Add --extension support to the formatter

crates/ruff_cli/src/args.rs

@@ -290,6 +290,10 @@ pub struct CheckCommand {
     /// The name of the file when passing it through stdin.
     #[arg(long, help_heading = "Miscellaneous")]
     pub stdin_filename: Option<PathBuf>,
+    /// List of mappings from file extension to language (one of ["python", "ipynb", "pyi"]). For
+    /// example, to treat `.ipy` files as IPython notebooks, use `--extension ipy:ipynb`.
+    #[arg(long, value_delimiter = ',')]
+    pub extension: Option<Vec<ExtensionPair>>,
     /// Exit with status code "0", even upon detecting lint violations.
     #[arg(
         short,
@@ -352,9 +356,6 @@ pub struct CheckCommand {
         conflicts_with = "watch",
     )]
     pub show_settings: bool,
-    /// List of mappings from file extension to language (one of ["python", "ipynb", "pyi"]).
-    #[arg(long, value_delimiter = ',', hide = true)]
-    pub extension: Option<Vec<ExtensionPair>>,
     /// Dev-only argument to show fixes
     #[arg(long, hide = true)]
     pub ecosystem_ci: bool,
@@ -423,6 +424,10 @@ pub struct FormatCommand {
     /// The name of the file when passing it through stdin.
     #[arg(long, help_heading = "Miscellaneous")]
     pub stdin_filename: Option<PathBuf>,
+    /// List of mappings from file extension to language (one of ["python", "ipynb", "pyi"]). For
+    /// example, to treat `.ipy` files as IPython notebooks, use `--extension ipy:ipynb`.
+    #[arg(long, value_delimiter = ',')]
+    pub extension: Option<Vec<ExtensionPair>>,
     /// The minimum Python version that should be supported.
     #[arg(long, value_enum)]
     pub target_version: Option<PythonVersion>,
@@ -571,6 +576,7 @@ impl FormatCommand {
                 force_exclude: resolve_bool_arg(self.force_exclude, self.no_force_exclude),
                 target_version: self.target_version,
                 cache_dir: self.cache_dir,
+                extension: self.extension,
 
                 // Unsupported on the formatter CLI, but required on `Overrides`.
                 ..CliOverrides::default()
@@ -739,7 +745,7 @@ impl ConfigurationTransformer for CliOverrides {
             config.target_version = Some(*target_version);
         }
         if let Some(extension) = &self.extension {
-            config.lint.extension = Some(extension.clone().into_iter().collect());
+            config.extension = Some(extension.iter().cloned().collect());
         }
 
         config

crates/ruff_cli/src/commands/format.rs

@@ -106,13 +106,19 @@ pub(crate) fn format(
             match entry {
                 Ok(resolved_file) => {
                     let path = resolved_file.path();
-                    let SourceType::Python(source_type) = SourceType::from(&path) else {
-                        // Ignore any non-Python files.
-                        return None;
-                    };
-
                     let settings = resolver.resolve(path);
 
+                    let source_type = match settings.formatter.extension.get(path) {
+                        None => match SourceType::from(path) {
+                            SourceType::Python(source_type) => source_type,
+                            SourceType::Toml(_) => {
+                                // Ignore any non-Python files.
+                                return None;
+                            }
+                        },
+                        Some(language) => PySourceType::from(language),
+                    };
+
                     // Ignore files that are excluded from formatting
                     if (settings.file_resolver.force_exclude || !resolved_file.is_root())
                         && match_exclusion(

crates/ruff_cli/src/commands/format_stdin.rs

@@ -53,16 +53,23 @@ pub(crate) fn format_stdin(cli: &FormatArguments, overrides: &CliOverrides) -> R
     }
 
     let path = cli.stdin_filename.as_deref();
+    let settings = &resolver.base_settings().formatter;
 
-    let SourceType::Python(source_type) = path.map(SourceType::from).unwrap_or_default() else {
-        if mode.is_write() {
-            parrot_stdin()?;
-        }
-        return Ok(ExitStatus::Success);
+    let source_type = match path.and_then(|path| settings.extension.get(path)) {
+        None => match path.map(SourceType::from).unwrap_or_default() {
+            SourceType::Python(source_type) => source_type,
+            SourceType::Toml(_) => {
+                if mode.is_write() {
+                    parrot_stdin()?;
+                }
+                return Ok(ExitStatus::Success);
+            }
+        },
+        Some(language) => PySourceType::from(language),
     };
 
     // Format the file.
-    match format_source_code(path, &resolver.base_settings().formatter, source_type, mode) {
+    match format_source_code(path, settings, source_type, mode) {
         Ok(result) => match mode {
             FormatMode::Write => Ok(ExitStatus::Success),
             FormatMode::Check | FormatMode::Diff => {

crates/ruff_cli/src/diagnostics.rs

@@ -17,7 +17,7 @@ use ruff_linter::logging::DisplayParseError;
 use ruff_linter::message::Message;
 use ruff_linter::pyproject_toml::lint_pyproject_toml;
 use ruff_linter::registry::AsRule;
-use ruff_linter::settings::types::{ExtensionMapping, UnsafeFixes};
+use ruff_linter::settings::types::UnsafeFixes;
 use ruff_linter::settings::{flags, LinterSettings};
 use ruff_linter::source_kind::{SourceError, SourceKind};
 use ruff_linter::{fs, IOError, SyntaxError};
@@ -179,11 +179,6 @@ impl AddAssign for FixMap {
     }
 }
 
