Fixed #35189 -- Improved admin collapsible fieldsets by using <details> elements.

This work improves the accessibility of the add and change pages in the
admin site by adding <details> and <summary> elements to the collapsible
fieldsets. This has the nice side effect of no longer requiring custom
JavaScript helpers to implement the fieldsets' show/hide capabilities.

Thanks to James Scholes for the accessibility advice, and to Sarah Boyce
and Tom Carrick for reviews.

Co-authored-by: Natalia <124304+nessita@users.noreply.github.com>
Co-authored-by: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>

11 files changed, 119 insertions, 88 deletions

diff --git a/django/contrib/admin/helpers.py b/django/contrib/admin/helpers.py
index c4613fa24e..a4aa8e40e3 100644
--- a/django/contrib/admin/helpers.py
+++ b/django/contrib/admin/helpers.py
@@ -18,6 +18,7 @@ from django.db.models.fields.related import (
 from django.forms.utils import flatatt
 from django.template.defaultfilters import capfirst, linebreaksbr
 from django.urls import NoReverseMatch, reverse
+from django.utils.functional import cached_property
 from django.utils.html import conditional_escape, format_html
 from django.utils.safestring import mark_safe
 from django.utils.translation import gettext
@@ -116,10 +117,14 @@ class Fieldset:
 
     @property
     def media(self):
-        if "collapse" in self.classes:
-            return forms.Media(js=["admin/js/collapse.js"])
         return forms.Media()
 
+    @cached_property
+    def is_collapsible(self):
+        if any([field in self.fields for field in self.form.errors]):
+            return False
+        return "collapse" in self.classes
+
     def __iter__(self):
         for field in self.fields:
             yield Fieldline(
@@ -438,6 +443,12 @@ class InlineAdminFormSet:
     def forms(self):
         return self.formset.forms
 
+    @cached_property
+    def is_collapsible(self):
+        if any(self.formset.errors):
+            return False
+        return "collapse" in self.classes
+
     def non_form_errors(self):
         return self.formset.non_form_errors()
 
diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index 47b4821fcc..12467de74d 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -2398,8 +2398,6 @@ class InlineModelAdmin(BaseModelAdmin):
         js = ["vendor/jquery/jquery%s.js" % extra, "jquery.init.js", "inlines.js"]
         if self.filter_vertical or self.filter_horizontal:
             js.extend(["SelectBox.js", "SelectFilter2.js"])
-        if self.classes and "collapse" in self.classes:
-            js.append("collapse.js")
         return forms.Media(js=["admin/js/%s" % url for url in js])
 
     def get_extra(self, request, obj=None, **kwargs):
diff --git a/django/contrib/admin/static/admin/css/forms.css b/django/contrib/admin/static/admin/css/forms.css
index fe60536d62..539a11ae61 100644
--- a/django/contrib/admin/static/admin/css/forms.css
+++ b/django/contrib/admin/static/admin/css/forms.css
@@ -76,6 +76,20 @@ form ul.inline li {
     padding-right: 7px;
 }
 
+/* FIELDSETS */
+
+fieldset .fieldset-heading,
+fieldset .inline-heading,
+:not(.inline-related) .collapse summary {
+    border: 1px solid var(--header-bg);
+    margin: 0;
+    padding: 8px;
+    font-weight: 400;
+    font-size: 0.8125rem;
+    background: var(--header-bg);
+    color: var(--header-link-color);
+}
+
 /* ALIGNED FIELDSETS */
 
 .aligned label {
@@ -207,35 +221,16 @@ form div.help ul {
     width: 450px;
 }
 
-/* COLLAPSED FIELDSETS */
+/* COLLAPSIBLE FIELDSETS */
 
-fieldset.collapsed * {
-    display: none;
-}
-
-fieldset.collapsed h2, fieldset.collapsed {
-    display: block;
-}
-
-fieldset.collapsed {
-    border: 1px solid var(--hairline-color);
-    border-radius: 4px;
-    overflow: hidden;
-}
-
-fieldset.collapsed h2 {
-    background: var(--darkened-bg);
-    color: var(--body-quiet-color);
-}
-
-fieldset .collapse-toggle {
-    color: var(--header-link-color);
-}
-
-fieldset.collapsed .collapse-toggle {
+.collapse summary .fieldset-heading,
+.collapse summary .inline-heading {
     background: transparent;
+    border: none;
+    color: currentColor;
     display: inline;
-    color: var(--link-fg);
+    margin: 0;
+    padding: 0;
 }
 
