Add hidden `--extension` to override inference of source type from file extension (#8373)

## Summary

This PR addresses the incompatibility with `jupyterlab-lsp` +
`python-lsp-ruff` arising from the inference of source type from file
extension, raised in #6847.

In particular it follows the suggestion in
https://github.com/astral-sh/ruff/issues/6847#issuecomment-1765724679 to
specify a mapping from file extension to source type.

The source types are

- python
- pyi
- ipynb

Usage:

```sh
ruff check --no-cache --stdin-filename Untitled.ipynb --extension ipynb:python
```

Unlike the original suggestion, `:` instead of `=` is used to associate
file extensions to language since that is what is used with
`--per-file-ignores` which is an existing option that accepts a mapping.

## Test Plan

2 tests added to `integration_test.rs` to ensure the override works as
expected

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/ruff_cli/src/args.rs

@@ -8,8 +8,8 @@ use ruff_linter::line_width::LineLength;
 use ruff_linter::logging::LogLevel;
 use ruff_linter::registry::Rule;
 use ruff_linter::settings::types::{
-    FilePattern, PatternPrefixPair, PerFileIgnore, PreviewMode, PythonVersion, SerializationFormat,
-    UnsafeFixes,
+    ExtensionPair, FilePattern, PatternPrefixPair, PerFileIgnore, PreviewMode, PythonVersion,
+    SerializationFormat, UnsafeFixes,
 };
 use ruff_linter::{RuleParser, RuleSelector, RuleSelectorParser};
 use ruff_workspace::configuration::{Configuration, RuleSelection};
@@ -351,6 +351,9 @@ 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,
@@ -535,6 +538,7 @@ impl CheckCommand {
                 force_exclude: resolve_bool_arg(self.force_exclude, self.no_force_exclude),
                 output_format: self.output_format,
                 show_fixes: resolve_bool_arg(self.show_fixes, self.no_show_fixes),
+                extension: self.extension,
             },
         )
     }
@@ -647,6 +651,7 @@ pub struct CliOverrides {
     pub force_exclude: Option<bool>,
     pub output_format: Option<SerializationFormat>,
     pub show_fixes: Option<bool>,
+    pub extension: Option<Vec<ExtensionPair>>,
 }
 
 impl ConfigurationTransformer for CliOverrides {
@@ -731,6 +736,9 @@ impl ConfigurationTransformer for CliOverrides {
         if let Some(target_version) = &self.target_version {
             config.target_version = Some(*target_version);
         }
+        if let Some(extension) = &self.extension {
+            config.lint.extension = Some(extension.clone().into_iter().collect());
+        }
 
         config
     }

crates/ruff_cli/src/commands/check.rs

@@ -30,6 +30,7 @@ use crate::diagnostics::Diagnostics;
 use crate::panic::catch_unwind;
 
 /// Run the linter over a collection of files.
+#[allow(clippy::too_many_arguments)]
 pub(crate) fn check(
     files: &[PathBuf],
     pyproject_config: &PyprojectConfig,
@@ -184,6 +185,7 @@ pub(crate) fn check(
 
 /// Wraps [`lint_path`](crate::diagnostics::lint_path) in a [`catch_unwind`](std::panic::catch_unwind) and emits
 /// a diagnostic if the linting the file panics.
+#[allow(clippy::too_many_arguments)]
 fn lint_path(
     path: &Path,
     package: Option<&Path>,

crates/ruff_cli/src/diagnostics.rs

@@ -17,13 +17,13 @@ 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::UnsafeFixes;
+use ruff_linter::settings::types::{ExtensionMapping, UnsafeFixes};
 use ruff_linter::settings::{flags, LinterSettings};
 use ruff_linter::source_kind::{SourceError, SourceKind};
 use ruff_linter::{fs, IOError, SyntaxError};
 use ruff_notebook::{Notebook, NotebookError, NotebookIndex};
 use ruff_python_ast::imports::ImportMap;
-use ruff_python_ast::{SourceType, TomlSourceType};
+use ruff_python_ast::{PySourceType, SourceType, TomlSourceType};
 use ruff_source_file::{LineIndex, SourceCode, SourceFileBuilder};
 use ruff_text_size::{TextRange, TextSize};
 use ruff_workspace::Settings;
@@ -177,6 +177,11 @@ 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,
@@ -221,31 +226,35 @@ pub(crate) fn lint_path(
 
     debug!("Checking: {}", path.display());
 
