Generate SDKSettings.json file for Swift SDKs for Swift 5.9-6.0 (#185)

I know that the warnings about the `SDKSettings.json` file were fixed in Swift 6.1 and later and that issue #110 was closed. However, we are still generating Swift SDKs for 5.9, 5.10, and 6.0 which all give the warnings. 

So, my suggestion is to generate this `SDKSettings.json` file for versions older than 6.1, similar to how the the Linux Static Swift SDKs do it. Here is the file that comes in the `swift-6.0.3-RELEASE_static-linux-0.0.1` Swift SDK for example:

```json
{
  "DisplayName": "Swift SDK for Statically Linked Linux (x86_64)",
  "Version": "0.0.1",
  "VersionMap": {},
  "CanonicalName": "x86_64-swift-linux-musl"
}
```

Taking inspiration from this, I am generating a similar file for Swift SDKs created by the generator:

```json
{
  "CanonicalName" : "x86_64-swift-linux-gnu",
  "DisplayName" : "Swift SDK for Ubuntu Jammy (x86_64)",
  "Version" : "0.0.1",
  "VersionMap" : {

  }
}
```

The ordering is not the same due to how `JSONEncoder()` sorts things, and the formatting is a little different too due to `.prettyPrinted`, but it works just the same. And, the "warning: Could not read SDKSettings.json for SDK at: <path>" warning is successfully suppressed.

This really is a minor change that is more "quality-of-life" then adding any functionality. But, not having those warnings printed when using the generated Swift SDKs are used is a nice to have.

Author: xtremekforever

Sources/SwiftSDKGenerator/Extensions/String+hasAnyPrefix.swift

@@ -0,0 +1,10 @@
+extension String {
+    func hasAnyPrefix(from array: [String]) -> Bool {
+        for item in array {
+            if self.hasPrefix(item) {
+                return true
+            }
+        }
+        return false
+    }
+}

Sources/SwiftSDKGenerator/Generator/SwiftSDKGenerator+Metadata.swift

@@ -112,4 +112,36 @@ extension SwiftSDKGenerator {
       )
     )
   }
+
+  struct SDKSettings: Codable {
+    var DisplayName: String
+    var Version: String
+    var VersionMap: [String: String] = [:]
+    var CanonicalName: String
+  }
+
+  /// Generates an `SDKSettings.json` file that looks like this:
+  /// 
+  /// ```json
+  /// {
+  ///   "CanonicalName" : "<arch>-swift-linux-[gnu|gnueabihf]",
+  ///   "DisplayName" : "Swift SDK for <distribution> (<arch>)",
+  ///   "Version" : "0.0.1",
+  ///   "VersionMap" : {
+  ///
+  ///   }
+  /// }
+  /// ```
+  func generateSDKSettingsFile(sdkDirPath: FilePath, distribution: LinuxDistribution) throws {
+    logger.info("Generating SDKSettings.json file to silence cross-compilation warnings...")
+
+    let sdkSettings = SDKSettings(
+      DisplayName: "Swift SDK for \(distribution) (\(targetTriple.archName))",
+      Version: bundleVersion,
+      CanonicalName: targetTriple.triple.replacingOccurrences(of: "unknown", with: "swift")
+    )
+
+    let sdkSettingsFilePath = sdkDirPath.appending("SDKSettings.json")
+    try writeFile(at: sdkSettingsFilePath, encoder.encode(sdkSettings))
+  }
 }

Sources/SwiftSDKGenerator/SwiftSDKRecipes/LinuxRecipe.swift

@@ -195,8 +195,7 @@ public struct LinuxRecipe: SwiftSDKRecipe {
     if self.hostSwiftSource == .preinstalled {
       // Swift 5.9 and 5.10 require `supportedTriples` to be set in info.json.
       // FIXME: This can be removed once the SDK generator does not support 5.9/5.10 any more.
-      if self.versionsConfiguration.swiftVersion.hasPrefix("5.9")
-          || self.versionsConfiguration.swiftVersion.hasPrefix("5.10") {
+      if self.versionsConfiguration.swiftVersion.hasAnyPrefix(from: ["5.9", "5.10"]) {
         return [
           Triple("x86_64-unknown-linux-gnu"),
           Triple("aarch64-unknown-linux-gnu"),
@@ -292,13 +291,18 @@ public struct LinuxRecipe: SwiftSDKRecipe {
 
     try await generator.fixAbsoluteSymlinks(sdkDirPath: sdkDirPath)
 
