fix(gpui): follow the macOS Reduce Motion setting

apps/desktop-gpui/Cargo.toml

@@ -210,10 +210,11 @@ x11rb = "0.13"
 objc2 = "0.5.2"
 # `NSVisualEffectView` is the pre-macOS-26 window-material fallback. Features
 # only -- the versions stay pinned, or a second objc2 universe gets built.
-objc2-app-kit = { version = "0.2.2", features = ["NSAppearance", "NSWindow", "NSView", "NSResponder", "NSGraphics", "NSPasteboard", "NSVisualEffectView"] }
+objc2-app-kit = { version = "0.2.2", features = ["NSAppearance", "NSWindow", "NSView", "NSResponder", "NSGraphics", "NSPasteboard", "NSVisualEffectView", "NSWorkspace", "NSAccessibility"] }
 # NSRect/NSPoint/NSSize for `setFrame:display:`. Already in the tree as
 # objc2-app-kit's own dependency, so this adds nothing to the build.
-objc2-foundation = "0.2.2"
+objc2-foundation = { version = "0.2.2", features = ["NSNotification", "NSOperation", "NSString", "block2"] }
+block2 = "0.5.1"
 raw-window-handle = "0.6"
 core-foundation = "0.10"
 core-video = { version = "0.5.2", features = ["metal"] }

apps/desktop-gpui/src/main.rs

@@ -316,6 +316,7 @@ fn main() {
         // the path runs (`gpui/src/window.rs:5280-5296`).
         ui::bind_text_input_keys(cx);
         crate::theme::init(cx);
+        platform::follow_system_reduce_motion(cx);
 
         let session = RecordingSession::init(cx);
         crate::sign_in::SignIn::init(cx);

apps/desktop-gpui/src/platform.rs

@@ -587,6 +587,15 @@ pub struct PanelBehavior {
 #[cfg(target_os = "macos")]
 pub use mac::*;
 
+/// GPUI keeps its own Reduce Motion flag and never reads the OS setting, so
+/// every animation ignored it until this fed it in.
+pub fn follow_system_reduce_motion(cx: &mut gpui::App) {
+    #[cfg(target_os = "macos")]
+    mac::follow_system_reduce_motion(cx);
+    #[cfg(not(target_os = "macos"))]
+    let _ = cx;
+}
+
 #[cfg(target_os = "macos")]
 mod macos_exception_guard;
 
@@ -595,6 +604,42 @@ mod macos_occlusion;
 
 #[cfg(target_os = "macos")]
 mod mac {
+    pub fn follow_system_reduce_motion(cx: &mut gpui::App) {
+        use objc2_app_kit::{
+            NSWorkspace, NSWorkspaceAccessibilityDisplayOptionsDidChangeNotification,
+        };
+        use objc2_foundation::{NSNotification, NSOperationQueue};
+
+        let reduce_motion = || {
+            let reduce =
+                unsafe { NSWorkspace::sharedWorkspace().accessibilityDisplayShouldReduceMotion() };
+            tracing::debug!(reduce, "system reduce motion");
+            reduce
+        };
+        cx.set_reduce_motion(reduce_motion());
+
+        let (changed, changes) = flume::unbounded::<()>();
+        let block = block2::RcBlock::new(move |_: std::ptr::NonNull<NSNotification>| {
+            let _ = changed.send(());
+        });
+        unsafe {
+            let center = NSWorkspace::sharedWorkspace().notificationCenter();
+            let observer = center.addObserverForName_object_queue_usingBlock(
+                Some(NSWorkspaceAccessibilityDisplayOptionsDidChangeNotification),
+                None,
+                Some(&NSOperationQueue::mainQueue()),
+                &block,
+            );
+            std::mem::forget(observer);
+        }
+        cx.spawn(async move |cx| {
+            while changes.recv_async().await.is_ok() {
+                cx.update(|cx| cx.set_reduce_motion(reduce_motion()));
+            }
+        })
+        .detach();
+    }
+
     use gpui::Window;
     use objc2::rc::Id;
     use objc2::runtime::{AnyObject, Sel};