ClassCastException because of property page shown when it should not be shown

[Bananeweizen]

The "Annotation Processing" property page is contributed to everything that adapts to IProject. However, the code of the (superclass of the) property page only adapts the current element to IResource. That's a problem for all non-project resources, as they will just be adapted to themselfes, not to their containing project, leading to an exception:

java.lang.ClassCastException: class org.eclipse.core.internal.resources.Folder cannot be cast to class org.eclipse.core.resources.IProject (org.eclipse.core.internal.resources.Folder and org.eclipse.core.resources.IProject are in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @6837a78)
	at org.eclipse.m2e.apt.ui.preferences.xpl.PropertyAndPreferencePage.setElement(PropertyAndPreferencePage.java:305)
	at org.eclipse.ui.internal.dialogs.RegistryPageContributor.createPage(RegistryPageContributor.java:145)
	at org.eclipse.ui.internal.dialogs.PropertyPageNode.createPage(PropertyPageNode.java:57)
	at org.eclipse.jface.preference.PreferenceDialog.createPage(PreferenceDialog.java:1280)
	at org.eclipse.ui.internal.dialogs.FilteredPreferenceDialog.createPage(FilteredPreferenceDialog.java:326)
	at org.eclipse.jface.preference.PreferenceDialog.showPage(PreferenceDialog.java:1166)
	at org.eclipse.ui.internal.dialogs.FilteredPreferenceDialog.showPage(FilteredPreferenceDialog.java:618)
	at org.eclipse.jface.preference.PreferenceDialog$5.lambda$0(PreferenceDialog.java:660)
	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:67)
	at org.eclipse.jface.preference.PreferenceDialog$5.selectionChanged(PreferenceDialog.java:657)
	at org.eclipse.jface.viewers.StructuredViewer$3.run(StructuredViewer.java:820)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:174)
	at org.eclipse.jface.viewers.StructuredViewer.firePostSelectionChanged(StructuredViewer.java:817)
	at org.eclipse.jface.viewers.ColumnViewer.firePostSelectionChanged(ColumnViewer.java:1065)
	at org.eclipse.jface.viewers.StructuredViewer.handlePostSelect(StructuredViewer.java:1185)
	at org.eclipse.swt.events.SelectionListener$1.widgetSelected(SelectionListener.java:84)
	at org.eclipse.jface.util.OpenStrategy.firePostSelectionEvent(OpenStrategy.java:283)
	at org.eclipse.jface.util.OpenStrategy$PostSelectionEvent.run(OpenStrategy.java:132)
	at org.eclipse.jface.util.Throttler.lambda$0(Throttler.java:59)
	at org.eclipse.jface.util.Throttler.lambda$1(Throttler.java:67)
	at org.eclipse.jface.util.Throttler.throttledExec(Throttler.java:94)
	at org.eclipse.jface.util.OpenStrategy$1.lambda$1(OpenStrategy.java:435)
	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:4047)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3663)
	at org.eclipse.jface.window.Window.runEventLoop(Window.java:823)
	at org.eclipse.jface.window.Window.open(Window.java:799)
	at org.eclipse.ui.dialogs.PropertyDialogAction.run(PropertyDialogAction.java:154)
	at org.eclipse.jface.action.Action.runWithEvent(Action.java:474)
	at org.eclipse.jface.commands.ActionHandler.execute(ActionHandler.java:124)
	at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:98)
	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.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:58)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:298)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:232)
	at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:174)
	at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:165)
	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:204)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:308)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:569)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:644)
	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:1287)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1065)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1090)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1075)
	at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1117)
	at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1113)
	at org.eclipse.swt.widgets.Widget.wmSysChar(Widget.java:2351)
	at org.eclipse.swt.widgets.Control.WM_SYSCHAR(Control.java:5452)
	at org.eclipse.swt.widgets.Control.windowProc(Control.java:4822)
	at org.eclipse.swt.widgets.Tree.windowProc(Tree.java:6142)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5039)
	at org.eclipse.swt.internal.win32.OS.DispatchMessage(Native Method)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3658)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1151)
	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:152)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:639)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:546)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:173)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:152)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:208)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:143)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:109)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:439)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:271)
	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:651)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:588)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1459)

I suggest to use "instanceof" in the property page declaration to fix this (and to not show the property page for all files and folders):

m2e-core/org.eclipse.m2e.apt.ui/plugin.xml

Line 27 in 5f94521

<adapt type="org.eclipse.core.resources.IProject">