Add method unrolling to Scala 3

About the Project

Implement the specification of SIP-61, which specifies code generation of forwarder methods that match the signature of a method, before a parameter was added.

Current Status

The PR was approved by the SIP committee and Scala 3 maintainers, merging on January 27th 2025. It will be available as an experimental feature in Scala 3.7.0.

Done:

• ✅ New annotation @scala.annotation.unroll to enable the feature.
• ✅ New phase after typechecking, before pickling, to generate forwarder methods.
• ✅ Detect correct usage of the annotation in prior "posttyper" phase.
• ✅ Lazy transform - only run transform where the annotation is used.
• ✅ Documentation page
• ✅ Report errors with incorrect usage.
• ✅ Detect problematic cases with transparent inline (where forwarders are not yet visible).
• ✅ Test edge cases such as incremental compilation.
• ✅ Test usage on case class, enum, class, trait and object.

Final changes:

• ✅ based on feedback, added more tests, and redesigned the test suite to integrate better - including source file splitting depending on target platform.