Add module for Java 16 validation tests

[marchof]

Also remove preview features from Java 14 validation tests.

[Godin]

@marchof currently InstanceofTest and RecordsTest are executed in following configurations

mvn package -Dbytecode.version=14 -Djdk.version=14
mvn package -Dbytecode.version=15 -Djdk.version=15
mvn package -Dbytecode.version=16 -Djdk.version=16
mvn package -Dbytecode.version=17 -Djdk.version=17

ie both as a preview feature in 14 and 15 and as a standard feature in 16+
so out of curiosity - why

Also remove preview features from Java 14 validation tests

? I guess this is because strategy in IDEs is to support preview features of latest release and stop supporting preview features of previous releases? Like Eclipse probably already did, and IntelliJ started to warn. Right?

[marchof]

@Godin Correct, the idea is to only test released features in the long run. To keep our test set maintainable we only test not-yet-released preview features primarily to prepare ourself and provide feedback to OpenJDK. I thought we discussed this once.

[Godin]

I thought we discussed this once.

oh, I see - https://groups.google.com/g/jacoco-dev/c/edIrAG85jho/m/k4c8_ZzIDwAJ
from which I remember part

On Monday, January 13, 2020 at 5:10:02 PM UTC+1 Marc R. Hoffmann wrote:
I needed some time to wrap my mind around the fact that it is now compiling successfully.
—> validation.java14 with JDK 15 is now compiled with to java 15 bytecode —> preview flag works :)
So reconsidering my earlier suggestion I would actually keep switch expressions and records in validation.java14 for now.

but not

Once features get official we can move them to the respective java version.

😆

[marchof]

@Godin I don't insist on this. We can also keep testing preview features. But given the fact the the respective Java versions are already EOL and we had version specific switches in our validation code from my point of view we can drop those preview tests.

[marchof]

Rebased and Maven versions fixed to get a green build.

[Godin]

@marchof Also this PR reminded me about absence of validation test with Sealed Classes - if it was present, we would not have missed #1097 (comment) and would have detected the problem automatically earlier 😉 Sealed Classes are preview feature in 15 and 16 and will be finalized in 17 - https://openjdk.java.net/jeps/409 And since for them there is a special handling in https://openjdk.java.net/jeps/406 will be indeed simpler to add them in/after/together with #1191 than alone in org.jacoco.core.test.validation.java15, so that org.jacoco.core.test.validation.java17 will be the only one with --enable-preview 👍

And indeed seems that in IntelliJ IDEA 2021.1 ability to use Java 14 with preview features already not available:

And seems that in upcoming Eclipse 2021-06 ability to use preview features available only for Java 16:

[Godin]

@marchof oops, we almost both almost missed that it also should be added to java17-bytecode profile - #1194 😉