Alexander Udalov
1d5d6b5b72
Preface: Kotlin 1.3 will be able to read metadata of .class files produced by Kotlin 1.4 (see KT-25972). Also, to simplify implementation and to improve diagnostic messages, we're going to advance JVM metadata version to 1.4.0 in Kotlin 1.4, and would like to keep it in sync with the compiler version thereafter. This presents a problem: in an unlikely event that before releasing 1.4, we find out that the metadata-reading implementation in 1.3 was incorrect, we'd like to be able to fix the bug in that implementation and _forbid_ 1.3 from reading metadata of 1.4. But prior to this commit the only way to do this was to advance the metadata version, in this case to 1.5, and that breaks the metadata/compiler version equivalence we'd like to keep. The solution is to add another boolean flag to the class file, called "strict metadata version semantics", which signifies that if this class file has metadata version 1.X, then it can only be read by the compilers of versions 1.X and greater. This flag effectively disables the smooth migration scenario proposed in KT-25972 (as does increasing metadata version by 2), and will be used only in hopeless situations as in the case described above.
kotlinx-metadata
This is the platform-agnostic part of the Kotlin Metadata library, intended to provide the possibility to read and modify metadata of Kotlin declarations in the binary (.class, .js) files emitted by the Kotlin compiler. This part of the library is currently not released on its own. Please refer to kotlinx-metadata-jvm for instructions on how to load and modify Kotlin Metadata in JVM binaries (.class and .kotlin_module files).