 /* MONOSPACE TEXTAREAS */
@@ -387,14 +382,16 @@ body.popup .submit-row {
     position: relative;
 }
 
-.inline-related h3 {
+.inline-related h4,
+.inline-related:not(.tabular) .collapse summary {
     margin: 0;
     color: var(--body-quiet-color);
     padding: 5px;
     font-size: 0.8125rem;
     background: var(--darkened-bg);
-    border-top: 1px solid var(--hairline-color);
-    border-bottom: 1px solid var(--hairline-color);
+    border: 1px solid var(--hairline-color);
+    border-left-color: var(--darkened-bg);
+    border-right-color: var(--darkened-bg);
 }
 
 .inline-related h3 span.delete {
diff --git a/django/contrib/admin/static/admin/css/responsive.css b/django/contrib/admin/static/admin/css/responsive.css
index b58cbd964e..932e824c1c 100644
--- a/django/contrib/admin/static/admin/css/responsive.css
+++ b/django/contrib/admin/static/admin/css/responsive.css
@@ -565,10 +565,6 @@ input[type="submit"], button {
         padding-top: 15px;
     }
 
-    fieldset.collapsed .form-row {
-        display: none;
-    }
-
     .aligned label {
         width: 100%;
         min-width: auto;
diff --git a/django/contrib/admin/templates/admin/edit_inline/stacked.html b/django/contrib/admin/templates/admin/edit_inline/stacked.html
index b0331c65f8..73f459ee47 100644
--- a/django/contrib/admin/templates/admin/edit_inline/stacked.html
+++ b/django/contrib/admin/templates/admin/edit_inline/stacked.html
@@ -4,6 +4,7 @@
      data-inline-type="stacked"
      data-inline-formset="{{ inline_admin_formset.inline_formset_data }}">
 <fieldset class="module {{ inline_admin_formset.classes }}" aria-labelledby="{{ inline_admin_formset.formset.prefix }}-heading">
+  {% if inline_admin_formset.is_collapsible %}<details><summary>{% endif %}
   <h2 id="{{ inline_admin_formset.formset.prefix }}-heading" class="inline-heading">
   {% if inline_admin_formset.formset.max_num == 1 %}
     {{ inline_admin_formset.opts.verbose_name|capfirst }}
@@ -11,6 +12,7 @@
     {{ inline_admin_formset.opts.verbose_name_plural|capfirst }}
   {% endif %}
   </h2>
+  {% if inline_admin_formset.is_collapsible %}</summary>{% endif %}
 {{ inline_admin_formset.formset.management_form }}
 {{ inline_admin_formset.formset.non_form_errors }}
 
