Build metal shaders for the minimum selected macOS version

This fixes crashes on older OSes when building apps built with newer OSes

Author: stackotter

Sources/swift-bundler/Bundler/MetalCompiler.swift

@@ -5,9 +5,10 @@ enum MetalCompiler {
   /// Compiles any metal shaders present in a directory into a `default.metallib` file (in the same directory).
   /// - Parameters:
   ///   - directory: The directory to compile shaders from.
+  ///   - minimumMacOSVersion: The macOS version that the built shaders should target.
   ///   - keepSources: If `false`, the sources will get deleted after compilation.
   /// - Returns: If an error occurs, a failure is returned.
-  static func compileMetalShaders(in directory: URL, keepSources: Bool) -> Result<Void, MetalCompilerError> {
+  static func compileMetalShaders(in directory: URL, minimumMacOSVersion: String, keepSources: Bool) -> Result<Void, MetalCompilerError> {
     guard let enumerator = FileManager.default.enumerator(at: directory, includingPropertiesForKeys: []) else {
       return .failure(.failedToEnumerateShaders(directory: directory))
     }
@@ -24,7 +25,7 @@ enum MetalCompiler {
     log.info("Compiling metal shaders")
 
     // Compile metal shaders, and if successful, delete all shader sources
-    return compileMetalShaders(shaderSources, destination: directory)
+    return compileMetalShaders(shaderSources, destination: directory, minimumMacOSVersion: minimumMacOSVersion)
       .flatMap { _ in
         if keepSources {
           return .success()
@@ -46,8 +47,9 @@ enum MetalCompiler {
   /// - Parameters:
   ///   - sources: The source files to comile.
   ///   - destination: The directory to output `default.metallib` to.
+  ///   - minimumMacOSVersion: The macOS version that the built shaders should target.
   /// - Returns: Returns the location of the resulting `metallib`. If an error occurs, a failure is returned.
-  static func compileMetalShaders(_ sources: [URL], destination: URL) -> Result<URL, MetalCompilerError> {
+  static func compileMetalShaders(_ sources: [URL], destination: URL, minimumMacOSVersion: String) -> Result<URL, MetalCompilerError> {
     // Create a temporary directory for compilation
     let tempDirectory = FileManager.default.temporaryDirectory
       .appendingPathComponent("metal_compilation-\(UUID().uuidString)")
@@ -62,7 +64,7 @@ enum MetalCompiler {
     for shaderSource in sources {
       let outputFileName = shaderSource.deletingPathExtension().appendingPathExtension("air").lastPathComponent
       let outputFile = tempDirectory.appendingPathComponent(outputFileName)
-      if case let .failure(error) = compileShader(shaderSource, to: outputFile) {
+      if case let .failure(error) = compileShader(shaderSource, to: outputFile, minimumMacOSVersion: minimumMacOSVersion) {
         return .failure(error)
       }
       airFiles.append(outputFile)
@@ -89,12 +91,14 @@ enum MetalCompiler {
   /// - Parameters:
   ///   - shader: The shader file to compile.
   ///   - outputFile: The resulting `air` file.
+  ///   - minimumMacOSVersion: The macOS version that the built shader should target.
   /// - Returns: If an error occurs, a failure is returned.
-  static func compileShader(_ shader: URL, to outputFile: URL) -> Result<Void, MetalCompilerError> {
+  static func compileShader(_ shader: URL, to outputFile: URL, minimumMacOSVersion: String) -> Result<Void, MetalCompilerError> {
     let process = Process.create(
       "/usr/bin/xcrun",
       arguments: [
         "-sdk", "macosx", "metal",
+        "-mmacosx-version-min=\(minimumMacOSVersion)",
         "-o", outputFile.path,
         "-c", shader.path
       ])

Sources/swift-bundler/Bundler/ResourceBundler.swift

@@ -83,13 +83,17 @@ enum ResourceBundler {
   ) -> Result<Void, ResourceBundlerError> {
     log.info("Fixing and copying resource bundle '\(bundle.lastPathComponent)'")
 
+    guard let minimumMacOSVersion = minimumMacOSVersion else {
+      return .failure(.mustProvideMinimimMacOSVersion)
+    }
+
     let destinationBundle = destination.appendingPathComponent(bundle.lastPathComponent)
     let destinationBundleResources = destinationBundle
       .appendingPathComponent("Contents")
       .appendingPathComponent("Resources")
 
     let compileMetalShaders: () -> Result<Void, ResourceBundlerError> = {
-      MetalCompiler.compileMetalShaders(in: destinationBundleResources, keepSources: false)
+      MetalCompiler.compileMetalShaders(in: destinationBundleResources, minimumMacOSVersion: minimumMacOSVersion, keepSources: false)
         .mapError { error in
           .failedToCompileMetalShaders(error)
         }

Sources/swift-bundler/Bundler/ResourceBundlerError.swift

@@ -9,6 +9,7 @@ enum ResourceBundlerError: LocalizedError {
   case failedToCopyResource(source: URL, destination: URL)
   case failedToEnumerateBundleContents(directory: URL, Error)
   case failedToCompileMetalShaders(MetalCompilerError)
+  case mustProvideMinimimMacOSVersion
 
   var errorDescription: String? {
     switch self {
@@ -26,6 +27,8 @@ enum ResourceBundlerError: LocalizedError {
         return "Failed to enumerate bundle contents at '\(directory.relativePath)'"
       case .failedToCompileMetalShaders(let metalCompilerError):
         return "Failed to compile Metal shaders: \(metalCompilerError.localizedDescription)"
+      case .mustProvideMinimimMacOSVersion:
+        return "Must provide 'minimum_macos_version' when app contains resources"
     }
   }
 }