[429636] Refactoring of IDifferenceGroupProvider

Replace "defaultSelected" by a rank mechanism.
Move description attribute to IDifferenceGroupProvider.Descriptor

Bug: 429636
Change-Id: I5daab85c14a9c0bfc4856f84af2ac2b336481ac0
Signed-off-by: Arthur Daussy <arthur.daussy@obeo.fr>

21 files changed, 562 insertions, 432 deletions

diff --git a/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/configuration/EMFCompareConfiguration.java b/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/configuration/EMFCompareConfiguration.java
index 212331d6f..7b188adbf 100644
--- a/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/configuration/EMFCompareConfiguration.java
+++ b/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/configuration/EMFCompareConfiguration.java
@@ -1,5 +1,5 @@
 /*******************************************************************************

- * Copyright (c) 2013 Obeo.

+ * Copyright (c) 2013, 2014 Obeo.

  * All rights reserved. This program and the accompanying materials

  * are made available under the terms of the Eclipse Public License v1.0

  * which accompanies this distribution, and is available at

@@ -31,8 +31,10 @@ import org.eclipse.emf.compare.rcp.ui.internal.configuration.impl.EMFComparatorC
 import org.eclipse.emf.compare.rcp.ui.internal.configuration.impl.MergePreviewModeChange;

 import org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.filters.StructureMergeViewerFilter;

 import org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.StructureMergeViewerGrouper;

+import org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl.DefaultGroupProvider;

 import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.filters.IDifferenceFilter;

 import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider;

+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor;

 import org.eclipse.emf.compare.scope.IComparisonScope;

 import org.eclipse.jface.util.IPropertyChangeListener;

 import org.eclipse.jface.util.PropertyChangeEvent;

@@ -200,8 +202,16 @@ public class EMFCompareConfiguration extends ForwardingCompareConfiguration impl
 		EMFCompareRCPUIPlugin plugin = EMFCompareRCPUIPlugin.getDefault();

 		IDifferenceGroupProvider.Descriptor.Registry groupProviderRegistry = plugin

 				.getDifferenceGroupProviderRegistry();

-		getStructureMergeViewerGrouper().setProvider(

-				groupProviderRegistry.getDefaultGroupProvider(comparisonScope, comparison));

+		Descriptor defaultGroupProvider = groupProviderRegistry.getDefaultGroupProvider(comparisonScope,

+				comparison);

+		IDifferenceGroupProvider defaultGroup = null;

+		if (defaultGroupProvider != null) {

+			defaultGroup = defaultGroupProvider.createGroupProvider();

+		}

+		if (defaultGroup == null) {

+			defaultGroup = new DefaultGroupProvider();

+		}

+		getStructureMergeViewerGrouper().setProvider(defaultGroup);

 	}

 

 	protected void initStructureMergeViewerFilter(Comparison comparison, IComparisonScope comparisonScope) {

diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/plugin.properties b/plugins/org.eclipse.emf.compare.rcp.ui/plugin.properties
index e20a38042..969954641 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/plugin.properties
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/plugin.properties
@@ -1,5 +1,5 @@
 ################################################################################
-# Copyright (c) 2012, 2013 Obeo.
+# Copyright (c) 2012, 2014 Obeo.
 # All rights reserved. This program and the accompanying materials
 # are made available under the terms of the Eclipse Public License v1.0
 # which accompanies this distribution, and is available at
@@ -10,7 +10,7 @@
 ################################################################################
 pluginName = EMF Compare RCP UI
 providerName = Eclipse Modeling Project
-emf.compare.no.group = No Group
+emf.compare.default = Default
 emf.compare.kind.groups = By Kind
 emf.compare.side.groups = By Side
 emf.compare.resource.group = By Resource
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/plugin.xml b/plugins/org.eclipse.emf.compare.rcp.ui/plugin.xml
index 4d522fe50..550e39a9d 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/plugin.xml
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/plugin.xml
@@ -21,24 +21,25 @@
    <extension
          point="org.eclipse.emf.compare.rcp.ui.groups">
       <group
-            activeByDefault="true"
             class="org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl.DefaultGroupProvider"
-            label="%emf.compare.no.group">
+            label="%emf.compare.default"
+            rank="100">
       </group>
       <group
-            activeByDefault="false"
             class="org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl.KindGroupProvider"
-            label="%emf.compare.kind.groups">
+            label="%emf.compare.kind.groups"
+            rank="80">
       </group>
       <group
-            activeByDefault="true"
             class="org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl.ThreeWayComparisonGroupProvider"
-            label="%emf.compare.side.groups">
+            label="%emf.compare.side.groups"
+            rank="120"
+            type="THREE_WAY">
       </group>
       <group
-            activeByDefault="false"
             class="org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl.ByResourceGroupProvider"
-            label="%emf.compare.resource.group">
+            label="%emf.compare.resource.group"
+            rank="60">
       </group>
    </extension>
    <extension
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/schema/groups.exsd b/plugins/org.eclipse.emf.compare.rcp.ui/schema/groups.exsd
index 6bfbe2f84..0928bbf9b 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/schema/groups.exsd
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/schema/groups.exsd
@@ -57,7 +57,7 @@ You can provide your own groups by adding an extension of type &lt;samp&gt;org.e
                   A class that implements &lt;samp&gt;org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider&lt;/samp&gt;.

                </documentation>

                <appinfo>

-                  <meta.attribute kind="java" basedOn=":org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider"/>

+                  <meta.attribute kind="java" basedOn=":org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.IDifferenceGroupProvider"/>

                </appinfo>

             </annotation>

          </attribute>

@@ -68,12 +68,53 @@ You can provide your own groups by adding an extension of type &lt;samp&gt;org.e
                </documentation>

             </annotation>

          </attribute>

-         <attribute name="activeByDefault" type="boolean" use="required">

+         <attribute name="activeByDefault" type="boolean">

             <annotation>

                <documentation>

-                  The initial activation state of the filter.

+                  The initial activation state of the group. (Deprecated use rank instead)

+               </documentation>

+               <appinfo>

+                  <meta.attribute deprecated="true"/>

+               </appinfo>

+            </annotation>

+         </attribute>

+         <attribute name="description" type="string">

+            <annotation>

+               <documentation>

+                  A description of the group. (Used in interface)

+               </documentation>

+            </annotation>

+         </attribute>

+         <attribute name="rank" type="string">

+            <annotation>

+               <documentation>

+                  The rank of the group. The highest rank enabled for a comparison is used.

+ 

+ Default value : 0

+               </documentation>

+            </annotation>

+         </attribute>

+         <attribute name="type">

+            <annotation>

+               <documentation>

+                  Type of comparison this group can handle.

+ THREE_WAY: This group can only handle three way comparison.

+ TWO_WAY: This group can handle two way comparison

+ BOTH: This group can handle two and three way comparison.

