为什么以及何时 Eclipse 将 Maven 依赖项放在 CLASSPATH 中而不是 MODULEPATH 中？

Question

I have a Java 11 project which defines a module-info.java and is compliant with JPMS - except that it requires unnamed modules from other developers that did not yet care about JPMS.

When I put the Maven dependencies in the module path, that is, in the .classpath of Eclipse I have

<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
    <attributes>
        <attribute name="maven.pomderived" value="true"/>
        <attribute name="module" value="true"/>
    </attributes>
</classpathentry>

then everything works just fine. However, when I select Maven -> Update Project in Eclipse, then Eclipse will remove the line

        <attribute name="module" value="true"/>

After that, the project shows an error in Eclipse (" The type xxx cannot be resolved. It is indirectly referenced from required.class file. ").

How can I tell Maven to keep the <attribute name="module" value="true"/> upon "Maven -> Update Project...".

(Eclipse version is 2020-03)

Answer 1

I use this in my pom.xml :

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.1</version>
    <configuration>
        <source>${java.version}</source>
        <target>${java.version}</target>
        <release>${java.version}</release>
        <fork>true</fork>
        <showWarnings>true</showWarnings>
        <debug>true</debug>
        <debuglevel>source,lines</debuglevel>
        <verbose>true</verbose>
        <modulePath>
            <dependency>org.apache.logging.log4j:log4j-api</dependency>
            <dependency>org.apache.logging.log4j.core:log4j-core</dependency>
            ... etc ...
        </modulePath>
    </configuration>
</plugin>

But, unfortunately, some modulePath > dependency work fine, others do not.