TypeDoesNotContainType false positive

[morozov]

Please see the code example in https://psalm.dev/r/fe40e86258.

Depending on the values of $flag and $options, a call to array_shift() may return a non-null value but this code is reported as:

Type null for $length is always null

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/fe40e86258

<?php

/**
 * @param mixed[] $options
 */
function doStuff(bool $flag, array $values, array $options): void
{
    $lengths = $flag ? $options['lengths'] : [];

    foreach ($values as $_) {
        $length = array_shift($lengths);

        if ($length !== null) {
            echo 1;
        }
    }
}

Psalm output (using commit f55e5ea):

INFO: PossiblyUndefinedStringArrayOffset - 8:24 - Possibly undefined array offset 'string(lengths)' is risky given expected type 'array-key'. Consider using isset beforehand.

INFO: MixedAssignment - 8:5 - Unable to determine the type that $lengths is being assigned to

INFO: MixedArgument - 11:31 - Argument 1 of array_shift cannot be array<empty, empty>|mixed, expecting array<array-key, mixed>

ERROR: TypeDoesNotContainType - 13:13 - Type null for $length is always null

[weirdan]

Simplified: https://psalm.dev/r/03258c2b11

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/03258c2b11

<?php

/**
 * @param mixed $options
 * @psalm-suppress MixedAssignment,MixedArgument
 */
function doStuff($options): void
{
    $options = rand(0,1) ? $options : [];
    $opt = array_shift($options);
    if (null === $opt) {}
}

Psalm output (using commit 211553c):

ERROR: RedundantCondition - 11:9 - Type null for $opt is always null