Constant as separator in explode() produces false-positives

[gndk]

Errors with const: https://psalm.dev/r/d5a6c69fdc
No errors without const: https://psalm.dev/r/76b2904ea2

Some relevant comments from Slack:

Error comes from here:

psalm/src/Psalm/Internal/Provider/ReturnTypeProvider/ExplodeReturnTypeProvider.php

Line 56 in b924032

if ($call_args[0]->value instanceof PhpParser\Node\Scalar\String_) {

this condition is suboptimal because it checks that the parameter is a literal string, not a variable nor a a constant

Yes with SPLIT_SEPARATOR psalm thinks, the separator could be empty. which would result in returning false before php 8.0.
So I think there are two bugs. psalm should detect that the constant is not empty. and psalm should know, that explode can not return false anymore since php 8.0.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/d5a6c69fdc

<?php

declare(strict_types=1);

namespace App\Domain\Addressing;

use RuntimeException;

use function array_key_exists;
use function explode;
use function sprintf;

/**
 * @psalm-immutable
 */
final class Name
{
    private const SPLIT_SEPARATOR             = ' ';
    private const SPLIT_ARRAY_KEY_GIVEN_NAME  = 'givenName';
    private const SPLIT_ARRAY_KEY_FAMILY_NAME = 'familyName';
    
    /**
     * @return array{givenName: string, familyName: string}
     */
    private function split(string $name): array
    {
        $parts = explode(self::SPLIT_SEPARATOR, $name, 2);

        if (! array_key_exists(0, $parts) || ! array_key_exists(1, $parts)) {
            throw new RuntimeException();
        }

        return [
            self::SPLIT_ARRAY_KEY_GIVEN_NAME => $parts[0],
            self::SPLIT_ARRAY_KEY_FAMILY_NAME => $parts[1],
        ];
    }
}

Psalm output (using commit 5baf85e):

INFO: LessSpecificReturnStatement - 33:16 - The type 'array{familyName: null|string, givenName: null|string}' is more general than the declared return type 'array{familyName: string, givenName: string}' for App\Domain\Addressing\Name::split

INFO: MoreSpecificReturnType - 23:16 - The declared return type 'array{familyName: string, givenName: string}' for App\Domain\Addressing\Name::split is more specific than the inferred return type 'array{familyName: null|string, givenName: null|string}'

https://psalm.dev/r/76b2904ea2

<?php

declare(strict_types=1);

namespace App\Domain\Addressing;

use RuntimeException;

use function array_key_exists;
use function explode;
use function sprintf;

/**
 * @psalm-immutable
 */
final class Name
{
    private const SPLIT_SEPARATOR             = ' ';
    private const SPLIT_ARRAY_KEY_GIVEN_NAME  = 'givenName';
    private const SPLIT_ARRAY_KEY_FAMILY_NAME = 'familyName';
    
    /**
     * @return array{givenName: string, familyName: string}
     */
    private function split(string $name): array
    {
        $parts = explode(' ', $name, 2);

        if (! array_key_exists(0, $parts) || ! array_key_exists(1, $parts)) {
            throw new RuntimeException();
        }

        return [
            self::SPLIT_ARRAY_KEY_GIVEN_NAME => $parts[0],
            self::SPLIT_ARRAY_KEY_FAMILY_NAME => $parts[1],
        ];
    }
}

Psalm output (using commit 5baf85e):

No issues!