[yoga] Support SPM (Swift Package Manager)

Package.swift

@@ -0,0 +1,48 @@
+// swift-tools-version:5.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "yoga",
+    platforms: [
+        .macOS(.v10_10), .iOS(.v9), .tvOS(.v9)
+    ],
+    products: [
+        // Products define the executables and libraries a package produces, and make them visible to other packages.
+        .library(
+            name: "YogaKit",
+            targets: ["YogaKit"]),
+        .library(
+            name: "Yoga",
+            targets: ["Yoga"])
+    ],
+    dependencies: [
+        // Dependencies declare other packages that this package depends on.
+        // .package(url: /* package url */, from: "1.0.0"),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
+        // Targets can depend on other targets in this package, and on products in packages this package depends on.
+        .target(
+            name: "YogaKit",
+            dependencies: ["Yoga"],
+            path: ".",
+            exclude: ["YogaKit/Source/YGLayoutExtensions.swift"],
+            sources: ["YogaKit/Source"],
+            publicHeadersPath: "YogaKit/Source",
+            cSettings: [
+                .headerSearchPath(".")
+            ]),
+        .target(
+            name: "Yoga",
+            path: ".",
+            sources: ["yoga"],
+            publicHeadersPath: "yoga/include",
+            cSettings: [
+                .headerSearchPath(".")
+            ])
+    ],
+    cLanguageStandard: .gnu11,
+    cxxLanguageStandard: .gnucxx14
+)

YogaKit/Source/UIView+Yoga.h

@@ -5,7 +5,15 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#import <TargetConditionals.h>
+
+#if TARGET_OS_OSX
+#import <AppKit/AppKit.h>
+#define UIView NSView
+#else
 #import <UIKit/UIKit.h>
+#endif
+
 #import "YGLayout.h"
 
 NS_ASSUME_NONNULL_BEGIN

YogaKit/Source/YGLayout.h

@@ -5,7 +5,14 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#import <TargetConditionals.h>
+
+#if TARGET_OS_OSX
+#import <AppKit/AppKit.h>
+#else
 #import <UIKit/UIKit.h>
+#endif
+
 #import <yoga/YGEnums.h>
 #import <yoga/YGMacros.h>
 #import <yoga/Yoga.h>

YogaKit/Source/YGLayout.m

@@ -157,6 +157,11 @@ YGValue YGPercentValue(CGFloat value) {
 }
 
 static YGConfigRef globalConfig;
+#if TARGET_OS_OSX
+NS_INLINE CGFloat scaleFactor() { return [NSScreen mainScreen].backingScaleFactor; }
+#else
+NS_INLINE CGFloat scaleFactor() { return [UIScreen mainScreen].scale; }
+#endif
 
 @interface YGLayout ()
 
@@ -175,7 +180,7 @@ static YGConfigRef globalConfig;
   globalConfig = YGConfigNew();
   YGConfigSetExperimentalFeatureEnabled(
       globalConfig, YGExperimentalFeatureWebFlexBasis, true);
-  YGConfigSetPointScaleFactor(globalConfig, [UIScreen mainScreen].scale);
+  YGConfigSetPointScaleFactor(globalConfig, scaleFactor());
 }
 
 - (instancetype)initWithView:(UIView*)view {
@@ -362,10 +367,18 @@ static YGSize YGMeasureView(
   //
   // See https://github.com/facebook/yoga/issues/606 for more information.
   if (!view.yoga.isUIView || [view.subviews count] > 0) {
+#if TARGET_OS_OSX
+    CGSize fittingSize = view.fittingSize;
+    sizeThatFits = (CGSize){
+        .width = fmin(constrainedWidth, fittingSize.width),
+        .height = fmin(constrainedHeight, fittingSize.height)
+    };
+#else
     sizeThatFits = [view sizeThatFits:(CGSize){
                                           .width = constrainedWidth,
                                           .height = constrainedHeight,
                                       }];
+#endif
   }
 
   return (YGSize){
@@ -452,7 +465,7 @@ static CGFloat YGRoundPixelValue(CGFloat value) {
   static CGFloat scale;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^() {
-    scale = [UIScreen mainScreen].scale;
+    scale = scaleFactor();
   });
 
   return roundf(value * scale) / scale;