appkit: let valid_attributes_for_marked_text report winit metadata.

- This allows IME devs to identify whether `winit` is used in the IMKTextInput client. If identified, IME devs can introduce compatibility behaviors against such IMKTextInput client. // InputMethodKit casts `NSTextInputClient` to `IMKTextInput`.

Author: ShikiSuen

winit-appkit/src/view.rs

@@ -336,7 +336,10 @@ define_class!(
         #[unsafe(method_id(validAttributesForMarkedText))]
         fn valid_attributes_for_marked_text(&self) -> Retained<NSArray<NSAttributedStringKey>> {
             trace_scope!("validAttributesForMarkedText");
-            NSArray::new()
+            // Advertise the winit version so IME clients can identify us.
+            let client_identifier =
+                NSString::from_str(concat!("_rust_winit_", env!("CARGO_PKG_VERSION")));
+            NSArray::from_slice(&[client_identifier.as_ref()])
         }
 
         #[unsafe(method_id(attributedSubstringForProposedRange:actualRange:))]

winit/src/changelog/unreleased.md

@@ -178,6 +178,18 @@ changelog entry.
 - Rename `VideoModeHandle` to `VideoMode`, now it only stores plain data.
 - Make `Fullscreen::Exclusive` contain `(MonitorHandle, VideoMode)`.
 - Reworked the file drag-and-drop API.
+- On macOS, `NSTextInputClient::validAttributesForMarkedText` now automatically attaches a value
+  called `_rust_winit_\(CARGO_PKG_VERSION)`.
+
+  This allows IME devs to identify whether `winit` is used in the IMKTextInput client.
+  If identified, IME devs can introduce compatibility behaviors against such IMKTextInput client.
+  InputMethodKit casts `NSTextInputClient` to `IMKTextInput`, but `validAttributesForMarkedText`
+  is shared between these two protocols and can all be parsed as `Array<NSString>`.
+
+  `validAttributesForMarkedText` specifically returns an `NSArray<NSAttributedStringKey>` which
+  are plain NSString*; Apple treats custom keys as legal, so slipping harmless metadata like
+  `_rust_winit_\(CARGO_PKG_VERSION)` in there is the one slot where such data is piggybackable.
+
 - On macOS, the default menu uses the bundle name or falls back to the process name as before.
 
   The `WindowEvent::DroppedFile`, `WindowEvent::HoveredFile` and `WindowEvent::HoveredFileCancelled`