Fix macOS Swift SDK selection

.github/workflows/ci.yml

@@ -159,6 +159,13 @@ jobs:
           node-version: '24'
           cache: true
 
+      # This example imports Foundation and Security. Run it with the same
+      # externally selected toolchain pattern supported by swift-node.
+      - name: Install selected macOS Swift toolchain
+        uses: SwiftyLab/setup-swift@38f54a76b70d989321de9dc7c840618c08cf56e9 # v1.14.0
+        with:
+          swift-version: 6.3.3
+
       - name: Verify toolchain
         run: |
           swiftc --version

packages/swift-node-unplugin/package.json

@@ -1,6 +1,6 @@
 {
   "name": "swift-node-unplugin",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "description": "Unplugin adapters that build and bundle Swift Node native assets.",
   "type": "module",
   "types": "./dist/index.d.ts",
@@ -102,7 +102,7 @@
     "test": "vp test run"
   },
   "peerDependencies": {
-    "swift-node": "^0.2.0"
+    "swift-node": "^0.3.0"
   },
   "dependencies": {
     "unplugin": "3.3.0"

packages/swift-node/package.json

@@ -1,6 +1,6 @@
 {
   "name": "swift-node",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "type": "module",
   "description": "Node-API bridge for Swift. Write Node native addons in Swift without C++ glue.",
   "bin": {

packages/swift-node/src/compiler.ts

@@ -275,9 +275,30 @@ export function swiftCompileArgs(
   return args
 }
 
+/**
+ * Invoke the macOS compiler through xcrun so it receives an Xcode SDK.
+ * Preserve an explicit SDKROOT; otherwise select the default macOS SDK.
+ * xcrun also honors TOOLCHAINS, which lets callers use a Swift toolchain
+ * installed alongside Xcode without losing access to Apple frameworks.
+ */
+export function swiftcInvocation(
+  args: string[],
+  platform = process.platform,
+  sdkRoot = process.env.SDKROOT,
+): { command: string; args: string[] } {
+  if (platform === 'darwin') {
+    return {
+      command: 'xcrun',
+      args: [...(sdkRoot ? [] : ['--sdk', 'macosx']), 'swiftc', ...args],
+    }
+  }
+  return { command: 'swiftc', args }
+}
+
 export function compileSwift(config: CompilerConfig): string {
   const outputFile = path.join(config.objDir, 'swift.o')
-  run('swiftc', swiftCompileArgs(config), config.projectDir)
+  const { command, args } = swiftcInvocation(swiftCompileArgs(config))
+  run(command, args, config.projectDir)
   return outputFile
 }
 

packages/swift-node/test/compiler.test.ts

@@ -10,6 +10,7 @@ import {
   needsNodeGypInstall,
   nodeGypDevDir,
   swiftCompileArgs,
+  swiftcInvocation,
 } from '../src/compiler'
 
 const config = {
@@ -44,6 +45,21 @@ describe('cross-platform compiler commands', () => {
     )
   })
 
+  it('uses xcrun for macOS Swift while preserving an explicit SDK selection', () => {
+    const swiftArgs = swiftCompileArgs(config, 'darwin', 'arm64')
+
+    expect(swiftcInvocation(swiftArgs, 'darwin', '')).toEqual({
+      command: 'xcrun',
+      args: ['--sdk', 'macosx', 'swiftc', ...swiftArgs],
+    })
+    expect(swiftcInvocation(swiftArgs, 'darwin', '/custom/MacOSX.sdk')).toEqual({
+      command: 'xcrun',
+      args: ['swiftc', ...swiftArgs],
+    })
+    expect(swiftcInvocation(swiftArgs, 'linux')).toEqual({ command: 'swiftc', args: swiftArgs })
+    expect(swiftcInvocation(swiftArgs, 'win32')).toEqual({ command: 'swiftc', args: swiftArgs })
+  })
+
   it('uses the configured deployment target consistently on Apple Silicon', () => {
     expect(macosDeploymentTarget('10.15', 'arm64')).toBe('10.15')
     expect(macosDeploymentTarget('10.15', 'x64')).toBe('10.15')