Accessing plugin properties within a Mojo source file?

[Im...@ubs.com]

I wonder if anyone else is struggling to understand the limitations of
the @parameter expression="..." default-value="..." construct.

I would like to create a generated-sources pathname in a Mojo plugin
that translates from a domain-specific language into Java. The
translator exists as a stand-alone at the moment. I understand that the
plugin should generate sources into
${project.build.directory}/generated-sources/${plugin.prefix} - but I
can't seem to find out what the plugin prefix is programmatically. For
the moment, I have hard-coded the default prefix value in the Mojo
itself, but this seems to go against the spirit of specifying things in
configurable ways.

I have tried using the following recipe to set the ${prefix} property in
the plugin's pom.xml file, as documented in
http://maven.apache.org/guides/introduction/introduction-to-plugin-prefi
x-mapping.html:

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-plugin-plugin</artifactId>
                <configuration>
                    <goalPrefix>myplugin</goalPrefix>
                </configuration>
            </plugin>
        </plugins>
    </build>

...but specifying "${prefix}" as the value for @parameter expression
within the plugin's Mojo source results in the default value.

Even if I found out a way to set the prefix explicitly through the
project POM, it turns out that you still can't use it as a property in
another expression or default-value. I specified another private
variable as @parameter expression="${project.generated.directory}"
default-value="${project.build.directory}/generated-sources/${prefix}"
and got the result ".../target/generated-sources/null".

Surely both these behaviours go against the Don't Repeat Yourself (DRY)
principle. Any help would be much appreciated.

Immo Huneke.