value based classes (see src/java.base/share/classes/java/lang/doc-files/ValueBased.html)
The present ticket is raised for the task of actually identifying the value based classes in JDK and annotating them with the new annotation type.
I envision that this work will be done by the core-libs team with hand holding help from Langtools/Javac to address any problems encountered in the form of excess/spurious warnings or other such problems while building openJDK.
For now I'll have the ticket against langtools and move it to core-libs once
JDK-8252181 [JEP 390] Define & apply annotation jdk.internal.ValueBased