debug-template.php

<?php
$expressions = [
    '$user.name',
    '$post.body | truncate(120)',
    '$app.debug ?? false',
    '$u$ser.name',
];

foreach ($expressions as $expression) {
    $placeholders = [];
    $counter = 0;

    $expression = preg_replace_callback(
        "/'([^']*)'/",
        function (array $m) use (&$placeholders, &$counter): string {
            $key = "\x00WAVE_STR_" . ($counter++) . "\x00";
            $placeholders[$key] = $m[0];
            return $key;
        },
        $expression,
    );

    $expression = preg_replace_callback(
        '/(\$?)([a-zA-Z_]\w*)((?:\.\w+)+)/',
        function ($m) use (&$placeholders, &$counter): string {
            $dollar = $m[1];
            $head   = $m[2];
            $rest   = $m[3];
            $parts  = explode('.', $rest);
            array_shift($parts);

            $result = $dollar . $head;
            foreach ($parts as $part) {
                $partKey = "\x00WAVE_PART_" . ($counter++) . "\x00";
                $placeholders[$partKey] = "'" . $part . "'";
                $result .= '[' . $partKey . ']';
            }
            return $result;
        },
        $expression,
    );

    $expression = preg_replace_callback(
        '/(?:^|(?<=\W))(?<![$\[])([a-zA-Z_]\w*)\b(?!\s*\()/',
        function ($m) {
            return '$' . $m[1];
        },
        $expression,
    );

    foreach ($placeholders as $key => $value) {
        $expression = str_replace($key, $value, $expression);
    }

    echo "Input:  $expression\n";
    echo "Output: " . str_replace("\x00", '', $expression) . " (NUL-stripped)\n";
    echo "Output: " . bin2hex($expression) . " (hex)\n\n";
}