Scala 2.13 and Scala 3 Binary Interoperability via TASTy

JVM Bytecode and TASTy Integration

Scala 3 introduces the TASTy (Typed Abstract Syntax Tree) format to decouple the compiler from the runtime representation, aiming to solve long-standing binary compatibility issues found in the Scala 2.x series. While the Scala 3 compiler can consume Scala 2.13 binaries, the reverse interaction and the stability of the binary interface across minor version increments remain complex.

The primary goal is to ensure that libraries compiled with different compiler versions can coexist on the same classpath without triggering NoSuchMethodError or ClassCastException, particularly when using reflection-based access to members that may undergo name mangling.

Given the differences in how Scala 2.13 and Scala 3 map traits and case classes to JVM bytecode, there is uncertainty regarding the long-term stability of the binary interface during minor version updates.

• How does the TASTy format specifically resolve the name mangling discrepancies between Scala 2.13 and Scala 3 binaries?
• What are the specific constraints when linking a Scala 3 project against a library compiled with a minor version of Scala 2.13?