feat: link feature (#271)

* feat: link feature

* fix

Cargo.toml

@@ -16,9 +16,10 @@ exclude = ["guide/**/*", "examples/texture/**/*", "tests/**/*", "Cargo.lock", "t
 default-target = "x86_64-apple-darwin"
 
 [features]
-default = []
+default = ["link"]
 private = []
 mps = []
+link = []
 
 [dependencies]
 core-graphics-types = "0.1"

src/device.rs

@@ -1458,7 +1458,7 @@ pub struct MTLAccelerationStructureSizes {
     pub refit_scratch_buffer_size: NSUInteger,
 }
 
-#[link(name = "Metal", kind = "framework")]
+#[cfg_attr(feature = "link", link(name = "Metal", kind = "framework"))]
 extern "C" {
     fn MTLCreateSystemDefaultDevice() -> *mut MTLDevice;
     #[cfg(not(target_os = "ios"))]
@@ -1473,11 +1473,11 @@ pub type dispatch_queue_t = *mut Object;
 type dispatch_block_t = *const Block<(), ()>;
 
 #[cfg_attr(
-    any(target_os = "macos", target_os = "ios"),
+    all(feature = "link", any(target_os = "macos", target_os = "ios")),
     link(name = "System", kind = "dylib")
 )]
 #[cfg_attr(
-    not(any(target_os = "macos", target_os = "ios")),
+    all(feature = "link", not(any(target_os = "macos", target_os = "ios"))),
     link(name = "dispatch", kind = "dylib")
 )]
 #[allow(improper_ctypes)]

src/mps.rs

@@ -9,7 +9,7 @@ use super::*;
 
 use objc::runtime::{BOOL, YES};
 
-#[link(name = "MetalPerformanceShaders", kind = "framework")]
+#[cfg_attr(feature = "link", link(name = "MetalPerformanceShaders", kind = "framework"))]
 extern "C" {
     fn MPSSupportsMTLDevice(device: *const std::ffi::c_void) -> BOOL;
 }