Suppress duplicated key event handling in Linux/GTK3 #4199

On GTK (Linux), a single physical key press can, in some situations, be
delivered to KeyBindingDispatcher twice for the very same native event:
once synchronously via an SWT.Traverse event dispatched from within the
native gtk3_key_press_event handling, and once more later via the async
message queue. Both deliveries resolve to and execute the exact same
bound command, which for page-traversal shortcuts like Ctrl+PageUp /
Ctrl+PageDown (Next/Previous Editor) causes an extra tab to be skipped,
since the CTabFolder selection is advanced twice per key press.

This does not reproduce on Windows or macOS, only on GTK.

Fix: track the last executed command together with the native timestamp
(Event#time) of its triggering event in executeCommand(...), and skip
(without re-executing the handler) a call that matches both the same
command and the same event timestamp, since that combination can only
happen when the very same native key event is redelivered. Genuinely
distinct key presses - including fast auto-repeat - always carry
different timestamps, so normal navigation and repeated shortcuts are
unaffected.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Fixes #4199

Author: fedejeanne

bundles/org.eclipse.e4.ui.bindings/src/org/eclipse/e4/ui/bindings/keys/KeyBindingDispatcher.java

@@ -267,6 +267,21 @@ private static boolean isOutOfOrderKey(List<KeyStroke> keyStrokes) {
 	@Optional
 	private Logger logger;
 
+	/**
+	 * The command executed the last time {@link #executeCommand(ParameterizedCommand, Event)} was
+	 * called, together with the native timestamp of the triggering event. On some platforms (e.g.
+	 * GTK on Linux) a single physical key press can be delivered to the dispatcher more than once
+	 * for the same native event (for example, once as an <code>SWT.Traverse</code> event and once
+	 * as a redundant <code>SWT.KeyDown</code> event), which would otherwise execute the resulting
+	 * command twice, e.g. skipping over an extra tab when navigating with Ctrl+PageUp/PageDown.
+	 * These fields are used to detect and suppress such a duplicate re-delivery of the very same
+	 * native key event, identified by its (platform-provided) timestamp.
+	 *
+	 * @see #isDuplicateKeyEvent(ParameterizedCommand, Event)
+	 */
+	private ParameterizedCommand lastExecutedCommand;
+	private int lastExecutedEventTime;
+
 	/**
 	 * Performs the actual execution of the command by looking up the current handler from the
 	 * command manager. If there is a handler and it is enabled, then it tries the actual execution.
@@ -292,6 +307,14 @@ public final boolean executeCommand(final ParameterizedCommand parameterizedComm
 			throw new NotEnabledException("Command should have been disabled via activity: " + parameterizedCommand); //$NON-NLS-1$
 		}
 
+		if (isDuplicateKeyEvent(parameterizedCommand, trigger)) {
+			if (isTracingEnabled()) {
+				logger.trace("Suppressed duplicate execution of " + parameterizedCommand + " for the same native event " //$NON-NLS-1$ //$NON-NLS-2$
+						+ "(time=" + trigger.time + ") in " + describe(context)); //$NON-NLS-1$ //$NON-NLS-2$
+			}
+			return true;
+		}
+
 		final EHandlerService handlerService = getHandlerService();
 		final Command command = parameterizedCommand.getCommand();
 
@@ -324,6 +347,37 @@ public final boolean executeCommand(final ParameterizedCommand parameterizedComm
 		return (commandDefined && commandHandled);
 	}
 
+	/**
+	 * Detects whether the given command execution is a duplicate re-delivery of the same native
+	 * key event that was already used to execute this very command. On some platforms (currently
+	 * known to affect GTK on Linux) a single physical key press can reach the dispatcher twice,
+	 * e.g. once via an <code>SWT.Traverse</code> event and once more via a subsequently generated
+	 * <code>SWT.KeyDown</code> event, both carrying the native event's original timestamp. Without
+	 * this guard, such duplicate delivery would execute the resulting command (e.g. "Next Editor"
+	 * bound to Ctrl+PageDown) twice for a single key press, which is, for example, visible as
+	 * navigation skipping over an extra tab.
+	 * <p>
+	 * As a side effect, this method records the given command/trigger pair as the last executed
+	 * one, so that a subsequent call can be compared against it.
+	 *
+	 * @param parameterizedCommand
+	 *            the command about to be executed; must not be <code>null</code>.
+	 * @param trigger
+	 *            the triggering event; may be <code>null</code>, in which case no event was
+	 *            involved and de-duplication does not apply.
+	 * @return <code>true</code> if this looks like a duplicate delivery of the same native event
+	 *         that already triggered the same command; <code>false</code> otherwise.
+	 */
+	private boolean isDuplicateKeyEvent(final ParameterizedCommand parameterizedCommand, final Event trigger) {
+		if (trigger == null) {
+			return false;
+		}
+		boolean duplicate = parameterizedCommand.equals(lastExecutedCommand) && trigger.time == lastExecutedEventTime;
+		lastExecutedCommand = parameterizedCommand;
+		lastExecutedEventTime = trigger.time;
+		return duplicate;
+	}
+
 	private boolean handleCommandExecution(final ParameterizedCommand parameterizedCommand,
 			final EHandlerService handlerService, final Event trigger, Object handler) {
 		final IEclipseContext staticContext = createContext(trigger);