SpringBoot Declare optional dependency on shade plugin to fix eclipse auto-completion

Trying with 2.3.1 today, I still didn't get auto-completion for our Maven plugin.

Comment From: philwebb

@wilkinsona discovered Eclipse is doing this:

java.lang.reflect.InvocationTargetException
    at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:397)
    at org.eclipse.ui.internal.WorkbenchWindow.lambda$5(WorkbenchWindow.java:2375)
    at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:72)
    at org.eclipse.ui.internal.WorkbenchWindow.run(WorkbenchWindow.java:2373)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.execute(MojoParameterMetadataProvider.java:229)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$2(MojoParameterMetadataProvider.java:177)
    at com.google.common.cache.LocalCache$LocalManualCache$1.load(LocalCache.java:4878)
    at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3529)
    at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2278)
    at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2155)
    at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2045)
    at com.google.common.cache.LocalCache.get(LocalCache.java:3953)
    at com.google.common.cache.LocalCache$LocalManualCache.get(LocalCache.java:4873)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.getMojoConfiguration(MojoParameterMetadataProvider.java:177)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.getMojoConfiguration(MojoParameterMetadataProvider.java:164)
    at org.eclipse.m2e.editor.xml.PomTemplateContext$2.addTemplates(PomTemplateContext.java:240)
    at org.eclipse.m2e.editor.xml.PomTemplateContext.getTemplates(PomTemplateContext.java:619)
    at org.eclipse.m2e.editor.xml.PomContentAssistProcessor.addTemplateProposals(PomContentAssistProcessor.java:363)
    at org.eclipse.m2e.editor.xml.PomContentAssistProcessor.addTagInsertionProposals(PomContentAssistProcessor.java:115)
    at org.eclipse.wst.xml.ui.internal.contentassist.AbstractXMLCompletionProposalComputer.computeContentProposals(AbstractXMLCompletionProposalComputer.java:613)
    at org.eclipse.wst.xml.ui.internal.contentassist.AbstractXMLCompletionProposalComputer.computeCompletionProposals(AbstractXMLCompletionProposalComputer.java:415)
    at org.eclipse.wst.xml.ui.internal.contentassist.AbstractXMLCompletionProposalComputer.computeCompletionProposals(AbstractXMLCompletionProposalComputer.java:171)
    at org.eclipse.wst.sse.ui.internal.contentassist.CompletionProposalComputerDescriptor.computeCompletionProposals(CompletionProposalComputerDescriptor.java:290)
    at org.eclipse.wst.sse.ui.internal.contentassist.CompletionProposalCategory.computeCompletionProposals(CompletionProposalCategory.java:292)
    at org.eclipse.wst.sse.ui.contentassist.StructuredContentAssistProcessor.collectProposals(StructuredContentAssistProcessor.java:486)
    at org.eclipse.wst.sse.ui.contentassist.StructuredContentAssistProcessor.computeCompletionProposals(StructuredContentAssistProcessor.java:257)
    at org.eclipse.wst.sse.ui.internal.contentassist.CompoundContentAssistProcessor.computeCompletionProposals(CompoundContentAssistProcessor.java:129)
    at org.eclipse.jface.text.contentassist.ContentAssistant$2.lambda$0(ContentAssistant.java:2015)
    at java.util.Collections$SingletonSet.forEach(Collections.java:4769)
    at org.eclipse.jface.text.contentassist.ContentAssistant$2.run(ContentAssistant.java:2014)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
    at org.eclipse.jface.text.contentassist.ContentAssistant.computeCompletionProposals(ContentAssistant.java:2011)
    at org.eclipse.jface.text.contentassist.CompletionProposalPopup.computeProposals(CompletionProposalPopup.java:576)
    at org.eclipse.jface.text.contentassist.CompletionProposalPopup.lambda$0(CompletionProposalPopup.java:506)
    at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:72)
    at org.eclipse.jface.text.contentassist.CompletionProposalPopup.showProposals(CompletionProposalPopup.java:501)
    at org.eclipse.jface.text.contentassist.ContentAssistant.showPossibleCompletions(ContentAssistant.java:1825)
    at org.eclipse.wst.sse.ui.internal.StructuredTextViewer.doOperation(StructuredTextViewer.java:490)
    at org.eclipse.ui.texteditor.ContentAssistAction.lambda$0(ContentAssistAction.java:85)
    at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:72)
    at org.eclipse.ui.texteditor.ContentAssistAction.run(ContentAssistAction.java:84)
    at org.eclipse.jface.action.Action.runWithEvent(Action.java:474)
    at org.eclipse.jface.commands.ActionHandler.execute(ActionHandler.java:121)
    at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:97)
    at sun.reflect.GeneratedMethodAccessor74.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:58)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:318)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:252)
    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.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:308)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:584)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:653)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.filterKeySequenceBindings(KeyBindingDispatcher.java:443)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.access$2(KeyBindingDispatcher.java:386)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher$KeyDownFilter.handleEvent(KeyBindingDispatcher.java:96)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
    at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1113)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4382)
    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.sendKeyEvent(Widget.java:1549)
    at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1545)
    at org.eclipse.swt.widgets.Canvas.sendKeyEvent(Canvas.java:522)
    at org.eclipse.swt.widgets.Control.doCommandBySelector(Control.java:1081)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6205)
