Guide for plugin maintainers: How to update plugins to Maven 4

[Bukama]

Improvement proposal

On Javaland 2025 conference the question about how to update plugins to Maven 4 as a plugin maintainer / where to find an guide for that raised multiple times (in the Maven panel, during the talk of Karl Heinz and me, in personal chats) and we had to admit that there is none (yet).
We need to change that.

Edit:
Topics from comments we should mention:

• maven 4 will support well maintained Maven 3 plugins
• plugin maintainer will have choice to create a Maven 4 specific release of their plugin, that won't work in Maven 3
  ** They need to decide if and how long they want to do this.

[hboutemy]

question: is it from a plugin user perspective? or from a plugin maintainer perspective?

I'd personally rephrase: we need to clarify that Maven 4 has a compatibility layer for Maven 3 plugins: in general, Maven 3 plugin can run both in Maven 3 and Maven 4.
I vaguely heard that there are edge cases: having a list of known plugins with issues would be useful

= clarify the situation from a plugin user's perspective first

then extend to plugin maintainer perspective:
as a plugin maintainer, you should check that your Maven 3 plugin works as expected in Maven 4: if not, there are proabably fixes that can be done.

then in the future, plugin maintainer will have choice to create a Maven 4 specific release of their plugin, that won't work in Maven 3

the tricky question being: maintain 2 branches in parallel? for how much time?

[hboutemy]

how do you see this issue vs #729 ?

[Bukama]

question: is it from a plugin user perspective? or from a plugin maintainer perspective?

This topic here aims for plugin maintainers, not for users.
#729 aims for users. For that (see my working file at https://github.com/Bukama/maven-site/blob/i729_maven4migguide/content/markdown/guides/mini/guide-migration-to-mvn4.md ) I currently wrote

Note: While Maven 4.0.0 aims to support all Maven 3.9 compatible plugins, this can not be guaranteed for custom plugins which use outdated plugin API methods.

I chose this wording, because I wanted to make clear that a well maintained plugin (not only the official ones) will work, but we can not promise it for custom ones.

then in the future, plugin maintainer will have choice to create a Maven 4 specific release of their plugin, that won't work in Maven 3
the tricky question being: maintain 2 branches in parallel? for how much time?

I agree that we should mention it in the guide and also that it will take time until most users have switched, but we should also add that each developer needs to decide that for his owns. It's their time and effort they put into it.