Support swift 5.9 with minimum 5.5 compatibility.

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.5
+// swift-tools-version:5.9
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 //
 // SPDX-License-Identifier: Apache-2.0
@@ -8,8 +8,11 @@ import PackageDescription
 
 let package = Package(
     name: "OpenTimelineIO",
-    platforms: [.macOS(.v10_13),
-        .iOS(.v11)],
+    platforms: [
+      .macOS(.v10_13),
+      .iOS(.v12),
+      .visionOS(.v1)
+    ],
     products: [
         .library(name: "OpenTime_CXX", targets: ["OpenTime_CXX"]),
         .library(name: "OpenTimelineIO_CXX", targets: ["OpenTimelineIO_CXX"]),
@@ -72,5 +75,5 @@ let package = Package(
             sources: ["OpenTimelineIOTests"],
             resources: [ .copy("data") ])
     ],
-    cxxLanguageStandard: CXXLanguageStandard.cxx17
+    cxxLanguageStandard: .cxx17
 )

Package@swift-5.5.swift

@@ -0,0 +1,76 @@
+// swift-tools-version:5.5
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+//
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Contributors to the OpenTimelineIO project
+
+import PackageDescription
+
+let package = Package(
+    name: "OpenTimelineIO",
+    platforms: [.macOS(.v10_13),
+        .iOS(.v11)],
+    products: [
+        .library(name: "OpenTime_CXX", targets: ["OpenTime_CXX"]),
+        .library(name: "OpenTimelineIO_CXX", targets: ["OpenTimelineIO_CXX"]),
+        .library(name: "OpenTimelineIO", targets: ["OpenTimelineIO"])
+    ],
+
+    dependencies: [],
+    targets: [
+        .target(name: "otio_header_root",
+            path: ".",
+            exclude: [
+                "CONTRIBUTORS.md", "NOTICE.txt", "CONTRIBUTING.md", "LICENSE.txt", "CODE_OF_CONDUCT.md",
+                "OTIO_CLA_Corporate.pdf", "OTIO_CLA_Individual.pdf",
+                "README.md", "Examples", "OpenTimelineIO", "Tests", "Sources/objc", "Sources/swift"],
+            sources: ["Sources/shims/otio_header_root-shim.cpp"],
+            publicHeadersPath:"OpenTimelineIO/src"),
+
+        .target(name: "OpenTime_CXX",
+            dependencies: ["otio_header_root"],
+            path: "OpenTimelineIO/src/opentime",
+            exclude: ["CMakeLists.txt", "OpenTimeConfig.cmake.in"],
+            sources: ["."],
+            publicHeadersPath: ".",
+            cxxSettings: [ .headerSearchPath(".")]),
+
+        .target(name: "OpenTimelineIO_CXX",
+            dependencies: ["OpenTime_CXX"],
+            path: "OpenTimelineIO/src/opentimelineio",
+            exclude: ["CMakeLists.txt", "CORE_VERSION_MAP.last.cpp", "OpenTimelineIOConfig.cmake.in"],
+            sources: ["."],
+            publicHeadersPath: ".",
+            cxxSettings: [
+                .headerSearchPath("."),
+                .headerSearchPath("../deps/any/"),
+                .headerSearchPath("../deps/Imath/src/Imath"),
+                .headerSearchPath("../../../Sources/cpp"),
+                .headerSearchPath("../deps/rapidjson/include")]),
+
+        .target(name: "OpenTimelineIO_objc",
+            dependencies: ["OpenTimelineIO_CXX"],
+            path: "Sources",
+            exclude: ["swift", "shims"],
+            sources: ["objc"],
+            publicHeadersPath: "objc/include",
+            cxxSettings: [
+                .headerSearchPath("../OpenTimelineIO/src/deps/Imath/src/Imath"),
+                .headerSearchPath("../Sources/cpp"),
+                .headerSearchPath("objc/include")]),
+
+        // public target
+        .target(name: "OpenTimelineIO",
+            dependencies: ["OpenTimelineIO_objc"],
+            path: "Sources",
+            exclude: ["objc", "shims"],
+            sources: ["swift"]),
+
+        .testTarget(name: "OpenTimelineIOTests",
+            dependencies: ["OpenTimelineIO"],
+            path: "Tests",
+            sources: ["OpenTimelineIOTests"],
+            resources: [ .copy("data") ])
+    ],
+    cxxLanguageStandard: .cxx17
+)