preg_replace_callback $count number of matches, number of replacements

Description

The following code:

https://3v4l.org/0E8mn#v8.5.0

<?php

$before = 'abca';
$after = preg_replace( '/a/', 'a', $before, -1, $count );
if ( $after === $before ) {
    echo "NO REPLACEMENTS" . PHP_EOL;
}

echo $count . " REPLACEMENTS";

Resulted in this output:

NO REPLACEMENTS
2 REPLACEMENTS

But I expected this output instead:

NO REPLACEMENTS
0 REPLACEMENTS

https://www.php.net/manual/en/function.preg-replace.php

If specified, this variable will be filled with the number of replacements done.

Technically, this is correct, since the replacement is identical to the search string.
While for preg_replace this makes practically no difference (except for cases where backslash is incorrectly escaped, you could end up with a preg that says it replaced even though it didn't change the input)

Practically for preg_replace_callback this means however, that you always have to compare before/after to be sure whether anything was replaced at all.
And there's no way of knowing how many replacements were actually done.

Changing the behavior should generally be safe I guess, but otherwise just adding an additional param "$replacement_count" for preg_replace_callback would make sense? (so the 1st param docs would be changed to be "number of matches")

PHP Version

8.5

Operating System

No response

Beginne damit, das verknüpfte PHP-8.5-Beispiel zu reproduzieren, und vergleiche preg_replace mit preg_replace_callback. Lies die Dokumentation zu preg_replace und verfolge, wie der bestehende count als Anzahl der Ersetzungen definiert ist; das Issue ist abgeschlossen, wenn das Projekt ein festgelegtes, dokumentiertes Verhalten für Match- und Ersetzungsanzahlen hat und die verknüpfte Callback-Einschränkung behoben ist.