3 files changed, 49 insertions, 1 deletions
diff --git a/cli/tests/integration/watcher_tests.rs b/cli/tests/integration/watcher_tests.rs
index 04320060b..2d41a74ed 100644
--- a/cli/tests/integration/watcher_tests.rs
+++ b/cli/tests/integration/watcher_tests.rs
@@ -1371,6 +1371,46 @@ async fn run_watch_reload_once() {
   check_alive_then_kill(child);
 }
 
+/// Regression test for https://github.com/denoland/deno/issues/18960. Ensures that Deno.serve
+/// operates properly after a watch restart.
+#[tokio::test]
+async fn test_watch_serve() {
+  let t = TempDir::new();
+  let file_to_watch = t.path().join("file_to_watch.js");
+  let file_content = r#"
+      console.error("serving");
+      await Deno.serve({port: 4600, handler: () => new Response("hello")});
+    "#;
+  write(&file_to_watch, file_content).unwrap();
+
+  let mut child = util::deno_cmd()
+    .current_dir(util::testdata_path())
+    .arg("run")
+    .arg("--watch")
+    .arg("--unstable")
+    .arg("--allow-net")
+    .arg("-L")
+    .arg("debug")
+    .arg(&file_to_watch)
+    .env("NO_COLOR", "1")
+    .stdout(std::process::Stdio::piped())
+    .stderr(std::process::Stdio::piped())
+    .spawn()
+    .unwrap();
+  let (mut stdout_lines, mut stderr_lines) = child_lines(&mut child);
+
+  wait_contains("Listening on", &mut stdout_lines).await;
+  // Note that we start serving very quickly, so we specifically want to wait for this message
+  wait_contains(r#"Watching paths: [""#, &mut stderr_lines).await;
+
+  write(&file_to_watch, file_content).unwrap();
+
+  wait_contains("serving", &mut stderr_lines).await;
+  wait_contains("Listening on", &mut stdout_lines).await;
+
+  check_alive_then_kill(child);
+}
+
 #[tokio::test]
 async fn run_watch_dynamic_imports() {
   let t = TempDir::new();
diff --git a/cli/tests/unit/serve_test.ts b/cli/tests/unit/serve_test.ts
index 5d5d0428f..ce7267f58 100644
--- a/cli/tests/unit/serve_test.ts
+++ b/cli/tests/unit/serve_test.ts
@@ -94,8 +94,9 @@ Deno.test(async function httpServerRejectsOnAddrInUse() {
     onListen: onListen(listeningPromise),
     onError: createOnErrorCb(ac),
   });
+  await listeningPromise;
 
-  assertRejects(
+  await assertRejects(
     () =>
       Deno.serve({
         handler: (_req) => new Response("ok"),
diff --git a/cli/util/file_watcher.rs b/cli/util/file_watcher.rs
index 05415f2a6..1ad5e9ba0 100644
--- a/cli/util/file_watcher.rs
+++ b/cli/util/file_watcher.rs
@@ -304,6 +304,13 @@ where
   }
 
   loop {
+    // We may need to give the runtime a tick to settle, as cancellations may need to propagate
+    // to tasks. We choose yielding 10 times to the runtime as a decent heuristic. If watch tests
+    // start to fail, this may need to be increased.
+    for _ in 0..10 {
+      tokio::task::yield_now().await;
+    }
+
     let mut watcher = new_watcher(watcher_sender.clone())?;
     consume_paths_to_watch(&mut watcher, &mut paths_to_watch_receiver);