Sourcekit-lsp SDK defaults to Mac when trying to select iOS, multiple ways tried

Development SourceKit-LSP
1

Hey there!

I hope this is in the right forum, if not please move it.
I am trying to use VSCode (or specifically, windsurf) to code for iOS.
As such I have downloaded Swift 2.2.0 .vix and other tools (SweetPad) to help with development. In order to get the symbols working they use sourcekit-lsp, and I am having trouble getting it to load the iOS SDKs!

As I am new to this I've been sitting with it for a day trying to figure it out and have asked ChatGPT for assistance, but no luck! I am pasting everything I tried below.

I am stumped on how to progress xD Any help appreciated.

1 Project & baseline

  • Xcode 16 / Swift 6.1 on Apple Silicon
  • Dummy Package.swift at repo root ( platforms: [.iOS(.v17), .macOS(.v10_15)])
    • Builds fine with Supabase dependency.
  • Hand build succeeds when flags are supplied:
SDK=$(xcrun --sdk iphonesimulator --show-sdk-path)
TRIPLE=arm64-apple-ios18.4-simulator
swift build \
  -Xswiftc -sdk "$SDK"       -Xswiftc -target "$TRIPLE" \
  -Xcc     -isysroot "$SDK"  -Xcc     -target "$TRIPLE"

→ 0 errors.

2 Goal

Get VS Code (v2.2.0 Swift extension installed from .vsix) to recognise iOS-only
SwiftUI modifiers (.textInputAutocapitalization, .keyboardType) instead of
flagging them as “no member”.

3 What I tried inside VS Code

Attempt What we did Result
a Added the four flag pairs to swift.sourcekit-lsp.serverArguments and swift.buildArguments Flags appear in settings.txt but do not appear in OUTPUT in VSCode → server still launches with macOS SDK
b Used Swift → Select Toolchain and Swift → Select Target Platform (iOS Simulator 18.4) swift.swiftSDK shows arm64-apple-ios, but launch line still macOS
c Workspace reset / language-server restart / re-index No change
d Captured minimal diagnostics – always reports Default SDK: …MacOSX15.4.sdk / Default Target: arm64-apple-macosx15.0
e Wrote .sourcekit-lsp/config.json next to Package.swift:json<br>{ "sdk": "/…/iPhoneSimulator18.4.sdk",<br> "target": "arm64-apple-ios18.4-simulator" }Restarted server Launch line in OUTPUT still shows macOS; SourceKit-LSP apparently not reading the file
f Ran xcrun sourcekit-lsp (no args) from repo root Process waits silently (expected), so can’t confirm which SDK it picked

4 Current symptoms

  • VS Code red-squiggle diagnostics
    • “Value of type ‘some View’ has no member ‘textInputAutocapitalization’”
    • “Cannot infer contextual base … ‘never’ / ‘emailAddress’”
    • “No such module ‘PackageDescription’” on Package.swift
  • OUTPUT ▸ Swift Language Server first line (after restart) always shows
/Applications/.../sourcekit-lsp  -module-cache-path ... 
  -sdk /Applications/.../MacOSX15.4.sdk
  -target arm64-apple-macosx15.0

→ iOS flags never applied.

  • .sourcekit-lsp/config.json exists and is valid JSON, but seems ignored.

5 What does work

  • Xcode resolves the symbols.
  • Command-line swift build resolves everything when the same four
    -sdk/-target pairs (and their -Xcc twins) are supplied.

Key open questions for maintainers

  1. Why are serverArguments / buildArguments silently ignored in extension v2.2.0?
  2. Does SourceKit-LSP still auto-discover .sourcekit-lsp/config.json in Swift 6.1?
    If so, where should it live relative to multi-package workspaces?
  3. Is there a recommended flag or env-var to print the active SDK & target on launch so I can confirm which path the server finally uses?

(Full minimal-diagnostics output attached below.)

extension-logs.txt

07:52:25: Activating Swift for Visual Studio Code...
07:52:25: Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Platform: darwin
Swift Path: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
Toolchain Path: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr
Runtime Library Path: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx:/usr/lib/swift
Default Target: arm64-apple-macosx15.0
Default SDK: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.4.sdk
XCTest Path: /Applications/Xcode.app/Contents/Developer/usr/bin
07:52:25: SourceKit-LSP setup
07:52:26: iOSApp: add: /Users/ca_ai/Desktop/Projects/3.Swift_Unity_ExerciseGames/iOSApp
07:52:26: iOSApp: Resolving Dependencies: starting ... 
07:52:26: Exec Task: (iOSApp) swift package resolve --swift-sdk arm64-apple-ios
07:52:26: iOSApp: focus: /Users/ca_ai/Desktop/Projects/3.Swift_Unity_ExerciseGames/iOSApp
07:52:26: iOSApp: Resolving Dependencies: ... done.
07:52:27: iOSApp: pluginsUpdated: /Users/ca_ai/Desktop/Projects/3.Swift_Unity_ExerciseGames/iOSApp

