GH-4107: jena-bom altered to include jena artifacts using flatten-maven-plugin

[Aklakan]

GitHub issue resolved #4107

Pull request Description: This proposal adds flatten-maven-plugin to jena-bom in order to produce a parent-free "jena-only" pom.

I think this should solve the reported issue that jena-bom overrides versions from a parent pom.

Minimal downstream project pom:

<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

    <groupId>org.example.jena</groupId>
    <artifactId>jena-bom-test</artifactId>
    <packaging>jar</packaging>

    <properties>
      <jena.version>6.3.0-SNAPSHOT</jena.version>
    </properties>

    <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>4.1.0</version>
    </parent>

    <dependencyManagement>
      <dependencies>
        <dependency>
          <groupId>org.apache.jena</groupId>
          <artifactId>jena-bom</artifactId>
          <version>${jena.version}</version>
          <type>pom</type>
          <scope>import</scope>
        </dependency>
     </dependencies>
  </dependencyManagement>

</project>

Creating the effective pom with and without the jena dependency commented out, and then creating a diff shows that the only difference is the jena deps. This means that all non-jena dependency versions are taken from spring-boot-starter-parent, and adding jena-bom does not alter any versions.

mvn help:effective-pom > without-jena.txt # jena dep commented out
mvn help:effective-pom > with-jena.txt
diff without-jena.txt with-jena.txt

+       <groupId>org.apache.jena</groupId>
+         <artifactId>apache-jena-libs</artifactId>
+         <version>6.3.0-SNAPSHOT</version>
+         <type>pom</type>
+       </dependency>
+       <dependency>
+         <groupId>org.apache.jena</groupId>
+         <artifactId>jena-base</artifactId>
+         <version>6.3.0-SNAPSHOT</version>
+       </dependency>
+       <dependency>
+         <groupId>org.apache.jena</groupId>
+         <artifactId>jena-core</artifactId>
+         <version>6.3.0-SNAPSHOT</version>
+       </dependency>

---

• [ ] Tests are included.
• [ ] Documentation change and updates are provided for the Apache Jena website
• Commits have been squashed to remove intermediate development commit messages.
• Key commit messages start with the issue number (GH-xxxx)

By submitting this pull request, I acknowledge that I am making a contribution to the Apache Software Foundation under the terms and conditions of the Contributor's Agreement.

---

See the Apache Jena "Contributing" guide.

[afs]

My understand is that the issue is BOM-related.

apache-jena-libs isn't a BOM - it does not have a <dependencyManagement> section.

It's also been around a very long time!

[Aklakan]

Right, I removed the flatten plugin from apache-jena-libs.

[afs]

Thanks.

As I understand it, a regular <dependence> on an artifact does not pull in the artifacts parent dependency management, only the recursive dependency tree.

Eclipse Jetty uses flatten-maven-plugin. Some other projects I looked at do not take any special actions for BOMs.

[Aklakan]

According to the spring-boot-starter-parent documentation this is a legit way to kick start a spring boot project. I wasn't aware of this approach of using their parent pom (and the doc also mentions that there may be reasons to avoid it) - but getting all the versions of a spring/spring-boot based app right is frequently a pain - and if this flattened pom helps with it, then all the better.

[afs]

Let's put this into the codebase.

I can't recreate a problem using apache-jena-libs on its own, either as a direct <dependency> or in <dependencyMangement>. Only if jena-bom is present.

[afs]

I've removed the "GitHub issue resolved" - that's pending clarification of the use of apache-jena-libs on it's own.

[afs]

The .flattened-pom.xml is not great. It includes the parent <properties>.

The best I have come up with so far is remove some POM elements (by looking at the source code for flatten-maven-plugin). For example, this is a quite heavy trimming:

        <configuration>
          <flattenMode>bom</flattenMode>
          <pomElements>
            <properties>remove</properties>
            <distributionManagement>remove</distributionManagement>
            <mailingLists>remove</mailingLists>
            <scm>remove</scm>
            <issueManagement>remove</issueManagement>
          </pomElements>
        </configuration>

(We should separately tidy up the top Jena POM.)