Maven-dependency-plugin and annotations with SOURCE RetentionPolicy

Question

In a mvn project where I am utilizing maven-dependency-plugin to detect unused dependencies, there is seemingly no dependency scope I can specify for Google's AutoValue (com.google.auto.value:auto-value) to that will convince the plugin that the dependency is being used in spite of the fact that annotations from the package are being used (e.g. @AutoValue) and the project won't build if auto-value is excluded.

Now one solution is simply adding a configuration entry to my plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <configuration>
        <usedDependencies>
            <usedDependency>com.google.auto.value:auto-value</usedDependency>
        </usedDependencies>
    </configuration>
</plugin>

But I would be curious to know whether it's possible to configure either the maven-dependency-plugin or the dependency entry for auto-value in a way that would detect usage of the dependency per its annotations?

My suspicion is that this isn't possible because the RetentionPolicy of the annotations I'm using from auto-value are of RetentionPolicy.SOURCE and are discarded by the compiler. Is this correct?

Answer 1

Unfortunately, your suspicion is correct. The maven-dependency-plugin documentation specifically lists this as a concern here for source level annotations: http://maven.apache.org/shared/maven-dependency-analyzer/

Warning: Analysis is not done at source but bytecode level, then some cases are not detected (constants, annotations with source-only retention, links in javadoc) which can lead to wrong result if they are the only use of a dependency.

You can force AutoValue as used with usedDependencies as you have in your example or use the ignoredUnusedDeclaredDependencies configuration instead (which is what I did recently).

I don't believe it is possible to configure the dependency section to avoid this because maven doesn't provide a scope level that is compile only. I mark AutoValue with the provided scope to keep it out of any shaded jars I might make.

Lastly, you could write (or find if it exists) a custom dependency analyzer that takes source level annotations into account. See the documentation here http://maven.apache.org/plugins/maven-dependency-plugin/analyze-mojo.html#analyzer. Probably not worth the effort.