mb_internal_encoding() always returns string when called without an argument

[ThomasLandauer]

mb_internal_encoding() returns string|bool in principle, but when called without an argument, it's always string: https://www.php.net/manual/en/function.mb-internal-encoding.php

Example:
https://psalm.dev/r/32218305f6

PHPStan does take this into account, and is not reporting anything.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/32218305f6

<?php
function foo(string $encoding): void
{
    echo $encoding;
}
foo(mb_internal_encoding());

Psalm output (using commit 9190294):

ERROR: InvalidScalarArgument - 6:5 - Argument 1 of foo expects string, bool|string provided

[orklah]

This can be handled by adding a new stub for this function, kinda like for strlen: https://github.com/vimeo/psalm/blob/4.x/stubs/CoreGenericFunctions.phpstub#L742

With a conditional return, you'll be able to check that if the param is an empty-string, the return will be a string.

Could you check if the function ever return true as well?

[derrabus]

Could you check if the function ever return true as well?

It does return true if you call it with a valid $encoding parameter. On PHP 8 though, it will never return false because calling the function with an invalid encoding will trigger a ValueError. Also, the behavior for null has changed in PHP 8.

The rules for the return type are:

$encoding	PHP 7	PHP 8
omitted	string	string
valid encoding string	true	true
invalid encoding string	false+ E_WARNING triggered	ValueError is thrown
null	false + E_WARNING triggered	string
non-stringable parameter	null + E_WARNING triggered	TypeError is thrown

[orklah]

Thanks @derrabus, looking at your chart, I thought better to create a return type provider instead of a stub with a big conditional return.

This will ship with Psalm 5 soon