No such module '<name>'

[MahdiBM]

Describe the bug
Getting no such module 'Benchmark' around import Benchmarks.
Half sourcekit-lsp stuff that are unrelated to the benchmarking package work, and the other half just don't.
sourcekit-lsp background indexing is enabled.
EDIT: sourcekit-lsp problems could be related to the fact that I was using backgroundPreparationMode: build, which i've figured is not a good move generally.

To Reproduce
Steps to reproduce the behavior:
Clone vapor/multipart-kit.
Open the Benchmarks folder as the root SwiftPM directory. Don't just open the multipart-kit folder and head to the Benchmarks directory.
Try to build.
Open a file like Parser.swift.
Observe error no such module 'Benchmark'.

Expected behavior
Things work.

Environment

• OS: macOS 15.2
• Swift version (output of swift --version): 6.0.3 release
• Visual Studio Code version: -
• vscode-swift version: v1.11.4

Additional context
This sub-swiftpm-package does have some uncommon stuff in it, possibly one of them is triggering this behavior. For example the fact that there is a sub-package at all + that the sub-package references its parent as a dependency.