ANTLR4 doesn't work with custom configuration in Maven - eclipse

Question

I always used succesfully ANTLR4 combined with Maven inside Eclipse.
I just want to change the default directory where I store my grammar, since I do not like the standard path which is src/main/antlr4. The issue of this path is the creation of a new java package, that I really do not want.
So I simply decided to create another directory inside my project named grammar which contains another directory called imports. I did this following simply the website guidelines.
Despite this, when I change the grammar it doesn't generate automatically the new sources, even with the maven commands!
So, this is my configuration file pom.xml:
<!-- ANTLR4 -->
<plugin>
<groupId>org.antlr</groupId>
<artifactId>antlr4-maven-plugin</artifactId>
<version>4.5.3</version>
<executions>
<execution>
<configuration>
<goals>
<goal>antlr4</goal>
</goals>
<libDirectory>grammar/imports</libDirectory>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
As you can see, the target directory is empty. Before this change, there was a generated-sources directory inside with all the .java files.
So, where is the error?

Answer 1

The correct way is:
<!-- ANTLR4 -->
<plugin>
<groupId>org.antlr</groupId>
<artifactId>antlr4-maven-plugin</artifactId>
<version>4.5.3</version>
<executions>
<execution>
<goals>
<goal>antlr4</goal>
</goals>
<configuration>
<libDirectory>grammar/imports</libDirectory>
</configuration>
</execution>
</executions>
</plugin>
The <configuration> tag must be at same level than <goals> tag, inside <execution> tag, according to Maven documentation: https://maven.apache.org/guides/mini/guide-configuring-plugins.html#Using_the_executions_Tag and https://maven.apache.org/guides/mini/guide-default-execution-ids.html
In fact, the documentation in ANTLR4 Maven plugin is wrong:
http://www.antlr.org/api/maven-plugin/latest/examples/libraries.html