Initialize reference extension participant (see #58)

org.eclipse.lsp4xml/src/main/java/org/eclipse/lsp4xml/XMLTextDocumentService.java

@@ -50,6 +50,7 @@
 import org.eclipse.lsp4j.Location;
 import org.eclipse.lsp4j.PublishDiagnosticsParams;
 import org.eclipse.lsp4j.Range;
+import org.eclipse.lsp4j.ReferenceParams;
 import org.eclipse.lsp4j.RenameParams;
 import org.eclipse.lsp4j.SymbolInformation;
 import org.eclipse.lsp4j.TextDocumentClientCapabilities;
@@ -270,6 +271,15 @@ public CompletableFuture<List<? extends Location>> definition(TextDocumentPositi
 			return getXMLLanguageService().findDefinition(xmlDocument, params.getPosition());
 		});
 	}
+
+	@Override
+	public CompletableFuture<List<? extends Location>> references(ReferenceParams params) {
+		return computeAsync((monitor) -> {
+			TextDocument document = getDocument(params.getTextDocument().getUri());
+			XMLDocument xmlDocument = getXMLDocument(document);
+			return getXMLLanguageService().findReferences(xmlDocument, params.getPosition(), params.getContext());
+		});
+	}
 
 	@Override
 	public CompletableFuture<List<Either<Command, CodeAction>>> codeAction(CodeActionParams params) {

org.eclipse.lsp4xml/src/main/java/org/eclipse/lsp4xml/services/XMLLanguageService.java

@@ -27,6 +27,7 @@
 import org.eclipse.lsp4j.Location;
 import org.eclipse.lsp4j.Position;
 import org.eclipse.lsp4j.Range;
+import org.eclipse.lsp4j.ReferenceContext;
 import org.eclipse.lsp4j.SymbolInformation;
 import org.eclipse.lsp4j.TextEdit;
 import org.eclipse.lsp4j.WorkspaceEdit;
@@ -53,6 +54,7 @@ public class XMLLanguageService extends XMLExtensionsRegistry {
 	private final XMLFoldings foldings;
 	private final XMLDocumentLink documentLink;
 	private XMLDefinition definition;
+	private XMLReference reference;
 	private final XMLCodeActions codeActions;
 
 	public XMLLanguageService() {
@@ -65,6 +67,7 @@ public XMLLanguageService() {
 		this.foldings = new XMLFoldings(this);
 		this.documentLink = new XMLDocumentLink(this);
 		this.definition = new XMLDefinition(this);
+		this.reference = new XMLReference(this);
 		this.codeActions = new XMLCodeActions(this);
 	}
 
@@ -113,6 +116,11 @@ public List<? extends Location> findDefinition(XMLDocument xmlDocument, Position
 		return definition.findDefinition(xmlDocument, position);
 	}
 
+	public List<? extends Location> findReferences(XMLDocument xmlDocument, Position position,
+			ReferenceContext context) {
+		return reference.findReferences(xmlDocument, position, context);
+	}
+
 	public List<CodeAction> doCodeActions(CodeActionContext context, Range range, XMLDocument document,
 			XMLFormattingOptions formattingSettings) {
 		return codeActions.doCodeActions(context, range, document, formattingSettings);
@@ -137,5 +145,4 @@ public String doAutoClose(XMLDocument xmlDocument, Position position) {
 			return null;
 		}
 	}
-
 }

org.eclipse.lsp4xml/src/main/java/org/eclipse/lsp4xml/services/XMLReference.java

@@ -0,0 +1,43 @@
+/**
+ *  Copyright (c) 2018 Angelo ZERR
+ *  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:
+ *  Angelo Zerr <[email protected]> - initial API and implementation
+ */
+package org.eclipse.lsp4xml.services;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.eclipse.lsp4j.Location;
+import org.eclipse.lsp4j.Position;
+import org.eclipse.lsp4j.ReferenceContext;
+import org.eclipse.lsp4xml.dom.XMLDocument;
+import org.eclipse.lsp4xml.services.extensions.IReferenceParticipant;
+import org.eclipse.lsp4xml.services.extensions.XMLExtensionsRegistry;
+
+/**
+ * XML reference support.
+ *
+ */
+class XMLReference {
+
+	private final XMLExtensionsRegistry extensionsRegistry;
+
+	public XMLReference(XMLExtensionsRegistry extensionsRegistry) {
+		this.extensionsRegistry = extensionsRegistry;
+	}
+
+	public List<? extends Location> findReferences(XMLDocument document, Position position, ReferenceContext context) {
+		List<Location> locations = new ArrayList<>();
+		for (IReferenceParticipant participant : extensionsRegistry.getReferenceParticipants()) {
+			participant.findReference(document, position, context, locations);
+		}
+		return locations;
+	}
+
+}

org.eclipse.lsp4xml/src/main/java/org/eclipse/lsp4xml/services/extensions/IReferenceParticipant.java

@@ -0,0 +1,28 @@
+/**
+ *  Copyright (c) 2018 Angelo ZERR.
+ *  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:
+ *  Angelo Zerr <[email protected]> - initial API and implementation
+ */
+package org.eclipse.lsp4xml.services.extensions;
+
+import java.util.List;
+
+import org.eclipse.lsp4j.Location;
+import org.eclipse.lsp4j.Position;
+import org.eclipse.lsp4j.ReferenceContext;
+import org.eclipse.lsp4xml.dom.XMLDocument;
+
+/**
+ * Reference participant API.
+ *
+ */
+public interface IReferenceParticipant {
+
+	void findReference(XMLDocument document, Position position, ReferenceContext context, List<Location> locations);
+
+}

org.eclipse.lsp4xml/src/main/java/org/eclipse/lsp4xml/services/extensions/XMLExtensionsRegistry.java

@@ -35,6 +35,7 @@ public class XMLExtensionsRegistry {
 	private final List<ICodeActionParticipant> codeActionsParticipants;
 	private final List<IDocumentLinkParticipant> documentLinkParticipants;
 	private final List<IDefinitionParticipant> definitionParticipants;
+	private final List<IReferenceParticipant> referenceParticipants;
 
 	private IXMLDocumentProvider documentProvider;
 
@@ -52,6 +53,7 @@ public XMLExtensionsRegistry() {
 		codeActionsParticipants = new ArrayList<>();
 		documentLinkParticipants = new ArrayList<>();
 		definitionParticipants = new ArrayList<>();
+		referenceParticipants = new ArrayList<>();
 	}
 
 	public void initializeParams(InitializeParams params) {
@@ -105,6 +107,11 @@ public Collection<IDefinitionParticipant> getDefinitionParticipants() {
 		return definitionParticipants;
 	}
 
+	public Collection<IReferenceParticipant> getReferenceParticipants() {
+		initializeIfNeeded();
+		return referenceParticipants;
+	}
+
 	private void initializeIfNeeded() {
 		if (initialized) {
 			return;
@@ -186,6 +193,14 @@ public void unregisterDefinitionParticipant(IDefinitionParticipant definitionPar
 		definitionParticipants.add(definitionParticipant);
 	}
 
+	public void registerReferenceParticipant(IReferenceParticipant referenceParticipant) {
+		referenceParticipants.add(referenceParticipant);
+	}
+
+	public void unregisterReferenceParticipant(IReferenceParticipant referenceParticipant) {
+		referenceParticipants.add(referenceParticipant);
+	}
+
 	/**
 	 * Returns the XML Document provider and null otherwise.
 	 *