Multi-release JAR detection broken on Windows (File.separatorChar mismatch)

[elharo]

Bug

Multi-release JAR detection is broken on Windows because File.separatorChar is used to build the path prefix, but FileSetManager.getIncludedFiles() always returns forward-slash paths regardless of the operating system.

Location

AbstractJarMojo.java:248-249:

p -> p.startsWith("META-INF" + File.separatorChar + "versions" + File.separatorChar)

On Windows, File.separatorChar is \, so the prefix becomes META-INF\versions\, which never matches the forward-slash paths returned by FileSetManager (e.g. META-INF/versions/9/module-info.class).

Effect

The Multi-Release: true manifest entry is never added for multi-release JARs when the build runs on Windows. The JAR is still created but lacks the manifest entry, so the JVM will not use versioned classes from META-INF/versions/.

Fix

Replace File.separatorChar with the forward slash character "/". JAR paths always use forward slashes per the JAR specification, and FileSetManager normalizes to forward slashes on all platforms.

[elharo]

After further investigation, this is not actually a bug. The Plexus DirectoryScanner.scandir() builds paths using File.separator (e.g., META-INF\\versions\\9\\test.txt on Windows), not forward slashes. The detection logic in AbstractJarMojo.java uses File.separatorChar to build the prefix, which is consistent on all platforms. Both sides use the platform separator, so the startsWith check works correctly everywhere.

The integration test from PR #563 passes on Windows CI without any code changes, confirming this.

Closing as not a bug — the existing code is correct.