RFR: JDK-8267936: PreserveAllAnnotations option isn't tested

[Peter Levart]

On Wed, 2 Jun 2021 05:59:05 GMT, David Holmes <david.holmes at oracle.com> wrote:

> Sorry Jaroslav but I don't really see this test as a basic functional
> test of the PreserveAllAnnotations flag. There is no need for any
> dynamic retention mode switch. All you need as I've said previously is a
> class with all the CLASS retention annotations of interest (8 IIRC)
> applied and a programs that reads them, and either expects to find them
> or not, based on the PreserveAllAnnotations flag.

`CLASS` retention annotations are never returned by reflection regardless of whether the `PreserveAllAnnotations` option was used or not. The only way (apart from hacking into encapsulated state and doing your own parsing) is to compile a class that uses an annotation with `CLASS` retention and then run a test that looks up the annotation on this class after the annotation has been changed to have `RUNTIME` retention, but the class that uses it has not been recompiled.
`AltClassLoader` does the trick which replaces the class file of _v1 class with the class file of _v2 class when loading the class which simulates this change and recompilation of the annotation without changing anything else.

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PR: https://git.openjdk.java.net/jdk/pull/4280