-    let source_type = match SourceType::from(path) {
-        SourceType::Toml(TomlSourceType::Pyproject) => {
-            let messages = if settings
-                .rules
-                .iter_enabled()
-                .any(|rule_code| rule_code.lint_source().is_pyproject_toml())
-            {
-                let contents = match std::fs::read_to_string(path).map_err(SourceError::from) {
-                    Ok(contents) => contents,
-                    Err(err) => {
-                        return Ok(Diagnostics::from_source_error(&err, Some(path), settings));
-                    }
+    let source_type = match override_source_type(Some(path), &settings.extension) {
+        Some(source_type) => source_type,
+        None => match SourceType::from(path) {
+            SourceType::Toml(TomlSourceType::Pyproject) => {
+                let messages = if settings
+                    .rules
+                    .iter_enabled()
+                    .any(|rule_code| rule_code.lint_source().is_pyproject_toml())
+                {
+                    let contents = match std::fs::read_to_string(path).map_err(SourceError::from) {
+                        Ok(contents) => contents,
+                        Err(err) => {
+                            return Ok(Diagnostics::from_source_error(&err, Some(path), settings));
+                        }
+                    };
+                    let source_file =
+                        SourceFileBuilder::new(path.to_string_lossy(), contents).finish();
+                    lint_pyproject_toml(source_file, settings)
+                } else {
+                    vec![]
                 };
-                let source_file = SourceFileBuilder::new(path.to_string_lossy(), contents).finish();
-                lint_pyproject_toml(source_file, settings)
-            } else {
-                vec![]
-            };
-            return Ok(Diagnostics {
-                messages,
-                ..Diagnostics::default()
-            });
-        }
-        SourceType::Toml(_) => return Ok(Diagnostics::default()),
-        SourceType::Python(source_type) => source_type,
+                return Ok(Diagnostics {
+                    messages,
+                    ..Diagnostics::default()
+                });
+            }
+            SourceType::Toml(_) => return Ok(Diagnostics::default()),
+            SourceType::Python(source_type) => source_type,
+        },
     };
 
     // Extract the sources from the file.
@@ -370,8 +379,15 @@ pub(crate) fn lint_stdin(
     fix_mode: flags::FixMode,
 ) -> Result<Diagnostics> {
     // TODO(charlie): Support `pyproject.toml`.
-    let SourceType::Python(source_type) = path.map(SourceType::from).unwrap_or_default() else {
-        return Ok(Diagnostics::default());
+    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
     };
 
     // Extract the sources from the file.

crates/ruff_cli/tests/integration_test.rs

@@ -320,6 +320,119 @@ fn stdin_fix_jupyter() {
     Found 2 errors (2 fixed, 0 remaining).
     "###);
 }
+#[test]
+fn stdin_override_parser_ipynb() {
+    let args = ["--extension", "py:ipynb", "--stdin-filename", "Jupyter.py"];
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        .args(args)
+        .pass_stdin(r#"{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "dccc687c-96e2-4604-b957-a8a89b5bec06",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "19e1b029-f516-4662-a9b9-623b93edac1a",
+   "metadata": {},
+   "source": [
+    "Foo"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "cdce7b92-b0fb-4c02-86f6-e233b26fa84f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import sys"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "e40b33d2-7fe4-46c5-bdf0-8802f3052565",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "1\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(1)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "a1899bc8-d46f-4ec0-b1d1-e1ca0f04bf60",
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "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": "3.11.2"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}"#), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    Jupyter.py:cell 1:1:8: F401 [*] `os` imported but unused
+    Jupyter.py:cell 3:1:8: F401 [*] `sys` imported but unused
+    Found 2 errors.
+    [*] 2 fixable with the `--fix` option.
+
+    ----- stderr -----
+    "###);
+}
+
+#[test]
+fn stdin_override_parser_py() {
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        .args(["--extension", "ipynb:python", "--stdin-filename", "F401.ipynb"])
+        .pass_stdin("import os\n"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    F401.ipynb:1:8: F401 [*] `os` imported but unused
+    Found 1 error.
+    [*] 1 fixable with the `--fix` option.
+
+    ----- stderr -----
+    "###);
+}
 
