Error in Preview of Custom Eclipse refactoring

Question

I am implementing an new eclipse refactoring. This will enable developers to Pull-up the preconditions statements from a child method to the parent method.

This all works perfectly when I select "Finish" in the refactoring wizard, but when I select "Preview" I get an error "No target edit provided." This seems to be caused by a problem in the TextEdit returned from ASTRewrite.rewriteAST(). However I cannot figure out why.

The stack trace of the exception happens after my Refactoring.createChange() code is run, and the change is used to generate the preview.

org.eclipse.text.edits.MalformedTreeException: No target edit provided.
at org.eclipse.text.edits.MoveSourceEdit.performConsistencyCheck(MoveSourceEdit.java:208)
at org.eclipse.text.edits.TextEdit.traverseConsistencyCheck(TextEdit.java:873)
at org.eclipse.text.edits.MoveSourceEdit.traverseConsistencyCheck(MoveSourceEdit.java:183)
at org.eclipse.text.edits.TextEdit.traverseConsistencyCheck(TextEdit.java:869)
at org.eclipse.text.edits.TextEdit.traverseConsistencyCheck(TextEdit.java:869)
at org.eclipse.text.edits.TextEditProcessor.checkIntegrityDo(TextEditProcessor.java:176)
at org.eclipse.text.edits.TextEdit.dispatchCheckIntegrity(TextEdit.java:743)
at org.eclipse.text.edits.TextEditProcessor.performEdits(TextEditProcessor.java:151)
at org.eclipse.ltk.core.refactoring.TextChange.getPreviewDocument(TextChange.java:534)
at org.eclipse.ltk.core.refactoring.TextChange.getPreviewDocument(TextChange.java:403)
at org.eclipse.ltk.core.refactoring.TextChange.getPreviewContent(TextChange.java:411)
at org.eclipse.ltk.internal.ui.refactoring.TextEditChangePreviewViewer.setInput(TextEditChangePreviewViewer.java:209)
at org.eclipse.ltk.internal.ui.refactoring.AbstractChangeNode.feedInput(AbstractChangeNode.java:99)
at org.eclipse.ltk.internal.ui.refactoring.PreviewWizardPage.showPreview(PreviewWizardPage.java:598)
at org.eclipse.ltk.internal.ui.refactoring.PreviewWizardPage.access$6(PreviewWizardPage.java:583)
at org.eclipse.ltk.internal.ui.refactoring.PreviewWizardPage$7.selectionChanged(PreviewWizardPage.java:574)
at org.eclipse.jface.viewers.Viewer$2.run(Viewer.java:162)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.runtime.Platform.run(Platform.java:888)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:48)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.Viewer.fireSelectionChanged(Viewer.java:160)
at org.eclipse.jface.viewers.StructuredViewer.updateSelection(StructuredViewer.java:2132)
at org.eclipse.jface.viewers.StructuredViewer.setSelection(StructuredViewer.java:1669)
at org.eclipse.jface.viewers.TreeViewer.setSelection(TreeViewer.java:1124)
at org.eclipse.jface.viewers.Viewer.setSelection(Viewer.java:392)
at org.eclipse.ltk.internal.ui.refactoring.PreviewWizardPage.setVisible(PreviewWizardPage.java:505)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2.makeVisible(RefactoringWizardDialog2.java:762)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2.showCurrentPage(RefactoringWizardDialog2.java:477)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2.nextOrPreviewPressed(RefactoringWizardDialog2.java:507)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2.access$2(RefactoringWizardDialog2.java:492)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2$1.widgetSelected(RefactoringWizardDialog2.java:691)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3880)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3473)
at org.eclipse.jface.window.Window.runEventLoop(Window.java:825)
at org.eclipse.jface.window.Window.open(Window.java:801)
at org.eclipse.ltk.ui.refactoring.RefactoringWizardOpenOperation$1.run(RefactoringWizardOpenOperation.java:143)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ltk.ui.refactoring.RefactoringWizardOpenOperation.run(RefactoringWizardOpenOperation.java:155)
at org.jmlspecs.eclipse.refactor.action.AbstractMethodActionDelegate.run(AbstractMethodActionDelegate.java:78)
at org.jmlspecs.eclipse.refactor.action.AbstractMethodActionDelegate.run(AbstractMethodActionDelegate.java:67)
at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:251)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:584)
at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:501)
at org.eclipse.jface.action.ActionContributionItem$6.handleEvent(ActionContributionItem.java:452)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3880)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3473)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:368)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
at org.eclipse.equinox.launcher.Main.run(Main.java:1311)
at org.eclipse.equinox.launcher.Main.main(Main.java:1287)

Currently the code that performs the change looks like this:

CompilationUnit sourceNode = ...
ASTRewrite sourceRewrite = ASTRewrite.create(sourceNode.getAST());

Statement statement = ...
sourceRewrite.createMoveTarget(statement);

CompilationUnit destinationNode = ...
MethodDeclaration destinationMethod = ...
ASTRewrite destinationRewrite = ASTRewrite.create(destinationNode.getAST());

ListRewrite lrw = destinationRewrite.getListRewrite(destinationMethod.getBody(),
    Block.STATEMENTS_PROPERTY);

lrw.insertFirst(statement, null);

I know that the way createMoveTarget is used is not how it is documented, but when I follow the documentation like below, the statement is deleted from the source but not moved to the destination and I still get the same error in the preview.

CompilationUnit sourceNode = ...
ASTRewrite sourceRewrite = ASTRewrite.create(sourceNode.getAST());

Statement statement = ...
Statement replacement = sourceRewrite.createMoveTarget(statement);
sourceRewrite.remove(statement, null);

CompilationUnit destinationNode = ...
MethodDeclaration destinationMethod = ...
ASTRewrite destinationRewrite = ASTRewrite.create(destinationNode.getAST());

ListRewrite lrw = destinationRewrite.getListRewrite(destinationMethod.getBody(),
    Block.STATEMENTS_PROPERTY);

lrw.insertFirst(replacement, null);

Here is an example of the Refactoring being performed.

Before:

class A {
    foo(int a) {
        return a * 2;
    }
}

class B {
    foo(int a) {
        JC.requires(a > 1);

        return a * 3;
    }
}

After:

class A {
    foo(int a) {
        JC.requires(a > 1);

        return a * 2;
    }
}

class B extends A {
    foo(int a) {        
        return a * 3;
    }
}

Answer 1

I found the eclipse.org article the most helpful to get me started.

A good place to get started debugging the code is to set breakpoints on org.eclipse.jdt.core.dom.rewrite.ASTRewrite, particularly the rewriteAST() method, then trigger some refactorings.

Here are a few you might find useful. Are you looking for anything in particular or a general sense of how to process the AST?

http://www.ibm.com/developerworks/opensource/library/os-ast/  
http://blog.sahits.ch/?p=228
http://www.vogella.com/articles/EclipseJDT/article.html