Fix fullscreen window messaging race on Windows (#2225)

CHANGELOG.md

@@ -26,6 +26,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - The internal bindings to the [Windows API](https://docs.microsoft.com/en-us/windows/) were changed from the unofficial [winapi](https://github.com/retep998/winapi-rs) bindings to the official Microsoft [windows-sys](https://github.com/microsoft/windows-rs) bindings.
 - On Wayland, fix resize and scale factor changes not being propagated properly.
 - On Wayland, fix polling during consecutive `EventLoop::run_return` invocations.
+- On Windows, fix race issue creating fullscreen windows with `WindowBuilder::with_fullscreen`
 
 # 0.26.1 (2022-01-05)
 
@@ -251,13 +252,13 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 - On X11, fix `ModifiersChanged` emitting incorrect modifier change events
 - **Breaking**: Overhaul how Winit handles DPI:
-  + Window functions and events now return `PhysicalSize` instead of `LogicalSize`.
-  + Functions that take `Size` or `Position` types can now take either `Logical` or `Physical` types.
-  + `hidpi_factor` has been renamed to `scale_factor`.
-  + `HiDpiFactorChanged` has been renamed to `ScaleFactorChanged`, and lets you control how the OS
+  - Window functions and events now return `PhysicalSize` instead of `LogicalSize`.
+  - Functions that take `Size` or `Position` types can now take either `Logical` or `Physical` types.
+  - `hidpi_factor` has been renamed to `scale_factor`.
+  - `HiDpiFactorChanged` has been renamed to `ScaleFactorChanged`, and lets you control how the OS
     resizes the window in response to the change.
-  + On X11, deprecate `WINIT_HIDPI_FACTOR` environment variable in favor of `WINIT_X11_SCALE_FACTOR`.
-  + `Size` and `Position` types are now generic over their exact pixel type.
+  - On X11, deprecate `WINIT_HIDPI_FACTOR` environment variable in favor of `WINIT_X11_SCALE_FACTOR`.
+  - `Size` and `Position` types are now generic over their exact pixel type.
 
 # 0.20.0 Alpha 6 (2020-01-03)
 
@@ -362,7 +363,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - `Window::set_fullscreen` now takes `Option<Fullscreen>` where `Fullscreen`
   consists of `Fullscreen::Exclusive(VideoMode)` and
   `Fullscreen::Borderless(MonitorHandle)` variants.
-    - Adds support for exclusive fullscreen mode.
+  - Adds support for exclusive fullscreen mode.
 - On iOS, add support for hiding the home indicator.
 - On iOS, add support for deferring system gestures.
 - On iOS, fix a crash that occurred while acquiring a monitor's name.
@@ -561,7 +562,7 @@ and `WindowEvent::HoveredFile`.
 # Version 0.16.1 (2018-07-02)
 
 - Added logging through `log`. Logging will become more extensive over time.
-- On X11 and Windows, the window's DPI factor is guessed before creating the window. This *greatly* cuts back on unsightly auto-resizing that would occur immediately after window creation.
+- On X11 and Windows, the window's DPI factor is guessed before creating the window. This _greatly_ cuts back on unsightly auto-resizing that would occur immediately after window creation.
 - Fixed X11 backend compilation for environments where `c_char` is unsigned.
 
 # Version 0.16.0 (2018-06-25)
@@ -711,7 +712,7 @@ and `WindowEvent::HoveredFile`.
 
 # Version 0.10.1 (2018-02-05)
 
-*Yanked*
+_Yanked_
 
 # Version 0.10.0 (2017-12-27)
 

src/platform_impl/windows/window.rs

@@ -62,8 +62,7 @@ use crate::{
     monitor::MonitorHandle as RootMonitorHandle,
     platform_impl::platform::{
         dark_mode::try_theme,
-        definitions::ITaskbarList2,
-        definitions::{CLSID_TaskbarList, IID_ITaskbarList2},
+        definitions::{CLSID_TaskbarList, IID_ITaskbarList2, ITaskbarList2},
         dpi::{dpi_to_scale_factor, enable_non_client_dpi_scaling, hwnd_dpi},
         drop_handler::FileDropHandler,
         event_loop::{self, EventLoopWindowTarget, DESTROY_MSG_ID},
@@ -486,6 +485,14 @@ impl Window {
                 );
             });
 
+            // Mark as fullscreen window wrt to z-order
+            //
+            // this needs to be called before the below fullscreen SetWindowPos as this itself
+            // will generate WM_SIZE messages of the old window size that can race with what we set below
+            unsafe {
+                taskbar_mark_fullscreen(window.0, fullscreen.is_some());
+            }
+
             // Update window bounds
             match &fullscreen {
                 Some(fullscreen) => {
@@ -533,10 +540,6 @@ impl Window {
                     }
                 }
             }
-
-            unsafe {
-                taskbar_mark_fullscreen(window.0, fullscreen.is_some());
-            }
         });
     }
 
@@ -842,19 +845,20 @@ impl<'a, T: 'static> InitData<'a, T> {
         // attribute is correctly applied.
         win.set_visible(attributes.visible);
 
-        let dimensions = attributes
-            .inner_size
-            .unwrap_or_else(|| PhysicalSize::new(800, 600).into());
-        win.set_inner_size(dimensions);
-        if attributes.maximized {
-            // Need to set MAXIMIZED after setting `inner_size` as
-            // `Window::set_inner_size` changes MAXIMIZED to false.
-            win.set_maximized(true);
-        }
-
         if attributes.fullscreen.is_some() {
             win.set_fullscreen(attributes.fullscreen);
             force_window_active(win.window.0);
+        } else {
+            let dimensions = attributes
+                .inner_size
+                .unwrap_or_else(|| PhysicalSize::new(800, 600).into());
+            win.set_inner_size(dimensions);
+
+            if attributes.maximized {
+                // Need to set MAXIMIZED after setting `inner_size` as
+                // `Window::set_inner_size` changes MAXIMIZED to false.
+                win.set_maximized(true);
+            }
         }
 
         if let Some(position) = attributes.position {