gnodet opened a new pull request, #12875:
URL: https://github.com/apache/maven/pull/12875
## Summary
Fixes #2520 — Maven Wrapper (and IDEs like IntelliJ) broken with Maven
4.0.0-beta-5+ because `maven.mainClass` is not set when launching through
external tools.
**Root cause:** `m2.conf` used `main is ${maven.mainClass}` which required
classworlds property resolution. When external tools bypassed the `mvn`
scripts, `-Dmaven.mainClass` was never set, causing `ConfigurationException: No
such property: maven.mainClass`. The previous fix (PR #10998, rc-5) added `set
maven.mainClass default` in `m2.conf`, but this kept the defaulting in
classworlds config rather than Java — as noted by @gnodet in the [issue
discussion](https://github.com/apache/maven/issues/2520#issuecomment-2406145979).
**Fix:** Move the main class defaulting from classworlds property resolution
to Java code:
- **`m2.conf`**: Hardcode `main is org.apache.maven.cling.MavenCling from
plexus.core` — no variable resolution needed, no possibility of classworlds
`ConfigurationException`
- **`MavenCling.java`**: Check `maven.mainClass` system property in the
ClassWorld Launcher entry point and delegate to the specified class via
reflection when set (e.g., `MavenEncCling`, `MavenShellCling`, `MavenUpCling`)
This makes `MavenCling` the Java-level default entry point that all external
tools can rely on without any special configuration.
## Behavior
| Scenario | Before | After |
|----------|--------|-------|
| `mvn` script (normal) | `-Dmaven.mainClass=MavenCling` → classworlds
resolves | `-Dmaven.mainClass=MavenCling` → classworlds calls `MavenCling` → no
dispatch |
| `mvn --enc` | `-Dmaven.mainClass=MavenEncCling` → classworlds resolves |
`-Dmaven.mainClass=MavenEncCling` → `MavenCling` delegates to `MavenEncCling` |
| Maven Wrapper (no `-Dmaven.mainClass`) | `m2.conf` default resolves |
classworlds calls `MavenCling` directly — no resolution needed |
| IDE (no `-Dmaven.mainClass`) | `m2.conf` default resolves | classworlds
calls `MavenCling` directly — no resolution needed |
## Test plan
- [x] New `MavenClingTest` with 3 tests: delegation to valid class, unknown
class error, missing method error
- [x] All new tests pass
- [x] `mvn verify -pl impl/maven-cli -DskipTests` — build + format checks
pass
- [x] Pre-existing test failures are unrelated (MimirInfuser version
mismatch)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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