ST4 saving javascript changes from compare editor fails

Saving changes in javascript file after comparing projects and editing fails with IllegalStateException. Uninstalled Wild Web Developer plugin avoids the issue.

Steps to reproduce

1. STS4 4.17.2 macos arm_64 (fresh install)
2. Create project comp1 and comp2
3. Create file comp1/hello.js with console.log("Hello Foo");
4. Create file comp2/hello.js with console.log("Hello Bar");
5. Select comp1 and comp2 projects and select Compare With->Each Other
6. In compare editor, double click on hello.js and make change(s) to either side
7. Try to save

Result:

Changes are not saved and exception found in the error log

!MESSAGE Unhandled event loop exception
!STACK 0
java.lang.IllegalStateException
    at org.eclipse.jface.text.TextViewer.setHyperlinkPresenter(TextViewer.java:5639)
    at org.eclipse.jface.text.source.SourceViewer.configure(SourceViewer.java:529)
    at org.eclipse.ui.internal.genericeditor.compare.GenericEditorMergeViewer.configureTextViewer(GenericEditorMergeViewer.java:68)
    at org.eclipse.ui.internal.genericeditor.compare.GenericEditorMergeViewer$1.inputDocumentChanged(GenericEditorMergeViewer.java:50)
    at org.eclipse.jface.text.TextViewer.fireInputDocumentChanged(TextViewer.java:2849)
    at org.eclipse.jface.text.TextViewer.setDocument(TextViewer.java:2890)
    at org.eclipse.jface.text.source.SourceViewer.setDocument(SourceViewer.java:663)
    at org.eclipse.jface.text.source.SourceViewer.setDocument(SourceViewer.java:603)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer$ContributorInfo.updateViewerDocument(TextMergeViewer.java:807)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer$ContributorInfo.internalSetDocument(TextMergeViewer.java:762)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer$ContributorInfo.setDocument(TextMergeViewer.java:679)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer.updateContent(TextMergeViewer.java:3029)
    at org.eclipse.compare.contentmergeviewer.ContentMergeViewer.internalRefresh(ContentMergeViewer.java:793)
    at org.eclipse.compare.contentmergeviewer.ContentMergeViewer.refresh(ContentMergeViewer.java:769)
    at org.eclipse.compare.contentmergeviewer.ContentMergeViewer.handleCompareInputChange(ContentMergeViewer.java:1389)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer.handleCompareInputChange(TextMergeViewer.java:5345)
    at org.eclipse.compare.contentmergeviewer.ContentMergeViewer.lambda$1(ContentMergeViewer.java:390)
    at org.eclipse.compare.structuremergeviewer.DiffNode.fireChange(DiffNode.java:140)
    at org.eclipse.compare.internal.ResourceCompareInput$MyDiffNode.fireChange(ResourceCompareInput.java:90)
    at org.eclipse.compare.internal.MergeViewerContentProvider.saveLeftContent(MergeViewerContentProvider.java:152)
    at org.eclipse.compare.contentmergeviewer.ContentMergeViewer.flushLeftSide(ContentMergeViewer.java:1272)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer.flushLeftSide(TextMergeViewer.java:5235)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer.flushContent(TextMergeViewer.java:5258)
    at org.eclipse.compare.contentmergeviewer.ContentMergeViewer.flush(ContentMergeViewer.java:1243)
    at org.eclipse.compare.CompareEditorInput.flushViewer(CompareEditorInput.java:1220)
    at org.eclipse.compare.CompareEditorInput.flushViewers(CompareEditorInput.java:1189)
    at org.eclipse.compare.internal.ResourceCompareInput.getAdapter(ResourceCompareInput.java:508)
    at org.eclipse.core.runtime.Adapters.adapt(Adapters.java:67)
    at org.eclipse.core.runtime.Adapters.adapt(Adapters.java:116)
    at org.eclipse.ui.ide.ResourceUtil.getFile(ResourceUtil.java:61)
    at org.eclipse.ui.internal.ide.actions.BuildUtilities.findSelectedProjects(BuildUtilities.java:108)
    at org.eclipse.ui.actions.BuildAction.isEnabled(BuildAction.java:231)
    at org.eclipse.ui.actions.RetargetAction.setActionHandler(RetargetAction.java:268)
    at org.eclipse.ui.internal.ide.actions.RetargetActionWithDefault.setActionHandler(RetargetActionWithDefault.java:51)
    at org.eclipse.ui.actions.RetargetAction.propagateChange(RetargetAction.java:204)
    at org.eclipse.ui.SubActionBars.firePropertyChange(SubActionBars.java:289)
    at org.eclipse.ui.SubActionBars.fireActionHandlersChanged(SubActionBars.java:273)
    at org.eclipse.ui.SubActionBars.updateActionBars(SubActionBars.java:603)
    at org.eclipse.compare.internal.CompareHandlerService.updateActionBars(CompareHandlerService.java:131)
    at org.eclipse.compare.internal.CompareHandlerService.updatePaneActionHandlers(CompareHandlerService.java:161)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer.connectGlobalActions(TextMergeViewer.java:2784)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer.setActiveViewer(TextMergeViewer.java:2719)
    at org.eclipse.compare.contentmergeviewer.TextMergeViewer$22.focusLost(TextMergeViewer.java:2682)
    at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:147)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4646)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1524)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1547)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1528)
    at org.eclipse.swt.widgets.Control.sendFocusEvent(Control.java:3433)
    at org.eclipse.swt.widgets.Canvas.sendFocusEvent(Canvas.java:80)
    at org.eclipse.swt.widgets.Display.checkFocus(Display.java:744)
