optional tag in dependencyManagement is not inherited

[hisener]

Describe the bug

The client-java-parent POM has a few "optional" dependencies; however, they are no-ops. For example, the dependency tree of a module that uses io.kubernetes:client-java:jar:19.0.1:

$ mvn dependency:tree
...
[INFO] +- io.kubernetes:client-java:jar:19.0.1:compile
[INFO] |  +- io.prometheus:simpleclient:jar:0.16.0:compile
[INFO] |  |  +- io.prometheus:simpleclient_tracer_otel:jar:0.16.0:compile
[INFO] |  |  |  \- io.prometheus:simpleclient_tracer_common:jar:0.16.0:compile
[INFO] |  |  \- io.prometheus:simpleclient_tracer_otel_agent:jar:0.16.0:compile
[INFO] |  +- io.prometheus:simpleclient_httpserver:jar:0.16.0:compile
[INFO] |  |  \- io.prometheus:simpleclient_common:jar:0.16.0:compile

This is because Maven doesn't take the tag into account. See also https://issues.apache.org/jira/browse/MNG-5227 and https://issues.apache.org/jira/browse/MNG-5632. We noticed this issue, because Coursier seems to take the tag into account unlike Maven.

Could we push optional tags to module POMs and drop them from dependencyManagement?

java/pom.xml

Lines 185 to 190 in d7f9391

	<dependency>
	<groupId>io.prometheus</groupId>
	<artifactId>simpleclient</artifactId>
	<version>${prometheus.client.version}</version>
	<optional>true</optional>
	</dependency>

java/util/pom.xml

Lines 14 to 17 in d7f9391

	<dependency>
	<groupId>io.prometheus</groupId>
	<artifactId>simpleclient</artifactId>
	</dependency>

Client Version
19.0.1

Kubernetes Version
1.26.15

Java Version
Java 21

To Reproduce

1. Create a module that depends on client-java and run mvn dependency:tree. io.prometheus:simpleclient:jar:0.16.0:compile will be listed there.

Expected behavior
Optional dependencies (e.g., io.prometheus:simpleclient) should not be pulled transitively in downstream modules.

KubeConfig
N/A

Server (please complete the following information):
N/A

[brendandburns]

If you move the optional tag into the module pom but you use a central property (e.g. ${prometheus.client.optional}) that is set in a single location, then I think that I'm ok with it. Please also add a comment that references that bug, so that we can remove this when that bug is fixed.

Ultimately, this feels like a bug in maven, so I don't really want to decentralize our pom files just to make up for their bug.

[hisener]

If you move the optional tag into the module pom but you use a central property (e.g. ${prometheus.client.optional}) that is set in a single location, then I think that I'm ok with it. Please also add a comment that references that bug, so that we can remove this when that bug is fixed.

This works for me.

Ultimately, this feels like a bug in maven, so I don't really want to decentralize our pom files just to make up for their bug.

The question is whether we want these dependencies to be pulled transitively.

• If so, we should drop optional tags to include them downstream. It's already the case for Maven due to the issue linked above, but Coursier doesn't include them. I don't know the Gradle behavior. Dropping them would make them behave the same.
• If not, we should apply your suggestion so that they are not included in downstream projects. This could be a breaking change for downstream users that don't depend on these dependencies.

FWIW, google-auth-library-oauth2-http has <optional>true</optional> in both dependencyManagement and dependencies sections.

java/util/pom.xml

Line 84 in b14c36d

<optional>true</optional>