Respect .ipynb and .pyi sources when linting from stdin (#6628)

## Summary

When running Ruff from stdin, we were always falling back to the default
source type, even if the user specified a path (as is the case when
running from the LSP). This PR wires up the source type inference, which
means we now get the expected result when checking `.pyi` and `.ipynb`
files.

Closes #6627.

## Test Plan

Verified that `cat
crates/ruff/resources/test/fixtures/jupyter/valid.ipynb | cargo run -p
ruff_cli -- --force-exclude --no-cache --no-fix --isolated --select ALL
--stdin-filename foo.ipynb -` yielded the expected results (and differs
from the errors you get if you omit the filename).

Verified that `cat foo.pyi | cargo run -p ruff_cli -- --force-exclude
--no-cache --no-fix --format json --isolated --select TCH
--stdin-filename path/to/foo.pyi -` yielded no errors.

crates/ruff/src/jupyter/notebook.rs

@@ -1,7 +1,7 @@
 use std::cmp::Ordering;
 use std::fmt::Display;
 use std::fs::File;
-use std::io::{BufReader, BufWriter, Read, Seek, SeekFrom, Write};
+use std::io::{BufReader, BufWriter, Cursor, Read, Seek, SeekFrom, Write};
 use std::iter;
 use std::path::Path;
 
@@ -26,7 +26,7 @@ pub const JUPYTER_NOTEBOOK_EXT: &str = "ipynb";
 
 /// Run round-trip source code generation on a given Jupyter notebook file path.
 pub fn round_trip(path: &Path) -> anyhow::Result<String> {
-    let mut notebook = Notebook::read(path).map_err(|err| {
+    let mut notebook = Notebook::from_path(path).map_err(|err| {
         anyhow::anyhow!(
             "Failed to read notebook file `{}`: {:?}",
             path.display(),
@@ -120,18 +120,30 @@ pub struct Notebook {
 
 impl Notebook {
     /// Read the Jupyter Notebook from the given [`Path`].
-    ///
+    pub fn from_path(path: &Path) -> Result<Self, Box<Diagnostic>> {
-    /// See also the black implementation
+        Self::from_reader(BufReader::new(File::open(path).map_err(|err| {
-    /// <https://github.com/psf/black/blob/69ca0a4c7a365c5f5eea519a90980bab72cab764/src/black/__init__.py#L1017-L1046>
-    pub fn read(path: &Path) -> Result<Self, Box<Diagnostic>> {
-        let mut reader = BufReader::new(File::open(path).map_err(|err| {
             Diagnostic::new(
                 IOError {
                     message: format!("{err}"),
                 },
                 TextRange::default(),
             )
-        })?);
+        })?))
+    }
+
+    /// Read the Jupyter Notebook from its JSON string.
+    pub fn from_contents(contents: &str) -> Result<Self, Box<Diagnostic>> {
+        Self::from_reader(Cursor::new(contents))
+    }
+
+    /// Read a Jupyter Notebook from a [`Read`] implementor.
+    ///
+    /// See also the black implementation
+    /// <https://github.com/psf/black/blob/69ca0a4c7a365c5f5eea519a90980bab72cab764/src/black/__init__.py#L1017-L1046>
+    fn from_reader<R>(mut reader: R) -> Result<Self, Box<Diagnostic>>
+    where
+        R: Read + Seek,
+    {
         let trailing_newline = reader.seek(SeekFrom::End(-1)).is_ok_and(|_| {
             let mut buf = [0; 1];
             reader.read_exact(&mut buf).is_ok_and(|_| buf[0] == b'\n')
@@ -144,7 +156,7 @@ impl Notebook {
                 TextRange::default(),
             )
         })?;
-        let raw_notebook: RawNotebook = match serde_json::from_reader(reader) {
+        let raw_notebook: RawNotebook = match serde_json::from_reader(reader.by_ref()) {
             Ok(notebook) => notebook,
             Err(err) => {
                 // Translate the error into a diagnostic
@@ -159,7 +171,11 @@ impl Notebook {
                         Category::Syntax | Category::Eof => {
                             // Maybe someone saved the python sources (those with the `# %%` separator)
                             // as jupyter notebook instead. Let's help them.
-                            let contents = std::fs::read_to_string(path).map_err(|err| {
+                            let mut contents = String::new();
+                            reader
+                                .rewind()
+                                .and_then(|_| reader.read_to_string(&mut contents))
+                                .map_err(|err| {
                                     Diagnostic::new(
                                         IOError {
                                             message: format!("{err}"),
@@ -167,6 +183,7 @@ impl Notebook {
                                         TextRange::default(),
                                     )
                                 })?;
+
                             // Check if tokenizing was successful and the file is non-empty
                             if lex(&contents, Mode::Module).any(|result| result.is_err()) {
                                 Diagnostic::new(
@@ -182,7 +199,7 @@ impl Notebook {
                                 Diagnostic::new(
                                     SyntaxError {
                                         message: format!(
-                                            "Expected a Jupyter Notebook (.{JUPYTER_NOTEBOOK_EXT} extension), \
+                                            "Expected a Jupyter Notebook (.{JUPYTER_NOTEBOOK_EXT}), \
                                     which must be internally stored as JSON, \
                                     but found a Python source file: {err}"
                                         ),
@@ -484,22 +501,22 @@ mod tests {
     fn test_invalid() {
         let path = Path::new("resources/test/fixtures/jupyter/invalid_extension.ipynb");
         assert_eq!(
-            Notebook::read(path).unwrap_err().kind.body,
+            Notebook::from_path(path).unwrap_err().kind.body,
-            "SyntaxError: Expected a Jupyter Notebook (.ipynb extension), \
+            "SyntaxError: Expected a Jupyter Notebook (.ipynb), \
             which must be internally stored as JSON, \
             but found a Python source file: \
             expected value at line 1 column 1"
         );
         let path = Path::new("resources/test/fixtures/jupyter/not_json.ipynb");
         assert_eq!(
-            Notebook::read(path).unwrap_err().kind.body,
+            Notebook::from_path(path).unwrap_err().kind.body,
             "SyntaxError: A Jupyter Notebook (.ipynb) must internally be JSON, \
             but this file isn't valid JSON: \
             expected value at line 1 column 1"
         );
         let path = Path::new("resources/test/fixtures/jupyter/wrong_schema.ipynb");
         assert_eq!(
-            Notebook::read(path).unwrap_err().kind.body,
+            Notebook::from_path(path).unwrap_err().kind.body,
             "SyntaxError: This file does not match the schema expected of Jupyter Notebooks: \
             missing field `cells` at line 1 column 2"
         );

