The Scala Center's roadmap for tasty-query

Scala Center Updates
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I have good news to share about tasty-query and TASTy-MiMa. We completed all the milestones mentioned above, and released a prototype of TASTy-MiMa.

Developing all the required features in tasty-query took more time than expected, but in the past few months, we made a lot of progress. We achieved enough coverage of the Scala type system to implement a meaningful prototype of TASTy-MiMa.

Relevant links

In particular, follow the link to tasty-mima for usage instructions in an sbt build.

Status and request for testing

We published a first prototype of TASTy-MiMa, along with an sbt plugin sbt-tasty-mima v0.1.2 v0.1.3. It is quite young, but you can already help by trying it out on your project. The readme of TASTy-MiMa contains essential usage instructions for sbt-tasty-mima.

If your public API exposes type refinements and/or match types, expect severe limitations. Otherwise, please file any issues you may encounter.

tasty-query is also used by other projects, including the debugger for Scala 3 in Metals, and a work-in-progress research project for a TASTy Interpreter.

Why not make this part of MiMa?

TASTy-MiMa and MiMa achieve different although related goals.
One can wonder why not merge them as a single tool?
There are several reasons for that, at least at this point:

  • Huge maturity gap: MiMa is very mature and should be used by every library that is serious about compatibility. TASTy-MiMa is still in its infancy and likely to break, so we cannot recommend using it yet.
  • Different underlying codebase: MiMa and TASTy-MiMa contain no code in common; their underlying model is vastly different (JVM type system versus Scala type system).
  • Different (although similar) user-level API: the set of problems reported by MiMa and TASTy-MiMa is not the same (because they don’t have the same underlying model at all), so even if they were exposed as a single sbt plugin, the configurations would have to be using separate keys. The only real key in common is the mimaPreviousArtifacts/tastyMiMaPreviousArtifacts.

Next steps

The next steps for this set of projects will be the following:

  • Enable TASTy-MiMa on real-world Scala 3 libraries
  • Identify and fix important bugs preventing the above
  • Expand the support of tasty-query for type refinements and match types
  • Provide a Mill plugin for TASTy-MiMa

How can you help?

  • Test sbt-tasty-mima on your library, if it does not expose type refinements nor match types in its public API. Report any issues you encounter.
  • If you are familiar with Mill plugins, contribute a Mill plugin for TASTy-MiMa. You will probably want to take inspiration from the sbt plugin of TASTy-MiMa as well the existing Mill plugin for MiMa.
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