Scala-3.3.0: dotty.tools.FatalError: cannot resolve reference to

I'm seeing this error with scala-3.3.0 and akka (or pekko):

dotty.tools.FatalError: cannot resolve reference to type akka.stream.scaladsl.type.Source
dotty.tools.FatalError: cannot resolve reference to type org.apache.pekko.stream.scaladsl.type.Source

In both cases I see no such reference in any of the sources or dependencies.

To demonstrate the problem, I created a small GitHub repo: https://github.com/abrighton/scala3-test

The main branch uses pekko and the "akka-version" branch uses akka. Both use java-17 and scala-3.3.0.

The closest issue I could find that might be related was: https://github.com/lampepfl/dotty/pull/16373

Any ideas what could be causing this?

You are using pekko-http as a dependency

The Pekko HTTP modules implement a full server- and client-side HTTP stack on top of pekko-actor and pekko-stream.

Which means you need to have also the dependencies pekko-actor and pekko-stream added in the classpath.

Just adding

libraryDependencies += "org.apache.pekko" %% "pekko-stream" % PekkoVersion

should fix your problem.

Side Note:

Not sure if the docs are incomplete or a hello world for pekko-http is hard to find. Checking the Pekko Modules, pekko-stream is not listed. I couldn't find g8 template or something similar.

Just based on the error message you shared

dotty.tools.FatalError: cannot resolve reference to type akka.stream.scaladsl.type.Source
dotty.tools.FatalError: cannot resolve reference to type org.apache.pekko.stream.scaladsl.type.Source

And knowing that Source comes from the stream module, I took a wild guess and added the pekko-stream dependency and the compilation succeed.

EDIT:

found a pekko http quickstart template