEFAULT_FORMATTER;
+function validateFormatter(raw: unknown, d = DEFAULT_FORMATTER): ExternalFormatterValid {
   const f = obj(raw);
   return {
     path: text(f.path, d.path),
+    configurationDirectory: text(f.configurationDirectory, d.configurationDirectory),
     languages: Array.isArray(f.languages)
       ? [...new Set(f.languages.filter((v): v is string => typeof v === "string"))]
       : d.languages,
@@ -299,6 +308,7 @@ export function validateLanguages(raw: unknown): LanguagesValid {
     typescript: { version: text(ts.version, d.typescript.version) || d.typescript.version },
     prettier: validateFormatter(l.prettier),
     oxfmt: validateFormatter(l.oxfmt),
+    ruff: validateFormatter(l.ruff, DEFAULT_RUFF_FORMATTER),
     java: {
       jdk: text(java.jdk, d.java.jdk),
       jdtlsJdk: text(java.jdtlsJdk, d.java.jdtlsJdk),

src/platform/locales/text/en.json

@@ -13,6 +13,19 @@
   "phpstan.neon, phpstan.neon.dist or phpstan.dist.neon": "phpstan.neon, phpstan.neon.dist or phpstan.dist.neon",
   "The configuration vendor/bin/phpstan checks saved files with. Empty uses phpstan.neon, phpstan.neon.dist or phpstan.dist.neon in the project root. Absolute, or relative to the project.": "The configuration vendor/bin/phpstan checks saved files with. Empty uses phpstan.neon, phpstan.neon.dist or phpstan.dist.neon in the project root. Absolute, or relative to the project.",
   "Select PHPStan Configuration File": "Select PHPStan Configuration File",
+  "Reformat with Ruff": "Reformat with Ruff",
+  "Ruff path": "Ruff path",
+  "Auto: managed installation, then PATH. An explicit path overrides auto detection.": "Auto: managed installation, then PATH. An explicit path overrides auto detection.",
+  "Configuration directory": "Configuration directory",
+  "Project configuration": "Project configuration",
+  "Select Ruff Configuration Directory": "Select Ruff Configuration Directory",
+  "Empty uses the nearest project pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. A configured directory must contain one of them.": "Empty uses the nearest project pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. A configured directory must contain one of them.",
+  "Ruff reads the nearest pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. Use it before the language server when preferred.": "Ruff reads the nearest pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. Use it before the language server when preferred.",
+  "Run Ruff on save for enabled languages when it is the selected formatting provider.": "Run Ruff on save for enabled languages when it is the selected formatting provider.",
+  "Ruff formatting failed": "Ruff formatting failed",
+  "Ruff formatting timed out": "Ruff formatting timed out",
+  "Ruff configuration path does not exist: {path}": "Ruff configuration path does not exist: {path}",
+  "Ruff configuration directory has no ruff.toml, .ruff.toml, or pyproject.toml with [tool.ruff]: {path}": "Ruff configuration directory has no ruff.toml, .ruff.toml, or pyproject.toml with [tool.ruff]: {path}",
   "Show lines added and deleted": "Show lines added and deleted",
   "{added} line added": "{added} line added",
   "{added} lines added": "{added} lines added",

src/platform/locales/text/zh.json

@@ -1714,15 +1714,24 @@
   "Reformat Code": "重新格式化代码",
   "Reformat with Prettier": "使用 Prettier 重新格式化",
   "Reformat with oxfmt": "使用 oxfmt 重新格式化",
+  "Reformat with Ruff": "使用 Ruff 重新格式化",
   "Prettier path": "Prettier 路径",
   "oxfmt path": "oxfmt 路径",
+  "Ruff path": "Ruff 路径",
   "Auto: nearest project node_modules, managed installation, then PATH. An explicit path overrides auto detection.": "自动：依次查找最近的项目 node_modules、受管安装和 PATH。指定路径将覆盖自动检测。",
+  "Auto: managed installation, then PATH. An explicit path overrides auto detection.": "自动：依次查找受管安装和 PATH。指定路径将覆盖自动检测。",
+  "Configuration directory": "配置目录",
+  "Project configuration": "项目配置",
+  "Select Ruff Configuration Directory": "选择 Ruff 配置目录",
+  "Empty uses the nearest project pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. A configured directory must contain one of them.": "留空时使用最近的 pyproject.toml（[tool.ruff]）、ruff.toml 或 .ruff.toml。指定目录必须包含其中一种配置。",
   "Formatting provider": "格式化工具",
   "Automatic (language server first)": "自动（优先语言服务器）",
   "Run on save": "保存时运行",
   "Run Prettier on save for enabled languages when it is the selected formatting provider.": "对已启用的语言，在选择 Prettier 作为格式化工具时于保存时运行。",
   "Run oxfmt on save for enabled languages when it is the selected formatting provider.": "对已启用的语言，在选择 oxfmt 作为格式化工具时于保存时运行。",
+  "Run Ruff on save for enabled languages when it is the selected formatting provider.": "对已启用的语言，在选择 Ruff 作为格式化工具时于保存时运行。",
   "oxfmt formats an enabled language instead of Prettier below an oxfmt configuration file (.oxfmtrc.json, oxfmt.config.ts) or when it is the selected provider.": "在 oxfmt 配置文件（.oxfmtrc.json、oxfmt.config.ts）所在目录及其子目录中，或选择 oxfmt 作为格式化工具时，oxfmt 将代替 Prettier 格式化已启用的语言。",
+  "Ruff reads the nearest pyproject.toml ([tool.ruff]), ruff.toml, or .ruff.toml. Use it before the language server when preferred.": "Ruff 会读取最近的 pyproject.toml（[tool.ruff]）、ruff.toml 或 .ruff.toml。选择优先使用 Ruff 时，将优先于语言服务器。",
   "Enabled languages": "启用的语言",
   "Reformat Code needs {name}. Install it via {method}?": "重新格式化代码需要 {name}。是否通过 {method} 安装？",
   "Install Missing Tool": "安装缺失的工具",
@@ -1730,6 +1739,10 @@
   "Prettier formatting timed out": "Prettier 格式化超时",
   "oxfmt formatting failed": "oxfmt 格式化失败",
   "oxfmt formatting timed out": "oxfmt 格式化超时",
+  "Ruff formatting failed": "Ruff 格式化失败",
+  "Ruff formatting timed out": "Ruff 格式化超时",
+  "Ruff configuration path does not exist: {path}": "Ruff 配置路径不存在：{path}",
+  "Ruff configuration directory has no ruff.toml, .ruff.toml, or pyproject.toml with [tool.ruff]: {path}": "Ruff 配置目录中没有 ruff.toml、.ruff.toml 或包含 [tool.ruff] 的 pyproject.toml：{path}",
   "{name} does not support selection formatting for this language; formatted the whole file": "{name} 不支持此语言的选区格式化，已格式化整个文件",
   "Formatting timed out": "格式化超时",
   "{name} executable": "{name} 可执行文件",

src/platform/locales/textCatalog.test.ts

@@ -91,6 +91,7 @@ const UNTRANSLATED = new Set<string>([
   "CMake",
   "Prettier",
   "oxfmt",
+  "Ruff",
   "IntelliJ IDEA",
   "PHPStan",
   // Go environment variables and placeholder values