lua: make gui_window() reconcile workspace

reconciling causes gui windows to be created and allows for stuff like
this, that would otherwise fail because the gui window hadn't been
created yet.

```lua
local wezterm = require 'wezterm'

local mux = wezterm.mux

wezterm.on("gui-startup", function()
  local tab, pane, window = mux.spawn_window{}
  window:gui_window():set_inner_size(1200, 1200)
end)

return {
}
```

lua-api-crates/mux/src/lib.rs

@@ -334,14 +334,14 @@ impl_lua_conversion_dynamic!(MuxTabInfo);
 impl UserData for MuxWindow {
     fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
         methods.add_method("window_id", |_, this, _: ()| Ok(this.0));
-        methods.add_method("gui_window", |lua, this, _: ()| {
+        methods.add_async_method("gui_window", |lua, this, _: ()| async move {
             // Weakly bound to the gui module; mux cannot hard-depend
             // on wezterm-gui, but we can runtime resolve the appropriate module
             let wezterm_mod = get_or_create_module(lua, "wezterm")
                 .map_err(|err| mlua::Error::external(format!("{err:#}")))?;
             let gui: mlua::Table = wezterm_mod.get("gui")?;
             let func: mlua::Function = gui.get("gui_window_for_mux_window")?;
-            func.call::<_, mlua::Value>(this.0)
+            func.call_async::<_, mlua::Value>(this.0).await
         });
         methods.add_method("get_workspace", |_, this, _: ()| {
             let mux = get_mux()?;

wezterm-gui/src/frontend.rs

@@ -7,6 +7,7 @@ pub use config::FrontEndSelection;
 use mux::client::ClientId;
 use mux::window::WindowId as MuxWindowId;
 use mux::{Mux, MuxNotification};
+use promise::{Future, Promise};
 use std::cell::RefCell;
 use std::collections::{BTreeMap, HashSet};
 use std::rc::Rc;
@@ -151,7 +152,8 @@ impl GuiFrontEnd {
             .context("running message loop")
     }
 
-    pub fn reconcile_workspace(&self) {
+    pub fn reconcile_workspace(&self) -> Future<()> {
+        let mut promise = Promise::new();
         let mux = Mux::get().expect("mux started and running on main thread");
         let workspace = mux.active_workspace_for_client(&self.client_id);
 
@@ -160,7 +162,8 @@ impl GuiFrontEnd {
             // be running in other workspaces, so let's pick one
             // and activate it
             if self.is_switching_workspace() {
-                return;
+                promise.ok(());
+                return promise.get_future().unwrap();
             }
             for workspace in mux.iter_workspaces() {
                 if !mux.is_workspace_empty(&workspace) {
@@ -211,6 +214,8 @@ impl GuiFrontEnd {
         log::trace!("reconcile: windows -> {:?}", windows);
         *self.known_windows.borrow_mut() = windows;
 
+        let future = promise.get_future().unwrap();
+
         // then spawn any new windows that are needed
         promise::spawn::spawn(async move {
             while let Some(mux_window_id) = mux_windows.next() {
@@ -238,8 +243,10 @@ impl GuiFrontEnd {
                 }
             }
             *front_end().switching_workspaces.borrow_mut() = false;
+            promise.ok(());
         })
         .detach();
+        future
     }
 
     fn has_mux_window(&self, mux_window_id: MuxWindowId) -> bool {

wezterm-gui/src/scripting/mod.rs

@@ -15,9 +15,10 @@ pub fn register(lua: &Lua) -> anyhow::Result<()> {
 
     window_mod.set(
         "gui_window_for_mux_window",
-        lua.create_function(|_, mux_window_id: MuxWindowId| {
+        lua.create_async_function(|_, mux_window_id: MuxWindowId| async move {
             let fe =
                 try_front_end().ok_or_else(|| mlua::Error::external("not called on gui thread"))?;
+            let _ = fe.reconcile_workspace().await;
             let win = fe.gui_window_for_mux_window(mux_window_id).ok_or_else(|| {
                 mlua::Error::external(format!(
                     "mux window id {mux_window_id} is not currently associated with a gui window"