Allow styling the cursor in MouseEventHandler

Co-Authored-By: Max Brunsfeld <max@zed.dev>
Co-Authored-By: Nathan Sobo <nathan@zed.dev>

gpui/src/platform/mac/platform.rs

@@ -1,6 +1,9 @@
 use super::{BoolExt as _, Dispatcher, FontSystem, Window};
 use crate::{
-    executor, keymap::Keystroke, platform, AnyAction, ClipboardItem, Event, Menu, MenuItem,
+    executor,
+    keymap::Keystroke,
+    platform::{self, CursorStyle},
+    AnyAction, ClipboardItem, Event, Menu, MenuItem,
 };
 use block::ConcreteBlock;
 use cocoa::{
@@ -544,6 +547,17 @@ impl platform::Platform for MacPlatform {
             Some((username.to_string(), password.bytes().to_vec()))
         }
     }
+
+    fn set_cursor_style(&self, style: CursorStyle) {
+        unsafe {
+            let cursor: id = match style {
+                CursorStyle::Arrow => msg_send![class!(NSCursor), arrowCursor],
+                CursorStyle::ResizeLeftRight => msg_send![class!(NSCursor), resizeLeftRightCursor],
+                CursorStyle::PointingHand => msg_send![class!(NSCursor), pointingHandCursor],
+            };
+            let _: () = msg_send![cursor, set];
+        }
+    }
 }
 
 unsafe fn get_foreground_platform(object: &mut Object) -> &MacForegroundPlatform {

gpui/src/platform/test.rs

@@ -1,3 +1,4 @@
+use super::CursorStyle;
 use crate::{AnyAction, ClipboardItem};
 use parking_lot::Mutex;
 use pathfinder_geometry::vector::Vector2F;
@@ -13,6 +14,7 @@ pub struct Platform {
     dispatcher: Arc<dyn super::Dispatcher>,
     fonts: Arc<dyn super::FontSystem>,
     current_clipboard_item: Mutex<Option<ClipboardItem>>,
+    cursor: Mutex<CursorStyle>,
 }
 
 #[derive(Default)]
@@ -84,6 +86,7 @@ impl Platform {
             dispatcher: Arc::new(Dispatcher),
             fonts: Arc::new(super::current::FontSystem::new()),
             current_clipboard_item: Default::default(),
+            cursor: Mutex::new(CursorStyle::Arrow),
         }
     }
 }
@@ -129,6 +132,10 @@ impl super::Platform for Platform {
     fn read_credentials(&self, _: &str) -> Option<(String, Vec<u8>)> {
         None
     }
+
+    fn set_cursor_style(&self, style: CursorStyle) {
+        *self.cursor.lock() = style;
+    }
 }
 
 impl Window {