Bug 123972 [Undo] Support approval of undoable operation execution
In GMF we do some common validation on our commands before we proceed to execute, undo or redo them. This validation is external to the command's ability to execute, undo or redo itself. Registering an IOperationApprover with the operation history for this of validation would give us an elegant solution. However, the IOperationApprover only supports approval of undo and redo. We also require support for approval of operation execution. Would you consider adding a proceedExecuting() method to the IOperationApprover interface, or to an extension of the IOperationApprover interface?
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IOperationHistory.java
* @param operation
	 *            the operation to be redone
	 * @param monitor
	 *            the progress monitor to be used for the redo, or code>null</code>
	 *            if no progress monitor is provided
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not <code>null</code>,
	 *            it should minimally contain an adapter for the
	 *            org.eclipse.swt.widgets.Shell.class.
	 * 
	 * @return the IStatus indicating whether the redo succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it remains in the history. <code>OK</code>
	 * severity indicates that the redo operation was successful. The operation
	 * will be placed on the undo history, provided it can be undone (answers
	 * <code>true</code> to {@link IUndoableOperation#canUndo()}). Listeners
	 * will receive the <code>REDONE</code> notification.
	 * </p>
	 * <p>
	 * Other severity codes (<code>CANCEL</code>, <code>ERROR</code>,
	 * <code>INFO</code>, etc.) are not specifically interpreted by the
	 * history. The operation will remain in the history and the returned status
	 * is simply passed back to the caller. For all severities other than
	 * <code>OK</code>, listeners will receive the
	 * <code>OPERATION_NOT_OK</code> notification instead of the
	 * <code>REDONE</code> notification.