+ 

+ Default value: BOTH

                </documentation>

             </annotation>

+            <simpleType>

+               <restriction base="string">

+                  <enumeration value="THREE_WAY">

+                  </enumeration>

+                  <enumeration value="TWO_WAY">

+                  </enumeration>

+                  <enumeration value="BOTH">

+                  </enumeration>

+               </restriction>

+            </simpleType>

          </attribute>

       </complexType>

    </element>

@@ -83,7 +124,7 @@ You can provide your own groups by adding an extension of type &lt;samp&gt;org.e
          <meta.section type="since"/>

       </appinfo>

       <documentation>

-         4.0

+         3.0.0

       </documentation>

    </annotation>

 

diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/EMFCompareRCPUIPlugin.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/EMFCompareRCPUIPlugin.java
index dbf92b78a..84fba16c9 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/EMFCompareRCPUIPlugin.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/EMFCompareRCPUIPlugin.java
@@ -19,8 +19,12 @@ import org.eclipse.core.runtime.IExtensionRegistry;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.Status;
+import org.eclipse.core.runtime.preferences.InstanceScope;
 import org.eclipse.emf.compare.rcp.EMFCompareRCPPlugin;
 import org.eclipse.emf.compare.rcp.extension.AbstractRegistryEventListener;
+import org.eclipse.emf.compare.rcp.internal.extension.IItemRegistry;
+import org.eclipse.emf.compare.rcp.internal.extension.impl.ItemRegistry;
+import org.eclipse.emf.compare.rcp.internal.preferences.EMFComparePreferences;
 import org.eclipse.emf.compare.rcp.ui.contentmergeviewer.accessor.factory.IAccessorFactory;
 import org.eclipse.emf.compare.rcp.ui.internal.configuration.ui.ConfigurationUIRegistryEventListener;
 import org.eclipse.emf.compare.rcp.ui.internal.configuration.ui.IConfigurationUIFactory;
@@ -78,6 +82,8 @@ public class EMFCompareRCPUIPlugin extends AbstractUIPlugin {
 
 	private AbstractRegistryEventListener groupProviderRegistryListener;
 
+	private IItemRegistry<IDifferenceGroupProvider.Descriptor> groupItemRegistry;
+
 	private IDifferenceGroupProvider.Descriptor.Registry groupProviderRegistry;
 
 	private AbstractRegistryEventListener filterRegistryListener;
@@ -97,6 +103,17 @@ public class EMFCompareRCPUIPlugin extends AbstractUIPlugin {
 	private ConfigurationUIRegistryEventListener matchEngineConfiguratorRegistryListener;
 
 	/**
+	 * Instance scope for preferences.
+	 * <p>
+	 * Do not use singleton to respect Helios compatibility
+	 * </p>
+	 * 
+	 * @see org.eclipse.core.runtime.preferences.InstanceScope#INSTANCE
+	 */
+	@SuppressWarnings("deprecation")
+	private InstanceScope instanceScope = new InstanceScope();
+
+	/**
 	 * The constructor.
 	 */
 	public EMFCompareRCPUIPlugin() {
@@ -114,9 +131,13 @@ public class EMFCompareRCPUIPlugin extends AbstractUIPlugin {
 
 		IExtensionRegistry extensionRegistry = Platform.getExtensionRegistry();
 
-		groupProviderRegistry = new DifferenceGroupRegistryImpl();
+		groupItemRegistry = new ItemRegistry<IDifferenceGroupProvider.Descriptor>();
+		groupProviderRegistry = new DifferenceGroupRegistryImpl(groupItemRegistry, instanceScope
+				.getNode(PLUGIN_ID), EMFComparePreferences.TWO_WAY_GROUP_RANKING,
+				EMFComparePreferences.THREE_WAY_GROUP_RANKING);
 		groupProviderRegistryListener = new DifferenceGroupProviderExtensionRegistryListener(PLUGIN_ID,
-				GROUP_PROVIDER_PPID, getLog(), groupProviderRegistry);
+				GROUP_PROVIDER_PPID, getLog(), groupItemRegistry);
+
 		extensionRegistry.addListener(groupProviderRegistryListener, PLUGIN_ID + "." + GROUP_PROVIDER_PPID); //$NON-NLS-1$
 		groupProviderRegistryListener.readRegistry(extensionRegistry);
 
@@ -176,6 +197,7 @@ public class EMFCompareRCPUIPlugin extends AbstractUIPlugin {
 
 		extensionRegistry.removeListener(groupProviderRegistryListener);
 		groupProviderRegistryListener = null;
+		groupItemRegistry = null;
 		groupProviderRegistry = null;
 
 		plugin = null;
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/emfcomparercpuimessages.properties b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/emfcomparercpuimessages.properties
index a825559f3..5445147ca 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/emfcomparercpuimessages.properties
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/emfcomparercpuimessages.properties
@@ -17,8 +17,6 @@ FilterActionMenu.tooltip = Filters
 
 GroupActionMenu.tooltip = Groups
 
-DefaultGroupProvider.label = Default
-
 KindGroupProvider.addition.label = Additions
 KindGroupProvider.deletion.label = Deletions
 KindGroupProvider.change.label = Changes
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupAction.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupAction.java
index 041887e5d..b96e54282 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupAction.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupAction.java
@@ -40,8 +40,8 @@ public class GroupAction extends Action {
 	 *            The group provider associated with this action.
 	 */
 	public GroupAction(StructureMergeViewerGrouper structureMergeViewerGrouper,
-			IDifferenceGroupProvider provider) {
-		super(provider.getLabel(), IAction.AS_RADIO_BUTTON);
+			IDifferenceGroupProvider provider, String label) {
+		super(label, IAction.AS_RADIO_BUTTON);
 		this.structureMergeViewerGrouper = structureMergeViewerGrouper;
 		this.provider = provider;
 	}
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupActionMenu.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupActionMenu.java
index 06562ac20..4f80b46be 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupActionMenu.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/actions/GroupActionMenu.java
@@ -71,11 +71,14 @@ public class GroupActionMenu extends Action implements IMenuCreator {
 	public void updateMenu(IComparisonScope scope, Comparison comparison) {
 		menuManager.removeAll();
 
-		for (IDifferenceGroupProvider dgp : registry.getGroupProviders(scope, comparison)) {
-			IAction action = new GroupAction(structureMergeViewerGrouper, dgp);
-			menuManager.add(action);
-			if (dgp == structureMergeViewerGrouper.getProvider()) {
-				action.setChecked(true);
+		for (IDifferenceGroupProvider.Descriptor dgp : registry.getGroupProviders(scope, comparison)) {
+			IDifferenceGroupProvider gp = dgp.createGroupProvider();
+			if (gp != null) {
+				IAction action = new GroupAction(structureMergeViewerGrouper, gp, dgp.getLabel());
+				menuManager.add(action);
+				if (dgp == structureMergeViewerGrouper.getProvider()) {
+					action.setChecked(true);
+				}
 			}
 		}
 	}
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ByResourceGroupProvider.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ByResourceGroupProvider.java
index 91c3c6233..e54974b82 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ByResourceGroupProvider.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ByResourceGroupProvider.java
@@ -47,9 +47,6 @@ import org.eclipse.emf.edit.tree.TreeNode;
  */
 public class ByResourceGroupProvider extends AbstractDifferenceGroupProvider {
 
