The reason for this is that this flag is used right now in 'cli-common'
to workaround the problem that this module is compiled with API version
1.4, but runs with stdlib of version 1.3 (bundled to Gradle). The same
problem would appear with adapted function references, since we use
kotlin/jvm/internal/AdaptedFunctionReference in the bytecode, only
available since 1.4.
The fix is to generate adapted references in this case as subclasses of
the already existing kotlin/jvm/internal/FunctionReference. This can
change behavior in some extreme corner cases (because such references
can now be observed to have reflection capabilities), but it's an -X
argument anyway.
Another option would be to introduce another compiler argument
specifically for this, but it looks like it would only complicate things
without much benefit.
Dmitriy Novozhilov