Parent POM is not flattened when deployed to Nexus - maven

Question

I have a multi-module Maven project where the project version is set via the revision variable.
<groupId>pricing</groupId>
<artifactId>pricing-backend-pom</artifactId>
<version>${revision}</version>
<packaging>pom</packaging>
<properties>
<revision>3.0.7</revision>
</properties>
<modules>
<module>pricing-backend-war</module>
<module>pricing-backend-model</module>
<module>pricing-backend-client</module>
</modules>
<build>
<plugins>
<!-- flatten before deploy. removes $revision -->
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>flatten-maven-plugin</artifactId>
<version>1.2.7</version>
<configuration>
</configuration>
<executions>
<!-- enable flattening -->
<execution>
<id>flatten</id>
<phase>process-resources</phase>
<goals>
<goal>flatten</goal>
</goals>
</execution>
<!-- ensure proper cleanup -->
<execution>
<id>flatten.clean</id>
<phase>clean</phase>
<goals>
<goal>clean</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
During the Gitlab build, the project is deployed to a Nexus repository. Each module and the parent appear in Nexus but only the modules appear to be flattened. The module POMs each contain <version>3.0.7</version> but the parent POM still contains <version>${revision}</version>.
I find it difficult to understand why the parent is deployed differently to the modules. I have checked the build logs but cannot see any indication that the parent is handled in a different way.
The parent POM taken from Nexus:
<groupId>pricing</groupId>
<artifactId>pricing-backend-pom</artifactId>
<version>${revision}</version>
<packaging>pom</packaging>
<properties>
<revision>3.0.7</revision>
...
A module POM:
<groupId>pricing</groupId>
<artifactId>pricing-backend-client</artifactId>
<version>3.0.7</version>
<dependencies>
...
The build applies the required version:
$ echo New version= ${MAVEN_VERSION}
New version= -Drevision=3.0.7-SNAPSHOT
$ mvn $MAVEN_CLI_OPTS ${MAVEN_VERSION} deploy -DskipTests

Answer 1

The pom file to be installed can be explicitly set:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-install-plugin</artifactId>
<version>2.4</version>
<configuration>
<pomFile>.flattened-pom.xml</pomFile>
</configuration>
</plugin>
Above, flatten-maven-plugin has been previously invoked to produce .flattened-pom.xml

Answer 2

If you do a test by adding -Drevision=<someVersion> to the command line, does that produce correct results in Nexus?
I suspect it will.
Properties are interpolated very early in the process. When the command first runs, ${revision} is undefined, so Maven leaves it as-is. The flatten then calculates ${revision}, but that only applies from the time the plugin runs and later.
You can try researching "late binding" properties (they start with '#' instead of '$') but I'm not sure if those work in top level fields like the GAV coords.