<?php declare(strict_types=1);
/*
 * This file is part of PHPUnit.
 *
 * (c) Sebastian Bergmann <sebastian@phpunit.de>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace PHPUnit\Framework\Constraint;

use function is_array;

/**
 * @no-named-arguments Parameter names are not covered by the backward compatibility promise for PHPUnit
 */
final class ArrayIsList extends Constraint
{
    /**
     * Returns a string representation of the constraint.
     */
    public function toString(): string
    {
        return 'is list';
    }

    /**
     * Evaluates the constraint for parameter $other. Returns true if the
     * constraint is met, false otherwise.
     */
    protected function matches(mixed $other): bool
    {
        if (!is_array($other)) {
            return false;
        }

        if ($other === []) {
            return true;
        }

        $expectedKey = 0;

        foreach ($other as $key => $value) {
            if ($key !== $expectedKey) {
                return false;
            }

            $expectedKey++;
        }

        return true;
    }

    /**
     * Returns the description of the failure.
     *
     * The beginning of failure messages is "Failed asserting that" in most
     * cases. This method should return the second part of that sentence.
     */
    protected function failureDescription(mixed $other): string
    {
        return 'an array ' . $this->toString();
    }
}

<?php declare(strict_types=1);
/*
 * This file is part of PHPUnit.
 *
 * (c) Sebastian Bergmann <sebastian@phpunit.de>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace PHPUnit\Framework\Constraint;

use function array_is_list;
use function is_array;

/**
 * @no-named-arguments Parameter names are not covered by the backward compatibility promise for PHPUnit
 */
final class ArrayIsList extends Constraint
{
    /**
     * Returns a string representation of the constraint.
     */
    public function toString(): string
    {
        return 'is list';
    }

    /**
     * Evaluates the constraint for parameter $other. Returns true if the
     * constraint is met, false otherwise.
     */
    protected function matches(mixed $other): bool
    {
        if (!is_array($other)) {
            return false;
        }

        if (function_exists('array_is_list')) {
            return array_is_list($other);
        }

        // @todo Remove this code once we require PHP >= 8.1
        if ($other === []) {
            return true;
        }

        $expectedKey = 0;

        foreach ($other as $key => $value) {
            if ($key !== $expectedKey) {
                return false;
            }

            $expectedKey++;
        }

        return true;
    }

    /**
     * Returns the description of the failure.
     *
     * The beginning of failure messages is "Failed asserting that" in most
     * cases. This method should return the second part of that sentence.
     */
    protected function failureDescription(mixed $other): string
    {
        return 'an array ' . $this->toString();
    }
}

Use array_is_list() function when available
Use array_is_list() function when available

Suggested by Alexander M. Turek <me@derrabus.de> in https://github.com/sebastianbergmann/phpunit/pull/4818#pullrequestreview-830852046