crates/ruff/src/test.rs

@@ -33,7 +33,7 @@ use crate::source_kind::SourceKind;
 #[cfg(not(fuzzing))]
 pub(crate) fn read_jupyter_notebook(path: &Path) -> Result<Notebook> {
     let path = test_resource_path("fixtures/jupyter").join(path);
-    Notebook::read(&path).map_err(|err| {
+    Notebook::from_path(&path).map_err(|err| {
         anyhow::anyhow!(
             "Failed to read notebook file `{}`: {:?}",
             path.display(),

crates/ruff_cli/src/diagnostics.rs

@@ -96,12 +96,14 @@ impl AddAssign for Diagnostics {
     }
 }
 
-/// Returns either an indexed python jupyter notebook or a diagnostic (which is empty if we skip)
+/// Read a Jupyter Notebook from disk.
-fn load_jupyter_notebook(path: &Path) -> Result<Notebook, Box<Diagnostics>> {
+///
-    let notebook = match Notebook::read(path) {
+/// Returns either an indexed Python Jupyter Notebook or a diagnostic (which is empty if we skip).
+fn notebook_from_path(path: &Path) -> Result<Notebook, Box<Diagnostics>> {
+    let notebook = match Notebook::from_path(path) {
         Ok(notebook) => {
             if !notebook.is_python_notebook() {
-                // Not a python notebook, this could e.g. be an R notebook which we want to just skip
+                // Not a python notebook, this could e.g. be an R notebook which we want to just skip.
                 debug!(
                     "Skipping {} because it's not a Python notebook",
                     path.display()
@@ -126,6 +128,44 @@ fn load_jupyter_notebook(path: &Path) -> Result<Notebook, Box<Diagnostics>> {
     Ok(notebook)
 }
 
+/// Parse a Jupyter Notebook from a JSON string.
+///
+/// Returns either an indexed Python Jupyter Notebook or a diagnostic (which is empty if we skip).
+fn notebook_from_contents(
+    contents: &str,
+    path: Option<&Path>,
+) -> Result<Notebook, Box<Diagnostics>> {
+    let notebook = match Notebook::from_contents(contents) {
+        Ok(notebook) => {
+            if !notebook.is_python_notebook() {
+                // Not a python notebook, this could e.g. be an R notebook which we want to just skip.
+                if let Some(path) = path {
+                    debug!(
+                        "Skipping {} because it's not a Python notebook",
+                        path.display()
+                    );
+                }
+                return Err(Box::default());
+            }
+            notebook
+        }
+        Err(diagnostic) => {
+            // Failed to read the jupyter notebook
+            return Err(Box::new(Diagnostics {
+                messages: vec![Message::from_diagnostic(
+                    *diagnostic,
+                    SourceFileBuilder::new(path.map(Path::to_string_lossy).unwrap_or_default(), "")
+                        .finish(),
+                    TextSize::default(),
+                )],
+                ..Diagnostics::default()
+            }));
+        }
+    };
+
+    Ok(notebook)
+}
+
 /// Lint the source code at the given `Path`.
 pub(crate) fn lint_path(
     path: &Path,
@@ -216,7 +256,7 @@ pub(crate) fn lint_path(
 
