Exit 13 on unsettled top-level await in the main entry instead of spinning

src/jsc/VirtualMachine.rs

@@ -2445,7 +2445,17 @@
                 return Ok(promise);
             }
             self.event_loop_mut().perform_gc();
-            self.wait_for_promise(jsc::AnyPromise::Internal(promise));
+            // Returns (promise still Pending) once the loop has nothing to settle it.
+            while crate::JSPromise::status_ptr(promise) == crate::js_promise::Status::Pending {
+                self.event_loop_mut().tick();
+                if crate::JSPromise::status_ptr(promise) != crate::js_promise::Status::Pending {
+                    break;
+                }
+                if !self.is_event_loop_alive() {
+                    break;
+                }
+                self.auto_tick();
+            }
         }
 
         Ok(self.pending_internal_promise.unwrap_or(promise))

src/runtime/cli/run_command.rs

@@ -1619,6 +1619,20 @@
             }
 
             vm.on_before_exit();
+
+            if let Some(p) = vm.pending_internal_promise {
+                // SAFETY: `p` is a live JSC heap cell tracked by the VM.
+                if unsafe { &*p }.status() == PromiseStatus::Pending {
+                    pretty_errorln!(
+                        "<r><yellow>Warning<r><d>:<r> Detected unsettled top-level await at {}",
+                        bstr::BStr::new(vm.main()),
+                    );
+                    Output::flush();
+                    if vm.exit_handler.exit_code == 0 {
+                        vm.exit_handler.exit_code = 13;
+                    }
+                }
+            }
         }
 
         if log_has_msgs(vm) {

test/js/node/process/unsettled-top-level-await.test.ts

@@ -0,0 +1,92 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDir } from "harness";
+
+// When the entry module's top-level await never settles and nothing else refs
+// the event loop, Bun used to spin `wait_for_promise` forever (100% CPU, no
+// epoll park). Node prints a warning and exits 13. Issue #33283.
+
+// Watchdog below the per-test timeout so a regression surfaces as a clean
+// SIGTERM assertion instead of a suite-level timeout. The fixed path exits in
+// well under a second.
+const watchdog = 3_000;
+
+async function run(cmd: string[], cwd?: string) {
+  await using proc = Bun.spawn({
+    cmd,
+    env: bunEnv,
+    cwd,
+    stdout: "pipe",
+    stderr: "pipe",
+    timeout: watchdog,
+  });
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+  return { stdout, stderr, exitCode, signalCode: proc.signalCode };
+}
+
+test.concurrent("never-settling top-level await exits 13 with a warning", async () => {
+  using dir = tempDir("tla-unsettled", {
+    "a.mjs": `await new Promise(() => {});\n`,
+  });
+  const { stderr, exitCode, signalCode } = await run([bunExe(), "a.mjs"], String(dir));
+  expect(stderr).toContain("Detected unsettled top-level await at");
+  expect(stderr).toContain("a.mjs");
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 13 });
+});
+
+test.concurrent("never-settling top-level await in a dependency exits 13", async () => {
+  using dir = tempDir("tla-unsettled-dep", {
+    "entry.mjs": `import { ready } from "./dep.mjs";\nawait ready;\n`,
+    "dep.mjs": `export const ready = new Promise(() => {});\n`,
+  });
+  const { stderr, exitCode, signalCode } = await run([bunExe(), "entry.mjs"], String(dir));
+  expect(stderr).toContain("Detected unsettled top-level await");
+  expect(stderr).toContain("entry.mjs");
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 13 });
+});
+
+test.concurrent("top-level await resolved by a ref'd timer exits 0", async () => {
+  using dir = tempDir("tla-timer", {
+    "a.mjs": `await new Promise(r => setTimeout(r, 50));\nconsole.log("done");\n`,
+  });
+  const { stdout, stderr, exitCode, signalCode } = await run([bunExe(), "a.mjs"], String(dir));
+  expect(stdout).toBe("done\n");
+  expect(stderr).not.toContain("Detected unsettled top-level await");
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 0 });
+});
+
+test.concurrent("top-level await resolved by a microtask exits 0", async () => {
+  using dir = tempDir("tla-micro", {
+    "a.mjs": `await new Promise(r => queueMicrotask(r));\nconsole.log("done");\n`,
+  });
+  const { stdout, stderr, exitCode, signalCode } = await run([bunExe(), "a.mjs"], String(dir));
+  expect(stdout).toBe("done\n");
+  expect(stderr).not.toContain("Detected unsettled top-level await");
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 0 });
+});
+
+test.concurrent("unsettled top-level await preserves a user-set process.exitCode", async () => {
+  using dir = tempDir("tla-exitcode", {
+    "a.mjs": `process.exitCode = 7;\nawait new Promise(() => {});\n`,
+  });
+  const { stderr, exitCode, signalCode } = await run([bunExe(), "a.mjs"], String(dir));
+  expect(stderr).toContain("Detected unsettled top-level await");
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 7 });
+});
+
+test.concurrent("beforeExit fires with 0 before the unsettled-TLA warning", async () => {
+  using dir = tempDir("tla-beforeexit", {
+    "a.mjs": `process.on("beforeExit", c => console.error("beforeExit", c));\n` + `await new Promise(() => {});\n`,
+  });
+  const { stderr, exitCode, signalCode } = await run([bunExe(), "a.mjs"], String(dir));
+  const before = stderr.indexOf("beforeExit 0");
+  const warn = stderr.indexOf("Detected unsettled top-level await");
+  expect(before).toBeGreaterThanOrEqual(0);
+  expect(warn).toBeGreaterThan(before);
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 13 });
+});
+
+test.concurrent("bun -e with a never-settling top-level await exits 13", async () => {
+  const { stderr, exitCode, signalCode } = await run([bunExe(), "-e", "await new Promise(() => {})"]);
+  expect(stderr).toContain("Detected unsettled top-level await");
+  expect({ signalCode, exitCode }).toEqual({ signalCode: null, exitCode: 13 });
+});