Update What's new in Maven 4 before release

[Bukama]

Improvement proposal

Release gets closer (see Mailing list) so we want to double check the "What's new in Maven 4?" article if everything is covered.

Points:

• add / highlight the Maven Upgrade Tool
• wrt CI-friendly versions, it's worth nothing that the name of the properties aren't limited anymore, however, they have to be defined at build time
• for automatic versioning, it could be worth mentioning that the parent itself can be inferred by simply using <parent/>, in which case, the pom from the parent directory will be used
• in consumer POM, we removed the non transitive dependencies, so mainly the test dependencies (given they're not transitive, their presence in the consumer pom is useless)
• Upgrade tool: update deprecated phases (see Add phase upgrade support for Maven 4.1.0 model upgrades maven#11215 )

edit: the points above a contained in #1429 and #1430

[desruisseaux]

Maybe the following?

New artefact types

Maven 4 introduces new types of artifacts. The types listed below can be used in <dependency> declarations of JAR files. The jar type existed in Maven 3 and is still the default in Maven 4. The other types are new:

• jar: for a JAR file that can be placed either on the class path or on the module path.
• classpath-jar: for a JAR file to unconditionally place on the class path.
• modular-jar: for a JAR file to unconditionally place on the module path.
• processor: for a JAR file that can be placed either on the annotation processor class path or module path.
• classpath-processor: for a JAR file to unconditionally place on the annotation processor class path.
• modular-processor: for a JAR file to unconditionally place on the annotation processor module path.

The jar and processor types use heuristic rules for deciding where to place the JAR file, but the result is not always what the developer wants. The types with classpath- or modular- prefix give control to the developer.

Limitation: as of October 2025, only Maven Compiler Plugin 4.0.0-beta-3 complies with the new types. Other plugins will be updated progressively.

New source declarations

Maven 4 introduces a new way to declare the root directories of source code. Instead of:

<project>
  <build>
    <sourceDirectory>my-custom-dir/foo</sourceDirectory>
    <testSourceDirectory>my-custom-dir/bar</testSourceDirectory>
  </build>
</project>

The source directories should be declared as below:

<project>
  <build>
    <sources>
      <source>
        <scope>main</scope>
        <directory>my-custom-dir/foo</directory>
      </source>
      <source>
        <scope>test</scope>
        <directory>my-custom-dir/bar</directory>
      </source>
    </sources>
  </build>
</project>

The <source> element can be repeated, thus allowing multiple source directories without the need to resort to external plugins. It also provides a unified way to declare include/exclude filters, makes easier to setup projects targeting multi Java releases, and enables module source hierarchy. The documentation of the Maven Compiler Plugin gives some examples.

[Bukama]

Opened #1431 to add the <source> element. About the new types, please see my question in Slack, Martin.

[desruisseaux]

Regarding whether the new dependency types should be mentioned in the "whats new" article, I think that it depends on the audience. The new dependency types are provided by Maven core to all plugins. Therefore, for plugin developers, this service is available now and developers should consider using the new types. But for plugin users, only the compiler plugin uses this service at this time. The other plugins still need to be updated.

[Bukama]

Regarding whether the new dependency types should be mentioned in the "whats new" article, I think that it depends on the audience. The new dependency types are provided by Maven core to all plugins. Therefore, for plugin developers, this service is available now and developers should consider using the new types. But for plugin users, only the compiler plugin uses this service at this time. The other plugins still need to be updated.

The article is for every audience out there, including the whole range from "I knew the mvn command to do my build" up to "I know every Maven detail". This is/was not my concern. I was a bit worried about the compatibility of the new types, but you removed those :) So I created a PR (#1433) to add them.

[gnodet]

We need to update the page to take into account the fact that we disabled the flattening of the Consumer POM in rc-5.

[Bukama]

We need to update the page to take into account the fact that we disabled the flattening of the Consumer POM in rc-5.

Done and merged.