Enforce page_breadcrumbs to be expanded when there is only one item

Rather than special-casing whether the page is root or not, just check
if there is only one item. If that's the case, then the user is
exploring the "explorable root instance", which may be the root Page
instance or the closest common ancestor where the user has permission.

In this case, we don't want to show the breadcrumbs toggle/expand button
(it's always expanded).

This also removes the incorrectly extraneous right arrow when exploring
the root instance.

wagtail/admin/templates/wagtailadmin/pages/page_listing_header.html

@@ -3,7 +3,7 @@
 
 {% block breadcrumbs %}
     {# breadcrumbs #}
-    {% page_breadcrumbs parent_page 'wagtailadmin_explore' url_root_name='wagtailadmin_explore_root' is_expanded=parent_page.is_root %}
+    {% page_breadcrumbs parent_page 'wagtailadmin_explore' url_root_name='wagtailadmin_explore_root' %}
 {% endblock %}
 
 {% block actions %}

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

@@ -18,21 +18,7 @@
         {% else %}
             {% url url_name page.id as breadcrumb_url %}
         {% endif %}
-        {% if page.is_root %}
-            <li
-                class="{{ breadcrumb_item_classes }} {% if forloop.last %}w-font-bold{% endif %} {% if not is_expanded %}w-max-w-0{% endif %}"
-                {% if not is_expanded %}hidden{% endif %}
-                data-w-breadcrumbs-target="content"
-            >
-                <a
-                    class="{{ breadcrumb_link_classes }}"
-                    href="{{ breadcrumb_url }}{{ querystring_value }}"
-                >
-                    {% trans "Root" %}
-                </a>
-                {% icon name="arrow-right" classname=icon_classes %}
-            </li>
-        {% elif forloop.last %}
+        {% if forloop.last %}
             <li
                 class="{{ breadcrumb_item_classes }} w-font-bold"
                 {% if trailing_breadcrumb_title and not is_expanded %}hidden{% endif %}

wagtail/admin/templatetags/wagtailadmin_tags.py

@@ -92,10 +92,17 @@ def page_breadcrumbs(
     if not cca:
         return {"items": Page.objects.none()}
 
-    return {
-        "items": page.get_ancestors(inclusive=include_self)
+    items = (
+        page.get_ancestors(inclusive=include_self)
         .descendant_of(cca, inclusive=True)
-        .specific(),
+        .specific()
+    )
+
+    if len(items) == 1:
+        is_expanded = True
+
+    return {
+        "items": items,
         "current_page": page,
         "is_expanded": is_expanded,
         "page_perms": page_perms,

wagtail/admin/tests/pages/test_explorer_view.py

@@ -1167,7 +1167,7 @@ class TestExplorablePageVisibility(WagtailTestUtils, TestCase):
         # When Josh is viewing his visible root page, he should the page title as a non-hidden, single-item breadcrumb.
         expected = """
             <li
-                class="w-h-full w-flex w-items-center w-overflow-hidden w-transition w-duration-300 w-whitespace-nowrap w-flex-shrink-0 w-font-bold">
+                class="w-h-full w-flex w-items-center w-overflow-hidden w-transition w-duration-300 w-whitespace-nowrap w-flex-shrink-0 w-font-bold" data-w-breadcrumbs-target="content">
                 <a class="w-flex w-items-center w-text-text-label w-pr-0.5 w-text-14 w-no-underline w-outline-offset-inside w-border-b w-border-b-2 w-border-transparent w-box-content hover:w-border-current hover:w-text-text-label"
                    href="/admin/pages/4/">
                     Welcome to example.com!