gnodet commented on issue #12304:
URL: https://github.com/apache/maven/issues/12304#issuecomment-4738567506
## Root Cause Analysis
### The POM pattern
The parent POM (`activemq-protobuf-pom`) declares `<dependencyManagement>`
using `${version}`:
```xml
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.apache.activemq.protobuf</groupId>
<artifactId>activemq-protobuf</artifactId>
<version>${version}</version>
</dependency>
</dependencies>
</dependencyManagement>
```
The child module `activemq-protobuf-test` then declares a dependency without
`<version>`, relying on the parent's `<dependencyManagement>` to provide it:
```xml
<dependency>
<groupId>org.apache.activemq.protobuf</groupId>
<artifactId>activemq-protobuf</artifactId>
<!-- no version — expects dependencyManagement to provide it -->
</dependency>
```
### Why Maven 3 accepted this
In Maven 3, `${version}` was a valid (though deprecated) alias for
`${project.version}`. The `<dependencyManagement>` version resolved to
`1.2-SNAPSHOT`, and the child's dependency inherited that version.
### Why Maven 4 rejects it
Maven 4 no longer supports the bare `${version}` property as a built-in
alias for `${project.version}`. When the model validator processes the child's
dependency, it tries to resolve the version from `<dependencyManagement>`, but
the managed version is the literal unresolved string `${version}` (which
evaluates to null/empty). So the dependency effectively has no version.
The error message says the version "is missing" because after property
interpolation, `${version}` resolves to nothing — the dependency management
entry provides no usable version.
### Verdict: **Project bug**, not a Maven 4 regression
The project uses the deprecated `${version}` shorthand instead of
`${project.version}`. This was a bad practice even in Maven 3 (it was
deprecated since Maven 2.x). Maven 4 correctly drops support for this
deprecated alias.
### Fix (project-side)
Replace `${version}` with `${project.version}` in the parent POM's
`<dependencyManagement>`:
```xml
<version>${project.version}</version>
```
Or better yet, since this is a simple reactor with all modules sharing the
same version, just use `${project.version}` everywhere.
_Claude Code on behalf of Guillaume Nodet_
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