gpui: Reset external_files_dragged after successful drag-drop on macOS (#48727)

after a successful file drag-drop, conclude_drag_operation did not reset
external_files_dragged to false. since dragging_exited (the only place
that resets this flag) is never called for successful drops (only for
cancelled ones), the flag stayed true permanently. this caused synthetic
drags (used for text selection during buffer scrolling) to be suppressed
for the lifetime of the window.

Release Notes:

- N/A

---------

Co-authored-by: MrSubidubi <finn@zed.dev>

Author: Albab-Hasan

crates/gpui/src/platform/mac/window.rs

@@ -2454,11 +2454,9 @@ extern "C" fn dragging_entered(this: &Object, _: Sel, dragging_info: id) -> NSDr
     let window_state = unsafe { get_window_state(this) };
     let position = drag_event_position(&window_state, dragging_info);
     let paths = external_paths_from_event(dragging_info);
-    if let Some(event) =
-        paths.map(|paths| PlatformInput::FileDrop(FileDropEvent::Entered { position, paths }))
-        && send_new_event(&window_state, event)
+    if let Some(event) = paths.map(|paths| FileDropEvent::Entered { position, paths })
+        && send_file_drop_event(window_state, event)
     {
-        window_state.lock().external_files_dragged = true;
         return NSDragOperationCopy;
     }
     NSDragOperationNone
@@ -2467,10 +2465,7 @@ extern "C" fn dragging_entered(this: &Object, _: Sel, dragging_info: id) -> NSDr
 extern "C" fn dragging_updated(this: &Object, _: Sel, dragging_info: id) -> NSDragOperation {
     let window_state = unsafe { get_window_state(this) };
     let position = drag_event_position(&window_state, dragging_info);
-    if send_new_event(
-        &window_state,
-        PlatformInput::FileDrop(FileDropEvent::Pending { position }),
-    ) {
+    if send_file_drop_event(window_state, FileDropEvent::Pending { position }) {
         NSDragOperationCopy
     } else {
         NSDragOperationNone
@@ -2479,21 +2474,13 @@ extern "C" fn dragging_updated(this: &Object, _: Sel, dragging_info: id) -> NSDr
 
 extern "C" fn dragging_exited(this: &Object, _: Sel, _: id) {
     let window_state = unsafe { get_window_state(this) };
-    send_new_event(
-        &window_state,
-        PlatformInput::FileDrop(FileDropEvent::Exited),
-    );
-    window_state.lock().external_files_dragged = false;
+    send_file_drop_event(window_state, FileDropEvent::Exited);
 }
 
 extern "C" fn perform_drag_operation(this: &Object, _: Sel, dragging_info: id) -> BOOL {
     let window_state = unsafe { get_window_state(this) };
     let position = drag_event_position(&window_state, dragging_info);
-    send_new_event(
-        &window_state,
-        PlatformInput::FileDrop(FileDropEvent::Submit { position }),
-    )
-    .to_objc()
+    send_file_drop_event(window_state, FileDropEvent::Submit { position }).to_objc()
 }
 
 fn external_paths_from_event(dragging_info: *mut Object) -> Option<ExternalPaths> {
@@ -2515,10 +2502,7 @@ fn external_paths_from_event(dragging_info: *mut Object) -> Option<ExternalPaths
 
 extern "C" fn conclude_drag_operation(this: &Object, _: Sel, _: id) {
     let window_state = unsafe { get_window_state(this) };
-    send_new_event(
-        &window_state,
-        PlatformInput::FileDrop(FileDropEvent::Exited),
-    );
+    send_file_drop_event(window_state, FileDropEvent::Exited);
 }
 
 async fn synthetic_drag(
@@ -2544,11 +2528,26 @@ async fn synthetic_drag(
     }
 }
 
-fn send_new_event(window_state_lock: &Mutex<MacWindowState>, e: PlatformInput) -> bool {
-    let window_state = window_state_lock.lock().event_callback.take();
-    if let Some(mut callback) = window_state {
-        callback(e);
-        window_state_lock.lock().event_callback = Some(callback);
+/// Sends the specified FileDropEvent using `PlatformInput::FileDrop` to the window
+/// state and updates the window state according to the event passed.
+fn send_file_drop_event(
+    window_state: Arc<Mutex<MacWindowState>>,
+    file_drop_event: FileDropEvent,
+) -> bool {
+    let mut window_state = window_state.lock();
+    let window_event_callback = window_state.event_callback.as_mut();
+    if let Some(mut callback) = window_event_callback {
+        let external_files_dragged = match file_drop_event {
+            FileDropEvent::Entered { .. } => Some(true),
+            FileDropEvent::Exited => Some(false),
+            _ => None,
+        };
+
+        callback(PlatformInput::FileDrop(file_drop_event));
+
+        if let Some(external_files_dragged) = external_files_dragged {
+            window_state.external_files_dragged = external_files_dragged;
+        }
         true
     } else {
         false