From now on, the old JVM backend will report an error by default when
compiling against class files produced by the JVM IR backend. This is
needed because we're not yet sure that the ABI generated by JVM IR is
fully correct and do not want to land in a 2-dimensional compatibility
situation where we'll need to consider twice more scenarios when
introducing any breaking change in the language. This is generally OK
since the JVM IR backend is still going to be experimental in 1.4.
However, for purposes of users which _do_ need to compile something with
the old backend against JVM IR, we provide two new compiler flags:
* -Xallow-jvm-ir-dependencies -- allows to suppress the error when
compiling with the old backend against JVM IR.
* -Xir-binary-with-stable-api -- allows to mark the generated binaries
as stable, when compiling anything with JVM IR, so that dependent
modules will compile even with the old backend automatically. In this
case, the author usually does not care for the generated ABI, or s/he
ensures that it's consistent with the one expected by the old compiler
with some external tools.
Internally, this is implemented by storing two new flags in
kotlin.Metadata: one tells if the class file was compiled with the JVM
IR, and another tells if the class file is stable (in case it's compiled
with JVM IR). Implementation is similar to the diagnostic reported by
the pre-release dependency checker.
Alexander Udalov
953b461c53