prevent page refresh on enter key in header seach

- resolves #3746
- add a hidden & disabled first submit input so that ‘enter’ does not trigger submit
- allow the behaviour of the actual submit button to still work as expected
- intentionally HTML only solution as it is simpler and more accessible than JS override

CHANGELOG.txt

@@ -25,6 +25,7 @@ Changelog
  * Migrate multiple documentation pages from RST to MD (Vibhakar Solanki, LB (Ben Johnston))
  * Add documentation for defining custom form validation on models used in Wagtail's `modelAdmin` (Serafeim Papastefanos)
  * Update `README.md` logo to work for GitHub dark mode (Paarth Agarwal)
+ * Avoid an unnecessary page reload when pressing enter within the header search bar (Images, Pages, Documents) (Riley de Mestre)
  * Fix: When using `simple_translations` ensure that the user is redirected to the page edit view when submitting for a single locale (Mitchel Cabuloy)
  * Fix: When previewing unsaved changes to `Form` pages, ensure that all added fields are correctly shown in the preview (Joshua Munn)
  * Fix: When Documents (e.g. PDFs) have been configured to be served inline via `WAGTAILDOCS_CONTENT_TYPES` & `WAGTAILDOCS_INLINE_CONTENT_TYPES` ensure that the filename is correctly set in the `Content-Disposition` header so that saving the files will use the correct filename (John-Scott Atlakson)

CONTRIBUTORS.rst

@@ -570,6 +570,7 @@ Contributors
 * Paarth Agarwal
 * Nicolas Ferrari
 * Vibhakar Solanki
+* Riley de Mestre
 
 Translators
 ===========

docs/releases/2.17.md

@@ -50,6 +50,7 @@ The panel types `StreamFieldPanel`, `RichTextFieldPanel`, `ImageChooserPanel`, `
  * Migrate multiple documentation pages from RST to MD (Vibhakar Solanki, LB (Ben Johnston))
  * Add documentation for defining [custom form validation](modeladmin_custom_clean) on models used in Wagtail's `modelAdmin` (Serafeim Papastefanos)
  * Update `README.md` logo to work for GitHub dark mode (Paarth Agarwal)
+ * Avoid an unnecessary page reload when pressing enter within the header search bar (Images, Pages, Documents) (Riley de Mestre)
 
 
 ### Bug fixes

wagtail/admin/templates/wagtailadmin/shared/header.html

@@ -29,6 +29,8 @@
                         {% for field in search_form %}
                             {% include "wagtailadmin/shared/field_as_li.html" with field=field field_classes="field-small iconfield" icon="search" %}
                         {% endfor %}
+                        {% comment %}Ad an initial disabled & hidden submit button so that pressing 'enter' will not submit form. Reload not required as the content is dynamically loaded.{% endcomment %}
+                        <li class="visuallyhidden"><input disabled type="submit" aria-hidden="true"/></li>
                         <li class="submit visuallyhidden"><input type="submit" value="Search" class="button" /></li>
                     </ul>
                 </form>