SourceKit-LSP fails loading the standard library while using Build Server Protocol

[martinez-karina]

Swift version

swift-driver version: 1.127.14.1 Apple Swift version 6.2 (swiftlang-6.2.0.19.9 clang-1700.3.19.1) Target: arm64-apple-macosx15.0

Platform

macOS 15.7.1

Editor

Cursor with Swift Extension (1.11.4)

Description

I am using sourcekit-bazel-bsp, the Bazel BSP implementation for SourceKit-LSP. The BSP ←→ LSP integration has been working well with Xcode 16.3 however, after upgrading our Xcode version to Xcode 26.0.1, I am seeing the following error on all Swift files in my project:

Internal SourceKit error: error response (Request Failed): Loading the standard library failed

This is my .sourcekit-lsp/config.json

{
  "backgroundIndexing": true,
  "backgroundPreparationMode": "build",
  "defaultWorkspaceType": "buildServer",
}

And the output of the Swift Output path:

10:27:43: Activating Swift for Visual Studio Code...
10:27:43: Apple Swift version 6.2 (swiftlang-6.2.0.19.9 clang-1700.3.19.1)
Platform: darwin
Swift Path: /Applications/Xcode26.0_17A400.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
Toolchain Path: /Applications/Xcode26.0_17A400.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr
Runtime Library Path: /Applications/Xcode26.0_17A400.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx:/usr/lib/swift
Default Target: arm64-apple-macosx15.0
Default SDK: /Applications/Xcode26.0_17A400.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX26.0.sdk
XCTest Path: /Applications/Xcode26.0_17A400.app/Contents/Developer/usr/bin
10:27:43: SourceKit-LSP setup
10:27:43: focus: undefined

For my project, I am specifically building and indexing against the iOS simulator sdk using the -target arm64-apple-ios14.0-simulator -sdk /Applications/Xcode26.0_17A400.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator26.0.sdk flags.

So far I have tried the following but no luck:

• Deleted all Xcodes + caches
• Re-installed only Xcode 26.0.1
• Tried setting Swift: SDK workspace setting

The LSP/BSP integration works well with Xcode 16.3 still. I’d appreciate any guidance on how to resolve these Loading the standard library failed errors. Thanks in advance!

Steps to Reproduce

At the moment, it is not reproducible with our Example project for SourceKit-Bazel-BSP. It is happening on our company's codebase.

Logging

Attaching the diagnose bundle. For security I did not enable private/sensitive/extended logging. Let me know if this is of any use!

sourcekit-lsp-diagnose-2025-10-22T11-28-32-07-00.zip

[bnbarham]

Attaching the diagnose bundle. For security I did not enable private/sensitive/extended logging. Let me know if this is of any use!

Unfortunately the main thing we need to see here is the arguments, which we don't include without extended logging. We do seem to be communicating with the BSP, so that at least doesn't seem to be the issue.

I’d appreciate any guidance on how to resolve these Loading the standard library failed errors. Thanks in advance!

Your best bet (if you can't send us the logs) is probably to compare the arguments between the two and see if there's anything missing/substantially difference. That error in particular is usually caused by a missing/incorrect -sdk and/or -target. The logs should include the full arguments split between messages of "Build settings for ".