fix(repl): Prevent panic on broken pipe (#21945)

cli/tools/repl/mod.rs

@@ -1,5 +1,8 @@
 // Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
 
+use std::io;
+use std::io::Write;
+
 use std::sync::Arc;
 
 use crate::args::CliOptions;
@@ -241,15 +244,24 @@ pub async fn run(
 
   // Doing this manually, instead of using `log::info!` because these messages
   // are supposed to go to stdout, not stderr.
+  // Using writeln, because println panics in certain cases
+  // (eg: broken pipes - https://github.com/denoland/deno/issues/21861)
   if !cli_options.is_quiet() {
-    println!("Deno {}", crate::version::DENO_VERSION_INFO.deno);
+    let mut handle = io::stdout().lock();
-    println!("exit using ctrl+d, ctrl+c, or close()");
+
+    writeln!(handle, "Deno {}", crate::version::DENO_VERSION_INFO.deno)?;
+    writeln!(handle, "exit using ctrl+d, ctrl+c, or close()")?;
+
     if repl_flags.is_default_command {
-      println!(
+      writeln!(
+        handle,
         "{}",
         colors::yellow("REPL is running with all permissions allowed.")
-      );
+      )?;
-      println!("To specify permissions, run `deno repl` with allow flags.")
+      writeln!(
+        handle,
+        "To specify permissions, run `deno repl` with allow flags."
+      )?;
     }
   }
 

tests/integration/run_tests.rs

@@ -4343,6 +4343,32 @@ fn broken_stdout() {
   assert!(!stderr.contains("panic"));
 }
 
+#[test]
+fn broken_stdout_repl() {
+  let (reader, writer) = os_pipe::pipe().unwrap();
+  // drop the reader to create a broken pipe
+  drop(reader);
+
+  let output = util::deno_cmd()
+    .current_dir(util::testdata_path())
+    .arg("repl")
+    .stdout(writer)
+    .stderr_piped()
+    .spawn()
+    .unwrap()
+    .wait_with_output()
+    .unwrap();
+
+  assert!(!output.status.success());
+  let stderr = std::str::from_utf8(output.stderr.as_ref()).unwrap().trim();
+  if cfg!(windows) {
+    assert_contains!(stderr, "The pipe is being closed. (os error 232)");
+  } else {
+    assert_contains!(stderr, "Broken pipe (os error 32)");
+  }
+  assert_not_contains!(stderr, "panic");
+}
+
 itest!(error_cause {
   args: "run run/error_cause.ts",
   output: "run/error_cause.ts.out",