private void updateRelativeOutputLocation(ProtoModule m)
    {
        String originalOutput = m.getOutput();
        String[] outputList = CompilerMain.COMMA.split(originalOutput);
        List<String> result = new ArrayList<String>();
        for (String output : outputList)
        {
            output = output.trim();
            boolean standardOutput = CompilerMain.isAvailableOutput(output);
            File basedir = baseDir.getAbsoluteFile();
            File currentDir = new File(".").getAbsoluteFile();
            if (!standardOutput)
            {
                // custom stg
                try
                {
                    File absolutePath = new File(output);
                    if (!absolutePath.exists())
                    {
                        File relativePath = new File(baseDir, output);
                        if (relativePath.exists())
                        {
                            // set full path to the stg
                            output = relativePath.getCanonicalPath();
                        }
                    }
                }
                catch (Exception e)
                {
                    getLog().debug("Can not determine full path for output=" + output, e);
                }
            }
            result.add(output);
        }
        String updatedOutput = Joiner.on(',').join(result);
        m.setOutput(updatedOutput);
    }
Plugin properties that are passed to the compiler

@since 1.3.1
protostuff-maven-plugin/src/main/java/io/protostuff/mojo/ProtoCompilerMojo.java