fix: treat cancelled hover requests as non-errors

Author: sebthom

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

@@ -14,6 +14,8 @@
 
 import java.net.URL;
 import java.util.UUID;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletionException;
 
 import org.eclipse.core.runtime.FileLocator;
 import org.eclipse.core.runtime.Platform;
@@ -171,6 +173,12 @@ public void setInput(@Nullable Object input) {
 					return; // input changed; ignore stale update
 				}
 				if (ex != null) {
+					if (ex instanceof CancellationException || (ex instanceof CompletionException ce
+							&& ce.getCause() instanceof CancellationException)) {
+						// Hover request was cancelled; treat as benign and hide placeholder.
+						super.setInput(""); //$NON-NLS-1$
+						return;
+					}
 					LanguageServerPlugin.logError(ex);
 					super.setInput(
 							"Unexpected error: " + ex.getClass().getSimpleName() + ": " + ex.getLocalizedMessage()); //$NON-NLS-1$ //$NON-NLS-2$

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

@@ -21,7 +21,9 @@
 import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.concurrent.CancellationException;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -78,8 +80,13 @@ public class LSPTextHover implements ITextHover, ITextHoverExtension, ITextHover
 		if (hoverInfoRequest_.isDone()) {
 			try {
 				return hoverInfoRequest_.getNow(null);
-			} catch (Exception e) {
-				LanguageServerPlugin.logError(e);
+			} catch (final Exception ex) {
+				if (ex instanceof CancellationException
+						|| (ex instanceof CompletionException ce && ce.getCause() instanceof CancellationException)) {
+					// Hover was cancelled; ignore as this is an expected fast-mouse-move scenario.
+					return null;
+				}
+				LanguageServerPlugin.logError(ex);
 			}
 		}
 		return null;
@@ -171,10 +178,12 @@ public class LSPTextHover implements ITextHover, ITextHoverExtension, ITextHover
 					LSPEclipseUtils.toOffset(range.getEnd(), document));
 			return this.lastRegion = new Region(regionStartOffset, regionEndOffset - regionStartOffset);
 		} catch (ExecutionException | BadLocationException e) {
-			LanguageServerPlugin.logError("Cannot get hover region for offset " + offset, e); //$NON-NLS-1$
+			if (!(e.getCause() instanceof CancellationException)) {
+				LanguageServerPlugin.logError("Cannot get hover region for offset " + offset, e); //$NON-NLS-1$
+			}
 		} catch (InterruptedException e) {
 			Thread.currentThread().interrupt();
-		} catch (NoSuchElementException | TimeoutException e) {
+		} catch (NoSuchElementException | TimeoutException | CancellationException e) {
 			// Fallback to heuristic region without blocking.
 		}