-	/** A human-readable label for this group provider. This will be displayed in the EMF Compare UI. */
-	private String label;
-
 	/** The initial activation state of the group provider. */
 	private boolean activeByDefault;
 
@@ -76,42 +73,6 @@ public class ByResourceGroupProvider extends AbstractDifferenceGroupProvider {
 	/**
 	 * {@inheritDoc}
 	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getLabel()
-	 */
-	public String getLabel() {
-		return label;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setLabel(java.lang.String)
-	 */
-	public void setLabel(String label) {
-		this.label = label;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#defaultSelected()
-	 */
-	public boolean defaultSelected() {
-		return activeByDefault;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setDefaultSelected(boolean)
-	 */
-	public void setDefaultSelected(boolean active) {
-		this.activeByDefault = active;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#isEnabled(org
 	 *      .eclipse.emf.compare.scope.IComparisonScope, org.eclipse.emf.compare.Comparison)
 	 */
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DefaultGroupProvider.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DefaultGroupProvider.java
index af34926aa..efa6d0bff 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DefaultGroupProvider.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DefaultGroupProvider.java
@@ -17,7 +17,6 @@ import com.google.common.collect.ImmutableList;
 import java.util.Collection;
 
 import org.eclipse.emf.compare.Comparison;
-import org.eclipse.emf.compare.rcp.ui.internal.EMFCompareRCPUIMessages;
 import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.AbstractDifferenceGroupProvider;
 import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroup;
 import org.eclipse.emf.compare.scope.IComparisonScope;
@@ -55,42 +54,6 @@ public class DefaultGroupProvider extends AbstractDifferenceGroupProvider {
 	/**
 	 * {@inheritDoc}
 	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getLabel()
-	 */
-	public String getLabel() {
-		return EMFCompareRCPUIMessages.getString("DefaultGroupProvider.label"); //$NON-NLS-1$
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setLabel(java.lang.String)
-	 */
-	public void setLabel(String label) {
-
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#defaultSelected()
-	 */
-	public boolean defaultSelected() {
-		return true;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setDefaultSelected(boolean)
-	 */
-	public void setDefaultSelected(boolean defaultSelected) {
-
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#isEnabled(org
 	 *      .eclipse.emf.compare.scope.IComparisonScope, org.eclipse.emf.compare.Comparison)
 	 */
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupDescriptorWrapper.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupDescriptorWrapper.java
new file mode 100644
index 000000000..3ea376952
--- /dev/null
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupDescriptorWrapper.java
@@ -0,0 +1,88 @@
+/******************************************************************************
+ * Copyright (c) 2014 Obeo.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl;
+
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.IConfigurationElement;
+import org.eclipse.emf.compare.rcp.internal.extension.impl.AbstractItemDescriptor;
+import org.eclipse.emf.compare.rcp.ui.EMFCompareRCPUIPlugin;
+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider;
+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.ComparisonType;
+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor;
+
+/**
+ * Implementation of {@link IDifferenceGroupProvider.Descriptor}.
+ * 
+ * @author <a href="mailto:arthur.daussy@obeo.fr">Arthur Daussy</a>
+ */
+public class DifferenceGroupDescriptorWrapper extends AbstractItemDescriptor<IDifferenceGroupProvider.Descriptor> implements IDifferenceGroupProvider.Descriptor {
+
+	/** {@link IConfigurationElement} used to instantiate the {@link IDifferenceGroupProvider} */
+	private final IConfigurationElement element;
+
+	/** Type of comparison the {@link IDifferenceGroupProvider} can handle. */
+	private final ComparisonType type;
+
+	/**
+	 * Constructor.
+	 * 
+	 * @param label
+	 *            Human-readable label of the underlying group provider.
+	 * @param description
+	 *            A more detailed description that can be displayed to the user for this group.
+	 * @param elem
+	 *            {@link IConfigurationElement} used to instantiate the {@link IDifferenceGroupProvider}
+	 * @param rank
+	 *            Rank of the descriptor
+	 * @param comparisonType
+	 *            Type of comparison the wrapped {@link IDifferenceGroupProvider} can handle.
+	 */
+	public DifferenceGroupDescriptorWrapper(String label, String description, IConfigurationElement elem,
+			int rank, ComparisonType comparisonType) {
+		super(label, description, rank, elem
+				.getAttribute(DifferenceGroupProviderExtensionRegistryListener.ATT_CLASS));
+		this.element = elem;
+		this.type = comparisonType;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public Descriptor getItem() {
+		return this;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public ComparisonType getType() {
+		return type;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public IDifferenceGroupProvider createGroupProvider() {
+		Object instance;
+		try {
+			instance = element
+					.createExecutableExtension(DifferenceGroupProviderExtensionRegistryListener.ATT_CLASS);
+			if (instance instanceof IDifferenceGroupProvider) {
+				IDifferenceGroupProvider groupProvider = (IDifferenceGroupProvider)instance;
+				return groupProvider;
+			}
+		} catch (CoreException e) {
+			EMFCompareRCPUIPlugin.getDefault().log(e);
+		}
+		return null;
+	}
+
+}
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderDescriptorImpl.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderDescriptorImpl.java
deleted file mode 100644
index 6387f947c..000000000
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderDescriptorImpl.java
+++ /dev/null
@@ -1,60 +0,0 @@
-/*******************************************************************************

- * Copyright (c) 2013, 2014 Obeo.

- * All rights reserved. This program and the accompanying materials

- * are made available under the terms of the Eclipse Public License v1.0

- * which accompanies this distribution, and is available at

- * http://www.eclipse.org/legal/epl-v10.html

- * 

- * Contributors:

- *     Obeo - initial API and implementation

- *******************************************************************************/

-package org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl;

-

-import org.eclipse.core.runtime.IConfigurationElement;

-import org.eclipse.emf.compare.rcp.extension.PluginClassDescriptor;

-import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider;

-

-/**

- * Default implementation of {@link IDifferenceGroupProvider.Descriptor}.

- * 

- * @author <a href="mailto:axel.richard@obeo.fr">Axel Richard</a>

- * @since 4.0

- */

-public class DifferenceGroupProviderDescriptorImpl extends PluginClassDescriptor<IDifferenceGroupProvider> implements IDifferenceGroupProvider.Descriptor {

-

-	/** The label of the group provider. */

-	private String label;

-

-	/** The state of the default selection of the group provider. */

-	private boolean defaultSelected;

-

-	/**

-	 * Creates a descriptor corresponding to the information of the given <em>element</em>.

-	 * 

-	 * @param element

-	 *            Configuration element from which to create this descriptor.

-	 * @param label

-	 *            The label of the group provider.

-	 * @param defaultSelected

-	 *            The state of the default selection of the group provider.

