fix(repl): handle EOF gracefully in JSON REPL mode (#32108)

Closes the JSON REPL cleanly when the IPC pipe is closed (e.g. ctrl+d /
EOF) instead of printing `error: unexpected end of file` and exiting
with code 1.

Author: magurotuna

cli/tools/repl/mod.rs

@@ -310,15 +310,25 @@ async fn run_json(mut repl_session: ReplSession) -> Result<i32, AnyError> {
 
   loop {
     let mut line_fut = std::pin::pin!(async {
-      let len = receiver.read_u32_le().await?;
-      let mut buf = vec![0; len as _];
+      let len = match receiver.read_u32_le().await {
+        Ok(n) => n,
+        // Treat the case of 0-byte input as "expected" EOF
+        Err(e) if e.kind() == io::ErrorKind::UnexpectedEof => {
+          return Ok(None);
+        }
+        Err(e) => return Err(e),
+      };
+      let mut buf = vec![0; len as usize];
       receiver.read_exact(&mut buf).await?;
-      Ok::<_, AnyError>(buf)
+      Ok(Some(buf))
     });
     let mut poll_worker = true;
     let line = loop {
       tokio::select! {
-        line = &mut line_fut => break line?,
+        line = &mut line_fut => match line? {
+          Some(line) => break line,
+          None => return Ok(repl_session.worker.exit_code()),
+        },
         _ = repl_session.run_event_loop(), if poll_worker => {
           poll_worker = false;
           continue;

tests/specs/repl/json/test.out

@@ -2,3 +2,4 @@
 hello
 { type: "RunSuccess", output: "2" }
 { type: "RunFailure", text: "Uncaught" }
+0

tests/specs/repl/json/test.ts

@@ -3,6 +3,7 @@ const {
   getExtraPipeRids,
   writableStreamForRid,
   readableStreamForRid,
+  core: { close },
 } = Deno[Deno.internal];
 
 const command = new Deno.Command(Deno.execPath(), {
@@ -99,3 +100,8 @@ const readable = readableStreamForRid(pipeRid);
   console.log(JSON.parse(new TextDecoder().decode(value)));
   reader.releaseLock();
 }
+
+// Test EOF (ctrl+d): closing the underlying socket should cause a clean exit
+close(pipeRid);
+const status = await child.status;
+console.log(status.code);