From c1bf410466bff62c58f2115b4a5f2e4861592d6b Mon Sep 17 00:00:00 2001
From: Ian Douglas Scott <idscott@system76.com>
Date: Wed, 31 Jul 2024 14:49:10 -0700
Subject: [PATCH] toplevel-info: Fix race between binding `wl_ouput` and
 `output_enter`

This fixes an issue with `cosmic-panel` where, when a workspace is moved
back to an output after a monitor is disconnected and reconnected, the
panel doesn't hide because `cosmic-panel` thinks no toplevel is open on
that monitor.

After some testing, it seems `output_enter` isn't being sent here. In
particular, the `output_leave` call happens before the client binds the
`wl_output`, so there is no `wl_output` to send in an event yet.

This is addressed by keeping track of a set of `wl_output`s that we have
sent the event to. So if an output is bound, `refresh` can add it to
this list and send the event.

This is not needed for workspaces (though it could be done similarly)
since the handle objects are created by server events. So no race should
occur as long as the workspaces global is bound before the toplevel info
one.
---
 src/wayland/protocols/toplevel_info.rs | 48 ++++++++++++++------------
 1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/src/wayland/protocols/toplevel_info.rs b/src/wayland/protocols/toplevel_info.rs
index ce094ca1..7e9fd36e 100644
--- a/src/wayland/protocols/toplevel_info.rs
+++ b/src/wayland/protocols/toplevel_info.rs
@@ -1,12 +1,12 @@
 // SPDX-License-Identifier: GPL-3.0-only
 
-use std::sync::Mutex;
+use std::{collections::HashSet, sync::Mutex};
 
 use smithay::{
     output::Output,
     reexports::wayland_server::{
         backend::{ClientId, GlobalId},
-        protocol::wl_surface::WlSurface,
+        protocol::{wl_output::WlOutput, wl_surface::WlSurface},
         Client, DataInit, Dispatch, DisplayHandle, GlobalDispatch, New, Resource, Weak,
     },
     utils::{user_data::UserDataMap, IsAlive, Logical, Rectangle},
@@ -59,6 +59,7 @@ pub(super) type ToplevelState = Mutex<ToplevelStateInner>;
 
 pub struct ToplevelHandleStateInner<W: Window> {
     outputs: Vec<Output>,
+    wl_outputs: HashSet<WlOutput>,
     workspaces: Vec<WorkspaceHandle>,
     title: String,
     app_id: String,
@@ -71,6 +72,7 @@ impl<W: Window> ToplevelHandleStateInner<W> {
     fn from_window(window: &W) -> ToplevelHandleState<W> {
         ToplevelHandleState::new(ToplevelHandleStateInner {
             outputs: Vec::new(),
+            wl_outputs: HashSet::new(),
             workspaces: Vec::new(),
             title: String::new(),
             app_id: String::new(),
@@ -399,27 +401,29 @@ fn send_toplevel_to_client<D, W: 'static>(
     }
 
     if let Ok(client) = dh.get_client(instance.id()) {
-        for new_output in state
-            .outputs
-            .iter()
-            .filter(|o| !handle_state.outputs.contains(o))
-        {
-            for wl_output in new_output.client_outputs(&client) {
-                instance.output_enter(&wl_output);
-            }
-            changed = true;
-        }
-        for old_output in handle_state
-            .outputs
-            .iter()
-            .filter(|o| !state.outputs.contains(o))
-        {
-            for wl_output in old_output.client_outputs(&client) {
-                instance.output_leave(&wl_output);
-            }
-            changed = true;
-        }
         handle_state.outputs = state.outputs.clone();
+
+        let handle_state = &mut *handle_state;
+        for output in &handle_state.outputs {
+            for wl_output in output.client_outputs(&client) {
+                if handle_state.wl_outputs.insert(wl_output.clone()) {
+                    instance.output_enter(&wl_output);
+                    changed = true;
+                }
+            }
+        }
+        handle_state.wl_outputs.retain(|wl_output| {
+            let retain = wl_output.is_alive()
+                && handle_state
+                    .outputs
+                    .iter()
+                    .any(|output| output.owns(wl_output));
+            if !retain {
+                instance.output_leave(&wl_output);
+                changed = true;
+            }
+            retain
+        });
     }
 
     for new_workspace in state