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https://issues.apache.org/jira/browse/LUCENE-10255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17448241#comment-17448241
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Dawid Weiss commented on LUCENE-10255:
--------------------------------------
> Normally you have a module-info.java that is compiled by javac? Or is this
> further additional metadata?
This is additional metadata injected by 'jar'. It's actually kind of funny to
look at the source code of that...
See "-module-version=" and "--main-class=" options here:
https://docs.oracle.com/en/java/javase/17/docs/specs/man/jar.html
> Because version numbers should not exist for modules, the JMS requires you to
> encode it into module name. Like a module "org.apache.lucene.core.v9".
It's not really like this. Modules can have numbers; it's just they're not
currently used for anything (you can't make a versioned dependency or enforce
it). This is "outside of the scope of the jms". But you can see those versions,
for example:
{code}
java --list-modules
...
[email protected]
[email protected]
...
{code}
The branch I created embeds Lucene's version into the created JAR (of Luke) as
well.
I also thought about what you suggested - keep a separate source folder for
just the module-info.java. It is an alternative that may be the easiest one to
follow (until all subprojects have module-info.java information). I just
thought it was... not elegant somehow. Seemed hacky... But given the complexity
of workarounds for ecj and javadoc it may be a lesser evil - I'll look into
this.
Robert - don't spent too much time on this; I'll reiterate with Uwe's
suggestion - it seems like a cleaner alternative. When all subprojects have
module-infos it may be easier to just move the tooling to use full modules
(instead of the classpath).
> 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
>
> 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.
> * 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).
> * 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).
> After poking a bit and trying it out I have to say I have mixed feelings
> about moving to the JMS. On the one hand, many things are great - the module
> path, module descriptors and access modes. On the other hand, the tooling
> tricks required to make it all work make you shiver.
> If anybody wants to play/ improve things on that experimental branch (I
> converted Luke to a full module - it works), please be my guest. I have to
> sit on this and think whether it's something I really like or not.
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