Autocompletion is broken in certain projects #2405
Description
Swift version
swift-driver version: 1.127.14.1 Apple Swift version 6.2.3 (swiftlang-6.2.3.3.21 clang-1700.6.3.2) Target: arm64-apple-macosx26.0
Platform
macOS 26.2
Editor
Cursor + the official VSCode extension
Description
I've noticed as of late that the autocompletion in https://github.com/swift-dns/swift-idna/ in VSCode is broken and rarely works.
This didn't use to be the case a few months ago.
That library has some C source files and I'm guessing those are the ones that sourcekit-lsp is failing to properly handle.
Steps to Reproduce
Clone https://github.com/swift-dns/swift-idna, open it up in VSCode/Cursor.
Observe no autocompletion.
Logging
I see references to swiftly in this diagnosis bundle, but I'm just using the Xcode 26.2 toolchain.