 #[test]
 fn stdin_fix_when_not_fixable_should_still_print_contents() {

crates/ruff_linter/src/settings/mod.rs

@@ -23,7 +23,7 @@ use crate::rules::{
     flake8_tidy_imports, flake8_type_checking, flake8_unused_arguments, isort, mccabe, pep8_naming,
     pycodestyle, pydocstyle, pyflakes, pylint, pyupgrade,
 };
-use crate::settings::types::{FilePatternSet, PerFileIgnore, PythonVersion};
+use crate::settings::types::{ExtensionMapping, FilePatternSet, PerFileIgnore, PythonVersion};
 use crate::{codes, RuleSelector};
 
 use super::line_width::IndentWidth;
@@ -50,6 +50,7 @@ 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>,
@@ -187,6 +188,7 @@ impl LinterSettings {
             pyupgrade: pyupgrade::settings::Settings::default(),
             preview: PreviewMode::default(),
             explicit_preview_rules: false,
+            extension: ExtensionMapping::default(),
         }
     }
 

crates/ruff_linter/src/settings/types.rs

@@ -7,13 +7,15 @@ use std::string::ToString;
 use anyhow::{bail, Result};
 use globset::{Glob, GlobSet, GlobSetBuilder};
 use pep440_rs::{Version as Pep440Version, VersionSpecifiers};
-use ruff_diagnostics::Applicability;
+use rustc_hash::FxHashMap;
 use serde::{de, Deserialize, Deserializer, Serialize};
 use strum::IntoEnumIterator;
 use strum_macros::EnumIter;
 
 use ruff_cache::{CacheKey, CacheKeyHasher};
+use ruff_diagnostics::Applicability;
 use ruff_macros::CacheKey;
+use ruff_python_ast::PySourceType;
 
 use crate::fs;
 use crate::registry::RuleSet;
@@ -289,6 +291,119 @@ impl FromStr for PatternPrefixPair {
     }
 }
 
