Compatibility modes

When a big team is migrating onto a new version, it may appear in an "inconsistent state" at some point, when some developers have already updated but others haven't. To prevent the former from writing and committing code that others may not be able to compile, we provide the following command line switches (also available in the IDE and Gradle/Maven):

• -language-version X.Y - compatibility mode for Kotlin language version X.Y, reports errors for all language features that came out later.

• -api-version X.Y - compatibility mode for Kotlin API version X.Y, reports errors for all code using newer APIs from the Kotlin Standard Library (including the code generated by the compiler).

Currently, we support the development for at least three previous language and API versions in addition to the latest stable one.