split the unsafeFlags-using manifest to a Swift 6.2 minimum version

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.7
+// swift-tools-version:6.2
 /*
  This source file is part of the Swift.org open source project
 
@@ -14,14 +14,6 @@ import class Foundation.ProcessInfo
 
 let cmarkPackageName = ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil ? "swift-cmark" : "cmark"
 
-// On non-Windows, do not include unsafe flags so SwiftPM allows tagged dependency usage.
-var markdownSwiftSettings: [SwiftSetting] = []
-#if os(Windows)
-markdownSwiftSettings.append(
-    .unsafeFlags(["-Xcc", "-DCMARK_GFM_STATIC_DEFINE"], .when(platforms: [.windows]))
-)
-#endif
-
 let package = Package(
     name: "swift-markdown",
     products: [
@@ -40,14 +32,15 @@ let package = Package(
             exclude: [
                 "CMakeLists.txt"
             ],
-            swiftSettings: markdownSwiftSettings
+            swiftSettings: [.unsafeFlags(["-Xcc", "-DCMARK_GFM_STATIC_DEFINE"], .when(platforms: [.windows]))]
         ),
         .testTarget(
             name: "MarkdownTests",
             dependencies: ["Markdown"],
             resources: [.process("Visitors/Everything.md")]),
         .target(name: "CAtomic"),
-    ]
+    ],
+    swiftLanguageModes: [.v5]
 )
 
 // If the `SWIFTCI_USE_LOCAL_DEPS` environment variable is set,

Package@swift-5.7.swift

@@ -0,0 +1,64 @@
+// swift-tools-version:5.7
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import PackageDescription
+import class Foundation.ProcessInfo
+
+let cmarkPackageName = ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil ? "swift-cmark" : "cmark"
+
+let package = Package(
+    name: "swift-markdown",
+    products: [
+        .library(
+            name: "Markdown",
+            targets: ["Markdown"]),
+    ],
+    targets: [
+        .target(
+            name: "Markdown",
+            dependencies: [
+                "CAtomic",
+                .product(name: "cmark-gfm", package: cmarkPackageName),
+                .product(name: "cmark-gfm-extensions", package: cmarkPackageName),
+            ],
+            exclude: [
+                "CMakeLists.txt"
+            ]
+        ),
+        .testTarget(
+            name: "MarkdownTests",
+            dependencies: ["Markdown"],
+            resources: [.process("Visitors/Everything.md")]),
+        .target(name: "CAtomic"),
+    ]
+)
+
+// If the `SWIFTCI_USE_LOCAL_DEPS` environment variable is set,
+// we're building in the Swift.org CI system alongside other projects in the Swift toolchain and
+// we can depend on local versions of our dependencies instead of fetching them remotely.
+if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
+    // Building standalone, so fetch all dependencies remotely.
+    package.dependencies += [
+        .package(url: "https://github.com/swiftlang/swift-cmark.git", branch: "gfm"),
+    ]
+
+    // SwiftPM command plugins are only supported by Swift version 5.6 and later.
+    #if swift(>=5.6)
+    package.dependencies += [
+        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.1.0"),
+    ]
+    #endif
+} else {
+    // Building in the Swift.org CI system, so rely on local versions of dependencies.
+    package.dependencies += [
+        .package(path: "../cmark"),
+    ]
+}