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    PartialOrd,
+    Ord,
+    PartialEq,
+    Eq,
+    Default,
+    Serialize,
+    Deserialize,
+    CacheKey,
+    EnumIter,
+)]
+#[serde(rename_all = "lowercase")]
+#[cfg_attr(feature = "clap", derive(clap::ValueEnum))]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub enum Language {
+    #[default]
+    Python,
+    Pyi,
+    Ipynb,
+}
+
+impl FromStr for Language {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.to_ascii_lowercase().as_str() {
+            "python" => Ok(Self::Python),
+            "pyi" => Ok(Self::Pyi),
+            "ipynb" => Ok(Self::Ipynb),
+            _ => {
+                bail!("Unrecognized language: `{s}`. Expected one of `python`, `pyi`, or `ipynb`.")
+            }
+        }
+    }
+}
+
+impl From<Language> for PySourceType {
+    fn from(value: Language) -> Self {
+        match value {
+            Language::Python => Self::Python,
+            Language::Ipynb => Self::Ipynb,
+            Language::Pyi => Self::Stub,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct ExtensionPair {
+    pub extension: String,
+    pub language: Language,
+}
+
+impl ExtensionPair {
+    const EXPECTED_PATTERN: &'static str = "<Extension>:<LanguageCode> pattern";
+}
+
+impl FromStr for ExtensionPair {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        let (extension_str, language_str) = {
+            let tokens = s.split(':').collect::<Vec<_>>();
+            if tokens.len() != 2 {
+                bail!("Expected {}", Self::EXPECTED_PATTERN);
+            }
+            (tokens[0].trim(), tokens[1].trim())
+        };
+        let extension = extension_str.into();
+        let language = Language::from_str(language_str)?;
+        Ok(Self {
+            extension,
+            language,
+        })
+    }
+}
+
+impl From<ExtensionPair> for (String, Language) {
+    fn from(value: ExtensionPair) -> Self {
+        (value.extension, value.language)
+    }
+}
+#[derive(Debug, Clone, Default, CacheKey)]
+pub struct ExtensionMapping {
+    mapping: FxHashMap<String, Language>,
+}
+
+impl ExtensionMapping {
+    /// Return the [`Language`] for the given extension.
+    pub fn get(&self, extension: &str) -> Option<Language> {
+        self.mapping.get(extension).copied()
+    }
+}
+
+impl From<FxHashMap<String, Language>> for ExtensionMapping {
+    fn from(value: FxHashMap<String, Language>) -> Self {
+        Self { mapping: value }
+    }
+}
+
+impl FromIterator<ExtensionPair> for ExtensionMapping {
+    fn from_iter<T: IntoIterator<Item = ExtensionPair>>(iter: T) -> Self {
+        Self {
+            mapping: iter
+                .into_iter()
+                .map(|pair| (pair.extension, pair.language))
+                .collect(),
+        }
+    }
+}
+
 #[derive(Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Debug, Hash)]
 #[cfg_attr(feature = "clap", derive(clap::ValueEnum))]
 #[serde(rename_all = "kebab-case")]

crates/ruff_workspace/src/configuration.rs

@@ -25,8 +25,8 @@ use ruff_linter::rule_selector::{PreviewOptions, Specificity};
 use ruff_linter::rules::pycodestyle;
 use ruff_linter::settings::rule_table::RuleTable;
 use ruff_linter::settings::types::{
-    FilePattern, FilePatternSet, PerFileIgnore, PreviewMode, PythonVersion, SerializationFormat,
-    UnsafeFixes, Version,
+    ExtensionMapping, FilePattern, FilePatternSet, PerFileIgnore, PreviewMode, PythonVersion,
+    SerializationFormat, UnsafeFixes, Version,
 };
 use ruff_linter::settings::{
     resolve_per_file_ignores, LinterSettings, DEFAULT_SELECTORS, DUMMY_VARIABLE_RGX, TASK_TAGS,
@@ -216,6 +216,7 @@ impl Configuration {
             linter: LinterSettings {
                 rules: lint.as_rule_table(lint_preview),
                 exclude: FilePatternSet::try_from_iter(lint.exclude.unwrap_or_default())?,
+                extension: lint.extension.unwrap_or_default(),
                 preview: lint_preview,
                 target_version,
                 project_root: project_root.to_path_buf(),
@@ -523,6 +524,7 @@ impl Configuration {
 pub struct LintConfiguration {
     pub exclude: Option<Vec<FilePattern>>,
     pub preview: Option<PreviewMode>,
+    pub extension: Option<ExtensionMapping>,
 
     // Rule selection
     pub extend_per_file_ignores: Vec<PerFileIgnore>,
@@ -589,6 +591,9 @@ impl LintConfiguration {
             .chain(options.common.extend_unfixable.into_iter().flatten())
             .collect();
         Ok(LintConfiguration {
+            // `--extension` is a hidden command-line argument that isn't supported in configuration
+            // files at present.
+            extension: None,
             exclude: options.exclude.map(|paths| {
                 paths
                     .into_iter()
@@ -905,6 +910,7 @@ impl LintConfiguration {
         Self {
             exclude: self.exclude.or(config.exclude),
             preview: self.preview.or(config.preview),
+            extension: self.extension.or(config.extension),
             rule_selections: config
                 .rule_selections
                 .into_iter()