Fix behavior of string->chunk() for empty string

This matches the PHP 8.2 str_split() behavior.

Author: nikic

doc/string_api.md

@@ -325,6 +325,7 @@ length of the main string is not divisible by the chunk length, then the last ch
 >
  * This function corresponds to `str_split`.
  * It is perfectly valid to have a chunk length that is longer than the main string.
+ * Chunking an empty string results in an empty array.
  * The name `chunk()` was chosen, because `split()` seems more appropriate for the `explode`
    equivalent. Furthermore the corresponding array functionality is also named `chunk()`.
 

handlers/string.php

@@ -125,6 +125,10 @@ public static function split($self, $separator, $limit = PHP_INT_MAX) {
 
     public static function chunk($self, $chunkLength = 1) {
         $self->verifyPositive($chunkLength, 'Chunk length');
+        if ($self === '') {
+            // str_split() prior to PHP 8.2 is buggy and returns [''] instead.
+            return [];
+        }
         return str_split($self, $chunkLength);
     }
 

tests/string.phpt

@@ -499,9 +499,7 @@ count(""): int(1)
 count("", 0): int(1)
 count("", 0, 0): int(1)
 repeat(3): string(0) ""
-chunk(3): array(1) {
-  [0]=>
-  string(0) ""
+chunk(3): array(0) {
 }
 replace("foo", "bar"): string(0) ""
 replace("foo", "bar", 1): string(0) ""