@@ -31,5 +33,6 @@
   {% if inline_admin_form.needs_explicit_pk_field %}{{ inline_admin_form.pk_field.field }}{% endif %}
   {% if inline_admin_form.fk_field %}{{ inline_admin_form.fk_field.field }}{% endif %}
 </div>{% endfor %}
+  {% if inline_admin_formset.is_collapsible %}</details>{% endif %}
 </fieldset>
 </div>
diff --git a/django/contrib/admin/templates/admin/edit_inline/tabular.html b/django/contrib/admin/templates/admin/edit_inline/tabular.html
index 845d3917a4..7acfda7bd1 100644
--- a/django/contrib/admin/templates/admin/edit_inline/tabular.html
+++ b/django/contrib/admin/templates/admin/edit_inline/tabular.html
@@ -5,6 +5,7 @@
   <div class="tabular inline-related {% if forloop.last %}last-related{% endif %}">
 {{ inline_admin_formset.formset.management_form }}
 <fieldset class="module {{ inline_admin_formset.classes }}" aria-labelledby="{{ inline_admin_formset.formset.prefix }}-heading">
+  {% if inline_admin_formset.is_collapsible %}<details><summary>{% endif %}
   <h2 id="{{ inline_admin_formset.formset.prefix }}-heading" class="inline-heading">
   {% if inline_admin_formset.formset.max_num == 1 %}
     {{ inline_admin_formset.opts.verbose_name|capfirst }}
@@ -12,6 +13,7 @@
     {{ inline_admin_formset.opts.verbose_name_plural|capfirst }}
   {% endif %}
   </h2>
+  {% if inline_admin_formset.is_collapsible %}</summary>{% endif %}
    {{ inline_admin_formset.formset.non_form_errors }}
    <table>
      <thead><tr>
@@ -63,6 +65,7 @@
      {% endfor %}
      </tbody>
    </table>
+  {% if inline_admin_formset.is_collapsible %}</details>{% endif %}
 </fieldset>
   </div>
 </div>
diff --git a/django/contrib/admin/templates/admin/includes/fieldset.html b/django/contrib/admin/templates/admin/includes/fieldset.html
index 66bf714e9a..b4eef47547 100644
--- a/django/contrib/admin/templates/admin/includes/fieldset.html
+++ b/django/contrib/admin/templates/admin/includes/fieldset.html
@@ -1,7 +1,9 @@
 {% with prefix=fieldset.formset.prefix|default:"fieldset" id_prefix=id_prefix|default:"0" id_suffix=id_suffix|default:"0" name=fieldset.name|default:""|slugify %}
 <fieldset class="module aligned {{ fieldset.classes }}"{% if name %} aria-labelledby="{{ prefix }}-{{ id_prefix}}-{{ name }}-{{ id_suffix }}-heading"{% endif %}>
     {% if name %}
+        {% if fieldset.is_collapsible %}<details><summary>{% endif %}
         <h{{ heading_level|default:2 }} id="{{ prefix }}-{{ id_prefix}}-{{ name }}-{{ id_suffix }}-heading" class="fieldset-heading">{{ fieldset.name }}</h{{ heading_level|default:2 }}>
+        {% if fieldset.is_collapsible %}</summary>{% endif %}
     {% endif %}
     {% if fieldset.description %}
         <div class="description">{{ fieldset.description|safe }}</div>
@@ -34,5 +36,6 @@
             {% if not line.fields|length == 1 %}</div>{% endif %}
         </div>
     {% endfor %}
+    {% if name and fieldset.is_collapsible %}</details>{% endif %}
 </fieldset>
 {% endwith %}
diff --git a/docs/ref/contrib/admin/index.txt b/docs/ref/contrib/admin/index.txt
index 2a5652c24b..b7e94c7387 100644
--- a/docs/ref/contrib/admin/index.txt
+++ b/docs/ref/contrib/admin/index.txt
@@ -424,9 +424,16 @@ subclass::
                 "classes": ["wide", "collapse"],
             }
 
-        Fieldsets with the ``collapse`` style will be initially collapsed in
-        the admin and replaced with a small "click to expand" link. Fieldsets
-        with the ``wide`` style will be given extra horizontal space.
+        Fieldsets with the ``wide`` style will be given extra horizontal
+        space in the admin interface.
+        Fieldsets with a name and the ``collapse`` style will be initially
+        collapsed, using an expandable widget with a toggle for switching
+        their visibility.
+
+        .. versionchanged:: 5.1
+
+            ``fieldsets`` using the ``collapse`` class now use ``<details>``
+            and ``<summary>`` elements, provided they define a ``name``.
 
     * ``description``
         A string of optional extra text to be displayed at the top of each
@@ -2308,8 +2315,12 @@ The ``InlineModelAdmin`` class adds or customizes:
     A list or tuple containing extra CSS classes to apply to the fieldset that
     is rendered for the inlines. Defaults to ``None``. As with classes
     configured in :attr:`~ModelAdmin.fieldsets`, inlines with a ``collapse``
-    class will be initially collapsed and their header will have a small "show"
-    link.
+    class will be initially collapsed using an expandable widget.
+
+    .. versionchanged:: 5.1
+
+        ``fieldsets`` using the ``collapse`` class now use ``<details>`` and
+        ``<summary>`` elements, provided they define a ``name``.
 
