NPE in StickyScrollingControl when deleting a project with opened text editor

[basilevs]

I can't reproduce this anymore, but I've observed following exception when deleting a project.
I assume this is a race in editor closing (probably does not check for disposals is async).

eclipse.buildId=4.39.0.20260205-1226
java.version=25
java.vendor=Oracle Corporation
BootLoader constants: OS=macosx, ARCH=aarch64, WS=cocoa, NL=en_GE
Framework arguments:  -product org.eclipse.epp.package.committers.product -keyring /Users/vasiligulevich/.eclipse_keyring
Command-line arguments:  -os macosx -ws cocoa -arch aarch64 -product org.eclipse.epp.package.committers.product -keyring /Users/vasiligulevich/.eclipse_keyring -data file:/Users/vasiligulevich/xored/rcptt/ws/pde/

org.eclipse.ui
Error
Wed Feb 18 16:58:11 GMT+04:00 2026
Unhandled event loop exception

java.lang.NullPointerException: Cannot invoke "org.eclipse.swt.custom.StyledText.getCharCount()" because "textWidget" is null
	at org.eclipse.ui.internal.texteditor.stickyscroll.StickyScrollingControl$StickyScollingCaretListener.lambda$0(StickyScrollingControl.java:525)
	at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:40)
	at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:132)
	at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4393)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4016)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1160)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1051)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:684)
	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:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:565)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:615)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:563)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1415)

[basilevs]

Confirmed a race:

eclipse.platform.ui/bundles/org.eclipse.ui.editors/src/org/eclipse/ui/internal/texteditor/stickyscroll/StickyScrollingControl.java

Lines 518 to 535 in abbe191

	public void caretMoved(CaretEvent event) {
	int offsetEndPosition= sourceViewer.getTextWidget().getCharCount();
	if (event.caretOffset == 0 || event.caretOffset == offsetEndPosition) {
	return;
	}
	Display.getDefault().asyncExec(() -> {
	StyledText textWidget= sourceViewer.getTextWidget();
	if (!enableCaretListener || event.caretOffset > textWidget.getCharCount()) {
	return;
	}
	int line= textWidget.getLineAtOffset(event.caretOffset);
	if (sourceViewer instanceof ITextViewerExtension5 extension) {
	line= extension.widgetLine2ModelLine(line);
	}
	ensureSourceViewerLineVisible(line);
	});
	}
	}

In my projects I've assumed a policy that any asyncs related to widget should go through following method:

public static void asyncExec(Widget widget, Runnable runnable) {
  if (widget == null) {
	  return;
  }
  if (widget.isDisposed()) {
	  return;
  }
  try {
	  Display display = widget.getDisplay();
	  display.asyncExec(() -> {
		  if (widget.isDisposed()) {
			  return;
		  }
		  runnable.run();
	  });
  } catch (SWTException e) {
	  if (e.code == SWT.ERROR_WIDGET_DISPOSED) {
		  return;
	  }
	  throw e;
  }
}

This is the only correct approach for dropping operation on disposal. Notably, the race (outside of UI thread) can't be avoided without catching an exception!
Ideally this should check for Device disposal too, but somehow I'm always forgetting about this.

[iloveeclipse]

Correct, see #3737 and linked fix PR.