"'build.plugins.plugin.version' for org.codehaus.mojo:build-helper-maven-plugin is missing" in case of multiple source directories

[dhendriks]

If I have multiple source directories in my plugin, I get the following warning:

$ mvn clean verify -Dtycho-version=4.0.1
Picked up _JAVA_OPTIONS: -Djava.net.preferIPv4Stack=true
[INFO] Scanning for projects...
[WARNING]
[WARNING] Some problems were encountered while building the effective model for tycho-its-project.compliler:tycho-its-project.compliler.multipleSourceDirs.bundle:eclipse-plugin:1.0.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.codehaus.mojo:build-helper-maven-plugin is missing.
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]
[INFO] Tycho Version:  4.0.1 (26e55402ca6295ab784674c5053c364ae7b428e7)
[INFO] Tycho Mode:     extension
[INFO] Tycho Builder:  maven
...

That is, I have a src and src-gen folder in my bundle. These folders are configured in .classpath and build.properties. The bundle has no pom.xml, as I use pomless build.

[laeubi]

You can add this to your main pom.xml

<plugin>
	<groupId>org.codehaus.mojo</groupId>
	<artifactId>build-helper-maven-plugin</artifactId>
	<version>3.4.0</version>
</plugin>

[dhendriks]

You can add this to your main pom.xml [...]

That seems to work. It still feels like a workaround to me.

[laeubi]

Since this is local for the bundle, can't Tycho generate in this file the version of this plugin, as it will only apply here locally?

But what version? If we force a version it will be fixed there and you can never override this (even when a newer/different version is defined in your pom). Therefore the "maven" way is to define this in your root pom.xml in the dependency management section.

[laeubi]

This is not a workaround but how maven "works" see:

https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#Dependency_Management

so child modules should usually never define a version but you mange them in the parent.

[dhendriks]

Still, I'm using Tycho. Tycho uses something. And then I have to decide on versions of dependencies that I don't directly need, but Tycho needs. This seems to leak implementation details of Tycho to my build configuration.

If I compare this to Eclipse plugins, then if bundle A depends on bundle B, and bundle B depends on bundle C, then B can re-export C, such that A doesn't have to directly depend on C. Much better.

Maybe Maven is just broken, and this is unavoidable, I don't know, but it is not very nice.

[laeubi]

Tycho don't "use" something, the tycho-build extension just generates a pom fragment for you but you still need to define at least the tycho-maven-plugin version in your root pom and probably more configuration (in this case build-helper-maven-plugin), this all has nothing to do with OSGi dependency (and reexport is discouraged anyways and bad practice).

[dhendriks]

I've created a reproducer at #2718.