 .. attribute:: InlineModelAdmin.extra
 
diff --git a/docs/releases/5.1.txt b/docs/releases/5.1.txt
index 68315205df..e4f0b37402 100644
--- a/docs/releases/5.1.txt
+++ b/docs/releases/5.1.txt
@@ -419,6 +419,12 @@ Miscellaneous
   a ``<footer>`` tag instead of a ``<div>``, and also moved below the
   ``<div id="main">`` element.
 
+* In order to improve accessibility, the expandable widget used for
+  :attr:`ModelAdmin.fieldsets <django.contrib.admin.ModelAdmin.fieldsets>` and
+  :attr:`InlineModelAdmin.fieldsets <django.contrib.admin.InlineModelAdmin>`,
+  when the fieldset has a name and use the ``collapse`` class, now includes
+  ``<details>`` and ``<summary>`` elements.
+
 * :meth:`.SimpleTestCase.assertURLEqual` and
   :meth:`~django.test.SimpleTestCase.assertInHTML` now add ``": "`` to the
   ``msg_prefix``. This is consistent with the behavior of other assertions.
diff --git a/tests/admin_inlines/tests.py b/tests/admin_inlines/tests.py
index 7b38619cc0..dee703825d 100644
--- a/tests/admin_inlines/tests.py
+++ b/tests/admin_inlines/tests.py
@@ -4,7 +4,9 @@ from django.contrib.admin.tests import AdminSeleniumTestCase
 from django.contrib.auth.models import Permission, User
 from django.contrib.contenttypes.models import ContentType
 from django.test import RequestFactory, TestCase, override_settings
+from django.test.selenium import screenshot_cases
 from django.urls import reverse
+from django.utils.translation import gettext
 
 from .admin import InnerInline
 from .admin import site as admin_site
@@ -1790,6 +1792,10 @@ class TestInlineWithFieldsets(TestDataMixin, TestCase):
             if "tabular" in inline_admin_formset.opts.template:
                 continue
 
+            if "collapse" in inline_admin_formset.classes:
+                formset_heading = f"<summary>{formset_heading}</summary>"
+                self.assertContains(response, formset_heading, html=True, count=1)
+
             # Headings for every formset (the amount depends on `extra`).
             for y, inline_admin_form in enumerate(inline_admin_formset):
                 y_plus_one = y + 1
@@ -1813,6 +1819,12 @@ class TestInlineWithFieldsets(TestDataMixin, TestCase):
                             f"Details</h4>"
                         )
                         self.assertContains(response, fieldset_heading)
+                        if "collapse" in fieldset.classes:
+                            self.assertContains(
+                                response,
+                                f"<summary>{fieldset_heading}</summary>",
+                                html=True,
+                            )
                         self.assertContains(response, f'id="{heading_id}"', count=1)
 
                     else:
@@ -2182,10 +2194,11 @@ class SeleniumTests(AdminSeleniumTestCase):
             "form#profilecollection_form tr.dynamic-profile_set#profile_set-2", 1
         )
 
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_collapsed_inlines(self):
         from selenium.webdriver.common.by import By
 
-        # Collapsed inlines have SHOW/HIDE links.
+        # Collapsed inlines use details and summary elements.
         self.admin_login(username="super", password="secret")
         self.selenium.get(
             self.live_server_url + reverse("admin:admin_inlines_author_add")
@@ -2195,19 +2208,21 @@ class SeleniumTests(AdminSeleniumTestCase):
             "#id_nonautopkbook_set-0-title",
             "#id_nonautopkbook_set-2-0-title",
         ]
-        show_links = self.selenium.find_elements(By.LINK_TEXT, "SHOW")
-        self.assertEqual(len(show_links), 3)
+        summaries = self.selenium.find_elements(By.TAG_NAME, "summary")
+        self.assertEqual(len(summaries), 3)
+        self.take_screenshot("loaded")
         for show_index, field_name in enumerate(test_fields, 0):
             self.wait_until_invisible(field_name)
-            show_links[show_index].click()
+            summaries[show_index].click()
             self.wait_until_visible(field_name)
-        hide_links = self.selenium.find_elements(By.LINK_TEXT, "HIDE")
-        self.assertEqual(len(hide_links), 2)
+        self.take_screenshot("expanded")
         for hide_index, field_name in enumerate(test_fields, 0):
             self.wait_until_visible(field_name)
-            hide_links[hide_index].click()
+            summaries[hide_index].click()
             self.wait_until_invisible(field_name)
+        self.take_screenshot("collapsed")
 
