Fix CGDisplayCreateUUIDFromDisplayID linking (again)

See also rust-windowing#1626.

The `cocoa` crate links to AppKit, which made the symbol `CGDisplayCreateUUIDFromDisplayID` from ColorSync (which AppKit uses internally) available to us (on macOS 10.13 or above).

Lately something changed in rustc so that this no longer works, see rust-lang/rust#91372. So instead, we link to AppKit directly within the `winit` crate, which, for now, allows us to use the private symbol.

README.md

@@ -119,13 +119,3 @@ fn main() {
 ```
 
 And run the application with `cargo apk run --example request_redraw_threaded`
-
-#### MacOS
-
-To ensure compatibility with older MacOS systems, winit links to
-CGDisplayCreateUUIDFromDisplayID through the CoreGraphics framework.
-However, under certain setups this function is only available to be linked
-through the newer ColorSync framework. So, winit provides the
-`WINIT_LINK_COLORSYNC` environment variable which can be set to `1` or `true`
-while compiling to enable linking via ColorSync.
-

src/platform_impl/macos/ffi.rs

@@ -165,20 +165,19 @@ pub const IO8BitOverlayPixels: &str = "O8";
 pub type CGWindowLevel = i32;
 pub type CGDisplayModeRef = *mut c_void;
 
-#[cfg_attr(
-    not(use_colorsync_cgdisplaycreateuuidfromdisplayid),
-    link(name = "CoreGraphics", kind = "framework")
-)]
-#[cfg_attr(
-    use_colorsync_cgdisplaycreateuuidfromdisplayid,
-    link(name = "ColorSync", kind = "framework")
-)]
-extern "C" {
-    pub fn CGDisplayCreateUUIDFromDisplayID(display: CGDirectDisplayID) -> CFUUIDRef;
-}
+// HACK:
+// `CGDisplayCreateUUIDFromDisplayID` moved from `CoreGraphics` to `ColorSync`
+// in macOS 10.13 (which is also where `ColorSync` was introduced).
+//
+// Since we want to support older versions, we can't link to `ColorSync`
+// directly. Fortunately `AppKit` links to `ColorSync` internally, so by
+// linking to `AppKit` in this crate, the symbol becomes available.
+#[link(name = "AppKit", kind = "framework")]
+extern "C" {}
 
 #[link(name = "CoreGraphics", kind = "framework")]
 extern "C" {
+    pub fn CGDisplayCreateUUIDFromDisplayID(display: CGDirectDisplayID) -> CFUUIDRef;
     pub fn CGRestorePermanentDisplayConfiguration();
     pub fn CGDisplayCapture(display: CGDirectDisplayID) -> CGError;
     pub fn CGDisplayRelease(display: CGDirectDisplayID) -> CGError;