RFR: 8311302: Implement JEP 493: Linking Run-Time Images without JMODs [v42]

[Severin Gehwolf]

On Fri, 1 Nov 2024 18:03:16 GMT, Mandy Chung <mchung at openjdk.org> wrote:

> I expect that the jmodless tests will first build an image (say `image1`) using jlink `--generate-linkable-runtime` option and then verify `image1/bin/jlink` that links from the run-time image. I don't see `--generate-linkable-runtime` option is used from jmodless tests. I looked at `AbstractLinkableRuntimeTest` which provides the support to create linkable runtime image but not obvious to me. Can you describe the idea of this test framework?

This has gone through a couple of iterations. The idea once was, as you describe now, to create a run-time image link capable JDK on the fly for testing. Then, once the build flag got introduced it changed to it assuming a run-time image link capable JDK (and only removed `jmods` if present - to provoke run-time image based linking) and tests would only activate on such builds.

> OK. I see this now (`@requires jlink.runtime.linkable` in all jmodless tests). I.e. No test for the default JDK build.

Correct. Though, I've been testing builds using `--enable-linkable-runtime` in GHA here for example (Linked in the description of the PR): https://github.com/jerboaa/jdk/actions/runs/11612287720
 
> I think this feature needs test verification even for the default JDK build. One way to do that is to build a test image (say `base-image`) using jlink `--generate-linkable-runtime` option and then verify `base-image/bin/jlink` instead of the JDK.

That makes sense. The framework mostly supported this use-case anyway so I've now extended it to run those tests also on the default build (`jlink` with `-run-time-image` capability). Those now do perform an extra step to create a JDK with the capability first. If the JDK build has the capability already turned on, this step is omitted.

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PR Comment: https://git.openjdk.org/jdk/pull/14787#issuecomment-2457744203