I have a property defined like this:
${project.parent.basedir}
Just an update to Sean's answer, I have had to make some minor adjustments in order to adapt it to the latest groovy maven plugin version:
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>groovy-maven-plugin</artifactId>
<dependencies>
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy-all</artifactId>
<version>2.0.1</version>
</dependency>
</dependencies>
<executions>
<execution>
<id>setproperty</id>
<phase>validate</phase>
<goals>
<goal>execute</goal>
</goals>
<configuration>
<source>
project.properties['basedir']=project.parent.basedir.absolutePath.replace('\\','/');
</source>
</configuration>
</execution>
</executions>
</plugin>
I don't think there is a non-programmatical way to do that. So I suggest a groovy one-liner with the Maven GMaven plugin (GMaven is usually the simplest way to embed programmatic code into a pom):
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>gmaven-plugin</artifactId>
<executions>
<execution>
<id>setproperty</id>
<phase>validate</phase>
<goals>
<goal>execute</goal>
</goals>
<configuration>
<source>
pom.properties['main.basedir']=project.parent.basedir.absolutePath.replace('\\','/');
</source>
</configuration>
</execution>
</executions>
</plugin>