Refs #10919 -- Refactored walk_items as module-level _walk_items and added truncated_unordered_list filter.

2 files changed, 94 insertions, 26 deletions

diff --git a/django/contrib/admin/templatetags/admin_filters.py b/django/contrib/admin/templatetags/admin_filters.py
index d0b17970a6..8c98a32c29 100644
--- a/django/contrib/admin/templatetags/admin_filters.py
+++ b/django/contrib/admin/templatetags/admin_filters.py
@@ -1,7 +1,10 @@
 from django import template
 from django.contrib.admin.options import EMPTY_VALUE_STRING
 from django.contrib.admin.utils import display_for_value
-from django.template.defaultfilters import stringfilter
+from django.template.defaultfilters import _walk_items, stringfilter
+from django.utils.html import conditional_escape
+from django.utils.safestring import mark_safe
+from django.utils.translation import ngettext
 
 register = template.Library()
 
@@ -10,3 +13,67 @@ register = template.Library()
 @stringfilter
 def to_object_display_value(value):
     return display_for_value(str(value), EMPTY_VALUE_STRING)
+
+
+@register.filter(is_safe=True, needs_autoescape=True)
+def truncated_unordered_list(value, max_items, autoescape=True):
+    """
+    Render an unordered list, showing at most ``max_items`` items and a
+    "...and N more objects." item at the end.
+
+    Usage::
+
+        {{ deleted_objects|truncated_unordered_list:100 }}
+    """
+
+    has_unlimited_items = max_items is None
+    if not has_unlimited_items:
+        max_items = int(max_items)
+        if max_items <= 0:
+            return mark_safe("")
+
+    if autoescape:
+        escaper = conditional_escape
+    else:
+
+        def escaper(x):
+            return x
+
+    item_count = 0
+
+    def list_formatter(item_list, tabs=1):
+        nonlocal item_count
+        indent = "\t" * tabs
+        output = []
+        for item, children in _walk_items(item_list):
+            sublist = ""
+            item_count += 1
+            should_display_item = has_unlimited_items or 0 < item_count <= max_items
+            if children:
+                sublist = "\n%s<ul>\n%s\n%s</ul>\n%s" % (
+                    indent,
+                    list_formatter(children, tabs + 1),
+                    indent,
+                    indent,
+                )
+
+            if should_display_item:
+                output.append("%s<li>%s%s</li>" % (indent, escaper(item), sublist))
+
+        return "\n".join(output)
+
+    rendered_object_list = list_formatter(value)
+    remaining_objects_message = ""
+
+    if not has_unlimited_items and item_count > max_items:
+        remaining_object_count = item_count - max_items
+        remaining_objects_message = "\n\t<li>%s</li>" % (
+            ngettext(
+                "…and %(count)d more object.",
+                "…and %(count)d more objects.",
+                remaining_object_count,
+            )
+            % {"count": remaining_object_count}
+        )
+
+    return mark_safe(rendered_object_list + remaining_objects_message)
diff --git a/django/template/defaultfilters.py b/django/template/defaultfilters.py
index 3ed9856c08..68641062a6 100644
--- a/django/template/defaultfilters.py
+++ b/django/template/defaultfilters.py
@@ -666,6 +666,31 @@ def slice_filter(value, arg):
         return value  # Fail silently.
 
 
+def _walk_items(item_list):
+    item_iterator = iter(item_list)
+    try:
+        item = next(item_iterator)
+        while True:
+            try:
+                next_item = next(item_iterator)
+            except StopIteration:
+                yield item, None
+                break
+            if isinstance(next_item, (list, tuple, types.GeneratorType)):
+                try:
+                    iter(next_item)
+                except TypeError:
+                    pass
+                else:
+                    yield item, next_item
+                    item = next(item_iterator)
+                    continue
+            yield item, None
+            item = next_item
+    except StopIteration:
+        pass
+
+
 @register.filter(is_safe=True, needs_autoescape=True)
 def unordered_list(value, autoescape=True):
     """
@@ -695,34 +720,10 @@ def unordered_list(value, autoescape=True):
         def escaper(x):
             return x
 
-    def walk_items(item_list):
-        item_iterator = iter(item_list)
-        try:
-            item = next(item_iterator)
-            while True:
-                try:
-                    next_item = next(item_iterator)
-                except StopIteration:
-                    yield item, None
-                    break
-                if isinstance(next_item, (list, tuple, types.GeneratorType)):
-                    try:
-                        iter(next_item)
-                    except TypeError:
-                        pass
-                    else:
-                        yield item, next_item
-                        item = next(item_iterator)
-                        continue
-                yield item, None
-                item = next_item
-        except StopIteration:
-            pass
-
     def list_formatter(item_list, tabs=1):
         indent = "\t" * tabs
         output = []
-        for item, children in walk_items(item_list):
+        for item, children in _walk_items(item_list):
             sublist = ""
             if children:
                 sublist = "\n%s<ul>\n%s\n%s</ul>\n%s" % (