Unable to fetch dependency version in <profile> when the dependency is managed by <dependencyManagement>

[stephaniewang526]

We're trying to implement flatten plugin in GCP cloud clients and we ran into the following issue where the dependency version in <profile> is not correctly added when the dependency is managed by <dependencyManagement>. Here's a common scenario found in numerous GCP clients:

In the parent pom (below example taken from google-cloud-pubsub-parent):

 <properties>
   <javax.annotations.version>1.3.2</javax.annotations.version>
 </properties>
 
 <dependencyManagement>
   <dependencies>
     <dependency>
       <groupId>javax.annotation</groupId>
       <artifactId>javax.annotation-api</artifactId>
       <version>${javax.annotations.version}</version>
     </dependency>
   </dependencies>
 </dependencyManagement>

In the cloud client pom (below example taken from google-cloud-pubsub)

  <profiles>
    <profile>
      <id>java9</id>
      <activation>
        <jdk>[9,)</jdk>
      </activation>
      <dependencies>
        <dependency>
          <groupId>javax.annotation</groupId>
          <artifactId>javax.annotation-api</artifactId>
        </dependency>
      </dependencies>
    </profile>
  </profiles>

Adding flatten plugin to the cloud client, in this instance, results in an invalid pom file since <version> for javax-annotaions-api will be missing.

Does anyone know if there's an existing configuration change that could resolve this issue? Or if this should be a new fix/feature?

We're currently addressing this issue by manually adding <version> in <profile> as such:

  <profiles>
    <profile>
      <id>java9</id>
      <activation>
        <jdk>[9,)</jdk>
      </activation>
      <dependencies>
        <dependency>
          <groupId>javax.annotation</groupId>
          <artifactId>javax.annotation-api</artifactId>
          **<version>${javax.annotations.version}</version>**
        </dependency>
      </dependencies>
    </profile>
  </profiles>

However, this is not ideal since it is manual there fore we cannot go GA with the current limitation -- please opine.

Thank you.
cc @saturnism