Support multiple clients for niri msg pick-window

WIP: Currently the ipc server gets stuck waiting for niri to return the
picked window, and if the ipc client closes it doesn't realize that until
niri returns the picked window leading to "ghost" window picking.

In general having `self.niri.pick_window.retain(|tx| !tx.is_closed());`
to cleanup closed clients in input events feels like the wrong place,
but should work since having stale senders doesn't effect anything else.

[skip ci]

src/input/mod.rs

@@ -361,13 +361,12 @@ impl State {
                     }
                 }
 
-                if let Some(tx) = this
-                    .niri
-                    .pick_window
-                    .take_if(move |_| raw == Some(Keysym::Escape))
-                {
-                    let _ = tx.send_blocking(None);
-                    return FilterResult::Intercept(None);
+                if pressed && raw == Some(Keysym::Escape) {
+                    this.niri.pick_window.retain(|tx| !tx.is_closed());
+                    if let Some(tx) = this.niri.pick_window.pop_front() {
+                        let _ = tx.send_blocking(None);
+                        return FilterResult::Intercept(None);
+                    }
                 }
 
                 should_intercept_key(
@@ -1842,12 +1841,13 @@ impl State {
             self.niri.pointer_hidden = false;
             self.niri.tablet_cursor_location = None;
 
-            if let Some(tx) = self.niri.pick_window.take() {
+            self.niri.pick_window.retain(|tx| !tx.is_closed());
+            if !self.niri.pick_window.is_empty() {
                 if let Some(mapped_id) = self.niri.window_under_cursor().map(|mapped| mapped.id()) {
+                    let tx = self.niri.pick_window.pop_front().unwrap();
                     let _ = tx.send_blocking(Some(mapped_id));
                     return;
                 }
-                self.niri.pick_window = Some(tx);
             }
 
             if let Some(mapped) = self.niri.window_under_cursor() {

src/ipc/server.rs

@@ -312,7 +312,7 @@ async fn process(ctx: &ClientCtx, request: Request) -> Reply {
         Request::PickWindow => {
             let (tx, rx) = async_channel::bounded(1);
             ctx.event_loop.insert_idle(move |state| {
-                state.niri.pick_window = Some(tx);
+                state.niri.pick_window.push_back(tx);
             });
             let result = rx.recv().await;
             let id = result.map_err(|_| String::from("error getting picked window info"))?;

src/niri.rs

@@ -1,5 +1,5 @@
 use std::cell::{Cell, OnceCell, RefCell};
-use std::collections::{HashMap, HashSet};
+use std::collections::{HashMap, HashSet, VecDeque};
 use std::ffi::OsString;
 use std::path::PathBuf;
 use std::rc::Rc;
@@ -333,7 +333,7 @@ pub struct Niri {
     pub hotkey_overlay: HotkeyOverlay,
     pub exit_confirm_dialog: Option<ExitConfirmDialog>,
 
-    pub pick_window: Option<async_channel::Sender<Option<MappedId>>>,
+    pub pick_window: VecDeque<async_channel::Sender<Option<MappedId>>>,
 
     pub debug_draw_opaque_regions: bool,
     pub debug_draw_damage: bool,
@@ -2078,7 +2078,7 @@ impl Niri {
             hotkey_overlay,
             exit_confirm_dialog,
 
-            pick_window: None,
+            pick_window: VecDeque::new(),
 
             debug_draw_opaque_regions: false,
             debug_draw_damage: false,