On Windows, fix left mouse button release event not being sent after Window::drag_window (#2564)

CHANGELOG.md

@@ -8,6 +8,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- On Windows, fix left mouse button release event not being sent after `Window::drag_window`.
 - On macOS, run most actions on the main thread, which is strictly more correct, but might make multithreaded applications block slightly more.
 - On macOS, fix panic when getting current monitor without any monitor attached.
 - On Windows and MacOS, add API to enable/disable window buttons (close, minimize, ...etc).

src/platform_impl/windows/event_loop.rs

@@ -1006,9 +1006,13 @@ unsafe fn public_window_callback_inner<T: 'static>(
         }
 
         WM_EXITSIZEMOVE => {
-            userdata
-                .window_state_lock()
-                .set_window_flags_in_place(|f| f.remove(WindowFlags::MARKER_IN_SIZE_MOVE));
+            let mut state = userdata.window_state_lock();
+            if state.dragging {
+                state.dragging = false;
+                PostMessageW(window, WM_LBUTTONUP, 0, lparam);
+            }
+
+            state.set_window_flags_in_place(|f| f.remove(WindowFlags::MARKER_IN_SIZE_MOVE));
             0
         }
 

src/platform_impl/windows/window.rs

@@ -418,6 +418,9 @@ impl Window {
                 y: points.y as i16,
             };
             ReleaseCapture();
+
+            self.window_state_lock().dragging = true;
+
             PostMessageW(
                 self.hwnd(),
                 WM_NCLBUTTONDOWN,

src/platform_impl/windows/window_state.rs

@@ -52,6 +52,8 @@ pub(crate) struct WindowState {
     pub is_active: bool,
     pub is_focused: bool,
 
+    pub dragging: bool,
+
     pub skip_taskbar: bool,
 }
 
@@ -162,6 +164,8 @@ impl WindowState {
             is_active: false,
             is_focused: false,
 
+            dragging: false,
+
             skip_taskbar: false,
         }
     }