-	 */

-	public DifferenceGroupProviderDescriptorImpl(IConfigurationElement element, String label,

-			boolean defaultSelected) {

-		super(element, DifferenceGroupProviderExtensionRegistryListener.ATT_CLASS);

-		this.label = label;

-		this.defaultSelected = defaultSelected;

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see IDifferenceGroupProvider.Descriptor#createGroupProvider()

-	 */

-	public IDifferenceGroupProvider createGroupProvider() {

-		IDifferenceGroupProvider differenceGroupProvider = this.createInstance();

-		differenceGroupProvider.setLabel(label);

-		differenceGroupProvider.setDefaultSelected(defaultSelected);

-		return differenceGroupProvider;

-	}

-

-}

diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderExtensionRegistryListener.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderExtensionRegistryListener.java
index 8c96449bd..b50f8afa9 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderExtensionRegistryListener.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupProviderExtensionRegistryListener.java
@@ -14,7 +14,11 @@ import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.ILog;

 import org.eclipse.core.runtime.IStatus;

 import org.eclipse.emf.compare.rcp.extension.AbstractRegistryEventListener;

+import org.eclipse.emf.compare.rcp.internal.extension.IItemDescriptor;

+import org.eclipse.emf.compare.rcp.internal.extension.IItemRegistry;

 import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider;

+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.ComparisonType;

+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor;

 

 /**

  * Utility class to listen to the {@link IDifferenceGroupProvider.Descriptor.Registry}.

@@ -24,20 +28,29 @@ import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGro
  */

 public class DifferenceGroupProviderExtensionRegistryListener extends AbstractRegistryEventListener {

 

+	/** Default value for the rank attribute if not specified. */

+	private static final int DEFAULT_RANK_VALUE = 0;

+

 	/** TAG_GROUP_PROVIDER. */

 	static final String TAG_GROUP_PROVIDER = "group"; //$NON-NLS-1$

 

-	/** ATT_CLASS. */

-	static final String ATT_CLASS = "class"; //$NON-NLS-1$

-

 	/** ATT_LABEL. */

 	static final String ATT_LABEL = "label"; //$NON-NLS-1$

 

-	/** ATT_ACTIVE. */

-	static final String ATT_ACTIVE = "activeByDefault"; //$NON-NLS-1$

+	/** ATT_DESCRIPTION. */

+	static final String ATT_DESCRIPTION = "description"; //$NON-NLS-1$

+

+	/** ATT_COMPARISON_TYPE. */

+	static final String ATT_COMPARISON_TYPE = "type"; //$NON-NLS-1$

+

+	/** ATT_RANK. */

+	static final String ATT_RANK = "rank"; //$NON-NLS-1$

+

+	/** ATT_CLASS. */

+	static final String ATT_CLASS = "class"; //$NON-NLS-1$

 

 	/** The IDifferenceGroupProvider.Descriptor.Registry to listen. */

-	private final IDifferenceGroupProvider.Descriptor.Registry groupProviderRegistry;

+	private final IItemRegistry<IDifferenceGroupProvider.Descriptor> groupProviderRegistry;

 

 	/**

 	 * Default constructor.

@@ -52,7 +65,7 @@ public class DifferenceGroupProviderExtensionRegistryListener extends AbstractRe
 	 *            The {@link IDifferenceGroupProvider.Descriptor.Registry} to listen.

 	 */

 	public DifferenceGroupProviderExtensionRegistryListener(String pluginID, String extensionPointID,

-			ILog log, IDifferenceGroupProvider.Descriptor.Registry registry) {

+			ILog log, IItemRegistry<IDifferenceGroupProvider.Descriptor> registry) {

 		super(pluginID, extensionPointID, log);

 		this.groupProviderRegistry = registry;

 	}

@@ -65,7 +78,6 @@ public class DifferenceGroupProviderExtensionRegistryListener extends AbstractRe
 	@Override

 	protected boolean validateExtensionElement(IConfigurationElement element) {

 		final boolean valid;

-

 		if (element.getName().equals(TAG_GROUP_PROVIDER)) {

 			if (element.getAttribute(ATT_CLASS) == null) {

 				logMissingAttribute(element, ATT_CLASS);

@@ -73,9 +85,22 @@ public class DifferenceGroupProviderExtensionRegistryListener extends AbstractRe
 			} else if (element.getAttribute(ATT_LABEL) == null) {

 				logMissingAttribute(element, ATT_LABEL);

 				valid = false;

-			} else if (element.getAttribute(ATT_ACTIVE) == null) {

-				logMissingAttribute(element, ATT_ACTIVE);

-				valid = false;

+			} else if (element.getAttribute(ATT_RANK) != null) {

+				try {

+					Integer.valueOf(element.getAttribute(ATT_RANK));

+				} catch (NumberFormatException e) {

+					log(element, e);

+					return false;

+				}

+				valid = true;

+			} else if (element.getAttribute(ATT_COMPARISON_TYPE) != null) {

+				try {

+					ComparisonType.valueOf(element.getAttribute(ATT_COMPARISON_TYPE));

+					valid = true;

+				} catch (IllegalArgumentException e) {

+					log(element, e);

+					return false;

+				}

 			} else {

 				valid = true;

 			}

@@ -92,11 +117,26 @@ public class DifferenceGroupProviderExtensionRegistryListener extends AbstractRe
 	 */

 	@Override

 	protected boolean addedValid(IConfigurationElement element) {

-		IDifferenceGroupProvider.Descriptor providerDescriptor = new DifferenceGroupProviderDescriptorImpl(

-				element, element.getAttribute(ATT_LABEL), Boolean.valueOf(element.getAttribute(ATT_ACTIVE))

-						.booleanValue());

-		IDifferenceGroupProvider.Descriptor previous = groupProviderRegistry.add(providerDescriptor, element

-				.getAttribute(ATT_CLASS));

+		String rankValue = element.getAttribute(ATT_RANK);

+		final int rank;

+		if (rankValue == null) {

+			rank = DEFAULT_RANK_VALUE;

+		} else {

+			rank = Integer.valueOf(rankValue).intValue();

+		}

+		String typeAttribute = element.getAttribute(ATT_COMPARISON_TYPE);

+		final ComparisonType type;

+		if (typeAttribute != null) {

+			type = ComparisonType.valueOf(typeAttribute);

+		} else {

+			type = ComparisonType.BOTH;

+		}

+		String label = element.getAttribute(ATT_LABEL);

+		String description = element.getAttribute(ATT_DESCRIPTION);

+		DifferenceGroupDescriptorWrapper itemDescriptor = new DifferenceGroupDescriptorWrapper(label, description,

+				element, rank, type);

+

+		IItemDescriptor<Descriptor> previous = groupProviderRegistry.add(itemDescriptor);

 		if (previous != null) {

 			log(IStatus.WARNING, element, "The group provider descriptor'" + element.getAttribute(ATT_CLASS) //$NON-NLS-1$

 					+ "' is registered twice."); //$NON-NLS-1$

diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupRegistryImpl.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupRegistryImpl.java
index 3875a8d39..ad757210d 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupRegistryImpl.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/DifferenceGroupRegistryImpl.java
@@ -10,23 +10,32 @@
  *******************************************************************************/

 package org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl;

 

-import static com.google.common.base.Predicates.instanceOf;

-import static com.google.common.collect.Iterables.indexOf;

 import static com.google.common.collect.Lists.newArrayList;

 

 import com.google.common.base.Preconditions;

+import com.google.common.base.Predicate;

 import com.google.common.collect.ImmutableList;

+import com.google.common.collect.Iterables;

+import com.google.common.collect.Lists;

 

+import java.util.Collections;

 import java.util.List;

-import java.util.Map;

-import java.util.concurrent.ConcurrentHashMap;

+import java.util.ListIterator;

 

 import org.eclipse.emf.compare.Comparison;

+import org.eclipse.emf.compare.rcp.internal.extension.IItemDescriptor;

+import org.eclipse.emf.compare.rcp.internal.extension.IItemRegistry;

+import org.eclipse.emf.compare.rcp.internal.extension.impl.ItemUtil;

+import org.eclipse.emf.compare.rcp.internal.extension.impl.WrapperItemDescriptor;

 import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider;

+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.ComparisonType;

+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor;

 import org.eclipse.emf.compare.scope.IComparisonScope;

+import org.osgi.service.prefs.Preferences;

 

 /**

- * The default implementation of the {@link IDifferenceGroupProvider.Descriptor.Registry}.

