Feature request: Make POM file configurable

[hgschmie]

Currently, the plugin operates on the pom file of the current project. This is mostly useful but there are use cases where a build wants to modify/flatten a pom file from another project. In this case, it would be great to specify the pom file e.g. with

<configuration>
    <pomFile>../../../some-other-project/pom.xml</pomFile>
...
</configuration>

and now the flattened pom file etc. is generated from that pom file. Currently, the plugin relies on the ${project} model that is passed in by maven and even though it reads the file directly, it mixes information from the maven project into the output.

If a pom file is specified, the plugin should build a new project and use this (instead of the main pom file).

(what is my use case):

I have a project with a large number of maven modules that I want to integration test using JPMS. The easiest way to do this is:

• in an integration test setup job:
• find the pom file for this maven module (it is at ../../../pom.xml :-) )
• replace the artifactId foo with foo-it-parent, replace the packaging with pom.
• strip the build section from the pom.
• write the pom to a new file
• install this file in the integration test repo as groupId:foo-it-parent:pom

use an integration test pom like this:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>groupId</groupId>
        <artifactId>foo-it-parent</artifactId>
        <version>@project.version@</version>
    </parent>

    <groupId>org.jdbi.it</groupId>
    <artifactId>test-module</artifactId>

    <dependencies>
        <dependency>
            <groupId>groupId</groupId>
            <artifactId>foo</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>groupId</groupId>
            <artifactId>foo</artifactId>
            <classifier>tests</classifier>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <configuration>
                    <dependenciesToScan>
                        <dependency>groupId:foo:*:*:tests</dependency>
                    </dependenciesToScan>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

This works surprisingly well and the flatten plugin is 90% of the way there (with the patches that I just sent), except that I can not load another pom file but the project file itself:

    <build>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>flatten-maven-plugin</artifactId>
                <version>1.5.1-SNAPSHOT</version>
                <configuration>
                    <pomFile>../../../pom.xml</pomFile>
                    <flattenedPomFilename>${project.build.directory}/it-parent-pom.xml</flattenedPomFilename>
                    <updatePomFile>false</updatePomFile>
                    <defaultOperation>keep</defaultOperation>
                    <pomElements combine.self="override">
                        <packaging>replace</packaging>
                        <artifactId>replace</artifactId>
                        <build>remove</build>
                    </pomElements>
                    <replacementValues>
                        <packaging>pom</packaging>
                        <artifactId>@project.artifactId@-it-parent</artifactId>
                    </replacementValues>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-install-plugin</artifactId>
                <configuration>
                    <file>${project.build.directory}/it-parent-pom.xml</file>
                    <pomFile>${project.build.directory}/it-parent-pom.xml</pomFile>
                </configuration>
            </plugin>
        </plugins>
    </build>