Add --exit-non-zero-on-format

crates/ruff/src/args.rs

@@ -527,6 +527,10 @@ pub struct FormatCommand {
     /// The option can only be used when formatting a single file. Range formatting of notebooks is unsupported.
     #[clap(long, help_heading = "Editor options", verbatim_doc_comment)]
     pub range: Option<FormatRange>,
+
+    /// Exit with a non-zero status code if any files were modified via format, even if all files were formatted successfully.
+    #[arg(long, help_heading = "Miscellaneous", alias = "exit-non-zero-on-fix")]
+    pub exit_non_zero_on_format: bool,
 }
 
 #[derive(Copy, Clone, Debug, clap::Parser)]
@@ -762,6 +766,7 @@ impl FormatCommand {
             no_cache: self.no_cache,
             stdin_filename: self.stdin_filename,
             range: self.range,
+            exit_non_zero_on_format: self.exit_non_zero_on_format,
         };
 
         let cli_overrides = ExplicitConfigOverrides {
@@ -1046,6 +1051,7 @@ pub struct FormatArguments {
     pub files: Vec<PathBuf>,
     pub stdin_filename: Option<PathBuf>,
     pub range: Option<FormatRange>,
+    pub exit_non_zero_on_format: bool,
 }
 
 /// A text range specified by line and column numbers.

crates/ruff/src/commands/format.rs

@@ -213,7 +213,11 @@ pub(crate) fn format(
     match mode {
         FormatMode::Write => {
             if errors.is_empty() {
-                Ok(ExitStatus::Success)
+                if cli.exit_non_zero_on_format && results.any_formatted() {
+                    Ok(ExitStatus::Failure)
+                } else {
+                    Ok(ExitStatus::Success)
+                }
             } else {
                 Ok(ExitStatus::Error)
             }

crates/ruff/tests/format.rs

@@ -581,6 +581,85 @@ if __name__ == "__main__":
     Ok(())
 }
 
+#[test]
+fn exit_non_zero_on_format() -> Result<()> {
+    let tempdir = TempDir::new()?;
+
+    let contents = r#"
+from test import say_hy
+
+if __name__ == "__main__":
+    say_hy("dear Ruff contributor")
+"#;
+
+    fs::write(tempdir.path().join("main.py"), contents)?;
+
+    let mut cmd = Command::new(get_cargo_bin(BIN_NAME));
+    cmd.current_dir(tempdir.path())
+        .args([
+            "format",
+            "--no-cache",
+            "--isolated",
+            "--exit-non-zero-on-format",
+        ])
+        .arg("main.py");
+
+    // First format should exit with code 1 since the file needed formatting
+    assert_cmd_snapshot!(cmd, @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    1 file reformatted
+
+    ----- stderr -----
+    ");
+
+    // Second format should exit with code 0 since no files needed formatting
+    assert_cmd_snapshot!(cmd, @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    1 file left unchanged
+
+    ----- stderr -----
+    ");
+
+    // Repeat the tests above with the --exit-non-zero-on-fix alias
+    fs::write(tempdir.path().join("main.py"), contents)?;
+
+    let mut cmd = Command::new(get_cargo_bin(BIN_NAME));
+    cmd.current_dir(tempdir.path())
+        .args([
+            "format",
+            "--no-cache",
+            "--isolated",
+            "--exit-non-zero-on-fix",
+        ])
+        .arg("main.py");
+
+    // First format should exit with code 1 since the file needed formatting
+    assert_cmd_snapshot!(cmd, @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    1 file reformatted
+
+    ----- stderr -----
+    ");
+
+    // Second format should exit with code 0 since no files needed formatting
+    assert_cmd_snapshot!(cmd, @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    1 file left unchanged
+
+    ----- stderr -----
+    ");
+
+    Ok(())
+}
+
 #[test]
 fn force_exclude() -> Result<()> {
     let tempdir = TempDir::new()?;

docs/configuration.md

@@ -726,6 +726,9 @@ Miscellaneous:
           Path to the cache directory [env: RUFF_CACHE_DIR=]
       --stdin-filename <STDIN_FILENAME>
           The name of the file when passing it through stdin
+      --exit-non-zero-on-format
+          Exit with a non-zero status code if any files were modified via
+          format, even if all files were formatted successfully
 
 File selection:
       --respect-gitignore