[Embedded] Can't find any module when background indexing is turned on

[kkebo]

Swift version

swift-DEVELOPMENT-SNAPSHOT-2025-11-25-a, swift-DEVELOPMENT-SNAPSHOT-2025-11-26-a

Platform

macOS 26.1

Editor

Visual Studio Code 1.106.2 with Swift extension, Vim 9.1 with vim-lsp

Description

Sourcekit-LSP has enabled backgroundIndexing by default on the main branch lately. However, since then, code completion has been broken.

Steps to Reproduce

Steps:

1. Clone https://github.com/kkebo/embedded-lsp-mre
2. Run cd embedded-lsp-mre
3. Run swiftly install
4. Open the current directory with VS Code or Vim
5. Open Sources/Foo/Foo.swift

Expected behavior:

No errors are displayed on a editor.

Actual behavior:

The "No such module 'Bar'" error is displayed at import Bar.

However, it can be built with swift build -c release --triple aarch64-none-none-elf --toolset toolset.json successfully.

In addition, if you add "backgroundIndexing": false to .sourcekit-lsp/config.json, the error disappears and it works fine just like it did before.

Logging

sourcekit-lsp-diagnose-2025-11-28T21-17-23+09-00.zip

[bnbarham]

@kkebo have you added the configuration, triple, and toolset to .sourcekit-lsp/config.json (https://github.com/swiftlang/sourcekit-lsp/blob/main/Documentation/Configuration%20File.md#structure)?

[kkebo]

@bnbarham Yes, please see my minimum reproducible example repo I described in the description.

[bnbarham]

Looks like we're not passing --toolset through during the preparation. Thanks @kkebo, I'll have a fix up soon.