From 80585e68c29c558fbc788237111c8e0e64db79b1 Mon Sep 17 00:00:00 2001
From: Stefan Hammer <stefan.hammer@wunderweiss.com>
Date: Thu, 15 Sep 2022 11:29:50 +0200
Subject: [PATCH] Retain filter params in ModelAdmin's search form

This basically uses the same code as django uses for the search form in
its ModelAdmin, to retain the current query params (template
admin/search_form.html).

Fixes #6006
---
 CHANGELOG.txt                                              | 1 +
 docs/releases/4.1.md                                       | 1 +
 .../templates/modeladmin/includes/search_form.html         | 4 ++++
 wagtail/contrib/modeladmin/tests/test_simple_modeladmin.py | 7 +++++++
 4 files changed, 13 insertions(+)

diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 4f4e41b056..0d4dbaee37 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -29,6 +29,7 @@ Changelog
  * Fix: Ensure that disabled buttons have a consistent presentation on hover to indicate no interaction is available (Paarth Agarwal)
  * Fix: Update the 'Locked pages' report menu title so that it is consistent with other pages reports and its own title on viewing (Nicholas Johnson)
  * Fix: Support `formfield_callback` handling on `ModelForm.Meta` for future Django 4.2 release (Matt Westcott)
+ * Fix: Ensure that `ModelAdmin` correctly supports filters in combination with subsequent searches without clearing the applied filters (Stefan Hammer)
 
 
 4.0.2 (xx.xx.xxxx) - IN DEVELOPMENT
diff --git a/docs/releases/4.1.md b/docs/releases/4.1.md
index 4552de0567..67314160de 100644
--- a/docs/releases/4.1.md
+++ b/docs/releases/4.1.md
@@ -41,6 +41,7 @@ Wagtail 4.1 is designated a Long Term Support (LTS) release. Long Term Support r
  * Ensure that disabled buttons have a consistent presentation on hover to indicate no interaction is available (Paarth Agarwal)
  * Update the 'Locked pages' report menu title so that it is consistent with other pages reports and its own title on viewing (Nicholas Johnson)
  * Support `formfield_callback` handling on `ModelForm.Meta` for future Django 4.2 release (Matt Westcott)
+ * Ensure that `ModelAdmin` correctly supports filters in combination with subsequent searches without clearing the applied filters (Stefan Hammer)
 
 ## Upgrade considerations
 
diff --git a/wagtail/contrib/modeladmin/templates/modeladmin/includes/search_form.html b/wagtail/contrib/modeladmin/templates/modeladmin/includes/search_form.html
index d2a516eb4e..6c3d7a5a0b 100644
--- a/wagtail/contrib/modeladmin/templates/modeladmin/includes/search_form.html
+++ b/wagtail/contrib/modeladmin/templates/modeladmin/includes/search_form.html
@@ -6,5 +6,9 @@
             <input id="id_q" name="{{ search_var }}" value="{{ view.query }}" placeholder="{% blocktrans trimmed with view.verbose_name_plural|lower as name %}Search {{ name }}{% endblocktrans %}" type="text">
         {% endfield %}
         <button type="submit" class="w-sr-only">{% trans 'Search' %}</button>
+        {# Keep all parameters from the query string (e.g. filter state). #}
+        {% for name, value in view.params.items %}
+            {% if name != search_var %}<input type="hidden" name="{{ name }}" value="{{ value }}">{% endif %}
+        {% endfor %}
     </form>
 {% endif %}
diff --git a/wagtail/contrib/modeladmin/tests/test_simple_modeladmin.py b/wagtail/contrib/modeladmin/tests/test_simple_modeladmin.py
index 60b748b902..6c23de93b3 100644
--- a/wagtail/contrib/modeladmin/tests/test_simple_modeladmin.py
+++ b/wagtail/contrib/modeladmin/tests/test_simple_modeladmin.py
@@ -156,6 +156,13 @@ class TestBookIndexView(TestCase, WagtailTestUtils):
             response, '<span class="result-count">2 out of 4</span>', html=True
         )
 
+        # The search form should retain the filter
+        self.assertContains(
+            response,
+            '<input type="hidden" name="author__id__exact" value="1">',
+            html=True,
+        )
+
         for book in response.context["object_list"]:
             self.assertEqual(book.author_id, 1)