Fix CGDisplayCreateUUIDFromDisplayID linking (again)

See also #1626.

The `cocoa` crate links to AppKit, which made the symbol `CGDisplayCreateUUIDFromDisplayID` from ApplicationServices/ColorSync (which AppKit uses internally) available to us (on macOS 10.8 to 10.13).

However, this does not work on macOS 10.7 (where AppKit doesn't link to ColorSync internally). Instead of relying on this, we should just link to ApplicationServices directly.

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+- Fix linking to the `ColorSync` framework on macOS 10.7.
+
 # 0.26.0 (2021-12-01)
 
 - Update `raw-window-handle` to `v0.4`. This is _not_ a breaking change, we still implement `HasRawWindowHandle` from `v0.3`, see [rust-windowing/raw-window-handle#74](https://github.com/rust-windowing/raw-window-handle/pull/74).

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

@@ -165,14 +165,14 @@ 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")
-)]
+// `CGDisplayCreateUUIDFromDisplayID` comes from the `ColorSync` framework.
+// However, that framework was only introduced "publicly" in macOS 10.13.
+//
+// Since we want to support older versions, we can't link to `ColorSync`
+// directly. Fortunately, it has always been available as a subframework of
+// `ApplicationServices`, see:
+// https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/OSX_Technology_Overview/SystemFrameworks/SystemFrameworks.html#//apple_ref/doc/uid/TP40001067-CH210-BBCFFIEG
+#[link(name = "ApplicationServices", kind = "framework")]
 extern "C" {
     pub fn CGDisplayCreateUUIDFromDisplayID(display: CGDirectDisplayID) -> CFUUIDRef;
 }