Problems with Java Editor window creation/setup in Plugin

[M-Marvin]

I am working an an integration plugin for my custom build system, and it requires its buildfile, which is written in Java, to be displayed in an Java Editor window, with its own classpath.

I already asked for help to do that in this discussion: eclipse-platform/eclipse.platform.ui#2857
And found a working solution:

@SuppressWarnings("restriction")
public class BuildscriptEditor extends CompilationUnitEditor {
	
	@Override
	protected void doSetInput(IEditorInput input) throws CoreException {
		super.doSetInput(input);
		setTitleImage(Icons.META_FILE_ICON.createImage());
	}
	
	public Collection<IClasspathEntry> getClasspath() {
		List<IClasspathEntry> classpath = new ArrayList<IClasspathEntry>();
		classpath.add(JavaRuntime.getDefaultJREContainerEntry());
		IResource resource = getEditorInput().getAdapter(IResource.class);
		if (resource == null) return classpath;
		IProject project = resource.getProject();
		MetaProjectNature nature = MetaProjectNature.getProjectNature(project);
		if (nature == null) return classpath;
		for (File entryPath : nature.getBuildfileClasspath()) {
			classpath.add(JavaCore.newLibraryEntry(IPath.fromFile(entryPath), null, null));
		}
		return classpath;
	}
	
	@Override
	protected ITypeRoot getInputJavaElement() {
		try {
			return MetaProjectNature.BUILDFILE_WORKING_COPY_OWNER.newWorkingCopy(
					this.getEditorInput().getName(), 
					getClasspath().toArray(IClasspathEntry[]::new),
					null
			);
		} catch (JavaModelException e) {
			e.printStackTrace();
			return null;
		}	
	}
	
}

But although this code seems to partially work (the syntax highlighting seems to not work properly) it does not look right.
I also today noticed, while debugging an completely unrelated problem, that it causes eclipse to throw an error only in production environment:

!ENTRY org.eclipse.jdt.core 2 0 2025-06-24 11:53:25.303
!MESSAGE JavaModel change during read only operation
!STACK 0
java.lang.IllegalStateException: JavaModel modified during 'read only' operation. Consider to report this warning to https://github.com/eclipse-jdt/eclipse.jdt.core/issues. delta=Java Model[*]: {CHILDREN}
	 [*]: {CHILDREN}
		<project root>[*]: {CHILDREN}
			<default>[*]: {CHILDREN}
				[Working copy] build.meta[+]: {}
	at org.eclipse.jdt.internal.core.DeltaProcessor.registerJavaModelDelta(DeltaProcessor.java:2027)
	at org.eclipse.jdt.internal.core.JavaModelOperation.addDelta(JavaModelOperation.java:187)
	at org.eclipse.jdt.internal.core.BecomeWorkingCopyOperation.executeOperation(BecomeWorkingCopyOperation.java:52)
	at org.eclipse.jdt.internal.core.JavaModelOperation.run(JavaModelOperation.java:751)
	at org.eclipse.jdt.internal.core.JavaModelOperation.runOperation(JavaModelOperation.java:816)
	at org.eclipse.jdt.internal.core.CompilationUnit.becomeWorkingCopy(CompilationUnit.java:116)
	at org.eclipse.jdt.core.WorkingCopyOwner.newWorkingCopy(WorkingCopyOwner.java:265)
	at de.m_marvin.eclipsemeta.ui.editors.BuildscriptEditor.getInputJavaElement(BuildscriptEditor.java:49)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaEditor$ActivationListener.windowActivatedCached(JavaEditor.java:1222)
	at org.eclipse.jdt.core.JavaCore.lambda$1(JavaCore.java:6172)
	at org.eclipse.jdt.internal.core.JavaModelManager.cacheZipFiles(JavaModelManager.java:5708)
	at org.eclipse.jdt.internal.core.JavaModelManager.callReadOnly(JavaModelManager.java:5697)
	at org.eclipse.jdt.core.JavaCore.callReadOnly(JavaCore.java:6156)
	at org.eclipse.jdt.core.JavaCore.runReadOnly(JavaCore.java:6171)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaEditor$ActivationListener.windowActivated(JavaEditor.java:1216)
	at org.eclipse.ui.internal.Workbench$8.run(Workbench.java:1074)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.ui.internal.Workbench.fireWindowActivated(Workbench.java:1071)
	at org.eclipse.ui.internal.WorkbenchWindow$6.shellActivated(WorkbenchWindow.java:2449)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:126)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4338)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1214)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1238)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1223)
	at org.eclipse.swt.widgets.Decorations.WM_ACTIVATE(Decorations.java:1535)
	at org.eclipse.swt.widgets.Shell.WM_ACTIVATE(Shell.java:2414)
	at org.eclipse.swt.widgets.Control.windowProc(Control.java:4776)
	at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:336)
	at org.eclipse.swt.widgets.Decorations.windowProc(Decorations.java:1494)
	at org.eclipse.swt.widgets.Shell.windowProc(Shell.java:2387)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5106)
	at org.eclipse.swt.internal.win32.OS.BringWindowToTop(Native Method)
	at org.eclipse.swt.widgets.Decorations.bringToTop(Decorations.java:215)
	at org.eclipse.swt.widgets.Shell.open(Shell.java:1293)
	at org.eclipse.e4.ui.workbench.renderers.swt.WBWRenderer.postProcess(WBWRenderer.java:743)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:676)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:762)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$2.run(PartRenderingEngine.java:727)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:711)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1079)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1042)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:678)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:583)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:173)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:185)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:219)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:149)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:115)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:467)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:298)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:627)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:575)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1431)
```

This error never appears during testing in an debug session in eclipse-committers.
It does not seem to have any consequences, the Java Editor still works, besides the syntax highlighting.
	
Are there better way to construct an Java Editor window with an custom classpath ?
The original discussion was closed, so I could not ask there any more.

Also, sometimes, if I leave the "custom editor" open for too long, it starts to get really slow.
Not the IDE, just that specific editor window, it then takes like 3 seconds to process input.
Closing and reopening is enough to reset that for some reason.
I sadly cant find any documentation about this.

[merks]

This seems like a question best asked in the eclipse-jdt GitHub organization.

[M-Marvin]

From what I know, there is no JDT discussion site.
That's why my other post also was in here, I think even someone from the eclipse community redirected me here because of that back then.

[iloveeclipse]

See https://github.com/eclipse-jdt/eclipse.jdt.core/discussions