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Clarify consumer POM behavior regarding dependency scopes #1606

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23 changes: 14 additions & 9 deletions content/markdown/whatsnewinmaven4.md
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Expand Up @@ -67,22 +67,24 @@ article [Introduction to Maven Toolchains][8] by Maven maintainer Maarten Mulder

### Consumer POM

Maven 4 can generate a stripped down consumer POM that removes build information not needed by consumers, and deploys this
to the remote repository.
It does not deploy the `pom.xml` used to build the project.
Maven 4 generates a consumer POM that removes build information not needed by consumers (such as plugin configuration
and properties), and deploys this to the remote repository instead of the full `pom.xml` used to build the project.

The consumer POM is a **flattened** version of the build POM, meaning:
By default, the consumer POM preserves all dependencies from the build POM, including `provided` scope dependencies.
Only build-time-only elements are stripped.

* It contains no parent POM references (all inherited elements are resolved and included directly)
Optionally, flattening can be enabled to produce a fully self-contained consumer POM. When flattening is enabled:

* Parent POM references are resolved (all inherited elements are included directly)
* BOM imports are flattened into the dependency list
* Only transitive dependencies are kept (compile and runtime scopes)
* Only transitive dependencies are kept (`compile` and `runtime` scopes); non-transitive scopes (`provided`, `test`, `system`) are stripped
* Managed dependencies are kept only if they are actually used by the project

This flattening ensures that consumers of your artifact have all the information they need without requiring access to
parent POMs or understanding the internal structure of your multi-project build.
When flattening is enabled, the full build POM (with all dependency scopes) is still published alongside the consumer
POM with a `build` classifier.

The flatten feature is disabled by default to avoid unexpected behavior and better control of listing (transitive) dependencies in the consumer POM.
To publish a flattened consumer POM instead of the full build POM, the user property `maven.consumer.pom.flatten` must be set to `true`.
To publish a flattened consumer POM, set the user property `maven.consumer.pom.flatten` to `true`.
User properties can be controlled using `${session.rootDirectory}/.mvn/maven-user.properties` for a per-reactor configuration.

### Model version 4.1.0
Expand Down Expand Up @@ -171,6 +173,9 @@ The following table shows a rough comparison of which content is available in wh
contain build information, for example plugin configuration!
* Some of the build-related content which is (as of now) still available in the consumer POM might be available only in
the build POM in the future.
* The "3rd party dependency information" row refers to the default (non-flattened) consumer POM, which preserves all
dependency scopes. When flattening is enabled (`maven.consumer.pom.flatten=true`), only `compile` and `runtime` scope
dependencies are included in the consumer POM.

| Content | Build POM | Consumer POM |
|:-------------------------------------------|:---------:|:------------:|
Expand Down