Fix split trailing newline

CHANGELOG

@@ -1,5 +1,7 @@
 # 3.30.0 (2026-XX-XX)
 
+ * Fix `split`, `random`, and `shuffle` merging a trailing newline into the last character of a string
+ * Speed up splitting a string into characters in `split`, `random`, and `shuffle`
  * Speed up adding extensions to an environment
  * Fix the escaping safe analysis retaining every compiled template node for the lifetime of the environment
  * Speed up loading a template that the environment has already loaded

src/Extension/CoreExtension.php

@@ -1263,19 +1263,19 @@ final class CoreExtension extends AbstractExtension
     }
 
     /**
-     * Unicode version of str_split(): splits at every position except after the start and before the end.
+     * Unicode version of str_split(), an empty string giving a single empty character.
      *
-     * @return list<string>
+     * @return non-empty-list<string>
      *
      * @throws RuntimeError When the string cannot be split into characters
      */
     private static function splitIntoCharacters(string $string, string $name): array
     {
-        if (false === $characters = preg_split('/(?<!^)(?!$)/u', $string)) {
+        if (false === preg_match_all('/./us', $string, $matches)) {
             throw new RuntimeError(\sprintf('Unable to split the string passed to "%s" into characters: %s.', $name, preg_last_error_msg()));
         }
 
-        return $characters;
+        return $matches[0] ?: [''];
     }
 
     /**

tests/Fixtures/filters/characters_trailing_newline.test

@@ -0,0 +1,14 @@
+--TEST--
+"reverse", "split", "shuffle", and "random" keep a trailing newline as its own character
+--TEMPLATE--
+{{ value|reverse|json_encode|raw }}
+{{ value|split('')|json_encode|raw }}
+{{ value|shuffle|length }}
+{{ random("a\n")|length }}
+--DATA--
+return ['value' => "ab\n"]
+--EXPECT--
+"\nba"
+["a","b","\n"]
+3
+1