[MNG-7683] Plugin configuration is merged incorrectly

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.0.0-alpha-3, 4.0.x-candidate
• Fix Version/s: 4.0.0-alpha-5, 4.0.0
• Component/s: Inheritance and Interpolation
• Assignee: Guillaume Nodet
• Reporter: Alexey Venderov
• Created: 06/Feb/23 15:46
• Updated: 20/Oct/23 07:57
• Resolved: 02/Mar/23 05:30

Description

Hi,

As was mentioned by my colleague here there is a regression in the plugin configuration merging logic introduced in version 4.0.0-alpha-3. The original assumption was that the issue is caused by this change in the plexus-utils library. I wrote a small reproducer test: https://github.com/c00ler/plexus-utils-merge-xml-reproducer/blob/main/src/test/java/com/github/avenderov/ReproducerTest.java and run it with the plexus-utils versions before and after the change. Test passes with both versions. So it's not the change in the plexus-utils.

After that, I checked Maven sources and found out that Maven 4 doesn't use Xpp3Dom and associated utilities from the plexus-utils anymore, and has its own merging logic implemented here. The behavior of the configuration merging logic was correct (same as in maven 3.x) up until version 4.0.0-alpha-2 and then was changed in version 4.0.0-alpha-3.

Problem description.

We have the following foo-bar-plugin configuration in the parent pom:

<pluginManagement>
  <plugins>
    <plugin>
      <groupId>foo.bar</groupId>
      <artifactId>foo-bar-plugin</artifactId>
      <configuration>
        <plugins>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <bar>
              <value>foo</value>
            </bar>
          </plugin>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <foo>
              <properties>
                <property>
                  <name>prop1</name>
                  <value>value1</value>
                </property>
              </properties>
            </foo>
          </plugin>
        </plugins>
      </configuration>
    </plugin>
  </plugins>
</pluginManagement>

In the child pom, we want to make changes to the foo-bar-plugin configuration:

<pluginManagement>
<plugins>
  <plugin>
    <groupId>foo.bar</groupId>
    <artifactId>foo-bar-plugin</artifactId>
    <configuration>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-surefire-plugin</artifactId>
          <foo>
            <properties combine.children="append">
              <property>
                <name>prop2</name>
                <value>value2</value>
              </property>
            </properties>
          </foo>
        </plugin>
      </plugins>
    </configuration>
  </plugin>
</plugins>
</pluginManagement>

The expected effective pom after merging (maven-compiler-plugin configuration is persisted, maven-surefire-plugin configuration is merged):

<pluginManagement>
<plugins>
  <plugin>
    <groupId>foo.bar</groupId>
    <artifactId>foo-bar-plugin</artifactId>
    <configuration>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <bar>
            <value>foo</value>
          </bar>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-surefire-plugin</artifactId>
          <foo>
            <properties combine.children="append">
              <property>
                <name>prop1</name>
                <value>value1</value>
              </property>
              <property>
                <name>prop2</name>
                <value>value2</value>
              </property>
            </properties>
          </foo>
        </plugin>
      </plugins>
    </configuration>
  </plugin>
</plugins>
</pluginManagement>

Instead Maven 4.0.0-alpha-3 produces the following result:

<pluginManagement>
<plugins>
  <plugin>
    <groupId>foo.bar</groupId>
    <artifactId>foo-bar-plugin</artifactId>
    <configuration>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <foo>
            <properties>
              <property>
                <name>prop1</name>
                <value>value1</value>
              </property>
            </properties>
          </foo>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-surefire-plugin</artifactId>
          <foo>
            <properties combine.children="append">
              <property>
                <name>prop2</name>
                <value>value2</value>
              </property>
            </properties>
          </foo>
        </plugin>
      </plugins>
    </configuration>
  </plugin>
</plugins>
</pluginManagement>

Steps to reproduce.

We have a repository with the reproducer: https://github.com/c00ler/maven-merge-xml-reproducer:

• the main branch produces a diff between maven 3.8.7 and maven 4.0.0-alpha-3. It shows the described example;
• the alpha2-alpha3 branch produces a diff between maven 4.0.0-alpha-2 and maven 4.0.0-alpha-3 that shows the change in the behavior;

After diving a little bit deeper I found out that the problem is actually caused by the fact that we have two nested plugins configurations, maven-compiler-plugin and maven-surefire-plugin, that need to be merged and it causes the problem. As can be seen from the example the configuration from the maven-surefire-plugin is getting merged to the maven-compiler-plugin and overrides its configuration. In the branch single-plugin-merge I've left only maven-surefire-plugin and then the configuration is correctly merged even in maven 4.0.0-alpha-3.

Issue Links

• is related to: MNG-7709 plexus-utils upgrade changes the way configuration is parsed
• links to: GitHub Pull Request #986