Calling foreach in maven-antrun-plugin

Question

I'm trying to set up maven to execute the LESS CSS preprocessor on a directory in my web project. The basic flow is:

1. Maven calls maven-antrun-plugin.
2. Ant-contrib <foreach/> loops through a directory and finds all the .less files and calls a target.
3. The target executes Rhino, which executes LESS which converts the file.

To do this, I have the following XML:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-antrun-plugin</artifactId>
            <version>1.7</version>
            <executions>
                <execution>
                    <phase>compile</phase>
                    <configuration>
                        <target name="processLessFile">
                            <!-- ... -->
                        </target>
                        <target name="main">
                            <taskdef resource="net/sf/antcontrib/antcontrib.properties" classpathref="maven.plugin.classpath"/>
                            <property name="css.dir" location="src/main/webapp/css"/>
                            <foreach param="file" target="processLessFile">
                                <fileset dir="${css.dir}">
                                    <filename name="**/*.less" />
                                </fileset>
                            </foreach>
                        </target>
                    </configuration>
                    <goals>
                        <goal>run</goal>
                    </goals>
                </execution>
            </executions>
            <dependencies>
                <dependency>
                    <groupId>ant</groupId>
                    <artifactId>ant-contrib</artifactId>
                    <version>1.0b2</version>
                </dependency>
            </dependencies>
        </plugin>

The problem I'm encountering is that the "main" target starts to execute but then fails in <foreach>:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-antrun-plugin:1.7:run (default) on project model-web-project: An Ant BuildException has occured: The following error occurred while executing this line:
[ERROR] /Users/.../pom.xml:4: Unexpected element "{http://maven.apache.org/POM/4.0.0}project" {antlib:org.apache.tools.ant}project
[ERROR] around Ant part ...<foreach param="file" target="processLessFile">... @ 6:50 in /Users/.../target/antrun/build-main.xml
[ERROR] -> [Help 1]

It appears that something in Ant is causing it to try read the POM file, possibly looking for the target. I see that both targets were generated into files target/antrun/build-main.xml and target/antrun/build-processLessFile.xml so that is the directory it should be looking in.

Answer 1

The ant plugin does not appear to support the declaration of more than one target section. You can check the generated ANT script to see what I'm talking about:

target/antrun/build-main.xml

Digging deeper the plug-in documentation states the following:

It is not the intention of this plugin to provide a means of polluting the POM, so it's encouraged to move all your Ant tasks to a build.xml file and just call it from the POM using Ant's task.

Harsh words, but the advice is sound. I'd recommend moving your ANT logic into a dedicated file and invoke it as follows:

        <plugin>
            <artifactId>maven-antrun-plugin</artifactId>
            <version>1.7</version>
            <executions>
                <execution>
                    <phase>compile</phase>
                    <configuration>
                        <target>
                            <ant antfile="${basedir}/src/main/ant/build.xml"/>
                        </target>
                    </configuration>
                    <goals>
                        <goal>run</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>