Provide a new viewer for the Restore from Local History action #1879

The new viewer implementation is used when the viewer factory is invoked
without a compare configuration. This is the case when it is called from
the "Restore from Local History" action. The existing merge viewer
cannot be used in this situation.

bundles/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/compare/CompareViewerCreator.java

@@ -9,6 +9,7 @@
  * SPDX-License-Identifier: EPL-2.0
  *
  * Contributors:
+ * - Ole Osterhagen - Issue #1879
  * - Mickael Istria (Red Hat Inc.)
  *******************************************************************************/
 package org.eclipse.ui.internal.genericeditor.compare;
@@ -20,8 +21,10 @@
 
 public class CompareViewerCreator implements IViewerCreator {
 
-	@Override public Viewer createViewer(Composite parent, CompareConfiguration compareConfiguration) {
-		return new GenericEditorMergeViewer(parent, compareConfiguration);
+	@Override
+	public Viewer createViewer(Composite parent, CompareConfiguration compareConfiguration) {
+		return compareConfiguration != null ? new GenericEditorMergeViewer(parent, compareConfiguration)
+				: new GenericEditorViewer(parent);
 	}
 
 }

bundles/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/compare/GenericEditorViewer.java

@@ -0,0 +1,201 @@
+/*******************************************************************************
+* Copyright (c) 2024 Ole Osterhagen and others.
+* 
+* This program and the accompanying materials
+* are made available under the terms of the Eclipse Public License 2.0
+* which accompanies this distribution, and is available at
+* https://www.eclipse.org/legal/epl-2.0/
+*
+* SPDX-License-Identifier: EPL-2.0
+* 
+* Contributors:
+*     Ole Osterhagen - initial API and implementation
+*******************************************************************************/
+package org.eclipse.ui.internal.genericeditor.compare;
+
+import java.io.InputStream;
+
+import org.eclipse.compare.IEncodedStreamContentAccessor;
+import org.eclipse.compare.ITypedElement;
+import org.eclipse.compare.SharedDocumentAdapter;
+import org.eclipse.compare.contentmergeviewer.TextMergeViewer;
+import org.eclipse.core.resources.IEncodedStorage;
+import org.eclipse.core.resources.IStorage;
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.IPath;
+import org.eclipse.core.runtime.IStatus;
+import org.eclipse.core.runtime.PlatformObject;
+import org.eclipse.core.runtime.Status;
+import org.eclipse.jface.preference.IPreferenceStore;
+import org.eclipse.jface.resource.ImageDescriptor;
+import org.eclipse.jface.resource.JFaceResources;
+import org.eclipse.jface.text.source.SourceViewer;
+import org.eclipse.jface.viewers.ISelection;
+import org.eclipse.jface.viewers.StructuredSelection;
+import org.eclipse.jface.viewers.Viewer;
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.widgets.Composite;
+import org.eclipse.swt.widgets.Control;
+import org.eclipse.ui.IEditorInput;
+import org.eclipse.ui.IPersistableElement;
+import org.eclipse.ui.IStorageEditorInput;
+import org.eclipse.ui.PlatformUI;
+import org.eclipse.ui.editors.text.EditorsUI;
+import org.eclipse.ui.internal.genericeditor.ExtensionBasedTextViewerConfiguration;
+import org.eclipse.ui.internal.genericeditor.GenericEditorPlugin;
+import org.eclipse.ui.texteditor.ChainedPreferenceStore;
+import org.eclipse.ui.texteditor.IDocumentProvider;
+
+public class GenericEditorViewer extends Viewer {
+
+	private final SourceViewer sourceViewer;
+
+	private IEditorInput editorInput;
+
+	public GenericEditorViewer(Composite parent) {
+		sourceViewer = new SourceViewer(parent, null, SWT.H_SCROLL | SWT.V_SCROLL);
+		sourceViewer.setEditable(false);
+
+		// use the same font as the TextMergeViewer
+		sourceViewer.getTextWidget().setFont(JFaceResources.getFont(TextMergeViewer.class.getName()));
+		sourceViewer.getTextWidget().addDisposeListener(e -> disconnect());
+	}
+
+	@Override
+	public Control getControl() {
+		return sourceViewer.getControl();
+	}
+
+	@Override
+	public Object getInput() {
+		return editorInput;
+	}
+
+	@Override
+	public ISelection getSelection() {
+		return StructuredSelection.EMPTY;
+	}
+
+	@Override
+	public void refresh() {
+		// empty implementation
+	}
+
+	@Override
+	public void setInput(Object input) {
+		disconnect();
+
+		if (!(input instanceof ITypedElement && input instanceof IEncodedStreamContentAccessor)) {
+			return;
+		}
+
+		IStorage storage = new Storage<>((ITypedElement & IEncodedStreamContentAccessor) input);
+		editorInput = new StorageEditorInput(storage);
+
+		IDocumentProvider documentProvider = SharedDocumentAdapter.getDocumentProvider(editorInput);
+		try {
+			documentProvider.connect(editorInput);
+		} catch (CoreException ex) {
+			GenericEditorPlugin.getDefault().getLog()
+					.log(new Status(IStatus.ERROR, GenericEditorPlugin.BUNDLE_ID, ex.getMessage(), ex));
+		}
+
+		sourceViewer.setDocument(documentProvider.getDocument(editorInput));
+
+		ExtensionBasedTextViewerConfiguration configuration = new ExtensionBasedTextViewerConfiguration(null,
+				new ChainedPreferenceStore(new IPreferenceStore[] { EditorsUI.getPreferenceStore(),
+						GenericEditorPlugin.getDefault().getPreferenceStore() }));
+		sourceViewer.unconfigure();
+		sourceViewer.configure(configuration);
+	}
+
+	@Override
+	public void setSelection(ISelection selection, boolean reveal) {
+		// empty implementation
+	}
+
+	private void disconnect() {
+		if (editorInput != null) {
+			sourceViewer.setDocument(null);
+			SharedDocumentAdapter.getDocumentProvider(editorInput).disconnect(editorInput);
+			editorInput = null;
+		}
+	}
+
+	private static class Storage<T extends ITypedElement & IEncodedStreamContentAccessor> extends PlatformObject
+			implements IEncodedStorage {
+
+		private final T element;
+
+		public Storage(T element) {
+			this.element = element;
+		}
+
+		@Override
+		public InputStream getContents() throws CoreException {
+			return element.getContents();
+		}
+
+		@Override
+		public IPath getFullPath() {
+			return null;
+		}
+
+		@Override
+		public String getName() {
+			return element.getName();
+		}
+
+		@Override
+		public boolean isReadOnly() {
+			return true;
+		}
+
+		@Override
+		public String getCharset() throws CoreException {
+			return element.getCharset();
+		}
+
+	}
+
+	private static class StorageEditorInput extends PlatformObject implements IStorageEditorInput {
+
+		private final IStorage storage;
+
+		public StorageEditorInput(IStorage storage) {
+			this.storage = storage;
+		}
+
+		@Override
+		public boolean exists() {
+			return false;
+		}
+
+		@Override
+		public ImageDescriptor getImageDescriptor() {
+			return PlatformUI.getWorkbench().getEditorRegistry().getImageDescriptor(storage.getName());
+		}
+
+		@Override
+		public String getName() {
+			return storage.getName();
+		}
+
+		@Override
+		public IPersistableElement getPersistable() {
+			return null;
+		}
+
+		@Override
+		public String getToolTipText() {
+			return storage.getName();
+		}
+
+		@Override
+		public IStorage getStorage() throws CoreException {
+			return storage;
+		}
+
+	}
+
+}