+ * Implementation of the {@link IDifferenceGroupProvider.Descriptor.Registry}. This implementation allow user

+ * to override ranking of each group using preferences.

  * 

  * @author <a href="mailto:axel.richard@obeo.fr">Axel Richard</a>

  * @since 4.0

@@ -34,13 +43,46 @@ import org.eclipse.emf.compare.scope.IComparisonScope;
 public class DifferenceGroupRegistryImpl implements IDifferenceGroupProvider.Descriptor.Registry {

 

 	/** A map that associates the class name to theirs {@link IDifferenceGroupProvider.Descriptor}s. */

-	private final Map<String, IDifferenceGroupProvider.Descriptor> map;

+	private final IItemRegistry<IDifferenceGroupProvider.Descriptor> registry;

+

+	/** Preference key for two way comparison group ranking. */

+	private final String twoWayPreferenceKey;

+

+	/** Preference key for three way comparison group ranking. */

+	private final String threeWayPrefenceKey;

+

+	/** Preferences holding ranked descriptors. */

+	private Preferences preferences;

 

 	/**

 	 * Constructs the registry.

+	 * 

+	 * @param twoWaygroupProviderDescriptors

+	 */

+	public DifferenceGroupRegistryImpl(IItemRegistry<IDifferenceGroupProvider.Descriptor> registry,

+			Preferences preferences, String twoWayPreferenceKey, String threeWayPrefenceKey) {

+		this.registry = registry;

+		this.twoWayPreferenceKey = twoWayPreferenceKey;

+		this.threeWayPrefenceKey = threeWayPrefenceKey;

+		this.preferences = preferences;

+	}

+

+	/**

+	 * Return an ordered list of IItemDescriptor<IDifferenceGroupProvider.Descriptor>.

+	 * 

+	 * @return Ordered list of IItemDescriptor<IDifferenceGroupProvider.Descriptor>.

 	 */

-	public DifferenceGroupRegistryImpl() {

-		map = new ConcurrentHashMap<String, IDifferenceGroupProvider.Descriptor>();

+	private List<IItemDescriptor<IDifferenceGroupProvider.Descriptor>> getOrderedGroupProviderDescriptors(

+			final Comparison comparison) {

+		final List<IItemDescriptor<Descriptor>> items;

+		if (comparison.isThreeWay()) {

+			items = ItemUtil.getOrderedItems(getDefaultThreeWayDescriptors(), registry, threeWayPrefenceKey,

+					preferences);

+		} else {

+			items = ItemUtil.getOrderedItems(getDefaultTwoWayDescriptors(), registry, twoWayPreferenceKey,

+					preferences);

+		}

+		return items;

 	}

 

 	/**

@@ -49,20 +91,23 @@ public class DifferenceGroupRegistryImpl implements IDifferenceGroupProvider.Des
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor.Registry#getGroupProviders(IComparisonScope,

 	 *      Comparison)

 	 */

-	public List<IDifferenceGroupProvider> getGroupProviders(IComparisonScope scope, Comparison comparison) {

-		List<IDifferenceGroupProvider> providers = newArrayList();

-		for (IDifferenceGroupProvider.Descriptor desc : map.values()) {

-			IDifferenceGroupProvider groupProvider = desc.createGroupProvider();

-			if (isGroupProviderActivable(groupProvider, scope, comparison)) {

-				providers.add(groupProvider);

+	public List<IDifferenceGroupProvider.Descriptor> getGroupProviders(IComparisonScope scope,

+			Comparison comparison) {

+		if (comparison != null) {

+			List<IDifferenceGroupProvider.Descriptor> providers = newArrayList();

+			List<IItemDescriptor<Descriptor>> groupProviderDescriptors = getOrderedGroupProviderDescriptors(comparison);

+			ListIterator<IItemDescriptor<Descriptor>> groupIterator = groupProviderDescriptors.listIterator();

+			while (groupIterator.hasNext()) {

+				IItemDescriptor<Descriptor> desc = groupIterator.next();

+				IDifferenceGroupProvider.Descriptor groupProviderDescriptor = desc.getItem();

+				IDifferenceGroupProvider gp = groupProviderDescriptor.createGroupProvider();

+				if (gp != null && isGroupProviderActivable(gp, scope, comparison)) {

+					providers.add(groupProviderDescriptor);

+				}

 			}

+			return ImmutableList.copyOf(providers);

 		}

-		int indexOfDefault = indexOf(providers, instanceOf(DefaultGroupProvider.class));

-		if (indexOfDefault >= 0) {

-			IDifferenceGroupProvider defaultGroupProvider = providers.remove(indexOfDefault);

-			providers.add(0, defaultGroupProvider);

-		}

-		return ImmutableList.copyOf(providers);

+		return Collections.emptyList();

 	}

 

 	/**

@@ -71,16 +116,13 @@ public class DifferenceGroupRegistryImpl implements IDifferenceGroupProvider.Des
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor.Registry#getDefaultGroupProvider(org.eclipse.emf.compare.scope.IComparisonScope,

 	 *      org.eclipse.emf.compare.Comparison)

 	 */

-	public IDifferenceGroupProvider getDefaultGroupProvider(IComparisonScope scope, Comparison comparison) {

-		IDifferenceGroupProvider selectedGroupProvider = null;

-		for (IDifferenceGroupProvider dgp : getGroupProviders(scope, comparison)) {

-			if (dgp.defaultSelected()) {

-				if (selectedGroupProvider == null || !(dgp instanceof DefaultGroupProvider)) {

-					selectedGroupProvider = dgp;

-				}

-			}

+	public IDifferenceGroupProvider.Descriptor getDefaultGroupProvider(IComparisonScope scope,

+			Comparison comparison) {

+		List<IDifferenceGroupProvider.Descriptor> descriptors = getGroupProviders(scope, comparison);

+		if (!descriptors.isEmpty()) {

+			return descriptors.get(0);

 		}

-		return selectedGroupProvider;

+		return null;

 	}

 

 	/**

@@ -108,7 +150,16 @@ public class DifferenceGroupRegistryImpl implements IDifferenceGroupProvider.Des
 	public IDifferenceGroupProvider.Descriptor add(IDifferenceGroupProvider.Descriptor providerDescriptor,

 			String className) {

 		Preconditions.checkNotNull(providerDescriptor);

