maven core extension to manage dependencies in the plugins section

This maven extension makes dependency management affect dependencies in the plugin section. There has been an issue about this for a long time, that only recently was closed - not to be fixed.

It turns out however, that implementing a maven extension doing exactly this is pretty straightforward.

use case

Assume a pom.xml with the following content:

<project>
 ...
 
 <properties>
  <postgres.version>42.7.3</postgres.version>
 </properties>
 
 <dependencies>
  <dependency> <!-- (2) -->
   <groupId>org.postgresql</groupId>
   <artifactId>postgresql</artifactId>
   <version>${postgres.version}</version>
  </dependency>
 </dependencies>
 
 <build>
  <plugins>
   <plugin>
    <groupId>org.liquibase</groupId>
    <artifactId>liquibase-maven-plugin</artifactId>
    <executions>
     ... <!-- create a database schemas tables, views etc. -->
    </executions>
    <dependencies>
     <dependency> <!-- (1) -->
      <groupId>org.postgresql</groupId>
      <artifactId>postgresql</artifactId>
      <version>${postgres.version}</version>
     </dependency>
    </dependencies>
   </plugin>
   <plugin>
    <groupId>org.jooq</groupId>
    <artifactId>jooq-codegen-maven</artifactId>
    <executions>
     ... <!-- create classes from the schema created -->
    </executions>
    <dependencies>
     <dependency> <!-- (1) -->
      <groupId>org.postgresql</groupId>
      <artifactId>postgresql</artifactId>
      <version>${postgres.version}</version>
     </dependency>
    </dependencies>
   </plugin>
  </plugins>
 </build>
</project>

Of course one wants to make sure that both plugins use the jdbc client in the same version (1). Which should be the same as the jdbc client the application itself uses (2).

In this example this is achieved using a property, but what if one needs to share this version in a way where properties cannot be used. For example, what if the jdbc drivers version is managed in the dependency management of an imported pom:

<project>
 ...

 <dependencyManagement>
  <dependencies>
   <dependency> <!-- (1) -->
    <groupId>my.organisation</groupId>
    <artifactId>organisation-bom</artifactId>
    <version>1.0.0</version>
    <type>bom</type>
    <scope>import</scope>
   </dependency>
  </dependencies>
 </dependencyManagement>

 <dependencies>
  <dependency> <!-- (2) -->
   <groupId>org.postgresql</groupId>
   <artifactId>postgresql</artifactId>
  </dependency>
 </dependencies>
 
 <build>
  <plugins>
   <plugin>
    <groupId>org.liquibase</groupId>
    <artifactId>liquibase-maven-plugin</artifactId>
    <executions>
     ... <!-- create a database schemas tables, views etc. -->
    </executions>
    <dependencies>
     <dependency> <!-- (3) -->
      <groupId>org.postgresql</groupId>
      <artifactId>postgresql</artifactId>
     </dependency>
    </dependencies>
   </plugin>
   <plugin>
    <groupId>org.jooq</groupId>
    <artifactId>jooq-codegen-maven</artifactId>
    <executions>
     ... <!-- create classes from the schema created -->
    </executions>
    <dependencies>
     <dependency> <!-- (3) -->
      <groupId>org.postgresql</groupId>
      <artifactId>postgresql</artifactId>
     </dependency>
    </dependencies>
   </plugin>
  </plugins>
 </build>
</project>

Now, the version is managed in a bill of materials which is imported (1), so that the version of the applications dependency may be omitted (2), the versions of the plugins dependencies (3), however are now unspecified. This would make maven fail the build while parsing the project. One could - of course - specify a property again, but it would not be guarantied that it is the same that is used in the bill of materials pom.

This extension fixes that. It does inject itself in mavens process of reading a project and adds the correct managed dependency versions to dependencies declared in the plugin section that have no versions specified.

usage

To activate the extension simply add a file .mvn/extensions.xml to the root of your project with the following content:

<extensions xmlns="http://maven.apache.org/EXTENSIONS/1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://maven.apache.org/EXTENSIONS/1.0.0 http://maven.apache.org/xsd/core-extensions-1.0.0.xsd">

    <extension>
        <groupId>de.eitco.cicd</groupId>
        <artifactId>manage-plugin-dependencies-maven-extension</artifactId>
        <version>0.0.2</version>
    </extension>

</extensions>

📘 There are other ways to activate core extensions.

Adding this file will enable maven to read (and execute) the example above - using the postgres clients version that is managed in the imported pom.

📘 The integration tests provide some example usages

⚠️ Note that, when importing a bill-of-materials pom.xml from the same build reactor, you need to make sure that the imported bill-of-materials is ordered before the importing pom.xml in the build reactor.

eitco/manage-plugin-dependencies-maven-extension

maven core extension to manage dependencies in the plugins section

use case

usage