non empty string constants should be considered as a non empty string

[VincentLanglet]

With the option

ignoreInternalFunctionFalseReturn="false"

In

/** @var non-empty-string $foo */
$foo = PHP_EOL;
$bar = explode($foo, $diff);

$bar is considered as always an array.

In

$bar = explode(PHP_EOL, $diff);

$bar is considered as array|false.

So I would say that explode is correctly supporting non-empty-string, but some constant are not considered as non-empty-string. I tried

• PHP_EOL
• DIRECTORY_SEPARATOR
• a custom class constant public const FOO = 'foo';

Should these be non-empty-string ?
https://psalm.dev/r/377464f1cd

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/377464f1cd

<?php

function foo(): void {
    /** @psalm-trace $a */
    $a = PHP_EOL;
    
    return;
}

Psalm output (using commit 3fb9e1c):

INFO: Trace - 5:5 - $a: string

INFO: UnusedVariable - 5:5 - $a is never referenced or the value is not used

[weirdan]

a custom class constant public const FOO = 'foo';

This one should be inferred as literal "foo".

[weirdan]

The other two, I believe, would safe to assume non-empty.

[orklah]

public const FOO = 'foo';

Can be inherited and change value in the child

[VincentLanglet]

public const FOO = 'foo';

Can be inherited and change value in the child

If I use static::FOO, or if it's final, it should be ok no ?