-		return map.put(className, providerDescriptor);

+		IDifferenceGroupProvider groupProvider = providerDescriptor.createGroupProvider();

+		WrapperItemDescriptor<IDifferenceGroupProvider.Descriptor> descriptor = new WrapperItemDescriptor<IDifferenceGroupProvider.Descriptor>(

+				providerDescriptor.getLabel(), providerDescriptor.getDescription(), providerDescriptor

+						.getRank(), groupProvider.getClass().getName(), providerDescriptor);

+

+		IItemDescriptor<Descriptor> oldValue = registry.add(descriptor);

+		if (oldValue != null) {

+			return oldValue.getItem();

+		}

+		return null;

 	}

 

 	/**

@@ -117,7 +168,11 @@ public class DifferenceGroupRegistryImpl implements IDifferenceGroupProvider.Des
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor.Registry#remove(java.lang.String)

 	 */

 	public IDifferenceGroupProvider.Descriptor remove(String className) {

-		return map.remove(className);

+		IItemDescriptor<IDifferenceGroupProvider.Descriptor> oldValue = registry.remove(className);

+		if (oldValue != null) {

+			return oldValue.getItem();

+		}

+		return null;

 	}

 

 	/**

@@ -126,6 +181,51 @@ public class DifferenceGroupRegistryImpl implements IDifferenceGroupProvider.Des
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider.Descriptor.Registry#clear()

 	 */

 	public void clear() {

-		map.clear();

+		registry.clear();

+	}

+

+	/**

+	 * Get an ordered list of default descriptors for a three way comparison.

+	 * 

+	 * @return

+	 */

+	private List<IItemDescriptor<Descriptor>> getDefaultTwoWayDescriptors() {

+		Iterable<IItemDescriptor<Descriptor>> threeWayGroups = Iterables.filter(

+				registry.getItemDescriptors(), new Predicate<IItemDescriptor<Descriptor>>() {

+

+					public boolean apply(IItemDescriptor<Descriptor> descriptor) {

+						if (descriptor == null) {

+							return false;

+						}

+						ComparisonType type = descriptor.getItem().getType();

+						return type == ComparisonType.BOTH || type == ComparisonType.TWO_WAY;

+					}

+				});

+		List<IItemDescriptor<Descriptor>> result = Lists.newArrayList(threeWayGroups);

+		Collections.sort(result, Collections.reverseOrder());

+		return result;

+	}

+

+	/**

+	 * Get an ordered list of default descriptors for a three way comparison.

+	 * 

+	 * @return

+	 */

+	private List<IItemDescriptor<Descriptor>> getDefaultThreeWayDescriptors() {

+		Iterable<IItemDescriptor<Descriptor>> twoWayComparison = Iterables.filter(registry

+				.getItemDescriptors(), new Predicate<IItemDescriptor<Descriptor>>() {

+

+			public boolean apply(IItemDescriptor<Descriptor> descriptor) {

+				if (descriptor == null) {

+					return false;

+				}

+				ComparisonType type = descriptor.getItem().getType();

+				return type == ComparisonType.BOTH || type == ComparisonType.THREE_WAY;

+			}

+		});

+		List<IItemDescriptor<Descriptor>> result = Lists.newArrayList(twoWayComparison);

+		Collections.sort(result, Collections.reverseOrder());

+		return result;

 	}

+

 }

diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/EmptyDifferenceGroupProvider.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/EmptyDifferenceGroupProvider.java
index 45af3a00d..d7516675c 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/EmptyDifferenceGroupProvider.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/EmptyDifferenceGroupProvider.java
@@ -1,98 +1,59 @@
-/*******************************************************************************

- * Copyright (c) 2014 Obeo.

- * All rights reserved. This program and the accompanying materials

- * are made available under the terms of the Eclipse Public License v1.0

- * which accompanies this distribution, and is available at

- * http://www.eclipse.org/legal/epl-v10.html

- * 

- * Contributors:

- *     Obeo - initial API and implementation

- *******************************************************************************/

-package org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl;

-

-import com.google.common.collect.ImmutableList;

-

-import java.util.Collection;

-

-import org.eclipse.emf.compare.Comparison;

-import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.AbstractDifferenceGroupProvider;

-import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroup;

-import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider;

-import org.eclipse.emf.compare.scope.IComparisonScope;

-

-/**

- * An empty difference group provider.

- * 

- * @author <a href="mailto:axel.richard@obeo.fr">Axel Richard</a>

- * @since 4.0

- */

-public class EmptyDifferenceGroupProvider extends AbstractDifferenceGroupProvider {

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getGroups(org.eclipse.emf.compare.Comparison)

-	 */

-	public Collection<? extends IDifferenceGroup> getGroups(Comparison comparison) {

-		return ImmutableList.of();

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getLabel()

-	 */

-	public String getLabel() {

-		return IDifferenceGroupProvider.class.getName() + ".EMPTY"; //$NON-NLS-1$

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setLabel(java.lang.String)

-	 */

-	public void setLabel(String label) {

-		// do nothing

-

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#defaultSelected()

-	 */

-	public boolean defaultSelected() {

-		return true;

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setDefaultSelected(boolean)

-	 */

-	public void setDefaultSelected(boolean defaultSelected) {

-		// do nothing;

-

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#isEnabled(Open

-	 *      Declaration org.eclipse.emf.compare.scope.IComparisonScope, org.eclipse.emf.compare.Comparison)

-	 */

-	public boolean isEnabled(IComparisonScope scope, Comparison comparison) {

-		return true;

-	}

-

-	/**

-	 * {@inheritDoc}

-	 * 

-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#dispose()

-	 */

-	public void dispose() {

-		// do nothing;

-

-	}

-

-}

+/*******************************************************************************
+ * Copyright (c) 2014 Obeo.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.emf.compare.rcp.ui.internal.structuremergeviewer.groups.impl;
+
+import com.google.common.collect.ImmutableList;
+
+import java.util.Collection;
+
+import org.eclipse.emf.compare.Comparison;
+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.AbstractDifferenceGroupProvider;
+import org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroup;
+import org.eclipse.emf.compare.scope.IComparisonScope;
+
+/**
+ * An empty difference group provider.
+ * 
+ * @author <a href="mailto:axel.richard@obeo.fr">Axel Richard</a>
+ * @since 4.0
+ */
+public class EmptyDifferenceGroupProvider extends AbstractDifferenceGroupProvider {
+
+	/**
+	 * {@inheritDoc}
+	 * 
+	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getGroups(org.eclipse.emf.compare.Comparison)
+	 */
+	public Collection<? extends IDifferenceGroup> getGroups(Comparison comparison) {
+		return ImmutableList.of();
+	}
+
+	/**
+	 * {@inheritDoc}
+	 * 
+	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#isEnabled(Open
+	 *      Declaration org.eclipse.emf.compare.scope.IComparisonScope, org.eclipse.emf.compare.Comparison)
+	 */
+	public boolean isEnabled(IComparisonScope scope, Comparison comparison) {
+		return true;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 * 
+	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#dispose()
+	 */
+	public void dispose() {
+		// do nothing;
+
+	}
+
+}
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/KindGroupProvider.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/KindGroupProvider.java
index 500ad626d..e3c4d84d0 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/KindGroupProvider.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/KindGroupProvider.java
@@ -34,12 +34,6 @@ import org.eclipse.emf.compare.scope.IComparisonScope;
  */
 public class KindGroupProvider extends AbstractDifferenceGroupProvider {
 
