fix: Use a Gson singleton which knows about the types from LSP4J

Author: FlorianKroiss

org.eclipse.lsp4e.test/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: Tests for language server bundle (Incubation)
 Bundle-SymbolicName: org.eclipse.lsp4e.test;singleton:=true
-Bundle-Version: 0.16.1.qualifier
+Bundle-Version: 0.16.2.qualifier
 Fragment-Host: org.eclipse.lsp4e
 Bundle-Vendor: Eclipse LSP4E
 Bundle-RequiredExecutionEnvironment: JavaSE-21

org.eclipse.lsp4e.test/pom.xml

@@ -8,7 +8,7 @@
 	</parent>
 	<artifactId>org.eclipse.lsp4e.test</artifactId>
 	<packaging>eclipse-test-plugin</packaging>
-	<version>0.16.1-SNAPSHOT</version>
+	<version>0.16.2-SNAPSHOT</version>
 
 	<properties>
 		<os-jvm-flags /> <!-- for the default case -->

org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/commands/DynamicRegistrationTest.java

@@ -45,8 +45,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import com.google.gson.Gson;
-
 public class DynamicRegistrationTest extends AbstractTestWithProject {
 
 	private static final String WORKSPACE_EXECUTE_COMMAND = "workspace/executeCommand";
@@ -143,7 +141,7 @@ private UUID registerWatchedFiles() throws Exception {
 		final var watcher = new org.eclipse.lsp4j.FileSystemWatcher(
 				org.eclipse.lsp4j.jsonrpc.messages.Either.forLeft("**/*.txt"), null);
 		options.setWatchers(List.of(watcher));
-		registration.setRegisterOptions(new Gson().toJsonTree(options));
+		registration.setRegisterOptions(options);
 		client.registerCapability(new RegistrationParams(List.of(registration))).get(1, TimeUnit.SECONDS);
 		return id;
 	}
@@ -165,7 +163,7 @@ private UUID registerCommands(String... command) throws Exception {
 		final var registration = new Registration();
 		registration.setId(id.toString());
 		registration.setMethod(WORKSPACE_EXECUTE_COMMAND);
-		registration.setRegisterOptions(new Gson().toJsonTree(new ExecuteCommandOptions(List.of(command))));
+		registration.setRegisterOptions(new ExecuteCommandOptions(List.of(command)));
 		client.registerCapability(new RegistrationParams(List.of(registration))).get(1, TimeUnit.SECONDS);
 		return id;
 	}

org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/completion/DynamicCompletionRegistrationTest.java

@@ -41,8 +41,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import com.google.gson.Gson;
-
 /**
  * Verifies that dynamic registration of completion updates LSP4E server
  * capabilities and enables content assist proposals.
@@ -82,7 +80,7 @@ public void testDynamicCompletionRegistrationProvidesProposalsAndTriggers() thro
         registration.setMethod("textDocument/completion");
         var opts = new CompletionOptions();
         opts.setTriggerCharacters(List.of(".", "/", "#"));
-        registration.setRegisterOptions(new Gson().toJsonTree(opts));
+        registration.setRegisterOptions(opts);
         client.registerCapability(new RegistrationParams(List.of(registration))).get(2, TimeUnit.SECONDS);
 
         // Compute proposals (manual invocation). Should return the mock item.

org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/internal/JsonUtilTest.java

@@ -0,0 +1,39 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Contributors to the Eclipse Foundation.
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *   See git history
+ *******************************************************************************/
+package org.eclipse.lsp4e.test.internal;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.eclipse.lsp4e.internal.JsonUtil;
+import org.eclipse.lsp4j.FileSystemWatcher;
+import org.eclipse.lsp4j.WatchKind;
+import org.junit.jupiter.api.Test;
+
+public class JsonUtilTest {
+
+	@Test
+	void testRoundtrip() throws Exception {
+		// Setup an object which uses Either internally.
+		// This can only be properly de/serialized with Gson instance which knows about LSP4J types.
+		var original = new FileSystemWatcher();
+		original.setGlobPattern("**");
+		original.setKind(WatchKind.Create | WatchKind.Change | WatchKind.Delete);
+		
+		String json = JsonUtil.getLSP4J_GSON().toJson(original);
+		assertEquals("""
+				{"globPattern":"**","kind":7}""", json);
+		
+		FileSystemWatcher copy = JsonUtil.getLSP4J_GSON().fromJson(json, FileSystemWatcher.class);
+		assertEquals(original, copy);
+	}
+
+}

org.eclipse.lsp4e/src/org/eclipse/lsp4e/LanguageServerWrapper.java

@@ -18,7 +18,7 @@
  *******************************************************************************/
 package org.eclipse.lsp4e;
 
-import static org.eclipse.lsp4e.internal.NullSafetyHelper.*;
+import static org.eclipse.lsp4e.internal.NullSafetyHelper.castNonNull;
 
 import java.io.BufferedReader;
 import java.io.File;
@@ -80,6 +80,7 @@
 import org.eclipse.lsp4e.internal.ArrayUtil;
 import org.eclipse.lsp4e.internal.CancellationUtil;
 import org.eclipse.lsp4e.internal.FileBufferListenerAdapter;
+import org.eclipse.lsp4e.internal.JsonUtil;
 import org.eclipse.lsp4e.internal.SupportedFeatures;
 import org.eclipse.lsp4e.internal.files.FileSystemWatcherManager;
 import org.eclipse.lsp4e.server.StreamConnectionProvider;
@@ -129,7 +130,6 @@
 
 import com.google.common.base.Functions;
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
-import com.google.gson.Gson;
 import com.google.gson.JsonObject;
 
