Widget Improvements in WordPress 4.9

On the heels of adding TinyMCE rich editing to the Text widget and the media widgets in 4.8, there are another round of improvements coming to the Text widget and Video widget in 4.9, among other improvements to widgets. Shortcodes in Text Widget
One very longstanding request—for over 8 years—has been to support shortcodes in the Text widget (#10457). This is finally implemented in WordPress 4.9. It is no longer required to have plugins and themes do add_filter( ‘widget_text’, ‘do_shortcode’ ). Core now will do_shortcode() at the widget_text_content filter (added in 4.8) in the same way it is applied in the_content at priority 11, after wpautop() and shortcode_unautop(). If a plugin has added do_shortcode() to widget_text then this filter will be suspended while the widget runs to prevent shortcodes from being applied twice. If a Text widget is in legacy mode then it will manually do_shortcode() as well.
One reason for the long delay with adding shortcode support in Text widgets was due to many shortcodes looking for a global $post when they run. Since the global $post varies depending on whatever the query is, the shortcodes in a Text widget could render wildly different
Source: https://managewp.org/articles/16384/widget-improvements-in-wordpress-4-9

source https://williechiu40.wordpress.com/2017/10/25/widget-improvements-in-wordpress-4-9/