fix: eliminate UI freezes in LSPTextHover via async updates

org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/hover/HoverTest.java

@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.lang.reflect.Field;
 import java.util.Collections;
+import java.util.concurrent.TimeUnit;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -65,7 +66,8 @@ public void setUp() {
 
 	@Test
 	public void testHoverRegion() throws CoreException {
-		final var hoverResponse = new Hover(List.of(Either.forLeft("HoverContent")), new Range(new Position(0,  0), new Position(0, 10)));
+		final var hoverResponse = new Hover(List.of(Either.forLeft("HoverContent")),
+				new Range(new Position(0, 0), new Position(0, 10)));
 		MockLanguageServer.INSTANCE.setHover(hoverResponse);
 
 		IFile file = TestUtils.createUniqueTestFile(project, "HoverRange Other Text");
@@ -81,24 +83,30 @@ public void testHoverRegionInvalidOffset() throws CoreException {
 		IFile file = TestUtils.createUniqueTestFile(project, "HoverRange Other Text");
 		ITextViewer viewer = TestUtils.openTextViewer(file);
 
-		assertEquals(new Region(15, 0), hover.getHoverRegion(viewer, 15));
+		var region = hover.getHoverRegion(viewer, 15);
+		assertNotNull(region);
+		assertTrue("region should include the hover offset",
+				region.getOffset() <= 15 && (region.getOffset() + region.getLength()) >= 15);
 	}
 
 	@Test
-	public void testHoverInfo() throws CoreException {
-		final var hoverResponse = new Hover(List.of(Either.forLeft("HoverContent")), new Range(new Position(0,  0), new Position(0, 10)));
+	public void testHoverInfo() throws Exception {
+		final var hoverResponse = new Hover(List.of(Either.forLeft("HoverContent")),
+				new Range(new Position(0, 0), new Position(0, 10)));
 		MockLanguageServer.INSTANCE.setHover(hoverResponse);
 
 		IFile file = TestUtils.createUniqueTestFile(project, "HoverRange Other Text");
 		ITextViewer viewer = TestUtils.openTextViewer(file);
 
-		// TODO update test when MARKDOWN to HTML will be finished
-		assertTrue(hover.getHoverInfo(viewer, new Region(0, 10)).contains("HoverContent"));
+		String html = hover.getHoverInfoFuture(viewer, new Region(0, 10)).get(2, TimeUnit.SECONDS);
+		assertNotNull(html);
+		assertTrue(html.contains("HoverContent"));
 	}
 
 	@Test
 	public void testHoverInfoEmptyContentList() throws CoreException {
-		final var hoverResponse = new Hover(Collections.emptyList(), new Range(new Position(0,  0), new Position(0, 10)));
+		final var hoverResponse = new Hover(Collections.emptyList(),
+				new Range(new Position(0, 0), new Position(0, 10)));
 		MockLanguageServer.INSTANCE.setHover(hoverResponse);
 
 		IFile file = TestUtils.createUniqueTestFile(project, "HoverRange Other Text");
@@ -119,7 +127,8 @@ public void testHoverInfoInvalidOffset() throws CoreException {
 
 	@Test
 	public void testHoverEmptyContentItem() throws CoreException {
-		final var hoverResponse = new Hover(List.of(Either.forLeft("")), new Range(new Position(0,  0), new Position(0, 10)));
+		final var hoverResponse = new Hover(List.of(Either.forLeft("")),
+				new Range(new Position(0, 0), new Position(0, 10)));
 		MockLanguageServer.INSTANCE.setHover(hoverResponse);
 
 		IFile file = TestUtils.createUniqueTestFile(project, "HoverRange Other Text");
@@ -129,27 +138,28 @@ public void testHoverEmptyContentItem() throws CoreException {
 	}
 
 	@Test
-	public void testHoverOnExternalFile() throws CoreException, IOException {
+	public void testHoverOnExternalFile() throws Exception {
 		final var hoverResponse = new Hover(List.of(Either.forLeft("blah")),
 				new Range(new Position(0, 0), new Position(0, 0)));
 		MockLanguageServer.INSTANCE.setHover(hoverResponse);
 
 		File file = TestUtils.createTempFile("testHoverOnExternalfile", ".lspt");
-		ITextViewer viewer = LSPEclipseUtils.getTextViewer(IDE.openInternalEditorOnFileStore(
-				UI.getActivePage(), EFS.getStore(file.toURI())));
-		Assert.assertTrue(hover.getHoverInfo(viewer, new Region(0, 0)).contains("blah"));
+		ITextViewer viewer = LSPEclipseUtils
+				.getTextViewer(IDE.openInternalEditorOnFileStore(UI.getActivePage(), EFS.getStore(file.toURI())));
+		String html = hover.getHoverInfoFuture(viewer, new Region(0, 0)).get(2, TimeUnit.SECONDS);
+		Assert.assertTrue(html != null && html.contains("blah"));
 	}
 
 	@Test
 	public void testMultipleHovers() throws Exception {
-		final var hoverResponse = new Hover(List.of(Either.forLeft("HoverContent")), new Range(new Position(0,  0), new Position(0, 10)));
+		final var hoverResponse = new Hover(List.of(Either.forLeft("HoverContent")),
+				new Range(new Position(0, 0), new Position(0, 10)));
 		MockLanguageServer.INSTANCE.setHover(hoverResponse);
 
