Maven profile-specific dependencies not being copied by maven-dependency-plugin

Question

I have a maven project, 'a', that builds a simple library. The project has an additional source folder that can be optionally included by specifying a named profile. This will do two things:

• Include an additional source folder in the built jar that is otherwise not included

• Add a dependency that is needed by this additional source, that is otherwise not needed

          <profile>
                  <id>special</id>
                  <dependencies>
                          <dependency>
                                  <groupId>com.example</groupId>
                                  <artifactId>dependency</artifactId>
                                  <version>1.0</version>
                          </dependency>
                  </dependencies>
          </profile>
  

There is also a twist. I cannot guarantee that the additional dependency is always available. That means I cannot list it as a dependency that is always included, because in some cases it cannot be resolved so the build will fail. Therefore I only want to include this dependency when the profile is explicitly activated.

Subsequently, I have another project 'b', that has 'a' as a dependency. I want project 'b' to be agnostic to whether 'a' was built with the regular profile or the special profile. Project 'b' uses the maven-dependency-plugin to copy dependencies to a folder:

  <plugin>
    <artifactId>maven-dependency-plugin</artifactId>
    <executions>
      <execution>
        <phase>package</phase>
        <goals>
          <goal>copy-dependencies</goal>
        </goals>
        <configuration>
          <outputDirectory>lib</outputDirectory>
        </configuration>
      </execution>
    </executions>
  </plugin>

What would be the easiest way to make sure project 'b' copies the additional dependency if project 'a' was built with the special profile, but not otherwise? I can make any modifications to project 'a' that I would like, but would prefer not to make modifications to project 'b' unless necessary.

As it stands, with the additional dependency specified as part of a profile, maven never includes it as part of the copy-dependencies - regardless of which profile I built project a with. Ultimately I get a ClassNotFoundException if I run project b having built project a with the special profile.

I will clarify the example if needed. Thanks in advance!