macOS: Enumerate GPUs first; prefer low-power non-removable; fall back to system default (#38164)

Problem: Some macOS environments report no devices via
MTLCopyAllDevices, causing startup failure with “unable to access a
compatible graphics device,” especially on Apple Silicon.
Change: Prefer MTLCreateSystemDefaultDevice
(metal::Device::system_default()) first. If None, enumerate devices and
select a non‑removable, low‑power device by preference.
Why this works: On Apple Silicon the system default is the unified GPU;
on Intel, the fallback keeps a stable policy and avoids accidentally
picking removable/high‑power devices.
Impact: Fixes startup on affected ASi systems; improves selection
consistency on Intel multi‑GPU. Behavior unchanged where
system_default() succeeds.
Risk: Low. Aligns with Apple’s recommended selection path. Still fails
early with a clearer message if no Metal devices exist.

Closes #37689.

Release Notes:
- Fixed: Startup failure on some Apple Silicon machines when Metal
device enumeration returned no devices by falling back to the system
default device.

---------

Co-authored-by: 张小白 <364772080@qq.com>
Co-authored-by: Kate <work@localcc.cc>

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

@@ -132,11 +132,21 @@ impl MetalRenderer {
         // Prefer low‐power integrated GPUs on Intel Mac. On Apple
         // Silicon, there is only ever one GPU, so this is equivalent to
         // `metal::Device::system_default()`.
-        let mut devices = metal::Device::all();
-        devices.sort_by_key(|device| (device.is_removable(), device.is_low_power()));
-        let Some(device) = devices.pop() else {
-            log::error!("unable to access a compatible graphics device");
-            std::process::exit(1);
+        let device = if let Some(d) = metal::Device::all()
+            .into_iter()
+            .min_by_key(|d| (d.is_removable(), !d.is_low_power()))
+        {
+            d
+        } else {
+            // For some reason `all()` can return an empty list, see https://github.com/zed-industries/zed/issues/37689
+            // In that case, we fall back to the system default device.
+            log::error!(
+                "Unable to enumerate Metal devices; attempting to use system default device"
+            );
+            metal::Device::system_default().unwrap_or_else(|| {
+                log::error!("unable to access a compatible graphics device");
+                std::process::exit(1);
+            })
         };
 
         let layer = metal::MetalLayer::new();