-fn override_source_type(path: Option<&Path>, extension: &ExtensionMapping) -> Option<PySourceType> {
-    let ext = path?.extension()?.to_str()?;
-    extension.get(ext).map(PySourceType::from)
-}
-
 /// Lint the source code at the given `Path`.
 pub(crate) fn lint_path(
     path: &Path,
@@ -228,7 +223,7 @@ pub(crate) fn lint_path(
 
     debug!("Checking: {}", path.display());
 
-    let source_type = match override_source_type(Some(path), &settings.extension) {
+    let source_type = match settings.extension.get(path).map(PySourceType::from) {
         Some(source_type) => source_type,
         None => match SourceType::from(path) {
             SourceType::Toml(TomlSourceType::Pyproject) => {
@@ -398,15 +393,14 @@ pub(crate) fn lint_stdin(
     fix_mode: flags::FixMode,
 ) -> Result<Diagnostics> {
     // TODO(charlie): Support `pyproject.toml`.
-    let source_type = if let Some(source_type) =
-        override_source_type(path, &settings.linter.extension)
-    {
-        source_type
-    } else {
-        let SourceType::Python(source_type) = path.map(SourceType::from).unwrap_or_default() else {
-            return Ok(Diagnostics::default());
-        };
-        source_type
+    let source_type = match path.and_then(|path| settings.linter.extension.get(path)) {
+        None => match path.map(SourceType::from).unwrap_or_default() {
+            SourceType::Python(source_type) => source_type,
+            SourceType::Toml(_) => {
+                return Ok(Diagnostics::default());
+            }
+        },
+        Some(language) => PySourceType::from(language),
     };
 
     // Extract the sources from the file.

crates/ruff_cli/tests/format.rs

@@ -1468,3 +1468,73 @@ fn test_notebook_trailing_semicolon() {
     ----- stderr -----
     "###);
 }
+
+#[test]
+fn extension() -> Result<()> {
+    let tempdir = TempDir::new()?;
+
+    let ruff_toml = tempdir.path().join("ruff.toml");
+    fs::write(
+        &ruff_toml,
+        r#"
+include = ["*.ipy"]
+"#,
+    )?;
+
+    fs::write(
+        tempdir.path().join("main.ipy"),
+        r#"
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ad6f36d9-4b7d-4562-8d00-f15a0f1fbb6d",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "x=1"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.12.0"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}
+"#,
+    )?;
+
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .current_dir(tempdir.path())
+        .arg("format")
+        .arg("--no-cache")
+        .args(["--config", &ruff_toml.file_name().unwrap().to_string_lossy()])
+        .args(["--extension", "ipy:ipynb"])
+        .arg("."), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    1 file reformatted
+
+    ----- stderr -----
+    "###);
+    Ok(())
+}

crates/ruff_cli/tests/lint.rs

@@ -436,3 +436,75 @@ ignore = ["D203", "D212"]
     "###);
     Ok(())
 }
+
+#[test]
+fn extension() -> Result<()> {
+    let tempdir = TempDir::new()?;
+
+    let ruff_toml = tempdir.path().join("ruff.toml");
+    fs::write(
+        &ruff_toml,
+        r#"
+include = ["*.ipy"]
+"#,
+    )?;
+
+    fs::write(
+        tempdir.path().join("main.ipy"),
+        r#"
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ad6f36d9-4b7d-4562-8d00-f15a0f1fbb6d",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.12.0"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}
+"#,
+    )?;
+
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .current_dir(tempdir.path())
+        .arg("check")
+        .args(STDIN_BASE_OPTIONS)
+        .args(["--config", &ruff_toml.file_name().unwrap().to_string_lossy()])
+        .args(["--extension", "ipy:ipynb"])
+        .arg("."), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    main.ipy:cell 1:1:8: F401 [*] `os` imported but unused
+    Found 1 error.
+    [*] 1 fixable with the `--fix` option.
+
+    ----- stderr -----
+    "###);
+    Ok(())
+}

crates/ruff_linter/src/settings/mod.rs

@@ -41,6 +41,7 @@ pub mod types;
 #[derive(Debug, CacheKey)]
 pub struct LinterSettings {
     pub exclude: FilePatternSet,
+    pub extension: ExtensionMapping,
     pub project_root: PathBuf,
 
     pub rules: RuleTable,
@@ -50,7 +51,6 @@ pub struct LinterSettings {
     pub target_version: PythonVersion,
     pub preview: PreviewMode,
     pub explicit_preview_rules: bool,
-    pub extension: ExtensionMapping,
 
     // Rule-specific settings
     pub allowed_confusables: FxHashSet<char>,

crates/ruff_linter/src/settings/types.rs

@@ -388,9 +388,10 @@ pub struct ExtensionMapping {
 }
 
 impl ExtensionMapping {
-    /// Return the [`Language`] for the given extension.
-    pub fn get(&self, extension: &str) -> Option<Language> {
-        self.mapping.get(extension).copied()
+    /// Return the [`Language`] for the given file.
+    pub fn get(&self, path: &Path) -> Option<Language> {
+        let ext = path.extension()?.to_str()?;
+        self.mapping.get(ext).copied()
     }
 }