count(array) should be positive-int|0, while count(Countable) should be int

[Ocramius]

https://psalm.dev/r/c5d1ba8607

<?php

/** @psalm-return positive-int|0 */
function gimmePositiveCount(array $input): int
{
    return \count($input);
}


/** @psalm-return positive-int|0 */
function gimmeCount(\Countable $input): int
{
    return \count($input); // expected violation here - `Countable#count()` can return negative!
}

Psalm output (using commit 1afce4d): 

INFO: LessSpecificReturnStatement - 6:12 - The type 'int' is more general than the declared return type 'int(0)|positive-int' for gimmePositiveCount

INFO: MoreSpecificReturnType - 3:19 - The declared return type 'int(0)|positive-int' for gimmePositiveCount is more specific than the inferred return type 'int'

INFO: LessSpecificReturnStatement - 13:12 - The type 'int' is more general than the declared return type 'int(0)|positive-int' for gimmeCount

INFO: MoreSpecificReturnType - 10:19 - The declared return type 'int(0)|positive-int' for gimmeCount is more specific than the inferred return type 'int'

In practice, count() needs better stubs:

• count(array): positive-int|0
• count(Countable): int

I'll try and see if I can send a patch :-)

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/c5d1ba8607

<?php

/** @psalm-return positive-int|0 */
function gimmePositiveCount(array $input): int
{
    return \count($input);
}


/** @psalm-return positive-int|0 */
function gimmeCount(\Countable $input): int
{
    return \count($input); // expected violation here - `Countable#count()` can return negative!
}

Psalm output (using commit 1afce4d):

INFO: LessSpecificReturnStatement - 6:12 - The type 'int' is more general than the declared return type 'int(0)|positive-int' for gimmePositiveCount

INFO: MoreSpecificReturnType - 3:19 - The declared return type 'int(0)|positive-int' for gimmePositiveCount is more specific than the inferred return type 'int'

INFO: LessSpecificReturnStatement - 13:12 - The type 'int' is more general than the declared return type 'int(0)|positive-int' for gimmeCount

INFO: MoreSpecificReturnType - 10:19 - The declared return type 'int(0)|positive-int' for gimmeCount is more specific than the inferred return type 'int'

[orklah]

I'm gonna be extremely naive here and say that noone sane could have returned a negative int in count. Could we maybe consider this an error anyway and say that every count return 0|positive-int ?

[Ocramius]

Not at type level, no.