[IMPORTANT] Re: Creating custom plugin with JDK9: conflict with Maven packages?

[Robert Scholte <rf...@apache.org>]

Just forgot to mention a general warning for anybody trying to work with  
Java9:
In case a project depends on auto modules (and it clearly does here),  
*please* don't publish/deploy such libraries to any public artifact  
repository. Such unnamed modules might change their name for unforced  
reasons(module name is not reflected by the artifactId) or forced reasons  
(non-unique module name, split packages might force rearranges classes  
over artifacts, etc.).
We don't control every repository publishing to Central, so adding such  
quality rules would cause a lot of trouble.
We need to depend on the awareness of the community that they publish  
their artifacts with care, otherwise the result could be that the concept  
of Jigsaw won't work and projects could be forced to stay on Java 8 for  
this.

thanks,
Robert

On Mon, 10 Apr 2017 19:22:15 +0200, Martin Desruisseaux  
<ma...@geomatys.com> wrote:

> Hello
>
> I'm trying to port an existing Maven plugin from JDK8 to JDK9, but got
> an error message which seems to be related (if I interpreted correctly)
> to the way Maven classes are distributed in packages. My Maven
> dependencies are:
>
>     <dependency>
>       <groupId>org.apache.maven</groupId>
>       <artifactId>maven-core</artifactId>
>       <version>3.5.0</version>
>     </dependency>
>     <dependency>
>       <groupId>org.apache.maven</groupId>
>       <artifactId>maven-plugin-api</artifactId>
>       <version>3.5.0</version>
>     </dependency>
>     <dependency>
>       <groupId>org.apache.maven.plugin-tools</groupId>
>       <artifactId>maven-plugin-annotations</artifactId>
>       <version>3.5</version>
>       <scope>provided</scope>
>     </dependency>
>
> My module-info.java file is:
>
>     module org.apache.sis.core.build {
>         requires java.xml;
>         requires jdk.javadoc;
>         requires maven.core;
>         requires maven.model;
>         requires maven.plugin.api;
>         requires maven.plugin.annotations;
>     }
>
> The error that I get is:
>
>     [ERROR] Failed to execute goal  
> org.apache.maven.plugins:maven-compiler-plugin:3.6.1:compile  
> (default-compile) on project sis-build-helper: Compilation failure:  
> Compilation failure:
>     [ERROR] module  reads package org.apache.maven.plugin from both  
> maven.plugin.api and maven.core
>     [ERROR] module maven.plugin.annotations reads package  
> org.apache.maven.plugin from both maven.core and maven.plugin.api
>     [ERROR] module maven.plugin.api reads package  
> org.apache.maven.plugin from both maven.core and maven.plugin.api
>     [ERROR] module maven.model reads package org.apache.maven.plugin  
> from both maven.core and maven.plugin.api
>     [ERROR] module plexus.build.api reads package  
> org.apache.maven.plugin from both maven.core and maven.plugin.api
>     [ERROR] module plexus.utils reads package org.apache.maven.plugin  
> from both maven.core and maven.plugin.api
>     [ERROR] module maven.core reads package org.apache.maven.plugin from  
> both maven.core and maven.plugin.api
>
> Looking for the first error, I can see that maven-core-3.5.0.jar
> contains the following files:
>
>     org/apache/maven/plugin/BuildPluginManager.class
>     org/apache/maven/plugin/CacheUtils.class
>     (etc...)
>
> and maven-plugin-api-3.5.0.jar contains the following files:
>
>     org/apache/maven/plugin/AbstractMojo.class
>     org/apache/maven/plugin/AbstractMojoExecutionException.class
>     org/apache/maven/plugin/ContextEnabled.class
>
> Maybe I misunderstood, but I though that we can not have two modules
> exporting the same package with Jigsaw. Did I misunderstood something?
> If not, is it a Maven work in progress or is there some know workaround?
>
>     Thanks,
>
>         Martin
>

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