Bazel includes the ijar tool, which strips regular JAR files down to their interfaces. Target hashes are computed based on the resulting ijars, ensuring that only the necessary targets are rebuilt when changes do not affect public interfaces (e.g., modifications to implementations or private method signatures).

However, this approach often falls short in practice. For Scala 2, as noted in this issue, scalac adds a ScalaSignature annotation to classes, causing cache misses and unnecessary rebuilds.

For Scala 3, ijar generation is explicitly disabled.

Is the situation with ijars similar for Scala 3?
If ijars are not a viable solution, would analyzing TASTy files for interface-level changes be a feasible alternative?