     // Read the file from disk
     let mut source_kind = if source_type.is_jupyter() {
-        match load_jupyter_notebook(path) {
+        match notebook_from_path(path) {
             Ok(notebook) => SourceKind::Jupyter(notebook),
             Err(diagnostic) => return Ok(*diagnostic),
         }
@@ -278,7 +318,7 @@ pub(crate) fn lint_path(
                             SourceKind::Jupyter(dest_notebook) => {
                                 // We need to load the notebook again, since we might've
                                 // mutated it.
-                                let src_notebook = match load_jupyter_notebook(path) {
+                                let src_notebook = match notebook_from_path(path) {
                                     Ok(notebook) => notebook,
                                     Err(diagnostic) => return Ok(*diagnostic),
                                 };
@@ -401,8 +441,19 @@ pub(crate) fn lint_stdin(
     noqa: flags::Noqa,
     autofix: flags::FixMode,
 ) -> Result<Diagnostics> {
-    let mut source_kind = SourceKind::Python(contents.to_string());
+    let source_type = path.map(PySourceType::from).unwrap_or_default();
-    let source_type = PySourceType::default();
+
+    let mut source_kind = if source_type.is_jupyter() {
+        // SAFETY: Jupyter isn't the default type, so we must have a path.
+        match notebook_from_contents(contents, path) {
+            Ok(notebook) => SourceKind::Jupyter(notebook),
+            Err(diagnostic) => return Ok(*diagnostic),
+        }
+    } else {
+        SourceKind::Python(contents.to_string())
+    };
+
+    let contents = source_kind.content().to_string();
 
     // Lint the inputs.
     let (
@@ -417,7 +468,7 @@ pub(crate) fn lint_stdin(
             transformed,
             fixed,
         }) = lint_fix(
-            contents,
+            &contents,
             path.unwrap_or_else(|| Path::new("-")),
             package,
             noqa,
@@ -433,7 +484,7 @@ pub(crate) fn lint_stdin(
                 flags::FixMode::Diff => {
                     // But only write a diff if it's non-empty.
                     if !fixed.is_empty() {
-                        let text_diff = TextDiff::from_lines(contents, &transformed);
+                        let text_diff = TextDiff::from_lines(contents.as_str(), &transformed);
                         let mut unified_diff = text_diff.unified_diff();
                         if let Some(path) = path {
                             unified_diff
@@ -453,7 +504,7 @@ pub(crate) fn lint_stdin(
         } else {
             // If we fail to autofix, lint the original source code.
             let result = lint_only(
-                contents,
+                &contents,
                 path.unwrap_or_else(|| Path::new("-")),
                 package,
                 settings,
@@ -472,7 +523,7 @@ pub(crate) fn lint_stdin(
         }
     } else {
         let result = lint_only(
-            contents,
+            &contents,
             path.unwrap_or_else(|| Path::new("-")),
             package,
             settings,
@@ -508,14 +559,21 @@ pub(crate) fn lint_stdin(
 mod tests {
     use std::path::Path;
 
-    use crate::diagnostics::{load_jupyter_notebook, Diagnostics};
+    use crate::diagnostics::{notebook_from_contents, notebook_from_path, Diagnostics};
 
     #[test]
     fn test_r() {
         let path = Path::new("../ruff/resources/test/fixtures/jupyter/R.ipynb");
-        // No diagnostics is used as skip signal
+        // No diagnostics is used as skip signal.
         assert_eq!(
-            load_jupyter_notebook(path).unwrap_err(),
+            notebook_from_path(path).unwrap_err(),
+            Box::<Diagnostics>::default()
+        );
+
+        let contents = std::fs::read_to_string(path).unwrap();
+        // No diagnostics is used as skip signal.
+        assert_eq!(
+            notebook_from_contents(&contents, Some(path)).unwrap_err(),
             Box::<Diagnostics>::default()
         );
     }

crates/ruff_cli/tests/integration_test.rs

@@ -81,6 +81,48 @@ Found 1 error.
     Ok(())
 }
 
+#[test]
+fn stdin_source_type() -> Result<()> {
+    // Raise `TCH` errors in `.py` files.
+    let mut cmd = Command::cargo_bin(BIN_NAME)?;
+    let output = cmd
+        .args([
+            "-",
+            "--format",
+            "text",
+            "--stdin-filename",
+            "TCH.py",
+            "--isolated",
+        ])
+        .write_stdin("import os\n")
+        .assert()
+        .failure();
+    assert_eq!(
+        str::from_utf8(&output.get_output().stdout)?,
+        r#"TCH.py:1:8: F401 [*] `os` imported but unused
+Found 1 error.
+[*] 1 potentially fixable with the --fix option.
+"#
+    );
+
+    // But not in `.pyi` files.
+    let mut cmd = Command::cargo_bin(BIN_NAME)?;
+    cmd.args([
+        "-",
+        "--format",
+        "text",
+        "--stdin-filename",
+        "TCH.pyi",
+        "--isolated",
+        "--select",
+        "TCH",
+    ])
+    .write_stdin("import os\n")
+    .assert()
+    .success();
+    Ok(())
+}
+
 #[cfg(unix)]
 #[test]
 fn stdin_json() -> Result<()> {