Make ruff-server panic hook more error resilient

crates/ruff/src/main.rs

@@ -87,14 +87,19 @@ pub fn main() -> ExitCode {
         Err(err) => {
             #[allow(clippy::print_stderr)]
             {
+                use std::io::Write;
+
+                // Use `writeln` instead of `eprintln` to avoid panicking when the stderr pipe is broken.
+                let mut stderr = std::io::stderr().lock();
+
                 // This communicates that this isn't a linter error but ruff itself hard-errored for
                 // some reason (e.g. failed to resolve the configuration)
-                eprintln!("{}", "ruff failed".red().bold());
+                writeln!(stderr, "{}", "ruff failed".red().bold()).ok();
                 // Currently we generally only see one error, but e.g. with io errors when resolving
                 // the configuration it is help to chain errors ("resolving configuration failed" ->
                 // "failed to read file: subdir/pyproject.toml")
                 for cause in err.chain() {
-                    eprintln!("  {} {cause}", "Cause:".bold());
+                    writeln!(stderr, "  {} {cause}", "Cause:".bold()).ok();
                 }
             }
             ExitStatus::Error.into()

crates/ruff_server/src/message.rs

@@ -16,6 +16,8 @@ pub(crate) fn init_messenger(client_sender: ClientSender) {
 
     // When we panic, try to notify the client.
     std::panic::set_hook(Box::new(move |panic_info| {
+        use std::io::Write;
+
         if let Some(messenger) = MESSENGER.get() {
             let _ = messenger.send(lsp_server::Message::Notification(
                 lsp_server::Notification {
@@ -33,12 +35,12 @@ pub(crate) fn init_messenger(client_sender: ClientSender) {
 
         let backtrace = std::backtrace::Backtrace::force_capture();
         tracing::error!("{panic_info}\n{backtrace}");
-        #[allow(clippy::print_stderr)]
-        {
-            // we also need to print to stderr directly in case tracing hasn't
-            // been initialized.
-            eprintln!("{panic_info}\n{backtrace}");
-        }
+
+        // we also need to print to stderr directly in case tracing hasn't
+        // been initialized.
+        // But use `writeln` instead of `eprintln` to avoid panicking when the stderr pipe is broken.
+        let mut stderr = std::io::stderr().lock();
+        writeln!(stderr, "{panic_info}\n{backtrace}").ok();
     }));
 }