maven.multiModuleProjectDirectory system property not set — breaks projects using it in POM

[chagong]

Problem

Projects that reference ${maven.multiModuleProjectDirectory} in their POM (e.g., Apache Dubbo, Google Guava) fail to import. The Maven CLI launcher (mvn) normally sets this as a JVM system property via -Dmaven.multiModuleProjectDirectory=..., but JDTLS does not replicate this behavior.

m2e computes the value per-project via MavenProperties.computeMultiModuleProjectDirectory() and calls request.setMultiModuleProjectDirectory(File), but this does not add it to request.getSystemProperties(). Maven's model interpolator uses system properties to resolve POM expressions, so ${maven.multiModuleProjectDirectory} remains unresolved in the MavenProject model.

Steps to Reproduce

1. Open Apache Dubbo (git clone https://github.com/apache/dubbo) in VS Code with JDTLS
2. Wait for project import to complete
3. dubbo-common fails to configure

Error

org.eclipse.core.runtime.CoreException: Could not update project dubbo-common configuration
Caused by: java.lang.IllegalArgumentException: Path must include project and resource name: /
    at org.eclipse.core.runtime.Assert.isLegal(Assert.java:68)
    at org.eclipse.core.internal.resources.Workspace.newResource(Workspace.java:2274)
    at org.eclipse.core.internal.resources.Container.getFolder(Container.java:211)
    at org.eclipse.m2e.jdt.internal.AbstractJavaProjectConfigurator.getFolder(AbstractJavaProjectConfigurator.java:1007)
    at org.eclipse.m2e.jdt.internal.AbstractJavaProjectConfigurator.addResourceDirs(AbstractJavaProjectConfigurator.java:639)
    at org.eclipse.m2e.jdt.internal.AbstractJavaProjectConfigurator.addProjectSourceFolders(AbstractJavaProjectConfigurator.java:431)
    at org.eclipse.m2e.jdt.internal.AbstractJavaProjectConfigurator.configure(AbstractJavaProjectConfigurator.java:170)
    at org.eclipse.m2e.core.project.configurator.AbstractLifecycleMapping.configure(AbstractLifecycleMapping.java:127)
    at org.eclipse.m2e.core.internal.project.ProjectConfigurationManager.lambda$6(ProjectConfigurationManager.java:506)
    ...
    at org.eclipse.jdt.ls.core.internal.managers.MavenProjectImporter.importToWorkspace(MavenProjectImporter.java:249)
    at org.eclipse.jdt.ls.core.internal.managers.ProjectsManager.importProjects(ProjectsManager.java:169)
    at org.eclipse.jdt.ls.core.internal.managers.ProjectsManager.initializeProjects(ProjectsManager.java:126)

The result is that dubbo-common has no .classpath and loses Java nature entirely:

The 'dubbo-common' project has no .classpath. Removing Java nature and builder.

Root Cause

Dubbo's parent POM declares resource directories using ${maven.multiModuleProjectDirectory}:

<resources>
    <resource>
        <directory>${maven.multiModuleProjectDirectory}</directory>
        <includes>
            <include>NOTICE</include>
            <include>LICENSE</include>
        </includes>
    </resource>
</resources>

Since JDTLS never sets maven.multiModuleProjectDirectory as a system property, the Maven model builder cannot interpolate it. The literal ${maven.multiModuleProjectDirectory} string flows into m2e's AbstractJavaProjectConfigurator.getFolder() which crashes.

Proposed Fix

In StandardPreferenceManager, walk root paths for .mvn/ directories and call System.setProperty("maven.multiModuleProjectDirectory", ...) to mirror the mvn launcher behavior.

Note: This is necessary but not sufficient. m2e also has a bug in AbstractJavaProjectConfigurator.getFolder() that crashes when the resolved resource directory is an ancestor of the project directory — see eclipse-m2e/m2e-core#1790 and fix PR eclipse-m2e/m2e-core#2160.

Environment

• JDTLS 1.58.0-SNAPSHOT
• m2e 2.11.0 (bundled)
• Java 25.0.2 (Eclipse Adoptium)
• Windows 10, x86_64