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.

[MahdiBM]

This is still an issue in 6.2 nightlies. Maybe @ahoppen has an idea what's going wrong here?
I didn't know that more people are having this issue, but it does appear so based on the reactions.

[bnbarham]

@MahdiBM do you have jemalloc installed? I see Benchmarks failing to build without it when I tried to reproduce, but after installing it all functionality worked as expected (with 6.2).

[MahdiBM]

@bnbarham thanks for the look; you're actually right. I just tried again in multipart-kit and things seem to be resolved.
I did have jemalloc installed since the benchmarking package requires that, but I was trying this in swift-dns in a dev container and there was another problem as well which might have affected this.

I'll try again in swift-dns to see what was wrong. For some reason I've completely forgot what was the other issue there although it was only 2 days ago. Eventually i gave up on having the benchmarking package as a sub-package when i tried this a few days ago.

[MahdiBM]

@bnbarham great it works in swift-dns as well. Thanks again.

Now I remember why I gave up on using a sub-package. Unrelated to this issue, but it was because i had to make a bunch of stuff "public" (with @_spi()) and I came to conclusion that's probably not worth having a sub-package at that point. So I preferred to use the same Package.swift file, with an env var to enable/disable benchmark related dependencies/targets. I can see there are other ways to achieve having a separate benchmarking package as well; for example I could duplicate Package.swift for the benchmarking sub-package and make sure the path for targets points to the parent directory where the targets actually are. Then i should be able to use package access modifiers as well. These are all suboptimal, but i'll try this next, and settle on something. Maybe i'll file an issue in SwiftPM repo as well to see if anything can be done there to make this easier.

[bnbarham]

Then i should be able to use package access modifiers as well.

Another option might be to allow overriding the package name, which would then allow using the package modifier across packages. That's not something SwiftPM has today (you could probably pass it through unsafe flags, haven't tried it though)

Thanks for verifying 🙇‍♂