Change linking of CGDisplayCreateUUIDFromDisplayID on macos (#1626)

* Link CGDisplayCreateUUIDFromDisplayID through ColorSync instead of CoreGraphics

* Conditionally link through ColorSync only if WINIT_LINK_COLORSYNC is set
to true

* Document new macos env var in README

README.md

@@ -110,3 +110,13 @@ 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.
+

build.rs

@@ -0,0 +1,10 @@
+fn main() {
+    // If building for macos and WINIT_LINK_COLORSYNC is set to true
+    // use CGDisplayCreateUUIDFromDisplayID from ColorSync instead of CoreGraphics
+    if std::env::var("CARGO_CFG_TARGET_OS").map_or(false, |os| os == "macos")
+        && std::env::var("WINIT_LINK_COLORSYNC")
+            .map_or(false, |v| v == "1" || v.eq_ignore_ascii_case("true"))
+    {
+        println!("cargo:rustc-cfg=use_colorsync_cgdisplaycreateuuidfromdisplayid");
+    }
+}

src/platform_impl/macos/ffi.rs

@@ -161,6 +161,18 @@ pub const IO8BitOverlayPixels: &str = "O8";
 pub type CGWindowLevel = i32;
 pub type CGDisplayModeRef = *mut libc::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;
+}
+
 #[link(name = "CoreGraphics", kind = "framework")]
 extern "C" {
     pub fn CGRestorePermanentDisplayConfiguration();
@@ -189,7 +201,6 @@ extern "C" {
         synchronous: Boolean,
     ) -> CGError;
     pub fn CGReleaseDisplayFadeReservation(token: CGDisplayFadeReservationToken) -> CGError;
-    pub fn CGDisplayCreateUUIDFromDisplayID(display: CGDirectDisplayID) -> CFUUIDRef;
     pub fn CGShieldingWindowLevel() -> CGWindowLevel;
     pub fn CGDisplaySetDisplayMode(
         display: CGDirectDisplayID,