+    // Swift 6.1 and later do not throw warnings about the SDKSettings.json file missing,
+    // so they don't need this file.
+    if self.versionsConfiguration.swiftVersion.hasAnyPrefix(from: ["5.9", "5.10", "6.0"]) {
+      try await generator.generateSDKSettingsFile(sdkDirPath: sdkDirPath, distribution: linuxDistribution)
+    }
+
     if self.hostSwiftSource != .preinstalled {
       if self.mainHostTriple.os != .linux && !self.versionsConfiguration.swiftVersion.hasPrefix("6.0") {
         try await generator.prepareLLDLinker(engine, llvmArtifact: downloadableArtifacts.hostLLVM)
       }
 
-      if self.versionsConfiguration.swiftVersion.hasPrefix("5.9") ||
-          self.versionsConfiguration.swiftVersion.hasPrefix("5.10") {
+      if self.versionsConfiguration.swiftVersion.hasAnyPrefix(from: ["5.9", "5.10"]) {
         try await generator.symlinkClangHeaders()
       }
 

Tests/SwiftSDKGeneratorTests/Generator/SwiftSDKGenerator+MetadataTests.swift

@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2022-2025 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 the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Logging
+import SystemPackage
+import XCTest
+
+@testable import SwiftSDKGenerator
+
+final class SwiftSDKGeneratorMetadataTests: XCTestCase {
+  let logger = Logger(label: "SwiftSDKGeneratorMetadataTests")
+
+  func testGenerateSDKSettingsFile() async throws {
+    let testCases = [
+      (
+        bundleVersion: "0.0.1",
+        targetTriple: Triple("x86_64-unknown-linux-gnu"),
+        expectedCanonicalName: "x86_64-swift-linux-gnu"
+      ),
+      (
+        bundleVersion: "0.0.2",
+        targetTriple: Triple("aarch64-unknown-linux-gnu"),
+        expectedCanonicalName: "aarch64-swift-linux-gnu"
+      ),
+      (
+        bundleVersion: "0.0.3",
+        targetTriple: Triple("armv7-unknown-linux-gnueabihf"),
+        expectedCanonicalName: "armv7-swift-linux-gnueabihf"
+      )
+    ]
+
+    for testCase in testCases {
+      let sdk = try await SwiftSDKGenerator(
+        bundleVersion: testCase.bundleVersion,
+        targetTriple: testCase.targetTriple,
+        artifactID: "6.0.3-RELEASE_ubuntu_jammy_\(testCase.targetTriple.archName)",
+        isIncremental: false,
+        isVerbose: false,
+        logger: logger
+      )
+      let linuxDistribution = try LinuxDistribution(name: .ubuntu, version: "22.04")
+
+      let sdkDirPath = FilePath(".")
+      try await sdk.generateSDKSettingsFile(sdkDirPath: sdkDirPath, distribution: linuxDistribution)
+
+      // Make sure the file exists
+      let sdkSettingsFile = sdkDirPath.appending("SDKSettings.json")
+      let fileExists = await sdk.doesFileExist(at: sdkSettingsFile)
+      XCTAssertTrue(fileExists)
+
+      // Read back file, make sure it contains the expected data
+      let data = String(data: try await sdk.readFile(at: sdkSettingsFile), encoding: .utf8)
+      XCTAssertNotNil(data)
+      XCTAssertTrue(data!.contains(testCase.bundleVersion))
+      XCTAssertTrue(data!.contains("(\(testCase.targetTriple.archName))"))
+      XCTAssertTrue(data!.contains(linuxDistribution.description))
+      XCTAssertTrue(data!.contains(testCase.expectedCanonicalName))
+
+      // Cleanup
+      try await sdk.removeFile(at: sdkSettingsFile)
+    }
+  }
+}