Removing breakpoint produces few errors in the log if Breakpoints view shows a tree

[iloveeclipse]

Seen in 4.38 latest nightly, however already present in 4.34, probably earlier.
I could not reproduce it in Eclipse 4.30, so it is a regression inbetween.

TL;DR: removing breakpoint if Breakpoints view shows a tree with breakpoint groups results in one or multiple errors reported to the error log.

• The code can be anything, just a trivial "helloworld" example with a single main method.
• Open Breakpoints view, enable "Group By" by anything except "Breakpoint", so a tree is shown with few breakpoints
• Create and delete breakpoint few times by double clicking on left editor ruler
• Errors are logged...

Typically there is at least a pair of errors like:

eclipse.buildId=4.38.0.I20250908-1800
java.version=21.0.8-9
java.vendor=N/A
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_US
Command-line arguments:  -os linux -ws gtk -arch x86_64 -data file:/data/4x_platform_workspace/

org.eclipse.debug.ui
Error
Tue Sep 09 11:56:49 CEST 2025
Error logged from Debug UI: 

java.lang.NullPointerException: Input to viewer update should not be null
	at org.eclipse.debug.internal.ui.viewers.model.ViewerUpdateMonitor.<init>(ViewerUpdateMonitor.java:90)
	at org.eclipse.debug.internal.ui.viewers.model.ChildrenUpdate.<init>(ChildrenUpdate.java:45)
	at org.eclipse.debug.internal.ui.viewers.model.TreeModelContentProvider.doUpdateElement(TreeModelContentProvider.java:1187)
	at org.eclipse.debug.internal.ui.viewers.model.TreeModelContentProvider.updateElement(TreeModelContentProvider.java:1759)
	at org.eclipse.jface.viewers.TreeViewer.virtualLazyUpdateWidget(TreeViewer.java:1001)
	at org.eclipse.jface.viewers.TreeViewer.lambda$1(TreeViewer.java:260)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5884)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1656)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1682)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1665)
	at org.eclipse.swt.widgets.Tree.checkData(Tree.java:375)
	at org.eclipse.swt.widgets.Tree.cellDataProc(Tree.java:307)
	at org.eclipse.swt.widgets.Display.cellDataProc(Display.java:997)
	at org.eclipse.swt.internal.gtk.GTK.gtk_tree_view_column_cell_set_cell_data(Native Method)
	at org.eclipse.swt.widgets.Tree.calculateWidth(Tree.java:446)
	at org.eclipse.swt.widgets.Tree.calculateWidth(Tree.java:521)
	at org.eclipse.swt.widgets.Tree.setScrollWidth(Tree.java:3888)
	at org.eclipse.swt.widgets.Tree.cellDataProc(Tree.java:356)
	at org.eclipse.swt.widgets.Display.cellDataProc(Display.java:997)
	at org.eclipse.swt.internal.gtk.GTK.gtk_tree_store_clear(Native Method)
	at org.eclipse.swt.widgets.Tree.removeAll(Tree.java:2978)
	at org.eclipse.jface.viewers.TreeViewer.removeAll(TreeViewer.java:289)
	at org.eclipse.jface.viewers.AbstractTreeViewer.lambda$2(AbstractTreeViewer.java:1627)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1391)
	at org.eclipse.jface.viewers.TreeViewer.preservingSelection(TreeViewer.java:367)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1352)
	at org.eclipse.jface.viewers.AbstractTreeViewer.inputChanged(AbstractTreeViewer.java:1623)
	at org.eclipse.debug.internal.ui.viewers.model.InternalTreeModelViewer.inputChanged(InternalTreeModelViewer.java:486)
	at org.eclipse.jface.viewers.ContentViewer.setInput(ContentViewer.java:279)
	at org.eclipse.jface.viewers.StructuredViewer.setInput(StructuredViewer.java:1635)
	at org.eclipse.debug.internal.ui.views.breakpoints.BreakpointsView.setViewerInput(BreakpointsView.java:295)
	at org.eclipse.debug.internal.ui.views.breakpoints.BreakpointsView.viewerInputUpdateComplete(BreakpointsView.java:309)
	at org.eclipse.debug.internal.ui.views.variables.VariablesView.lambda$0(VariablesView.java:297)
	at org.eclipse.debug.internal.ui.viewers.model.provisional.ViewerInputService.lambda$1(ViewerInputService.java:54)
	at org.eclipse.debug.internal.ui.viewers.model.ViewerInputUpdate$1.runInUIThread(ViewerInputUpdate.java:75)
	at org.eclipse.ui.progress.UIJob.lambda$0(UIJob.java:148)
	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:5074)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4543)

followed by

eclipse.buildId=4.38.0.I20250908-1800
java.version=21.0.8-9
java.vendor=N/A
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_US
Command-line arguments:  -os linux -ws gtk -arch x86_64 -data file:/data/4x_platform_workspace/

org.eclipse.ui
Error
Tue Sep 09 11:56:49 CEST 2025
Unhandled event loop exception

