Bytecode transforming record class to be mutable

[Christian Beikov]

I just saw that EBean does bytecode transformation of record class files 
in a way that feels odd to me and I seek an answer about whether this is 
legal from a JVM point of view.

Apparently, it is possible to have a class file, where the class extends 
`java.lang.Record` and defines record component attributes (so it's a 
"record" like javac would create it), but with the following additional 
"features" which javac would not allow:

* Make fields for record components non-final
* Add additional fields that are not set through the canonical 
constructor, nor exposed through record component attributes

To me, this seems illegal and I would have expected a JVM verification 
error. I would like to know if this is something that is "supported", 
which I can build upon, or if the lack of verification is a JVM bug. Are 
records just a Java language feature without JVM support?! I read that 
final fields of records are "truly final" and can't be changed even 
through reflection and assumed there must be special JVM support that 
makes sure records match the Java language semantics...

Cross posting from StackOverflow: 
https://stackoverflow.com/questions/73377190/bytecode-transforming-record-class-to-be-mutable

Regards,

Christian