mvn:effective-pom claims my project uses
<plugin>
<artifactId>maven-release-plugin</artifactId>
<version>2.3.2</version>
</plugin>
but nowhere in the project I have this defined. I tried grepping in the project dir and in the apache-maven dir for "maven-release" but it didn't find anything interesting.
It's defined in one of the parent POMs, or in the Super POM, which is an implicit parent of every other POM.
Here's how the Super POM looks like for Maven version 3.3.9: https://maven.apache.org/ref/3.3.9/maven-model-builder/super-pom.html
the relevant snippet:
<plugin>
<artifactId>maven-release-plugin</artifactId>
<version>2.3.2</version>
</plugin>
If the version is not defined in the or sections of your pom or parent pm. It will depend on the maven version you are using.