    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:606)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6037)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
    at org.eclipse.swt.widgets.Widget.callSuper(Widget.java:235)
    at org.eclipse.swt.widgets.Widget.windowSendEvent(Widget.java:2150)
    at org.eclipse.swt.widgets.Shell.windowSendEvent(Shell.java:2401)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:6157)
    at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
    at org.eclipse.swt.widgets.Display.applicationSendEvent(Display.java:5407)
    at org.eclipse.swt.widgets.Display.applicationProc(Display.java:5543)
    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:3788)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1160)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1049)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:155)
    at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:658)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:557)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:154)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:150)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:203)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:137)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:107)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:401)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:657)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:594)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1447)
Caused by: java.lang.NoClassDefFoundError: org/apache/maven/plugins/shade/resource/ResourceTransformer
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClassFromSelf(ClassRealm.java:425)
    at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:42)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
    at org.eclipse.m2e.editor.xml.mojo.PlexusConfigHelper.getCandidateClasses(PlexusConfigHelper.java:327)
    at org.eclipse.m2e.editor.xml.mojo.PlexusConfigHelper.getItemParameters(PlexusConfigHelper.java:200)
    at org.eclipse.m2e.editor.xml.mojo.PlexusConfigHelper.addParameter(PlexusConfigHelper.java:144)
    at org.eclipse.m2e.editor.xml.internal.mojo.DefaultMojoParameterMetadata.loadMojoParameters(DefaultMojoParameterMetadata.java:81)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.loadMojoParameters(MojoParameterMetadataProvider.java:319)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.loadMojoParameters(MojoParameterMetadataProvider.java:208)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$3(MojoParameterMetadataProvider.java:182)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:114)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$5(MojoParameterMetadataProvider.java:238)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:153)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:101)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$4(MojoParameterMetadataProvider.java:235)
    at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:122)
Caused by: java.lang.ClassNotFoundException: org.apache.maven.plugins.shade.resource.ResourceTransformer
    at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:50)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
    ... 29 more
Root exception:
java.lang.NoClassDefFoundError: org/apache/maven/plugins/shade/resource/ResourceTransformer
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClassFromSelf(ClassRealm.java:425)
    at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:42)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
    at org.eclipse.m2e.editor.xml.mojo.PlexusConfigHelper.getCandidateClasses(PlexusConfigHelper.java:327)
    at org.eclipse.m2e.editor.xml.mojo.PlexusConfigHelper.getItemParameters(PlexusConfigHelper.java:200)
    at org.eclipse.m2e.editor.xml.mojo.PlexusConfigHelper.addParameter(PlexusConfigHelper.java:144)
    at org.eclipse.m2e.editor.xml.internal.mojo.DefaultMojoParameterMetadata.loadMojoParameters(DefaultMojoParameterMetadata.java:81)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.loadMojoParameters(MojoParameterMetadataProvider.java:319)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.loadMojoParameters(MojoParameterMetadataProvider.java:208)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$3(MojoParameterMetadataProvider.java:182)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:114)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$5(MojoParameterMetadataProvider.java:238)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:153)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:101)
    at org.eclipse.m2e.editor.xml.internal.mojo.MojoParameterMetadataProvider.lambda$4(MojoParameterMetadataProvider.java:235)
    at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:122)
Caused by: java.lang.ClassNotFoundException: org.apache.maven.plugins.shade.resource.ResourceTransformer
    at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:50)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
    ... 29 more

Comment From: wilkinsona

This works with 2.2.8 but fails with 2.3.1. There's no mention of ResourceTransformer in either version's plugin metadata. One notable difference between the 2.2.8 and 2.3.1 plugins, is that 2.2.8 declares an optional dependency on the Shade plugin in its pom.xml whereas 2.3.1 does not. Updating 2.3.x's pom to include such a dependency declaration appears to fix the problem. In other words, m2e appears to rely upon optional dependencies in a plugin's pom to give it a complete view of the plugin's possible classpath.

I'm not sure that it is intentional for this to be necessary. ClassNotFoundException is caught but that doesn't help in this case as it's a NoClassDefFoundError (caused by a ClassNotFoundException that is being thrown. Even if a fix in m2e is warranted and made, we'd need to wait for it to be released and adopted. In the meantime, we should reinstate the optional dependency as a fix/workaround.