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_added_stacked_inline_with_collapsed_fields(self):
         from selenium.webdriver.common.by import By
 
@@ -2215,20 +2230,22 @@ class SeleniumTests(AdminSeleniumTestCase):
         self.selenium.get(
             self.live_server_url + reverse("admin:admin_inlines_teacher_add")
         )
-        self.selenium.find_element(By.LINK_TEXT, "Add another Child").click()
+        add_text = gettext("Add another %(verbose_name)s") % {"verbose_name": "Child"}
+        self.selenium.find_element(By.LINK_TEXT, add_text).click()
         test_fields = ["#id_child_set-0-name", "#id_child_set-1-name"]
-        show_links = self.selenium.find_elements(By.LINK_TEXT, "SHOW")
-        self.assertEqual(len(show_links), 2)
+        summaries = self.selenium.find_elements(By.TAG_NAME, "summary")
+        self.assertEqual(len(summaries), 3)
+        self.take_screenshot("loaded")
         for show_index, field_name in enumerate(test_fields, 0):
             self.wait_until_invisible(field_name)
-            show_links[show_index].click()
+            summaries[show_index].click()
             self.wait_until_visible(field_name)
-        hide_links = self.selenium.find_elements(By.LINK_TEXT, "HIDE")
-        self.assertEqual(len(hide_links), 2)
+        self.take_screenshot("expanded")
         for hide_index, field_name in enumerate(test_fields, 0):
             self.wait_until_visible(field_name)
-            hide_links[hide_index].click()
+            summaries[hide_index].click()
             self.wait_until_invisible(field_name)
+        self.take_screenshot("collapsed")
 
     def assertBorder(self, element, border):
         width, style, color = border.split(" ")
@@ -2264,9 +2281,9 @@ class SeleniumTests(AdminSeleniumTestCase):
         self.wait_until_visible("#id_dummy")
         self.selenium.find_element(By.ID, "id_dummy").send_keys(1)
         fields = ["id_inner5stacked_set-0-dummy", "id_inner5tabular_set-0-dummy"]
-        show_links = self.selenium.find_elements(By.LINK_TEXT, "SHOW")
+        summaries = self.selenium.find_elements(By.TAG_NAME, "summary")
         for show_index, field_name in enumerate(fields):
-            show_links[show_index].click()
+            summaries[show_index].click()
             self.wait_until_visible("#" + field_name)
             self.selenium.find_element(By.ID, field_name).send_keys(1)
 
@@ -2304,49 +2321,40 @@ class SeleniumTests(AdminSeleniumTestCase):
         self.selenium.get(
             self.live_server_url + reverse("admin:admin_inlines_holder5_add")
         )
-        stacked_inline_formset_selector = (
-            "div#inner5stacked_set-group fieldset.module.collapse"
+        stacked_inline_details_selector = (
+            "div#inner5stacked_set-group fieldset.module.collapse details"
         )
-        tabular_inline_formset_selector = (
-            "div#inner5tabular_set-group fieldset.module.collapse"
+        tabular_inline_details_selector = (
+            "div#inner5tabular_set-group fieldset.module.collapse details"
         )
         # Inlines without errors, both inlines collapsed
         self.selenium.find_element(By.XPATH, '//input[@value="Save"]').click()
         self.assertCountSeleniumElements(
-            stacked_inline_formset_selector + ".collapsed", 1
+            stacked_inline_details_selector + ":not([open])", 1
         )
         self.assertCountSeleniumElements(
-            tabular_inline_formset_selector + ".collapsed", 1
+            tabular_inline_details_selector + ":not([open])", 1
         )
-        show_links = self.selenium.find_elements(By.LINK_TEXT, "SHOW")
-        self.assertEqual(len(show_links), 2)
+        summaries = self.selenium.find_elements(By.TAG_NAME, "summary")
+        self.assertEqual(len(summaries), 2)
 