    at org.eclipse.swt.widgets.Shell.makeFirstResponder(Shell.java:1317)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6522)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSend_bool(Native Method)
    at org.eclipse.swt.internal.cocoa.NSWindow.makeFirstResponder(NSWindow.java:197)
    at org.eclipse.swt.widgets.Control.forceFocus(Control.java:1472)
    at org.eclipse.swt.widgets.Control.forceFocus(Control.java:1452)
    at org.eclipse.swt.widgets.Control.setFocus(Control.java:3880)
    at org.eclipse.swt.widgets.Composite.setFocus(Composite.java:1129)
    at org.eclipse.swt.widgets.Composite.setFocus(Composite.java:1127)
    at org.eclipse.swt.widgets.Composite.setFocus(Composite.java:1127)
    at org.eclipse.swt.widgets.Composite.setFocus(Composite.java:1127)
    at org.eclipse.swt.widgets.Composite.setFocus(Composite.java:1127)
    at org.eclipse.swt.widgets.Control.fixFocus(Control.java:1377)
    at org.eclipse.swt.widgets.Control.setEnabled(Control.java:3860)
    at org.eclipse.ui.internal.WorkbenchWindow.disableControl(WorkbenchWindow.java:2278)
    at org.eclipse.ui.internal.WorkbenchWindow.run(WorkbenchWindow.java:2324)
    at org.eclipse.ui.internal.SaveableHelper.runProgressMonitorOperation(SaveableHelper.java:278)
    at org.eclipse.ui.internal.SaveableHelper.runProgressMonitorOperation(SaveableHelper.java:260)
    at org.eclipse.ui.internal.SaveableHelper.saveModels(SaveableHelper.java:207)
    at org.eclipse.ui.internal.SaveableHelper.savePart(SaveableHelper.java:150)
    at org.eclipse.ui.internal.WorkbenchPage.saveSaveable(WorkbenchPage.java:3802)
    at org.eclipse.ui.internal.WorkbenchPage.saveEditor(WorkbenchPage.java:3815)
    at org.eclipse.ui.internal.handlers.SaveHandler.execute(SaveHandler.java:82)
    at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:283)
    at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:97)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:58)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:317)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:251)
    at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:173)
    at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:156)
    at org.eclipse.core.commands.Command.executeWithChecks(Command.java:488)
    at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:485)
    at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:213)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:308)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:580)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:647)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.filterKeySequenceBindings(KeyBindingDispatcher.java:439)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher$KeyDownFilter.handleEvent(KeyBindingDispatcher.java:96)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
    at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1217)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4641)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1524)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1547)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1532)
    at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1561)
    at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1557)
    at org.eclipse.swt.widgets.Canvas.sendKeyEvent(Canvas.java:522)
    at org.eclipse.swt.widgets.Control.doCommandBySelector(Control.java:1085)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6492)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSend(Native Method)
    at org.eclipse.swt.internal.cocoa.NSResponder.interpretKeyEvents(NSResponder.java:59)
    at org.eclipse.swt.widgets.Composite.keyDown(Composite.java:607)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6324)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
    at org.eclipse.swt.widgets.Widget.callSuper(Widget.java:236)
    at org.eclipse.swt.widgets.Widget.windowSendEvent(Widget.java:2264)
    at org.eclipse.swt.widgets.Shell.windowSendEvent(Shell.java:2511)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6444)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
    at org.eclipse.swt.widgets.Display.applicationSendEvent(Display.java:5692)
    at org.eclipse.swt.widgets.Display.applicationProc(Display.java:5831)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSend(Native Method)
    at org.eclipse.swt.internal.cocoa.NSApplication.sendEvent(NSApplication.java:117)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3986)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1155)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1046)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:155)
    at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:643)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:550)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:171)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:152)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:203)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:136)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:402)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:659)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:596)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1467)

記載されている STS4 4.17.2 の macOS ARM 手順で比較エディターの保存失敗を再現し、その後 GenericEditorMergeViewer.configureTextViewer とスタックエントリ TextViewer.setHyperlinkPresenter から調査を開始します。比較エディターのどちら側で行った JavaScript の変更も、IllegalStateException が発生せず正常に保存できれば完了です。