Allow ignoring a page when finding an available slug

This is useful for when using this function to update a pages slug

wagtail/core/tests/test_utils.py

@@ -125,7 +125,9 @@ class TestFindAvailableSlug(TestCase):
         self.root_page = Page.objects.get(depth=1)
         self.home_page = Page.objects.get(depth=2)
 
-        self.root_page.add_child(instance=Page(title="Second homepage", slug="home-1"))
+        self.second_home_page = self.root_page.add_child(
+            instance=Page(title="Second homepage", slug="home-1")
+        )
 
     def test_find_available_slug(self):
         with self.assertNumQueries(1):
@@ -140,6 +142,12 @@ class TestFindAvailableSlug(TestCase):
 
         self.assertEqual(slug, "home-2")
 
+    def test_find_available_slug_ignore_page_id(self):
+        with self.assertNumQueries(1):
+            slug = find_available_slug(self.root_page, "home", ignore_page_id=self.second_home_page.id)
+
+        self.assertEqual(slug, "home-1")
+
 
 @override_settings(
     USE_I18N=True,

wagtail/core/utils.py

@@ -176,7 +176,7 @@ class InvokeViaAttributeShortcut:
         return method(name)
 
 
-def find_available_slug(parent, requested_slug):
+def find_available_slug(parent, requested_slug, ignore_page_id=None):
     """
     Finds an available slug within the specified parent.
 
@@ -187,12 +187,17 @@ def find_available_slug(parent, requested_slug):
      - 'requested-slug-2'
 
     And so on, until an available slug is found.
+
+    The `ignore_page_id` keyword argument is useful for when you are updating a page,
+    you can pass the page being updated here so the page's current slug is not
+    treated as in use by another page.
     """
-    existing_slugs = set(
-        parent.get_children()
-        .filter(slug__startswith=requested_slug)
-        .values_list("slug", flat=True)
-    )
+    pages = parent.get_children().filter(slug__startswith=requested_slug)
+
+    if ignore_page_id:
+        pages = pages.exclude(id=ignore_page_id)
+
+    existing_slugs = set(pages.values_list("slug", flat=True))
     slug = requested_slug
     number = 1