From f60fdccac210371ebfb039741b95f1cb69f4a64b Mon Sep 17 00:00:00 2001
From: emme1t <149944796+emme1t@users.noreply.github.com>
Date: Fri, 11 Sep 2026 23:53:59 -0700
Subject: [PATCH] Preserve fitting post-replacement output during modern
 truncation

---
 slugify/slugify.py |  3 +++
 test_release.py    | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/slugify/slugify.py b/slugify/slugify.py
index f4e5faf..aedcf8d 100644
--- a/slugify/slugify.py
+++ b/slugify/slugify.py
@@ -119,6 +119,9 @@ def _modern_truncate(text: str, max_length: int, word_boundary: bool, separator:
     """
     if max_length <= 0:
         return text.replace(DEFAULT_SEPARATOR, separator)
+    output_length = len(text) + text.count(DEFAULT_SEPARATOR) * (len(separator) - 1)
+    if output_length <= max_length:
+        return text.replace(DEFAULT_SEPARATOR, separator)
     tokens = text.split(DEFAULT_SEPARATOR)
     if word_boundary:
         words: list[str] = []
diff --git a/test_release.py b/test_release.py
index 0978362..2f0fbd5 100644
--- a/test_release.py
+++ b/test_release.py
@@ -40,6 +40,19 @@ def test_modern_separator_does_not_strip_word_content(self):
         self.assertEqual(slugify('xy xy', separator='xy', max_length=5), 'xyxyx')
         self.assertEqual(slugify('a b c', separator='::', max_length=3), 'a')
 
+    def test_modern_fitting_post_replacements_preserve_delimiters(self):
+        for replacement in ('one--two', '-one-two-', 'one---two'):
+            for separator in ('-', '::', ''):
+                expected = replacement.replace('-', separator)
+                for boundary, order, limit in itertools.product(
+                        (False, True), (False, True), (len(expected), len(expected) + 10)):
+                    with self.subTest(replacement=replacement, separator=separator,
+                                      boundary=boundary, order=order, limit=limit):
+                        self.assertEqual(slugify('x', replacements=[('x', replacement)],
+                                                 replacement_stage='post', allow_unicode=True,
+                                                 separator=separator, max_length=limit,
+                                                 word_boundary=boundary, save_order=order), expected)
+
     def test_cli_preserves_legacy_default_shape(self):
         expected = dict(text='', entities=True, decimal=True, hexadecimal=True,
                         max_length=0, word_boundary=False, save_order=False, separator='-',