Avoid trailing post-replacement delimiters in modern hard cuts

slugify/slugify.py

@@ -92,13 +92,18 @@ def _modern_truncate(text: str, max_length: int, word_boundary: bool, separator:
     # A hard cut may shorten a word but must not emit a partial/trailing delimiter.
     parts: list[str] = []
     length = 0
+    previous_index = 0
     for index, word in enumerate(tokens):
-        delimiter = separator if index else ''
+        if not word:
+            continue
+        # Keep repeated delimiters with the next nonempty word until it fits.
+        delimiter = separator * (index - previous_index)
         remaining = max_length - length - len(delimiter)
         if remaining <= 0:
             break
         parts.append(delimiter + word[:remaining])
         length += len(delimiter) + min(len(word), remaining)
+        previous_index = index
         if len(word) > remaining:
             break
     return ''.join(parts)

tests/test_release.py

@@ -53,6 +53,32 @@ def test_modern_fitting_post_replacements_preserve_delimiters(self):
                                                  separator=separator, max_length=limit,
                                                  word_boundary=boundary, save_order=order), expected)
 
+    def test_modern_hard_cut_does_not_end_in_post_replacement_delimiters(self):
+        cases = (
+            ('one--two', '-', 4, 'one'),
+            ('one--two', '-', 5, 'one'),
+            ('one--two', '-', 6, 'one--t'),
+            ('one--two', '::', 6, 'one'),
+            ('one--two', '::', 7, 'one'),
+            ('one--two', '::', 8, 'one::::t'),
+            ('--one', '-', 2, ''),
+            ('--one', '-', 3, '--o'),
+            ('---', '-', 2, ''),
+            ('x--two', 'x', 3, 'x'),
+            ('one--two', '', 4, 'onet'),
+        )
+        for replacement, separator, limit, expected in cases:
+            with self.subTest(replacement=replacement, separator=separator, limit=limit):
+                self.assertEqual(slugify('value', replacements=[('value', replacement)],
+                                         replacement_stage='post', allow_unicode=True,
+                                         separator=separator, max_length=limit), expected)
+
+    def test_modern_word_boundary_hard_cut_keeps_delimiters_with_the_next_word(self):
+        for order in (False, True):
+            self.assertEqual(slugify('value', replacements=[('value', '--longword')],
+                                     replacement_stage='post', allow_unicode=True,
+                                     max_length=2, word_boundary=True, save_order=order), '')
+
     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='-',