Attempted to beginRule: MultiRule[], does not match outer scope rule: R/

[basilevs]

Prerequisites

• Two distinct installations of Java
• Eclipse IDE for Eclipse Committers 2024-03

Test steps

• Open a fresh empty workspace
• Create a single project of General type (no natures, no builders)
• Restart
• Open Preferences/Plugin Dvelopment/Target platform (no need to change anything, just make sure the page opens)
• Open Preferences/Java/Installed JREs
• Add (or remove) a second installation of Java
• Hit Apply and Close

Note: to reproduce repeatedly, repeat last 3 steps

Expected result

No errors

Actual result

eclipse.buildId=4.31.0.20240307-1200
java.version=17.0.4.1
java.vendor=Oracle Corporation
BootLoader constants: OS=macosx, ARCH=aarch64, WS=cocoa, NL=en_GE
Framework arguments:  -product org.eclipse.epp.package.committers.product
Command-line arguments:  -os macosx -ws cocoa -arch aarch64 -product org.eclipse.epp.package.committers.product

org.eclipse.core.jobs
Error
Fri Mar 29 14:34:41 GET 2024
An internal error occurred during: "Re-resolve Target state after VM-Install or EE change".

java.lang.IllegalArgumentException: Attempted to beginRule: MultiRule[], does not match outer scope rule: R/
	at org.eclipse.core.runtime.Assert.isLegal(Assert.java:68)
	at org.eclipse.core.internal.jobs.ThreadJob.illegalPush(ThreadJob.java:144)
	at org.eclipse.core.internal.jobs.ThreadJob.push(ThreadJob.java:416)
	at org.eclipse.core.internal.jobs.ImplicitJobs.begin(ImplicitJobs.java:88)
	at org.eclipse.core.internal.jobs.JobManager.beginRule(JobManager.java:341)
	at org.eclipse.core.internal.resources.WorkManager.checkIn(WorkManager.java:124)
	at org.eclipse.core.internal.resources.Workspace.prepareOperation(Workspace.java:2398)
	at org.eclipse.core.internal.resources.Project$1.run(Project.java:601)
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2448)
	at org.eclipse.core.internal.resources.Project.internalBuild(Project.java:642)
	at org.eclipse.core.internal.resources.Project.build(Project.java:162)
	at org.eclipse.pde.internal.core.MinimalState.reloadSystemPackagesIntoState(MinimalState.java:339)
	at org.eclipse.pde.internal.core.MinimalState$2.runInWorkspace(MinimalState.java:312)
	at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:43)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)

Workaround

Keep a dummy project with PDE nature in the workspace.

Also observed when RCPTT loads an Appllication Under Test with a new VM

[basilevs]

ManifestConsistencyChecker wants to lock all PDE projects and produces an empty MultiRule:

@Override
public ISchedulingRule getRule(int kind, Map<String, String> args) {
return new MultiRule(Arrays.stream(getProject().getWorkspace().getRoot().getProjects())
		.filter(PDEBuilderHelper::isPDEProject).toArray(ISchedulingRule[]::new));
}

Empty MultiRule does not conflict with workspace root, and is treated as an external entity in the context of the whole-workspace operation.

The builders can't just return null, as BuildManager will then fall-back to a full-workspace lock:

// Bug 306824 - Builders returning a null rule can't work safely if other builders require a non-null rule
// Be pessimistic and fall back to the default build rule (workspace root) in this case.
if (!hasNullBuildRule)
	return new MultiRule(rules.toArray(new ISchedulingRule[rules.size()]));
...
return workspace.getRoot();

So when builder does not need to lock any resources, it has to return a rule that is contained in workspace, but does not conflict with any resources. A non-existent project would do.