annotationProcessorPaths "leak" version from parent to child pom

[svpace]

Affected version

3.14.0

Bug description

Not quite sure if this should be reported here or in the Maven Jira. But as it seems to be related to #180 reporting here first. Please let me know if I should report there.

When a parent POM or pluginManagement defines a set of annotation processors with versions, and the child POM or plugins defines another set of processors without versions (relying on dependencyManagement), the version is inherited from the processor defined at the corresponding position in the list instead of the dependency management.

The following POM shows the issue:

<?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>com.example</groupId>
	<artifactId>maven-compiler-plugin-issue</artifactId>
	<version>1.0.0-SNAPSHOT</version>

	<properties>
		<maven.compiler.source>17</maven.compiler.source>
		<maven.compiler.target>17</maven.compiler.target>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.mapstruct</groupId>
				<artifactId>mapstruct-processor</artifactId>
				<version>1.6.3</version>
			</dependency>
		</dependencies>
	</dependencyManagement>
	<build>
		<pluginManagement>
			<plugins>
				<plugin>
					<groupId>org.apache.maven.plugins</groupId>
					<artifactId>maven-compiler-plugin</artifactId>
					<version>3.14.0</version>
					<configuration>
						<annotationProcessorPaths>
							<path>
								<groupId>org.projectlombok</groupId>
								<artifactId>lombok</artifactId>
								<version>1.18.38</version>
							</path>
						</annotationProcessorPaths>
					</configuration>
				</plugin>
			</plugins>
		</pluginManagement>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<configuration>
					<annotationProcessorPaths>
						<path>
							<groupId>org.mapstruct</groupId>
							<artifactId>mapstruct-processor</artifactId>
						</path>
					</annotationProcessorPaths>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

The resulting effective POM end up like this:

    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.14.0</version>
            <executions>
                <execution>
                    <id>default-compile</id>
                    <phase>compile</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                    <configuration>
                        <annotationProcessorPaths>
                            <path>
                                <groupId>org.mapstruct</groupId>
                                <artifactId>mapstruct-processor</artifactId>
                                <version>1.18.38</version>
                            </path>
                        </annotationProcessorPaths>
                    </configuration>
                </execution>

If I omit the groupId from plugins it also inherits it from parent. It feels like Maven's list and non-list merge behavior gets mixed up and it replaces the list but fills in any missing fields.

I am pretty sure that a combine.children or combine.self may workaround this, but the current way fells wrong.

Let me know if you need any more infos.

[frommeyerc]

I stumbled over this as well. Here is also a repository with a small setup to reproduce the issue.