 		IFile file = TestUtils.createUniqueTestFileMultiLS(project, "HoverRange Other Text");
 		ITextViewer viewer = TestUtils.openTextViewer(file);
 
-		// TODO update test when MARKDOWN to HTML will be finished
-		String hoverInfo = hover.getHoverInfo(viewer, new Region(0, 10));
+		String hoverInfo = hover.getHoverInfoFuture(viewer, new Region(0, 10)).get(2, TimeUnit.SECONDS);
 		int index = hoverInfo.indexOf("HoverContent");
 		assertNotEquals("Hover content not found", -1, index);
 		index += "HoverContent".length();
@@ -167,12 +177,12 @@ public void testIntroUrlLink() throws Exception {
 
 		IFile file = TestUtils.createUniqueTestFile(project, "HoverRange Other Text");
 		IEditorPart editorPart = TestUtils.openEditor(file);
-		
+
 		waitForAndAssertCondition(5_000, () -> LSPEclipseUtils.getTextViewer(editorPart) != null);
 		ITextViewer viewer = LSPEclipseUtils.getTextViewer(editorPart);
 		assertEquals(UI.getActivePart(), editorPart);
 
-		String hoverContent = hover.getHoverInfo(viewer, new Region(0, 10));
+		String hoverContent = hover.getHoverInfoFuture(viewer, new Region(0, 10)).get(2, TimeUnit.SECONDS);
 
 		final var hoverManager = new LSPTextHover();
 
@@ -188,8 +198,8 @@ public void testIntroUrlLink() throws Exception {
 
 			wrapperControl = (BrowserInformationControl) hoverManager.getHoverControlCreator()
 					.createInformationControl(shell);
-			control = (BrowserInformationControl) wrapperControl
-					.getInformationPresenterControlCreator().createInformationControl(shell);
+			control = (BrowserInformationControl) wrapperControl.getInformationPresenterControlCreator()
+					.createInformationControl(shell);
 			Field f = BrowserInformationControl.class.getDeclaredField("fBrowser"); //
 			f.setAccessible(true);
 
@@ -209,7 +219,7 @@ public void completed(ProgressEvent event) {
 			});
 
 			assertNotNull("Editor should be opened", viewer.getTextWidget());
-			
+
 			UI.getActivePage().activate(editorPart);
 			browser.setText(hoverContent);
 

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

@@ -0,0 +1,37 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Vegard IT GmbH and others.
+ * 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:
+ *  Sebastian Thomschke (Vegard IT GmbH) - initial implementation.
+ *******************************************************************************/
+package org.eclipse.lsp4e.operations.hover;
+
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+
+import org.eclipse.jdt.annotation.Nullable;
+
+/**
+ * Lightweight carrier for asynchronous hover HTML content.
+ *
+ * Holds a placeholder HTML to show immediately and a future that will
+ * eventually provide the final HTML. The {@link #token} acts as an identity to
+ * guard UI updates against races when the control input changes quickly.
+ */
+@SuppressWarnings("javadoc")
+final class AsyncHtmlHoverInput {
+
+	final UUID token = UUID.randomUUID();
+	final CompletableFuture<@Nullable String> future;
+	final String placeholderHtml;
+
+	AsyncHtmlHoverInput(CompletableFuture<@Nullable String> future, String placeholderHtml) {
+		this.future = future;
+		this.placeholderHtml = placeholderHtml;
+	}
+}

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

@@ -8,10 +8,12 @@
  *
  * Contributors:
  *  Mickael Istria (Red Hat Inc.) - initial implementation
+ *  Sebastian Thomschke (Vegard IT GmbH) - Prevent UI freezes through non-blocking hover rendering
  *******************************************************************************/
 package org.eclipse.lsp4e.operations.hover;
 
 import java.net.URL;
+import java.util.UUID;
 
 import org.eclipse.core.runtime.FileLocator;
 import org.eclipse.core.runtime.Platform;
@@ -62,6 +64,8 @@ public void changed(LocationEvent event) {
 		}
 	};
 
+	private @Nullable UUID currentAsyncToken;
+
 	public FocusableBrowserInformationControl(Shell parent, String symbolicFontName, boolean resizable) {
 		super(parent, JFaceResources.DEFAULT_FONT, resizable);
 	}
@@ -155,6 +159,31 @@ private static boolean safeExecute(Browser browser, String expression) {
 
 	@Override
 	public void setInput(@Nullable Object input) {
+		if (input instanceof AsyncHtmlHoverInput async) {
+			this.currentAsyncToken = async.token;
+			super.setInput(styleHtml(async.placeholderHtml));
+			async.future.whenComplete((html, ex) -> UI.getDisplay().asyncExec(() -> {
+				if (getShell() == null || getShell().isDisposed()) {
+					return;
+				}
+				final var currentAsyncToken = this.currentAsyncToken;
+				if (currentAsyncToken != null && !currentAsyncToken.equals(async.token)) {
+					return; // input changed; ignore stale update
+				}
+				if (ex != null) {
+					LanguageServerPlugin.logError(ex);
+					dispose();
+					return;
+				}
+				if (html != null && !html.isBlank()) {
+					super.setInput(styleHtml(html));
+				} else {
+					// No content from LS; hide placeholder
+					dispose();
+				}
+			}));
+			return;
+		}
 		if (input instanceof String html) {
 			input = styleHtml(html);
 		}
@@ -239,5 +268,4 @@ private static void appendAsHexString(StringBuilder buffer, int intValue) {
 			}
 		};
 	}
-
-}
+}