settings.txt

Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Platform: darwin
Swift Path: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
Toolchain Path: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr
Runtime Library Path: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx:/usr/lib/swift
Default Target: arm64-apple-macosx15.0
Default SDK: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.4.sdk
XCTest Path: /Applications/Xcode.app/Contents/Developer/usr/bin
Settings:
{
  "path": "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin",
  "buildArguments": [
    "-Xswiftc",
    "-sdk",
    "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk",
    "-Xswiftc",
    "-target",
    "arm64-apple-ios18.4-simulator",
    "-Xcc",
    "-isysroot",
    "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk",
    "-Xcc",
    "-target",
    "arm64-apple-ios18.4-simulator"
  ],
  "scriptSwiftLanguageVersion": "6",
  "packageArguments": [],
  "additionalTestArguments": [],
  "testEnvironmentVariables": {},
  "sanitizer": "off",
  "searchSubfoldersForPackages": false,
  "autoGenerateLaunchConfigurations": true,
  "disableAutoResolve": false,
  "diagnosticsCollection": "keepSourceKit",
  "diagnosticsStyle": "llvm",
  "backgroundCompilation": false,
  "actionAfterBuildError": "Focus Terminal",
  "buildPath": "",
  "disableSwiftPackageManagerIntegration": false,
  "warnAboutSymlinkCreation": true,
  "enableTerminalEnvironment": true,
  "pluginArguments": [],
  "pluginPermissions": {},
  "attachmentsPath": ".build/attachments",
  "excludeFromCodeCoverage": [],
  "excludePathsFromPackageDependencies": [
    ".git",
    ".github"
  ],
  "showBuildStatus": "swiftStatus",
  "showCreateSwiftProjectInWelcomePage": true,
  "openAfterCreateNewProject": "prompt",
  "sourcekit-lsp": {
    "serverPath": "",
    "serverArguments": [
      "-Xswiftc",
      "-sdk",
      "-Xswiftc",
      "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk",
      "-Xswiftc",
      "-target",
      "-Xswiftc",
      "arm64-apple-ios18.4-simulator",
      "-Xcc",
      "-isysroot",
      "-Xcc",
      "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk",
      "-Xcc",
      "-target",
      "-Xcc",
      "arm64-apple-ios18.4-simulator"
    ],
    "supported-languages": [
      "swift",
      "objective-c",
      "objective-cpp",
      "c",
      "cpp"
    ],
    "backgroundIndexing": "auto",
    "trace": {
      "server": "verbose"
    },
    "disable": false
  },
  "debugger": {
    "debugAdapter": "auto",
    "path": "",
    "setupCodeLLDB": "prompt",
    "useDebugAdapterFromToolchain": false
  },
  "swiftEnvironmentVariables": {
    "DEVELOPER_DIR": "/Applications/Xcode.app/Contents/Developer"
  },
  "runtimePath": "",
  "SDK": "",
  "swiftSDK": "arm64-apple-ios",
  "disableSandox": false,
  "diagnostics": {
    "exclude": [
      "Package.swift"
    ]
  },
  "index": {
    "store": {
      "path": "${workspaceFolder}/.build/Index.noindex/DataStore"
    }
  }
}
2

Sorry you weren't able to get this working @pogestudio!

To clarify the meaning of a few settings (which hopefully answers your (1) and part of (2)):

  • VS Code swift.sourcekit-lsp.serverArguments: The arguments passed to the LSP server on launch, intended for eg. setting log level. They not the arguments used for semantic functionality.
  • VS Code swift.buildArguments: These are passed from the extension to swift build and swift test and are not sent to SourceKit-LSP.
  • .sourcekit-lsp/config.json: This is the correct location for what you're trying to do, but the keys you've listed don't exist (where did you find them?). It's documented here.

What you're after is the following .sourcekit-lsp/config.json:

{
  "swiftPM": {
    "swiftCompilerFlags": ["-sdk", "<your SDK>", "-target", "arm64-apple-ios18.4-simulator"],
    "cCompilerFlags": ["-isysroot", "<your SDK>", "-target", "arm64-apple-ios18.4-simulator"]
  }
}

That this needs to be specified in so many places is obviously not ideal though and this is an area we'd like to improve, both in terms of documentation and simplifying the different settings.

  1. Is there a recommended flag or env-var to print the active SDK & target on launch so I can confirm which path the server finally uses?

There is no active SDK or target "on launch" - a single SourceKit-LSP server is able to handle many open projects at once. The simplest way to check this right now is via Console (filtered to sourcekit-lsp), where we log the following when you open a file:

Build settings for file:///path/to/your/file.swift
... all the settings ...

I've opened an issue for this one, since we should probably include a window/logMessage for things like settings given how important they are.