Library Evolution Support (Flight-School#37)

* enabled library evolution support

* annotated public structs with @Frozen
to prevent crashes if referenced in a file initialized by a storybaord. https://bugs.swift.org/browse/SR-11969

* Added a swift version check for older versions of Swift that don't support `@frozen`

* `@frozen` is only available in swift 5.1

Author: Bradley S. Maskell

AnyCodable.xcodeproj/project.pbxproj

@@ -112,7 +112,7 @@
 			name = Products;
 			sourceTree = BUILT_PRODUCTS_DIR;
 		};
-		OBJ_5 /*  */ = {
+		OBJ_5 = {
 			isa = PBXGroup;
 			children = (
 				OBJ_6 /* Package.swift */,
@@ -125,7 +125,6 @@
 				OBJ_23 /* README.md */,
 				OBJ_24 /* AnyCodable.xcconfig */,
 			);
-			name = "";
 			sourceTree = "<group>";
 		};
 		OBJ_7 /* Sources */ = {
@@ -214,7 +213,7 @@
 				English,
 				en,
 			);
-			mainGroup = OBJ_5 /*  */;
+			mainGroup = OBJ_5;
 			productRefGroup = OBJ_17 /* Products */;
 			projectDirPath = "";
 			projectRoot = "";
@@ -275,6 +274,7 @@
 		OBJ_27 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				DYLIB_COMPATIBILITY_VERSION = 1;
 				DYLIB_CURRENT_VERSION = 1;
 				ENABLE_TESTABILITY = YES;
@@ -305,6 +305,7 @@
 		OBJ_28 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				DYLIB_COMPATIBILITY_VERSION = 1;
 				DYLIB_CURRENT_VERSION = 1;
 				ENABLE_TESTABILITY = YES;
@@ -362,6 +363,7 @@
 		OBJ_36 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				LD = /usr/bin/true;
 				OTHER_SWIFT_FLAGS = "-swift-version 5 -I $(TOOLCHAIN_DIR)/usr/lib/swift/pm/4_2 -target x86_64-apple-macosx10.10 -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk";
 				SWIFT_VERSION = 5.0;
@@ -371,6 +373,7 @@
 		OBJ_37 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				LD = /usr/bin/true;
 				OTHER_SWIFT_FLAGS = "-swift-version 5 -I $(TOOLCHAIN_DIR)/usr/lib/swift/pm/4_2 -target x86_64-apple-macosx10.10 -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk";
 				SWIFT_VERSION = 5.0;
@@ -404,12 +407,14 @@
 		OBJ_42 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 			};
 			name = Debug;
 		};
 		OBJ_43 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 			};
 			name = Release;
 		};

Sources/AnyCodable/AnyCodable.swift

@@ -11,13 +11,23 @@
  - SeeAlso: `AnyEncodable`
  - SeeAlso: `AnyDecodable`
  */
+#if swift(>=5.1)
+@frozen public struct AnyCodable: Codable {
+    public let value: Any
+
+    public init<T>(_ value: T?) {
+        self.value = value ?? ()
+    }
+}
+#else
 public struct AnyCodable: Codable {
     public let value: Any
 
     public init<T>(_ value: T?) {
         self.value = value ?? ()
     }
 }
+#endif
 
 extension AnyCodable: _AnyEncodable, _AnyDecodable {}
 

Sources/AnyCodable/AnyDecodable.swift

@@ -30,13 +30,23 @@ import Foundation
      let decoder = JSONDecoder()
      let dictionary = try! decoder.decode([String: AnyDecodable].self, from: json)
  */
+#if swift(>=5.1)
+@frozen public struct AnyDecodable: Decodable {
+    public let value: Any
+
+    public init<T>(_ value: T?) {
+        self.value = value ?? ()
+    }
+}
+#else
 public struct AnyDecodable: Decodable {
     public let value: Any
 
     public init<T>(_ value: T?) {
         self.value = value ?? ()
     }
 }
+#endif
 
 #if swift(>=4.2)
 @usableFromInline

Sources/AnyCodable/AnyEncodable.swift

@@ -28,13 +28,23 @@ import Foundation
      let encoder = JSONEncoder()
      let json = try! encoder.encode(dictionary)
  */
+#if swift(>=5.1)
+@frozen public struct AnyEncodable: Encodable {
+    public let value: Any
+
+    public init<T>(_ value: T?) {
+        self.value = value ?? ()
+    }
+}
+#else
 public struct AnyEncodable: Encodable {
     public let value: Any
 
     public init<T>(_ value: T?) {
         self.value = value ?? ()
     }
 }
+#endif
 
 #if swift(>=4.2)
 @usableFromInline