Preserve compatibility with older versions.

Author: bsneed

Package.resolved

@@ -4,36 +4,57 @@
 import PackageDescription
 
 let dependencies: [Package.Dependency]
+let versionedTargets: [Target]
+let versionedDependencies: [Target.Dependency]
+
 #if swift(>=5.9)
 dependencies = [
     .package(url: "https://github.com/apple/swift-argument-parser.git", .exact("1.2.3")),
     .package(name: "SwiftPM", url: "https://github.com/apple/swift-package-manager.git", .branch("release/5.9")),
     .package(url: "https://github.com/apple/swift-tools-support-core.git", .branch("release/5.9")),
 ]
+versionedTargets = [
+    .target(
+        name: "Xcodeproj",
+        dependencies: [
+            .product(name: "SwiftPM-auto", package: "SwiftPM"),
+            .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
+        ]
+    )
+]
+versionedDependencies = ["Xcodeproj"]
 #elseif swift(>=5.7)
 dependencies = [
     .package(url: "https://github.com/apple/swift-argument-parser.git", .exact("1.0.3")),
     .package(name: "SwiftPM", url: "https://github.com/apple/swift-package-manager.git", .branch("release/5.7")),
     .package(url: "https://github.com/apple/swift-tools-support-core.git", .branch("release/5.7")),
 ]
+versionedTargets = []
+versionedDependencies = []
 #elseif swift(>=5.6)
 dependencies = [
     .package(url: "https://github.com/apple/swift-argument-parser.git", .exact("1.0.3")),
     .package(name: "SwiftPM", url: "https://github.com/apple/swift-package-manager.git", .branch("release/5.6")),
     .package(url: "https://github.com/apple/swift-tools-support-core.git", .exact("0.2.5"))
 ]
+versionedTargets = []
+versionedDependencies = []
 #elseif swift(>=5.5)
 dependencies = [
     .package(url: "https://github.com/apple/swift-argument-parser.git", .exact("0.4.4")),
     .package(name: "SwiftPM", url: "https://github.com/apple/swift-package-manager.git", .branch("release/5.5")),
     .package(url: "https://github.com/apple/swift-tools-support-core.git", .exact("0.2.3"))
 ]
+versionedTargets = []
+versionedDependencies = []
 #else
 dependencies = [
     .package(url: "https://github.com/apple/swift-argument-parser.git", .exact("0.3.2")),
     .package(name: "SwiftPM", url: "https://github.com/apple/swift-package-manager.git", .revision("swift-5.3.3-RELEASE")),
     .package(url: "https://github.com/apple/swift-tools-support-core.git", .exact("0.1.12"))
 ]
+versionedTargets = []
+versionedDependencies = []
 #endif
 
 let platforms: [SupportedPlatform]
@@ -59,16 +80,8 @@ let package = Package(
 
     dependencies: dependencies,
 
-    targets: [
-        .target(
-            name: "Xcodeproj",
-            dependencies: [
-                .product(name: "SwiftPM-auto", package: "SwiftPM"),
-                .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
-            ]
-        ),
-        .target(name: "CreateXCFramework", dependencies: [
-            "Xcodeproj",
+    targets: versionedTargets + [
+        .target(name: "CreateXCFramework", dependencies: versionedDependencies + [
             .product(name: "ArgumentParser", package: "swift-argument-parser"),
             .product(name: "SwiftPM-auto", package: "SwiftPM"),
             .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),

Package.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 /// A enum representing data types for legacy PropertyList type.
 /// Note that the `identifier` enum is not strictly necessary,
 /// but useful to semantically distinguish the strings that
@@ -148,3 +150,5 @@ extension PropertyList {
         }
     }
 }
+
+#endif

Sources/Xcodeproj/PropertyList.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 import TSCBasic
 import PackageGraph
 import PackageModel
@@ -309,3 +311,5 @@ func legacySchemeGenerator(container: String, graph: PackageGraph, codeCoverageE
         </Scheme>
         """)
 }
+
+#endif

Sources/Xcodeproj/SchemesGenerator.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 /*
  In an effort to provide:
 
@@ -88,3 +90,5 @@ extension ResolvedTarget {
         }
     }
 }
+
+#endif

Sources/Xcodeproj/Target+PBXProj.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 /*
  A very simple rendition of the Xcode project model.  There is only sufficient
  functionality to allow creation of Xcode projects in a somewhat readable way,
@@ -517,3 +519,5 @@ public func += (lhs: inout [String]?, rhs: [String]) {
         lhs = lhs! + rhs
     }
 }
+
+#endif

Sources/Xcodeproj/XcodeProjectModel.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 /*
  An extemely simple rendition of the Xcode project model into a plist.  There
  is only enough functionality to allow serialization of Xcode projects.
@@ -643,3 +645,5 @@ extension PropertyList {
         }
     }
 }
+
+#endif

Sources/Xcodeproj/XcodeProjectModelSerialization.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 import Basics
 import PackageGraph
 import PackageModel
@@ -335,3 +337,5 @@ public enum XcodeProject {
         }) ?? []
     }
 }
+
+#endif

Sources/Xcodeproj/generate.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if swift(>=5.9)
+
 import Basics
 import TSCBasic
 import PackageGraph
@@ -896,3 +898,5 @@ func appendSetting(
         throw InternalError("Unhandled decl \(decl)")
     }
 }
+
+#endif