[slf4j-dev] [JIRA] (SLF4J-487) module-info.class must be in root of jar, not META-INF/versions/9

[QOS.CH (JIRA)]

    [ https://jira.qos.ch/browse/SLF4J-487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=20361#comment-20361 ] 

Joakim Erdfelt commented on SLF4J-487:
--------------------------------------

I'm not sure this is a bug in {{javac}}.

Think about it, why would {{javac}} need to know runtime differences in order to compile?
It doesn't know what the runtime will be, so it has to assume default behavior.

Everything in the {{META-INF/versions/}} tree is optional behavior based on the runtime you are in.

I'm curious to see what the {{javac}} maintainers say about it.

> module-info.class must be in root of jar, not META-INF/versions/9
> -----------------------------------------------------------------
>
>                 Key: SLF4J-487
>                 URL: https://jira.qos.ch/browse/SLF4J-487
>             Project: SLF4J
>          Issue Type: Bug
>          Components: Core API
>    Affects Versions: 2.0.0-alpha1
>         Environment: All environments
>            Reporter: Joakim Erdfelt
>            Assignee: SLF4J developers list
>
> Also reported here [https://github.com/qos-ch/slf4j/commit/fb418db538a4990#r37662713]
> This triggers build warnings on javac.
> The {{module-info.class}} shouldn't be in the {{META-INF/versions/9}} in the jar file, it should be in the root of the jar file.
> Yes, I'm aware of -SLF4J-456-, but that's a bug in websphere's annotation parsing (a similar bug that *all* web containers have had to fix since [JEP238|https://openjdk.java.net/jeps/238] became a reality).
> From maven (Eclipse Jetty 10.x is migrating to Slf4j 2.0.0-alpha1 btw).
> {noformat}
>  [INFO] — maven-compiler-plugin:3.8.1:compile (default-compile) @ jetty-slf4j-impl —
>  [INFO] Changes detected - recompiling the module!
>  [INFO] Compiling 9 source files to /home/joakim/code/jetty/jetty.project-10.0.x/jetty-slf4j-impl/target/classes
>  [WARNING] /home/joakim/code/jetty/jetty.project-10.0.x/jetty-slf4j-impl/src/main/java/module-info.java:[26,28] requires transitive directive for an automatic module
> {noformat}
> Using {{javac -Xlint:all ...}} on a project using {{slf4j-api-2.0.0-alpha1.jar}} with it's own {{module-info.class}} will show the above warning.
> If you want a small example project, I'll be happy to make one for you.
> The warning is because the {{module-info.class}} is not present at the root of the jar file (where it must be, despite the jigsaw devs brief suggestion in 2018 that {{META-INF/versions/9}} could be a solution for bytecode scanning problems, other tooling in the JDK hasn't caught up yet to that suggestion, even in JDK 14, even including {{javac}}).
> javac sees {{slf4j-api-2.0.0-alpha1.jar}} as having no {{module-info.class}} and is instead using the jar as one with an automatic module name.
> Manually repackaging {{slf4j-api-2.0.0-alpha1.jar}} with the {{module-info.class}} in the root fixes the javac warnings.



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