-	/** A human-readable label for this group provider. This will be displayed in the EMF Compare UI. */
-	private String label;
-
-	/** The initial activation state of the group provider. */
-	private boolean activeByDefault;
-
 	/** The groups provided by this provider. */
 	private ImmutableList<IDifferenceGroup> differenceGroups;
 
@@ -88,42 +82,6 @@ public class KindGroupProvider extends AbstractDifferenceGroupProvider {
 	/**
 	 * {@inheritDoc}
 	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getLabel()
-	 */
-	public String getLabel() {
-		return label;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setLabel(java.lang.String)
-	 */
-	public void setLabel(String label) {
-		this.label = label;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#defaultSelected()
-	 */
-	public boolean defaultSelected() {
-		return activeByDefault;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setDefaultSelected(boolean)
-	 */
-	public void setDefaultSelected(boolean active) {
-		this.activeByDefault = active;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#isEnabled(org
 	 *      .eclipse.emf.compare.scope.IComparisonScope, org.eclipse.emf.compare.Comparison)
 	 */
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ThreeWayComparisonGroupProvider.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ThreeWayComparisonGroupProvider.java
index 8f106dda7..efb1e7f5d 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ThreeWayComparisonGroupProvider.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/internal/structuremergeviewer/groups/impl/ThreeWayComparisonGroupProvider.java
@@ -61,12 +61,6 @@ import org.eclipse.emf.edit.tree.TreeNode;
  */
 public class ThreeWayComparisonGroupProvider extends AbstractDifferenceGroupProvider {
 
-	/** A human-readable label for this group provider. This will be displayed in the EMF Compare UI. */
-	private String label;
-
-	/** The initial activation state of the group provider. */
-	private boolean activeByDefault;
-
 	/** The groups provided by this provider. */
 	private ImmutableList<IDifferenceGroup> differenceGroups;
 
@@ -102,42 +96,6 @@ public class ThreeWayComparisonGroupProvider extends AbstractDifferenceGroupProv
 	/**
 	 * {@inheritDoc}
 	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#getLabel()
-	 */
-	public String getLabel() {
-		return label;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setLabel(java.lang.String)
-	 */
-	public void setLabel(String label) {
-		this.label = label;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#defaultSelected()
-	 */
-	public boolean defaultSelected() {
-		return activeByDefault;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
-	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#setDefaultSelected(boolean)
-	 */
-	public void setDefaultSelected(boolean active) {
-		this.activeByDefault = active;
-	}
-
-	/**
-	 * {@inheritDoc}
-	 * 
 	 * @see org.eclipse.emf.compare.rcp.ui.structuremergeviewer.groups.IDifferenceGroupProvider#isEnabled(org
 	 *      .eclipse.emf.compare.scope.IComparisonScope, org.eclipse.emf.compare.Comparison)
 	 */
diff --git a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/structuremergeviewer/groups/IDifferenceGroupProvider.java b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/structuremergeviewer/groups/IDifferenceGroupProvider.java
index 019b2f3dd..1c9ccf429 100644
--- a/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/structuremergeviewer/groups/IDifferenceGroupProvider.java
+++ b/plugins/org.eclipse.emf.compare.rcp.ui/src/org/eclipse/emf/compare/rcp/ui/structuremergeviewer/groups/IDifferenceGroupProvider.java
@@ -41,37 +41,6 @@ public interface IDifferenceGroupProvider extends Adapter {
 	Collection<? extends IDifferenceGroup> getGroups(Comparison comparison);
 
 	/**
-	 * A human-readable label for this group. This will be displayed in the EMF Compare UI.
-	 * 
-	 * @return The label for this group.
-	 */
-	String getLabel();
-
-	/**
-	 * Set the label for this group. This will be displayed in the EMF Compare UI.
-	 * 
-	 * @param label
-	 *            A human-readable label for this group.
-	 */
-	void setLabel(String label);
-
-	/**
-	 * Returns the initial activation state that the group should have.
-	 * 
-	 * @return The initial activation state that the group should have.
-	 */
-	boolean defaultSelected();
-
-	/**
-	 * Set the initial activation state that the group should have.
-	 * 
-	 * @param defaultSelected
-	 *            The initial activation state that the group should have (true if the group should be active
-	 *            by default).
-	 */
-	void setDefaultSelected(boolean defaultSelected);
-
-	/**
 	 * Returns the activation condition based on the scope and comparison objects.
 	 * 
 	 * @param scope
@@ -109,15 +78,43 @@ public interface IDifferenceGroupProvider extends Adapter {
 		/**
 		 * Creates a group provider.
 		 * 
-		 * @return the newly created group provider.
+		 * @return the newly created group provider or null if error.
 		 */
 		IDifferenceGroupProvider createGroupProvider();
 
 		/**
+		 * A human-readable label for this group. This will be displayed in the EMF Compare UI.
+		 * 
+		 * @return The label for this group.
+		 */
+		public String getLabel();
+
+		/**
+		 * A human-readable description for this group. This will be displayed in EMF Compare UI.
+		 * 
+		 * @return
+		 */
+		public String getDescription();
+
+		/**
+		 * Rank of this group. The highest rank enabled {@link IDifferenceGroupProvider} will be used as
+		 * default group provider.
+		 * 
+		 * @return the rank.
+		 */
+		public int getRank();
+
+		/**
+		 * Return the type of Comparison this group provider can handle.
+		 * 
+		 * @return {@link ComparisonType}
+		 */
+		public ComparisonType getType();
+
+		/**
 		 * A registry of {@link IDifferenceGroupProvider}.
 		 */
 		interface Registry {
-
 			/**
 			 * Returns the list of {@link IDifferenceGroupProvider} contained in the registry.
 			 * 
@@ -127,7 +124,7 @@ public interface IDifferenceGroupProvider extends Adapter {
 			 *            The comparison which is to be displayed in the structural view.
 			 * @return The list of {@link IDifferenceGroupProvider} contained in the registry.
 			 */
-			Collection<IDifferenceGroupProvider> getGroupProviders(IComparisonScope scope,
+			Collection<IDifferenceGroupProvider.Descriptor> getGroupProviders(IComparisonScope scope,
 					Comparison comparison);
 
 			/**
@@ -137,9 +134,10 @@ public interface IDifferenceGroupProvider extends Adapter {
 			 *            The scope on which the group providers will be applied.
 			 * @param comparison
 			 *            The comparison which is to be displayed in the structural view.
-			 * @return the default group provider.
+			 * @return the default group provider or null if none.
 			 */
-			IDifferenceGroupProvider getDefaultGroupProvider(IComparisonScope scope, Comparison comparison);
+			IDifferenceGroupProvider.Descriptor getDefaultGroupProvider(IComparisonScope scope,
+					Comparison comparison);
 
