Interfaces (regular and sealed) are by default polymorphic. To benefit
from sealing (i.e. knowledge of all inheritors in compile-time), @Serializable
annotation may be added on sealed interface, generating the same serializer
that can be used for sealed classes.
Synthetic nested classes are not generated in DEFAULT_IMPLS mode because
it causes problems when adding a synthetic companion to an interface.
Fixes https://github.com/Kotlin/kotlinx.serialization/issues/1576
Originally reportFromPlugin method was introduced to address the problem
with loading of DefaultErrorMessages.Extension vis ServiceLoader.
For some cases this extension was not loaded by ServiceLoader because
classes was loaded via different class loader, common scenario here is
compiler plugins. Ideally we should load such extension point via
getService approach, but unfortunately to do that we need project and
DefaultErrorMessages.render is static method for now.
Also with reportFromPlugin approach is a problem -- all diagnostics
reported via this method has the same id: PLUGIN_[WARNING|ERROR|INFO]
and it isn't possible to suppress only one particular diagnostic.
To bypass this problem the new method
initializeFactoryNamesAndDefaultErrorMessages was introduced.
It basically store DiagnosticRenderer inside DiagnosticFactory.
It is not ideal, because one DiagnosticFactory could have different
renderers for different scenarios -- for compiler and for IDE, but
I think that it is better than reportByPlugin approach.
It is required when enum members contain some special annotations which should be recorded in descriptor.
Due to some recursive/lazy resolve problems, compiler plugin frontend can't infer @Serializable on enum automatically, therefore, we ask a user to explicitly provide it.
Also fix ir tests
Leonid Startsev