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https://issues.apache.org/jira/browse/LUCENE-10255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17456388#comment-17456388
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Dawid Weiss commented on LUCENE-10255:
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Finally! I think we have all the pieces that are needed to introduce proper
java module support in Lucene. The change basically folds down to:
- separation of dependency configurations between classpath and module-path
conventions,
- turning off the default module support in gradle (yeah, sorry - I can't make
it work the way we need it to work) and collecting the module-path and
classpath manually for javac and tests. This is not as invasive as it sounds -
gradle is fairly elegant here.
- supporting test subprojects with full module support. I think these should be
done as separate subprojects because otherwise Eclipse and many other IDEs will
go tumbling down - multiple sourcesets with a module-info will confuse the hell
out of them.
All of these things are working and validated in the draft PR at
https://github.com/apache/lucene/pull/470 - thanks everyone for their support
and persistence.
I will clean up the repetitive parts of the patch, clean up the unnecessary or
experimental unrelated changes and will create a cleaned up PR soon. I think
now, that everything is working, it should be downhill.
> Fully embrace the java module system
> ------------------------------------
>
> Key: LUCENE-10255
> URL: https://issues.apache.org/jira/browse/LUCENE-10255
> Project: Lucene - Core
> Issue Type: New Feature
> Reporter: Dawid Weiss
> Priority: Major
> Attachments: screenshot-1.png, screenshot-2.png
>
> Time Spent: 21h 50m
> Remaining Estimate: 0h
>
> I've experimented a bit trying to move the code to the JMS. It is
> _surprisingly difficult_... A PoC that almost passes all checks is here:
> https://github.com/dweiss/lucene/tree/jms
> Here are my conclusions so far:
> * The JMS and gradle add a lot of complexity (this applies to any
> higher-level tooling, including IDEs, I think). For starters, -modules have
> to be JARs. The effect of this is that what was previously a set of
> directories from dependencies now has to be a JAR. What was previously an
> incremental update of a single .class file now ripples throughout the build
> recreating module JARs (ZIPs!)... I didn't realize it at first, but it's a
> costly thing to do. I'm not even sure how IDEs handle this issue.- (not true)
> * A Java module contains metadata (such as the module version or main class)
> that is completely detached from any source file. These things live in a
> class bytecode of the compiled module-info; interestingly, there is no
> source-level way to specify it - these class attributes are injected by the
> 'jar' tool. Gradle has some fancy on-the-fly asm conversion filter that
> injects it.
> * Dependencies between modules will effectively live in two places: in gradle
> build files and in module-info files. -And they can go out of sync, although
> it's probably easy to catch (since javac would complain about missing classes
> during compilation, even if they're in module path).- (with separate module
> and classpath configurations there is a possibility to verify the
> consistency).
> * Probably the biggest challenge (not covered in the PoC) are with our custom
> javadoc and ecj linter tasks - they see the module-info.java and can't cope
> with it. At the same time, there is no easy way to exclude that one
> particular file: ecj would have to accept a full set of sources (command
> argument limit will be a problem), javac can accept a full set of java
> sources (external file) but then it doesn't copy doc-files properly anymore
> (this is probably easier to fix).
> * There are differences at runtime that are hard to anticipate - for example
> resource lookups via class loader no longer work (I fixed this in Luke).
> * We will have to rethink the long-term strategy of how white-box tests work.
> There are some guidelines here but all of them have some cons (IDEs being
> confused).
> https://docs.gradle.org/current/userguide/java_testing.html#sec:java_testing_modular
> * it's pretty much impossible to exclude transitive dependencies from modules
> we depend on - if they're not compile-time only (static) requirements, they
> will have to be present on module path.
> * supporting modules may or may not work in your IDE.
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