         # Inlines with errors, both inlines expanded
         test_fields = ["#id_inner5stacked_set-0-dummy", "#id_inner5tabular_set-0-dummy"]
         for show_index, field_name in enumerate(test_fields):
-            show_links[show_index].click()
+            summaries[show_index].click()
             self.wait_until_visible(field_name)
             self.selenium.find_element(By.ID, field_name[1:]).send_keys(1)
-        hide_links = self.selenium.find_elements(By.LINK_TEXT, "HIDE")
-        self.assertEqual(len(hide_links), 2)
         for hide_index, field_name in enumerate(test_fields):
-            hide_link = hide_links[hide_index]
+            summary = summaries[hide_index]
             self.selenium.execute_script(
-                "window.scrollTo(0, %s);" % hide_link.location["y"]
+                "window.scrollTo(0, %s);" % summary.location["y"]
             )
-            hide_link.click()
+            summary.click()
             self.wait_until_invisible(field_name)
         with self.wait_page_loaded():
             self.selenium.find_element(By.XPATH, '//input[@value="Save"]').click()
-        with self.disable_implicit_wait():
-            self.assertCountSeleniumElements(
-                stacked_inline_formset_selector + ".collapsed", 0
-            )
-            self.assertCountSeleniumElements(
-                tabular_inline_formset_selector + ".collapsed", 0
-            )
-        self.assertCountSeleniumElements(stacked_inline_formset_selector, 1)
-        self.assertCountSeleniumElements(tabular_inline_formset_selector, 1)
+        self.assertCountSeleniumElements(stacked_inline_details_selector, 0)
+        self.assertCountSeleniumElements(tabular_inline_details_selector, 0)
 
     def test_inlines_verbose_name(self):
         """
diff --git a/tests/admin_views/tests.py b/tests/admin_views/tests.py
index 5fab253f80..d49e7d028b 100644
--- a/tests/admin_views/tests.py
+++ b/tests/admin_views/tests.py
@@ -1939,7 +1939,6 @@ class AdminJavaScriptTest(TestCase):
             self.assertContains(response, "vendor/jquery/jquery.min.js")
             self.assertContains(response, "prepopulate.js")
             self.assertContains(response, "actions.js")
-            self.assertContains(response, "collapse.js")
             self.assertContains(response, "inlines.js")
         with override_settings(DEBUG=True):
             response = self.client.get(reverse("admin:admin_views_section_add"))
@@ -1947,7 +1946,6 @@ class AdminJavaScriptTest(TestCase):
             self.assertNotContains(response, "vendor/jquery/jquery.min.js")
             self.assertContains(response, "prepopulate.js")
             self.assertContains(response, "actions.js")
-            self.assertContains(response, "collapse.js")
             self.assertContains(response, "inlines.js")
 
 
@@ -6086,11 +6084,8 @@ class SeleniumTests(AdminSeleniumTestCase):
         )
         self.assertFalse(self.selenium.find_element(By.ID, "id_title").is_displayed())
         self.take_screenshot("collapsed")
-        self.selenium.find_elements(By.LINK_TEXT, "Show")[0].click()
+        self.selenium.find_elements(By.TAG_NAME, "summary")[0].click()
         self.assertTrue(self.selenium.find_element(By.ID, "id_title").is_displayed())
-        self.assertEqual(
-            self.selenium.find_element(By.ID, "fieldsetcollapser0").text, "Hide"
-        )
         self.take_screenshot("expanded")
 
     @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
@@ -6104,7 +6099,7 @@ class SeleniumTests(AdminSeleniumTestCase):
         )
         url = self.live_server_url + reverse("admin7:admin_views_pizza_add")
         self.selenium.get(url)
-        self.selenium.find_elements(By.ID, "fieldsetcollapser0")[0].click()
+        self.selenium.find_elements(By.TAG_NAME, "summary")[0].click()
         from_filter_box = self.selenium.find_element(By.ID, "id_toppings_filter")
         from_box = self.selenium.find_element(By.ID, "id_toppings_from")
         to_filter_box = self.selenium.find_element(By.ID, "id_toppings_filter_selected")