Bug 58777 [Viewers] add API to not deactivate CellEditor on FocusLost
TableViewerImpl installs a FocusListener on CellEditors, which calls applyEditorValue() on focusLost events. This FocusListener must be removed since applying the editor value is not always the wanted behavior on focusLost. Subclasses of CellEditor already handle focus loss in an extensible way: they install their own FocusListener and call a hook method focusLost() (which can be extended or reimplemented by subclasses with special needs). To support content assist in table cells (such as in the Change Method Signature dialog), we need to stay in editing mode even while the proposal list has focus. This is currently not implementable, since TableViewerImpl deactivates the CellEditor even if the CellEditor's focusLost() is reimplemented. The fix is to simply remove the redundant FocusListener in TableViewerImpl.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CellEditor.java
*
     * @see ICellEditorListener#applyEditorValue
     */
    protected void fireApplyEditorValue() {
        Object[] array = listeners.getListeners();
        for (int i = 0; i < array.length; i++) {
            final ICellEditorListener l = (ICellEditorListener) array[i];
            SafeRunnable.run(new SafeRunnable() {
                public void run() {
                    l.applyEditorValue();
                }
            });
        }
    }
    /**
     * Notifies all registered cell editor listeners that editing has been
     * canceled.
     *
     * @see ICellEditorListener#cancelEditor
     */
    protected void fireCancelEditor() {
        Object[] array = listeners.getListeners();
        for (int i = 0; i < array.length; i++) {
            final ICellEditorListener l = (ICellEditorListener) array[i];
            SafeRunnable.run(new SafeRunnable() {
                public void run() {
                    l.cancelEditor();
                }
            });
        }