False positive with base64_decode()

[OwnerOfThisIsle]

https://psalm.dev/r/1dbb7e9f9f

<?php
$encryptedString = "";
$decryptedString = base64_decode($encryptedString);
if ($decryptedString === false) {
    // throw some error
}

will lead to:
ERROR: [DocblockTypeContradiction](https://psalm.dev/155) - 4:5 - string does not contain false

I think base64_decode() can return string|false, so I do not understand why psalm is complaining here.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/1dbb7e9f9f

<?php
$encryptedString = "";
$decryptedString = base64_decode($encryptedString);
if ($decryptedString === false) {
    // throw some error
}

Psalm output (using commit be82c3a):

ERROR: DocblockTypeContradiction - 4:5 - string does not contain false

[OwnerOfThisIsle]

I just found
#9832

But after reading the php manual page for base64_decode I am still not sure, if there might be other reasons for the function to return false, even when not in strict mode.

[ygottschalk]

As of right now the only cases where base64_decode fails is when strict = true. See php source:

https://github.com/php/php-src/blob/master/ext/standard/base64.c#L282
https://github.com/php/php-src/blob/master/ext/standard/base64.c#L307
https://github.com/php/php-src/blob/master/ext/standard/base64.c#L313

[weirdan]

As discussed, not a false positive.