fix: Create singleton instances of Markdown Parser and Renderer and add some tests

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

@@ -0,0 +1,64 @@
+/*******************************************************************************
+ * Copyright (c) 2026 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 java.util.stream.Stream;
+
+import org.eclipse.lsp4e.internal.MarkdownUtil;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class MarkdownUtilTest {
+
+	public static Stream<Arguments> renderToHtml() {
+		return Stream.of( //
+				Arguments.argumentSet("Simple", """
+						# Heading 1
+						- this is a test""", """
+						<h1>Heading 1</h1>
+						<ul>
+						<li>this is a test</li>
+						</ul>
+												"""), //
+				Arguments.argumentSet("With table", """
+						| Header  | Another Header |
+						|---------|----------------|
+						| field 1 | value one      |""", """
+						<table>
+						<thead>
+						<tr>
+						<th>Header</th>
+						<th>Another Header</th>
+						</tr>
+						</thead>
+						<tbody>
+						<tr>
+						<td>field 1</td>
+						<td>value one</td>
+						</tr>
+						</tbody>
+						</table>
+						""") //
+		);
+	}
+
+	@ParameterizedTest
+	@MethodSource
+	void renderToHtml(String markdown, String expectedHtml) throws Exception {
+		// Simple test to make sure we configured CommonMark correctly.
+		assertEquals(expectedHtml, MarkdownUtil.renderToHtml(markdown));
+	}
+
+}

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

@@ -0,0 +1,43 @@
+/*******************************************************************************
+ * Copyright (c) 2026 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.List;
+
+import org.commonmark.Extension;
+import org.commonmark.ext.gfm.tables.TablesExtension;
+import org.commonmark.parser.Parser;
+import org.commonmark.renderer.Renderer;
+import org.commonmark.renderer.html.HtmlRenderer;
+
+public class MarkdownUtil {
+
+	/**
+	 * Used commonmark extensions
+	 */
+	private static final List<Extension> EXTENSIONS = List.of(TablesExtension.create());
+
+	/**
+	 * Singleton instance, as both classes are thread-safe, see
+	 * https://github.com/commonmark/commonmark-java?tab=readme-ov-file#thread-safety
+	 */
+	private static final Parser PARSER = Parser.builder().extensions(EXTENSIONS).build();
+	private static final Renderer RENDERER = HtmlRenderer.builder().extensions(EXTENSIONS).build();
+
+	/**
+	 * Renders the given markdown content to HTML.
+	 */
+	public static String renderToHtml(String markdown) {
+		return RENDERER.render(PARSER.parse(markdown));
+	}
+
+}

org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/hover/LSPTextHover.java

@@ -29,11 +29,6 @@
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
-import org.commonmark.Extension;
-import org.commonmark.ext.gfm.tables.TablesExtension;
-import org.commonmark.node.Node;
-import org.commonmark.parser.Parser;
-import org.commonmark.renderer.html.HtmlRenderer;
 import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.jface.internal.text.html.BrowserInformationControl;
 import org.eclipse.jface.text.AbstractReusableInformationControlCreator;
@@ -53,6 +48,7 @@
 import org.eclipse.lsp4e.LanguageServers;
 import org.eclipse.lsp4e.internal.CancellationUtil;
 import org.eclipse.lsp4e.internal.IdentifierUtil;
+import org.eclipse.lsp4e.internal.MarkdownUtil;
 import org.eclipse.lsp4j.Hover;
 import org.eclipse.lsp4j.HoverParams;
 import org.eclipse.lsp4j.MarkedString;
@@ -113,11 +109,7 @@ public class LSPTextHover implements ITextHover, ITextHoverExtension, ITextHover
 					.collect(Collectors.joining("\n\n")) //$NON-NLS-1$
 					.trim();
 			if (!result.isEmpty()) {
-				List<Extension> extensions = List.of(TablesExtension.create());
-				Parser parser = Parser.builder().extensions(extensions).build();
-				Node document = parser.parse(result);
-				HtmlRenderer renderer = HtmlRenderer.builder().extensions(extensions).build();
-				return renderer.render(document);
+				return MarkdownUtil.renderToHtml(result);
 			} else {
 				return null;
 			}