java.lang.NullPointerException: Cannot invoke "Object.equals(Object)" because the return value of "org.eclipse.debug.internal.ui.viewers.model.ChildrenUpdate.getViewerInput()" is null
	at org.eclipse.debug.internal.ui.viewers.model.ChildrenUpdate.doEquals(ChildrenUpdate.java:212)
	at org.eclipse.debug.internal.ui.viewers.model.ViewerUpdateMonitor.equals(ViewerUpdateMonitor.java:256)
	at java.base/java.util.LinkedList.remove(LinkedList.java:376)
	at org.eclipse.debug.internal.ui.viewers.model.TreeModelContentProvider.coalesce(TreeModelContentProvider.java:971)
	at org.eclipse.debug.internal.ui.viewers.model.TreeModelContentProvider.schedule(TreeModelContentProvider.java:955)
	at org.eclipse.debug.internal.ui.viewers.model.TreeModelContentProvider.doUpdateElement(TreeModelContentProvider.java:1188)
	at org.eclipse.debug.internal.ui.viewers.model.TreeModelContentProvider.updateElement(TreeModelContentProvider.java:1759)
	at org.eclipse.jface.viewers.TreeViewer.virtualLazyUpdateWidget(TreeViewer.java:1001)
	at org.eclipse.jface.viewers.TreeViewer.lambda$1(TreeViewer.java:260)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5884)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1656)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1682)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1665)
	at org.eclipse.swt.widgets.Tree.checkData(Tree.java:375)
	at org.eclipse.swt.widgets.Tree.cellDataProc(Tree.java:307)
	at org.eclipse.swt.widgets.Display.cellDataProc(Display.java:997)
	at org.eclipse.swt.internal.gtk.GTK.gtk_tree_view_column_cell_set_cell_data(Native Method)
	at org.eclipse.swt.widgets.Tree.calculateWidth(Tree.java:446)
	at org.eclipse.swt.widgets.Tree.calculateWidth(Tree.java:521)
	at org.eclipse.swt.widgets.Tree.setScrollWidth(Tree.java:3888)
	at org.eclipse.swt.widgets.Tree.cellDataProc(Tree.java:356)
	at org.eclipse.swt.widgets.Display.cellDataProc(Display.java:997)
	at org.eclipse.swt.internal.gtk.GTK.gtk_tree_store_clear(Native Method)
	at org.eclipse.swt.widgets.Tree.removeAll(Tree.java:2978)
	at org.eclipse.jface.viewers.TreeViewer.removeAll(TreeViewer.java:289)
	at org.eclipse.jface.viewers.AbstractTreeViewer.lambda$2(AbstractTreeViewer.java:1627)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1391)
	at org.eclipse.jface.viewers.TreeViewer.preservingSelection(TreeViewer.java:367)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1352)
	at org.eclipse.jface.viewers.AbstractTreeViewer.inputChanged(AbstractTreeViewer.java:1623)
	at org.eclipse.debug.internal.ui.viewers.model.InternalTreeModelViewer.inputChanged(InternalTreeModelViewer.java:486)
	at org.eclipse.jface.viewers.ContentViewer.setInput(ContentViewer.java:279)
	at org.eclipse.jface.viewers.StructuredViewer.setInput(StructuredViewer.java:1635)
	at org.eclipse.debug.internal.ui.views.breakpoints.BreakpointsView.setViewerInput(BreakpointsView.java:295)
	at org.eclipse.debug.internal.ui.views.breakpoints.BreakpointsView.viewerInputUpdateComplete(BreakpointsView.java:309)
	at org.eclipse.debug.internal.ui.views.variables.VariablesView.lambda$0(VariablesView.java:297)
	at org.eclipse.debug.internal.ui.viewers.model.provisional.ViewerInputService.lambda$1(ViewerInputService.java:54)
	at org.eclipse.debug.internal.ui.viewers.model.ViewerInputUpdate$1.runInUIThread(ViewerInputUpdate.java:75)
	at org.eclipse.ui.progress.UIJob.lambda$0(UIJob.java:148)
	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:5074)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4543)

[iloveeclipse]

Can reproduce Input to viewer update should not be null on 4.31 RC2, but it happens very seldom.
Starting with 4.36 there is also Unhandled event loop exception reported and it is easier to reproduce.

[iloveeclipse]

While debugging I see VariablesView.becomesHidden() is one candidate for setting input to ViewerInputService.NULL_INPUT, but in my tests Breakpoint view was not hidden... But at least this is a valid case where input can be null and at least that should be fixed. I didn't run into "original" issue yet (without hiding Breakpoints view) in debugger. I will push a PR.

[iloveeclipse]

Hmm, it seem to be a defect caused by "observer": once I've found errors in the Error log view, I've tried to reproduce the problem and in order to see whether deleting breakpoints causes the issue, I've switched from Breakpoints view to the Error log view and back, and that causes the problem!.

So in order to reproduce the problem, after deleting breakpoint and Breakpoints view active, one has to switch to the Error log view, and this switch tries to hide all content in the Breakpoints view and that causes the error.

[iloveeclipse]

Works for me with I20250910-1800. Let see if there are other use cases not covered yet.