 			/**
 			 * Add to the registry the given {@link IDifferenceGroupProvider}.
@@ -171,4 +169,18 @@ public interface IDifferenceGroupProvider extends Adapter {
 			void clear();
 		}
 	}
+
+	/**
+	 * Type of comparison a {@link IDifferenceGroupProvider} can handle.
+	 * 
+	 * @author <a href="mailto:arthur.daussy@obeo.fr">Arthur Daussy</a>
+	 */
+	public static enum ComparisonType {
+		/** Only three way comparison. */
+		THREE_WAY, //
+		/** Only two way comparison. */
+		TWO_WAY, // Two way comparison
+		/** Can handle both comparison type. */
+		BOTH
+	}
 }
diff --git a/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/AbstractItemDescriptor.java b/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/AbstractItemDescriptor.java
index 03a226137..013537e65 100644
--- a/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/AbstractItemDescriptor.java
+++ b/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/AbstractItemDescriptor.java
@@ -128,4 +128,9 @@ public abstract class AbstractItemDescriptor<T> implements IItemDescriptor<T> {
 		};

 	}

 

+	@Override

+	public String toString() {

+		return "StaticItemDescriptor [Label=" + getLabel() + ", Description=" + getDescription() + ", rank=" //$NON-NLS-1$//$NON-NLS-2$//$NON-NLS-3$ 	

+				+ getRank() + ", id=" + getID() + "]"; //$NON-NLS-1$ //$NON-NLS-2$ 

+	}

 }

diff --git a/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/ItemUtil.java b/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/ItemUtil.java
index 63c7493d8..2497c746d 100644
--- a/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/ItemUtil.java
+++ b/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/extension/impl/ItemUtil.java
@@ -10,9 +10,12 @@
  *******************************************************************************/
 package org.eclipse.emf.compare.rcp.internal.extension.impl;
 
+import com.google.common.collect.Iterables;
 import com.google.common.collect.Sets;
+import com.google.common.collect.Sets.SetView;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -121,13 +124,13 @@ public final class ItemUtil {
 	 * @param preferenceKey
 	 *            Key for this {@link IItemDescriptor} in preferences
 	 * @param itemPreferences
-	 *            {@link IEclipsePreferences} where are stored {@link IItemDescriptor} values
+	 *            {@link Preferences} where are stored {@link IItemDescriptor} values
 	 * @param <T>
 	 *            Type of {@link IItemDescriptor}
 	 * @return List of {@link IItemDescriptor} or null if nothing in preferences
 	 */
 	public static <T> List<IItemDescriptor<T>> getItemsDescriptor(IItemRegistry<T> registry,
-			String preferenceKey, IEclipsePreferences itemPreferences) {
+			String preferenceKey, Preferences itemPreferences) {
 		String diffEngineKey = itemPreferences.get(preferenceKey, null);
 		List<IItemDescriptor<T>> result = null;
 		if (diffEngineKey != null) {
@@ -188,4 +191,49 @@ public final class ItemUtil {
 
 		return activeFactory;
 	}
+
+	/**
+	 * Return an ordered list of {@link IItemDescriptor}. The order in the list is either define by the rank
+	 * in the registry or from preference is the rank has been overloaded. If any descriptor has been added or
+	 * removed from last modification in the preference. This method will merge the modification.
+	 * 
+	 * @param orderedDefaultDescriptor
+	 *            List of ordered default {@link IItemDescriptor}.
+	 * @param descriptorRegistry
+	 *            Registry of descriptor.
+	 * @param orderedItemPreferenceKey
+	 *            Key in preferences where are stored the new order of descriptor
+	 * @param preferences
+	 *            holding user preferences.
+	 * @return Ordered list of descriptor.
+	 * @param <T>
+	 *            Descriptor type.
+	 */
+	public static <T> List<IItemDescriptor<T>> getOrderedItems(
+			List<IItemDescriptor<T>> orderedDefaultDescriptor, IItemRegistry<T> descriptorRegistry,
+			String orderedItemPreferenceKey, Preferences preferences) {
+		List<IItemDescriptor<T>> itemsDescriptor = ItemUtil.getItemsDescriptor(descriptorRegistry,
+				orderedItemPreferenceKey, preferences);
+
+		if (itemsDescriptor == null) {
+			itemsDescriptor = orderedDefaultDescriptor;
+		} else {
+			HashSet<IItemDescriptor<T>> descriptorFromPrefSet = Sets.newLinkedHashSet(itemsDescriptor);
+			HashSet<IItemDescriptor<T>> defaultDescriptorSet = Sets
+					.newLinkedHashSet(orderedDefaultDescriptor);
+
+			// Remove descriptor
+			SetView<IItemDescriptor<T>> descriptorToRemove = Sets.difference(descriptorFromPrefSet,
+					defaultDescriptorSet);
+			Iterables.removeAll(itemsDescriptor, descriptorToRemove);
+
+			// Add new descriptor
+			SetView<IItemDescriptor<T>> descriptorToAdd = Sets.difference(defaultDescriptorSet,
+					descriptorFromPrefSet);
+			Iterables.addAll(itemsDescriptor, descriptorToAdd);
+
+		}
+		return itemsDescriptor;
+	}
+
 }
diff --git a/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/preferences/EMFComparePreferences.java b/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/preferences/EMFComparePreferences.java
index b3a82e1ef..49ad5463d 100644
--- a/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/preferences/EMFComparePreferences.java
+++ b/plugins/org.eclipse.emf.compare.rcp/src/org/eclipse/emf/compare/rcp/internal/preferences/EMFComparePreferences.java
@@ -35,6 +35,12 @@ public final class EMFComparePreferences {
 	/** Disabled post processors preference. */

 	public static final String DISABLED_POST_PROCESSOR = "org.eclipse.emf.compare.preference.postprocessor.disabled"; //$NON-NLS-1$

 

+	/** Ordered list of groups for two way comparison. */

+	public static final String TWO_WAY_GROUP_RANKING = "org.eclipse.emf.compare.preference.groups.2way"; //$NON-NLS-1$

+

+	/** Ordered list of groups for three way comparison. */

+	public static final String THREE_WAY_GROUP_RANKING = "org.eclipse.emf.compare.preference.groups.3way"; //$NON-NLS-1$

+

 	/**

 	 * Private constructor. Not to be called.

 	 */

@@ -42,4 +48,19 @@ public final class EMFComparePreferences {
 		// Hide default constructor.

 	}

 

+	/**

+	 * Value of {@link EMFComparePreferences#THREE_WAY_COMPARISON_AUTOMATIC_BEHAVIOR} and

+	 * {@link EMFComparePreferences#TWO_WAY_COMPARISON_AUTOMATIC_BEHAVIOR}.

+	 * 

+	 * @author <a href="mailto:arthur.daussy@obeo.fr">Arthur Daussy</a>

+	 */

+	public static enum GroupAutomaticBehavior {

+		/** Never synchronize current selected group with preferences. */

+		NEVER,

+		/** Always synchronize current selected group with preferences. */

+		ALWAYS,

+		/** Ask each time the user if he want to synchronize. */

+		ASK_EACH_TIME

+	}

+

 }