Use SourceKind::diff for formatter

crates/ruff_cli/src/commands/format.rs

@@ -11,7 +11,6 @@ use itertools::Itertools;
 use log::{error, warn};
 use rayon::iter::Either::{Left, Right};
 use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
-use similar::TextDiff;
 use thiserror::Error;
 use tracing::debug;
 
@@ -472,11 +471,7 @@ impl<'a> FormatResults<'a> {
             })
             .sorted_unstable_by_key(|(path, _, _)| *path)
         {
-            let text_diff =
-                TextDiff::from_lines(unformatted.source_code(), formatted.source_code());
-            let mut unified_diff = text_diff.unified_diff();
-            unified_diff.header(&fs::relativize_path(path), &fs::relativize_path(path));
-            unified_diff.to_writer(&mut *f)?;
+            unformatted.diff(formatted, Some(path), f)?;
         }
 
         Ok(())
@@ -566,6 +561,7 @@ pub(crate) enum FormatCommandError {
     Read(Option<PathBuf>, SourceError),
     Format(Option<PathBuf>, FormatModuleError),
     Write(Option<PathBuf>, SourceError),
+    Diff(Option<PathBuf>, io::Error),
 }
 
 impl FormatCommandError {
@@ -581,7 +577,8 @@ impl FormatCommandError {
             Self::Panic(path, _)
             | Self::Read(path, _)
             | Self::Format(path, _)
-            | Self::Write(path, _) => path.as_deref(),
+            | Self::Write(path, _)
+            | Self::Diff(path, _) => path.as_deref(),
         }
     }
 }
@@ -649,6 +646,24 @@ impl Display for FormatCommandError {
                     write!(f, "{}{} {err}", "Failed to format".bold(), ":".bold())
                 }
             }
+            Self::Diff(path, err) => {
+                if let Some(path) = path {
+                    write!(
+                        f,
+                        "{}{}{} {err}",
+                        "Failed to generate diff for ".bold(),
+                        fs::relativize_path(path).bold(),
+                        ":".bold()
+                    )
+                } else {
+                    write!(
+                        f,
+                        "{}{} {err}",
+                        "Failed to generate diff".bold(),
+                        ":".bold()
+                    )
+                }
+            }
             Self::Panic(path, err) => {
                 let message = r#"This indicates a bug in Ruff. If you could open an issue at:
 

crates/ruff_cli/src/commands/format_stdin.rs

@@ -3,8 +3,6 @@ use std::path::Path;
 
 use anyhow::Result;
 use log::error;
-use ruff_linter::fs;
-use similar::TextDiff;
 
 use ruff_linter::source_kind::SourceKind;
 use ruff_python_ast::{PySourceType, SourceType};
@@ -109,14 +107,9 @@ fn format_source_code(
             }
             FormatMode::Check => {}
             FormatMode::Diff => {
-                let mut writer = stdout().lock();
-                let text_diff =
-                    TextDiff::from_lines(source_kind.source_code(), formatted.source_code());
-                let mut unified_diff = text_diff.unified_diff();
-                if let Some(path) = path {
-                    unified_diff.header(&fs::relativize_path(path), &fs::relativize_path(path));
-                }
-                unified_diff.to_writer(&mut writer).unwrap();
+                source_kind
+                    .diff(formatted, path, &mut stdout().lock())
+                    .map_err(|err| FormatCommandError::Diff(path.map(Path::to_path_buf), err))?;
             }
         },
         FormattedSource::Unchanged => {

crates/ruff_cli/tests/format.rs

@@ -509,21 +509,27 @@ fn test_diff() {
         success: false
         exit_code: 1
         ----- stdout -----
-        --- resources/test/fixtures/unformatted.ipynb
-        +++ resources/test/fixtures/unformatted.ipynb
-        @@ -1,12 +1,20 @@
+        --- resources/test/fixtures/unformatted.ipynb:cell 1
+        +++ resources/test/fixtures/unformatted.ipynb:cell 1
+        @@ -1,3 +1,4 @@
          import numpy
         -maths = (numpy.arange(100)**2).sum()
         -stats= numpy.asarray([1,2,3,4]).median()
         +
         +maths = (numpy.arange(100) ** 2).sum()
         +stats = numpy.asarray([1, 2, 3, 4]).median()
+        --- resources/test/fixtures/unformatted.ipynb:cell 3
+        +++ resources/test/fixtures/unformatted.ipynb:cell 3
+        @@ -1,4 +1,6 @@
          # A cell with IPython escape command
          def some_function(foo, bar):
              pass
         +
         +
          %matplotlib inline
+        --- resources/test/fixtures/unformatted.ipynb:cell 4
+        +++ resources/test/fixtures/unformatted.ipynb:cell 4
+        @@ -1,5 +1,10 @@
          foo = %pwd
         -def some_function(foo,bar,):
         +
@@ -535,6 +541,7 @@ fn test_diff() {
              # Another cell with IPython escape command
              foo = %pwd
              print(foo)
+
         --- resources/test/fixtures/unformatted.py
         +++ resources/test/fixtures/unformatted.py
         @@ -1,3 +1,3 @@
@@ -543,6 +550,7 @@ fn test_diff() {
         +y = 2
          z = 3
 
+
         ----- stderr -----
         2 files would be reformatted, 1 file left unchanged
         "###);
@@ -572,6 +580,7 @@ fn test_diff_no_change() {
         +y = 2
          z = 3
 
+
         ----- stderr -----
         1 file would be reformatted
         "###
@@ -605,6 +614,7 @@ fn test_diff_stdin_unformatted() {
     +y = 2
      z = 3
 
+
     ----- stderr -----
     "###);
 }

crates/ruff_linter/src/source_kind.rs

@@ -2,7 +2,7 @@ use std::io;
 use std::io::Write;
 use std::path::Path;
 
-use anyhow::{bail, Result};
+use anyhow::Result;
 use similar::TextDiff;
 use thiserror::Error;
 
@@ -88,7 +88,12 @@ impl SourceKind {
     }
 
     /// Write a diff of the transformed source file to `stdout`.
-    pub fn diff(&self, other: &Self, path: Option<&Path>, writer: &mut dyn Write) -> Result<()> {
+    pub fn diff(
+        &self,
+        other: &Self,
+        path: Option<&Path>,
+        writer: &mut dyn Write,
+    ) -> io::Result<()> {
         match (self, other) {
             (SourceKind::Python(src), SourceKind::Python(dst)) => {
                 let text_diff = TextDiff::from_lines(src, dst);
@@ -154,7 +159,7 @@ impl SourceKind {
 
                 Ok(())
             }
-            _ => bail!("cannot diff Python source code with Jupyter notebook source code"),
+            _ => panic!("cannot diff Python source code with Jupyter notebook source code"),
         }
     }
 }