 public class LanguageServerWrapper {
@@ -1173,7 +1173,7 @@ public void registerCapability(RegistrationParams params) {
 				break;
 			case "workspace/executeCommand": //$NON-NLS-1$
 				try {
-					ExecuteCommandOptions executeCommandOptions = castNonNull(new Gson().fromJson((JsonObject) reg.getRegisterOptions(),
+					ExecuteCommandOptions executeCommandOptions = castNonNull(JsonUtil.getLSP4J_GSON().fromJson((JsonObject) reg.getRegisterOptions(),
 							ExecuteCommandOptions.class));
 					List<String> newCommands = executeCommandOptions.getCommands();
 					if (!newCommands.isEmpty()) {
@@ -1212,7 +1212,7 @@ public void registerCapability(RegistrationParams params) {
 			case "textDocument/completion": { //$NON-NLS-1$
 				CompletionOptions previous = serverCapabilities.getCompletionProvider();
 				try {
-					final var completionOpts = new Gson().fromJson((JsonObject) reg.getRegisterOptions(),
+					final var completionOpts = JsonUtil.getLSP4J_GSON().fromJson((JsonObject) reg.getRegisterOptions(),
 							CompletionOptions.class);
 					serverCapabilities.setCompletionProvider(completionOpts);
 					addRegistration(reg, () -> serverCapabilities.setCompletionProvider(previous));
@@ -1255,8 +1255,9 @@ public void registerCapability(RegistrationParams params) {
 			return null;
 		if (registerOptions instanceof DidChangeWatchedFilesRegistrationOptions direct)
 			return direct;
-		if (registerOptions instanceof JsonObject jsonObject)
-			return new Gson().fromJson(jsonObject, DidChangeWatchedFilesRegistrationOptions.class);
+		if (registerOptions instanceof JsonObject jsonObject) {
+			return JsonUtil.getLSP4J_GSON().fromJson(jsonObject, DidChangeWatchedFilesRegistrationOptions.class);
+		}
 		return null;
 	}
 

org.eclipse.lsp4e/src/org/eclipse/lsp4e/command/CommandExecutor.java

@@ -8,7 +8,8 @@
  *******************************************************************************/
 package org.eclipse.lsp4e.command;
 
-import static org.eclipse.lsp4e.command.LSPCommandHandler.*;
+import static org.eclipse.lsp4e.command.LSPCommandHandler.LSP_COMMAND_PARAMETER_ID;
+import static org.eclipse.lsp4e.command.LSPCommandHandler.LSP_PATH_PARAMETER_ID;
 
 import java.net.URI;
 import java.util.ArrayList;
@@ -33,6 +34,7 @@
 import org.eclipse.lsp4e.LSPEclipseUtils;
 import org.eclipse.lsp4e.LanguageServerPlugin;
 import org.eclipse.lsp4e.command.internal.CommandEventParameter;
+import org.eclipse.lsp4e.internal.JsonUtil;
 import org.eclipse.lsp4j.Command;
 import org.eclipse.lsp4j.TextEdit;
 import org.eclipse.lsp4j.WorkspaceEdit;
@@ -192,7 +194,7 @@ private static WorkspaceEdit createWorkspaceEdit(List<Object> commandArguments,
 			} else if (arg instanceof TextEdit textEdit) {
 				currentEntry.value.add(textEdit);
 			} else if (arg instanceof Map) {
-				final var gson = new Gson(); // TODO? retrieve the GSon used by LS
+				Gson gson = JsonUtil.getLSP4J_GSON();
 				TextEdit edit = gson.fromJson(gson.toJson(arg), TextEdit.class);
 				if (edit != null) {
 					currentEntry.value.add(edit);
@@ -210,15 +212,15 @@ private static WorkspaceEdit createWorkspaceEdit(List<Object> commandArguments,
 					}
 				}
 			} else if (arg instanceof JsonArray jsonArray) {
-				final var gson = new Gson(); // TODO? retrieve the GSon used by LS
+				Gson gson = JsonUtil.getLSP4J_GSON();
 				jsonArray.forEach(elt -> {
 					TextEdit edit = gson.fromJson(gson.toJson(elt), TextEdit.class);
 					if (edit != null) {
 						currentEntry.value.add(edit);
 					}
 				});
 			} else if (arg instanceof JsonObject jsonObject) {
-				final var gson = new Gson(); // TODO? retrieve the GSon used by LS
+				Gson gson = JsonUtil.getLSP4J_GSON();
 				WorkspaceEdit wEdit = gson.fromJson(jsonObject, WorkspaceEdit.class);
 				if (wEdit != null) {
 					Map<String, List<TextEdit>> entries = wEdit.getChanges();

org.eclipse.lsp4e/src/org/eclipse/lsp4e/internal/JsonUtil.java

@@ -0,0 +1,35 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Contributors to the Eclipse Foundation.
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *   See git history
+ *******************************************************************************/
+package org.eclipse.lsp4e.internal;
+
+import java.util.Map;
+import java.util.Objects;
+
+import org.eclipse.lsp4j.jsonrpc.json.MessageJsonHandler;
+
+import com.google.gson.Gson;
+
+/**
+ * Provides a {@link Gson} instance which can properly serialize and deserialize LSP4J JSON-RPC objects
+ */
+public class JsonUtil {
+
+	private static final Gson LSP4J_GSON = Objects.requireNonNull(new MessageJsonHandler(Map.of()).getGson());
+
+	/**
+	 * Obtain a singleton Gson instance to work with LSP4J JSON objects.
+	 */
+	public static Gson getLSP4J_GSON() {
+		return LSP4J_GSON;
+	}
+
+}