Description Thomas Wolf 2022-06-17 07:36:49 EDT

Reproducer:

* Start Eclipse on a fresh workspace
* Import an existing git repository in the Git repositories view (mine
  is a test repo that conveniently is already in rebase w/merge state).
* Open the Git Staging view on that repo.
* In the global preferences choose on the Diff/Merge page "External, use this
  tool" for the merge tool. On my Mac, the list presented is emerge, opendiff,
  vimdiff, vimdiff2, vimdiff3, with the first entry chosen by default (emerge).
* Double click a conflicting file in the unstaged viewer of the Git Staging
  view.

Expected:

An error dialog that the emerge tool could not be started.

Actual:

Nothing happens, except the following error log:

!ENTRY org.eclipse.egit.ui 2 0 2022-06-17 13:25:35.616
!MESSAGE Failed to run external merge tool.
!STACK 0
org.eclipse.jgit.internal.diffmergetool.ToolException: External merge tool is not defined: none
	at org.eclipse.jgit.internal.diffmergetool.MergeTools.merge(MergeTools.java:161)
	at org.eclipse.egit.ui.internal.actions.MergeToolActionHandler.mergeModified(MergeToolActionHandler.java:197)
	at org.eclipse.egit.ui.internal.actions.MergeToolActionHandler.executeExternalToolForChildren(MergeToolActionHandler.java:138)
	at org.eclipse.egit.ui.internal.actions.MergeToolActionHandler.executeExternalToolForChildren(MergeToolActionHandler.java:134)
	at org.eclipse.egit.ui.internal.actions.MergeToolActionHandler.openMergeToolExternal(MergeToolActionHandler.java:123)
	at org.eclipse.egit.ui.internal.actions.MergeToolActionHandler.execute(MergeToolActionHandler.java:98)
	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:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:58)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:319)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:253)
	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:487)
	at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:213)
	at org.eclipse.ui.internal.handlers.LegacyHandlerService.executeCommandInContext(LegacyHandlerService.java:440)
	at org.eclipse.egit.ui.internal.CommonUtils.runCommand(CommonUtils.java:218)
	at org.eclipse.egit.ui.internal.CommonUtils.runCommand(CommonUtils.java:182)
	at org.eclipse.egit.ui.internal.staging.StagingView.compareWith(StagingView.java:3105)
	at org.eclipse.jface.viewers.StructuredViewer$2.run(StructuredViewer.java:802)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
	at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:174)
	at org.eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java:799)
	at org.eclipse.jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1118)
	at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:275)
	at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:270)
	at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:310)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4443)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1512)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1535)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1520)
	at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1324)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4229)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3839)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1157)
	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:644)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:551)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:156)
	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:134)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:401)
	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:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:653)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:590)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1461)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1434)

There are three problems here:

1. The message claims no tool was selected. But the UI showed "emerge" to be
   active. Probably some initial setting is missing in the preferences.
2. The message is only logged; the user is not informed.
3. The Git Staging view shows three untracked files for the BASE, LOCAL, and
   REMOTE versions. Evidently they were created, then the tool run failed,
   and the files were not cleaned up.