From e61e3daaf037507211028494d61f24382be31e5a Mon Sep 17 00:00:00 2001
From: Matti Pohjanvirta <matti.pohjanvirta@iki.fi>
Date: Sun, 20 Apr 2025 18:22:51 +0300
Subject: [PATCH] [4.2.x] Fixed #36341 -- Preserved whitespaces in wordwrap
 template filter.

Regression in 55d89e25f4115c5674cdd9b9bcba2bb2bb6d820b.

This work improves the django.utils.text.wrap() function to ensure that
empty lines and lines with whitespace only are kept instead of being
dropped.

Thanks Matti Pohjanvirta for the report and fix.

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

Backport of 1e9db35836d42a3c72f3d1015c2f302eb6fee046 from main.
---
 django/utils/text.py                          | 13 +++++-
 .../filter_tests/test_wordwrap.py             | 41 +++++++++++++++++++
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/django/utils/text.py b/django/utils/text.py
index 81ae88dc76..b018f2601f 100644
--- a/django/utils/text.py
+++ b/django/utils/text.py
@@ -102,10 +102,19 @@ def wrap(text, width):
         width=width,
         break_long_words=False,
         break_on_hyphens=False,
+        replace_whitespace=False,
     )
     result = []
-    for line in text.splitlines(True):
-        result.extend(wrapper.wrap(line))
+    for line in text.splitlines():
+        wrapped = wrapper.wrap(line)
+        if not wrapped:
+            # If `line` contains only whitespaces that are dropped, restore it.
+            result.append(line)
+        else:
+            result.extend(wrapped)
+    if text.endswith("\n"):
+        # If `text` ends with a newline, preserve it.
+        result.append("")
     return "\n".join(result)
 
 
diff --git a/tests/template_tests/filter_tests/test_wordwrap.py b/tests/template_tests/filter_tests/test_wordwrap.py
index 4afa1dd234..1692332e1e 100644
--- a/tests/template_tests/filter_tests/test_wordwrap.py
+++ b/tests/template_tests/filter_tests/test_wordwrap.py
@@ -89,3 +89,44 @@ class FunctionTests(SimpleTestCase):
             "I'm afraid",
             wordwrap(long_text, 10),
         )
+
+    def test_wrap_preserve_newlines(self):
+        cases = [
+            (
+                "this is a long paragraph of text that really needs to be wrapped\n\n"
+                "that is followed by another paragraph separated by an empty line\n",
+                "this is a long paragraph of\ntext that really needs to be\nwrapped\n\n"
+                "that is followed by another\nparagraph separated by an\nempty line\n",
+                30,
+            ),
+            ("\n\n\n", "\n\n\n", 5),
+            ("\n\n\n\n\n\n", "\n\n\n\n\n\n", 5),
+        ]
+        for text, expected, width in cases:
+            with self.subTest(text=text):
+                self.assertEqual(wordwrap(text, width), expected)
+
+    def test_wrap_preserve_whitespace(self):
+        width = 5
+        width_spaces = " " * width
+        cases = [
+            (
+                f"first line\n{width_spaces}\nsecond line",
+                f"first\nline\n{width_spaces}\nsecond\nline",
+            ),
+            (
+                "first line\n \t\t\t \nsecond line",
+                "first\nline\n \t\t\t \nsecond\nline",
+            ),
+            (
+                f"first line\n{width_spaces}\nsecond line\n\nthird{width_spaces}\n",
+                f"first\nline\n{width_spaces}\nsecond\nline\n\nthird\n",
+            ),
+            (
+                f"first line\n{width_spaces}{width_spaces}\nsecond line",
+                f"first\nline\n{width_spaces}{width_spaces}\nsecond\nline",
+            ),
+        ]
+        for text, expected in cases:
+            with self.subTest(text=text):
+                self.assertEqual(wordwrap(text, width), expected)