Migration from 0.20.0 version to 1.0.0

For adopters of earlier versions of kotlinx.serialization, a dedicated migration path is prepared. During the preparation of serialization 1.0.0 release, most of the API has been changed, renamed, moved to a separate package or made internal. IDEA migrations were introduced, but unfortunately not all API can be migrated with automatic replacements.

To simplify your migrations path, it is recommended to enable star imports in IDE (so all extensions are imported automatically) first.

1. Update kotlinx.serialization to version 1.0.0-RC2 (this is the last version that has migrations for pre-1.0.0 versions. 1.0.0 version itself does not have any migration aids.)
2. Rename dependency from kotlinx-serialization-runtime to kotlinx-serialization-json.
3. For multiplatform usages, remove dependencies to platform-specific artifacts (e.g. kotlinx-serialization-runtime-js), they are no longer required by Gradle.
4. Update Kotlin to 1.4.0 or higher.
5. Start applying replacements for the deprecated code.
6. If some signatures are not resolved, try to hit alt + Enter and import the signature.
7. If methods are still not resolved, it is recommended to use star imports for kotlinx.serialization signatures in the problematic file.
8. When there are no usages of deprecated code left, you can change dependency version from 1.0.0-RC2 to 1.0.0.

For less trivial issues, it is recommended to study the changelog or to ask for help in #serialization Kotlin's Slack channel.