missinglink VS soot

You can also use the upstream https://github.com/spotify/missinglink if you're using Maven instead of sbt.

There's been a recent release of missing-link with support for Mult-Release JARs and running analysis on multiple projects concurrently. More info here (applies not only to Scala/sbt, so it's worth linking it here): https://old.reddit.com/r/scala/comments/lxmi4w/sbtmissinglink_032_has_been_released_multirelease/

There are still some issues with MissingLink, like that it can't handle Multi-Release JARs (but that's being fixed I write) or that it uses thread-unsafe caches and so it can't be executed in parallel (and so it can take a long time to finish on big projects with many modules). But taken all together I swear by it. It has already saved us from runtime failures after deployment many times (it's easy to get incompatible versions when working on big projects with big number of dependencies). Instead, we get a red build in CI -- just anybody should expect for goodness sake when using a strongly-typed language like Scala.

Yeah, I think a cross compiler would be the only way such a thing could be possible. It would be interesting to see how many collections are actually changed though. I have written similar things using soot. The biggest question is whether there would be enough people who would want such a thing. I can't imagine the time savings vs time spent would pay off for me personally.