ensure that we spawn open calls on a background thread

Otherwise we can block the gui waiting for eg: a freshly opened firefox to
terminate.

See also comment worrying about this in
75066cb522.
That fear was realized but now resolved!

refs: https://github.com/wez/wezterm/issues/2245

docs/changelog.md

@@ -43,6 +43,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Tab bar could show a gap to the right when resizing
 * Padding could show window background rather than pane background around split panes at certain window sizes [#2210](https://github.com/wez/wezterm/issues/2210)
 * Loading dynamic escape sequence scripts from the [iTerm2-Color-Scheme dynamic-colors directory](https://github.com/mbadolato/iTerm2-Color-Schemes/tree/master/dynamic-colors) would only apply the first 7 colors
+* Unix: Clicking a URL when no browser is open could cause wezterm to hang until the newly opened browser is closed. [#2245](https://github.com/wez/wezterm/issues/2245)
 
 #### Updated
 * Bundled harfbuzz to 4.4.1

lua-api-crates/spawn-funcs/src/lib.rs

@@ -20,9 +20,11 @@ fn open_with<'lua>(_: &'lua Lua, (url, app): (String, Option<String>)) -> mlua::
     if let Some(app) = app {
         open::with_in_background(url, app);
     } else {
+        std::thread::spawn(move || {
             if let Err(err) = open::that(&url) {
                 log::error!("Error opening {}: {:#}", url, err);
             }
+        });
     }
     Ok(())
 }

wezterm-gui/src/termwindow/mod.rs

@@ -2519,10 +2519,12 @@ impl TermWindow {
                     None => true,
                 };
                 if default_click {
+                    std::thread::spawn(move || {
                         log::info!("clicking {}", link);
                         if let Err(err) = open::that(&link) {
                             log::error!("Error opening {}: {:#}", link, err);
                         }
+                    });
                 }
                 Ok(())
             }

wezterm-toast-notification/src/dbus.rs

@@ -126,7 +126,10 @@ async fn show_notif_impl(notif: ToastNotification) -> Result<(), Box<dyn std::er
                 let args = signal.args()?;
                 if args.nid == notification {
                     if let Some(url) = notif.url.as_ref() {
+                        let url = url.clone();
+                        std::thread::spawn(move || {
                             let _ = open::that(url);
+                        });
                         abort_closed.abort();
                         break;
                     }