feat(update): background update check with post-command notice (#104)

Spawn the GitHub release check in a background thread before the command
runs, then join it (recv_timeout 6 s) after the command finishes so the
notice always appears at the bottom of output. Uses mpsc::Receiver instead
of JoinHandle::join to prevent blocking if the HTTP request stalls past
its own 5 s timeout. Unifies the notice message to "hotdata update" for
all install methods.

Co-authored-by: Eddie A Tejeda <669988+eddietejeda@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: eddietejeda

src/main.rs

@@ -172,11 +172,15 @@ fn main() {
         skill::maybe_auto_update_after_cli_upgrade();
     }
 
-    // Quiet update-available notice. Skip during `hotdata update` itself so
-    // we don't talk over the updater's own output.
-    if !matches!(&cli.command, Some(Commands::Update)) {
-        update::maybe_print_update_notice();
-    }
+    // Kick off the update check in the background so it runs concurrently
+    // with the command.  We join and print after the command finishes so the
+    // notice always appears at the bottom of the output.  Skipped during
+    // `hotdata update` itself so it doesn't talk over the updater's output.
+    let update_handle = if !matches!(&cli.command, Some(Commands::Update)) {
+        update::spawn_update_check()
+    } else {
+        None
+    };
 
     match cli.command {
         None => {
@@ -1008,6 +1012,9 @@ fn main() {
             Commands::Update => update::run_update(),
         },
     }
+
+    // Print update notice after command output (joined from background thread).
+    update::maybe_print_update_notice(update_handle);
 }
 
 /// Parse a database target like `airbnb.listings` or `airbnb.public.listings`

src/update.rs

@@ -120,31 +120,45 @@ fn stderr_is_tty() -> bool {
     std::io::stderr().is_terminal()
 }
 
-/// Print a one-line notice if a newer release exists. No-op when stderr
-/// isn't a TTY, when --no-input is set, or when the cache says we're up
-/// to date. Best-effort: network/cache errors are swallowed silently so
-/// commands never fail because of the update check.
-pub fn maybe_print_update_notice() {
-    if !stderr_is_tty() {
-        return;
-    }
-    if !util::is_interactive() {
-        return;
-    }
-    if std::env::var_os("HOTDATA_NO_UPDATE_CHECK").is_some() {
-        return;
+fn should_check() -> bool {
+    stderr_is_tty()
+        && util::is_interactive()
+        && std::env::var_os("HOTDATA_NO_UPDATE_CHECK").is_none()
+}
+
+/// How long `maybe_print_update_notice` will wait for the background thread
+/// before giving up.  In practice the thread finishes well within this window
+/// because `fetch_latest_version` has its own 5-second HTTP timeout and cache
+/// hits resolve in microseconds.
+const NOTICE_WAIT_MS: u64 = 6_000;
+
+/// Spawn a background thread that checks for a newer release.  Returns a
+/// channel receiver that `maybe_print_update_notice` can poll after the
+/// command runs.  No-op (returns None) when stderr isn't a TTY, `--no-input`
+/// is set, or `HOTDATA_NO_UPDATE_CHECK` is set.
+pub fn spawn_update_check() -> Option<std::sync::mpsc::Receiver<Option<Version>>> {
+    if !should_check() {
+        return None;
     }
-    let Some(latest) = cached_latest_if_newer() else {
+    let (tx, rx) = std::sync::mpsc::channel();
+    std::thread::spawn(move || {
+        let _ = tx.send(cached_latest_if_newer());
+    });
+    Some(rx)
+}
+
+/// Poll the receiver returned by `spawn_update_check` and print a one-line
+/// notice if a newer release was found.  Call this *after* the command has
+/// produced its own output so the notice appears at the bottom.
+pub fn maybe_print_update_notice(rx: Option<std::sync::mpsc::Receiver<Option<Version>>>) {
+    let Some(rx) = rx else { return };
+    let Ok(Some(latest)) = rx.recv_timeout(Duration::from_millis(NOTICE_WAIT_MS)) else {
         return;
     };
-    let how = match detect_install_method() {
-        InstallMethod::Homebrew => format!("Run: brew upgrade {HOMEBREW_FORMULA}"),
-        InstallMethod::Other => "Run: hotdata update".to_string(),
-    };
     eprintln!(
         "{}",
         format!(
-            "A new version of hotdata is available (v{CURRENT_VERSION} → v{latest}). {how}"
+            "\nA new version of hotdata is available (v{CURRENT_VERSION} → v{latest}). Run: hotdata update"
         )
         .yellow()
     );