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https://issues.apache.org/jira/browse/MNGSITE-550?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17908525#comment-17908525
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ASF GitHub Bot commented on MNGSITE-550:
----------------------------------------
Bukama commented on code in PR #598:
URL: https://github.com/apache/maven-site/pull/598#discussion_r1898710847
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content/markdown/whatsnewinmaven4.md:
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+# What's New in Maven 4?
+
+Maven is over 20 years old and is one of the most used build tools in the Java
world.
+Throughout the years, one important rule has been maintaining the highest
backward compatibility possible, especially
+with its [POM-schema with Model version 4.0.0][2], used not only for the build
itself but also by consumers.
+This made Maven more than a tool; it became a whole ecosystem with many
dependencies on the POM, especially the Maven
+Central repository, other build tools, and IDEs.
+But this stable schema comes at a price - the lack of flexibility.
+
+> "With the Maven build schema preserved in amber, we can’t evolve much: we’ll
stay forever with Maven 3 minor releases,
+> unable to implement improvements that we imagine will require seriously
updating the POM schema…"
+> — <cite>[Hervé Boutemy (in Javaadvent 2021)][1]</cite>
+
+Maven 4 will prepare for changes which are impossible nowadays, like a
completely new build schema.
+
+Another pain point of Maven 3 is a codebase with a lot of deprecated,
convoluted, non-performant, and duplicated code
+which costs the volunteers who maintain Maven a lot of time.
+This not only means that the Maven codebase contains old Java code that can be
optimized nowadays but also old
+dependencies and poor API design of its own APIs, especially for Maven plugins.
+Therefore, Maven 4 will also be a maintenance release.
+
+This article presents and explains major changes brought by Maven 4, grouped
into several topics.
+
+## POM Changes
+
+### Build-POM and Consumer-POM
+
+As written in the introduction, Model version 4.0.0 is used not only for the
build but also by consumers of the
+artifact.
+However, several contents of the POM are only necessary for the build while
others, like the dependencies, are also
+needed by the consumer.
+Maven 4 will therefore differentiate between a "Build-POM" and a
"Consumer-POM".
+As the names suggest, the "Build-POM" will contain all information needed to
build the artifact, e.g., used plugins and
+their configuration, while the "Consumer-POM", which is created during the
Maven build, will not contain those.
+This POM will only keep what is really needed to use the artifact, e.g.,
dependency information.
+
+**Note**: See below for a comparison of the content of both POMs.
+
+### Model version 4.1.0
+
+With now having two types of POM, Maven 4 can already make additions to the
Build-POM as it will only be used by Maven (
+and of course IDEs).
+Therefore, with Maven 4, a new Model version 4.1.0 is introduced.
+This version introduces some new elements and attributes, while others are
marked as deprecated.
+To not break the ecosystem, this version is only available for the Build-POM,
while the Consumer-POM will still use
+version 4.0.0.
+This means Maven will generate the Consumer-POM during the build.
+
+**Note**: Maven 4 will of course continue to build your model version 4.0.0
project!
+There is no need to update your POMs to 4.1.0 as long as you don't want to
make use of the new features.
+But as with every software update - it's suggested to update them to 4.1.0,
e.g., to avoid problems when deprecated
+features are removed in future updates.
+
+### Modules are now subprojects
+
+From the early days of Maven 1 until today, all build information is stored in
the POM, short for "Project Object
+Model".
+Together with build folders and other files, the wording "Maven project" is
used.
+However, for projects containing multiple parts, e.g., an API and a client,
each of those parts was called a "module"
+and listed in the `<modules>` section of the POM, leading to the terms
"multi-module project".
+This wording introduced some inconsistency, especially as projects without any
`<modules>` section are often called "
+single-module".
+Since the introduction of the [Java Platform Module System][3] in Java 9, the
term "module" has raised additional
+confusion.
+
+Maven 4 gets rid of this by naming "modules" as what they are - subprojects.
+Model version 4.1.0 contains a new element `<subprojects>` analogous to the
now deprecated, but still usable, element
+`<modules>`.
+
+**Note**: It's suggested to use the terms `multi-project setup` and
`single-project setup` to differentiate between a
+Maven project with or without subprojects.
+
+### New packaging type: bom
+
+Maven 4 introduces a dedicated packaging type to provide a [Bill of Material
BOM][4] called "bom" to differentiate more
+precisely between "parent POMs" and dependency-managing BOMs.
+While the new type is only available with Model Version 4.1.0, the final
outcome is a full Maven 3 compatible (model
+4.0.0) POM file!
+For an example, see the link above or
+the [live coding by Maven maintainer Karl Heinz Marbaise at IntelliJ IDEA Conf
2024][5].
+
+**Note**: With Maven 4, it's also possible to exclude dependencies that are
declared by BOMs using the existing
+`<exclusions>` element.
+Also note that in Maven 4, importing BOMs with a classifier is now possible.
+Therefore, the Maven team suggests that project BOMs should be generated as
classified artifacts, using the
+`<bomClassifier>` element.
+This means that an imported BOM must **not** come from the same reactor as the
current build but be available outside
+the project before the build (in other words, "you should import only external
BOMs") or it may break your build (as
+shown in [MNG-8009][32]).
+That's why Maven 4.0 will show a warning if a BOM comes from the same reactor.
+In the future, this will most probably be changed to make the build fail.
+
+### Comparing Build-POM and Consumer-POM
+
+The following table shows a rough comparison of which content is available in
which POM type when using Maven 4.
+
+**Notes**:
+
+* The column "Consumer-POM" obviously does not apply to artifacts that are of
type "pom"!
Review Comment:
> That's not obvious to me
Explanation added (will be visible after next push)
> Information about "What's new in Maven 4?"
> ------------------------------------------
>
> Key: MNGSITE-550
> URL: https://issues.apache.org/jira/browse/MNGSITE-550
> Project: Maven Project Web Site
> Issue Type: Improvement
> Reporter: Matthias Bünger
> Priority: Major
>
> A comprehensive article/list of the important changes in Maven 4 is needed.
> ----
>
> Issue based on the slack message / thread, started by [~cstamas]
> {quote}
> More and more times we get questions like "and what is new in Maven4?". We
> have no document that distills the relevant changes. Could someone try to
> collect that in cwiki or somewhere?
> {quote}
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