How to use pseudo scalar type trait-string

[smoench]

Unfortunately I couldn't find much documentation about trait-string and couldn't get it running as I thought it should be used:

https://psalm.dev/r/615d86ff95

Probably there is a bug or documentation needs to be updated.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/615d86ff95

<?php
namespace Bar;

trait Foo {}

/**
 * @param trait-string $traitString
 * @return trait-string
 */
function takesTraitString(string $traitString) {
    return $traitString;
}


takesTraitString('Bar\Foo');
takesTraitString(Foo::class);

Psalm output (using commit 983f233):

ERROR: InvalidScalarArgument - 15:18 - Argument 1 of Bar\takesTraitString expects trait-string, string(Bar\Foo) provided

ERROR: InvalidScalarArgument - 16:18 - Argument 1 of Bar\takesTraitString expects trait-string, Bar\Foo::class provided

[orklah]

I think trait-string is inferred when you pass through trait_exists:
https://psalm.dev/r/3bff912a5b

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3bff912a5b

<?php
namespace Bar;

trait Foo {}

/**
 * @param trait-string $traitString
 * @return trait-string
 */
function takesTraitString(string $traitString) {
    return $traitString;
}
$a = Foo::class;
if(trait_exists($a)){
	takesTraitString($a);
}

Psalm output (using commit 983f233):

No issues!

[smoench]

Interesting 🤔 Thank you @orklah

[muglug]

I would say trait-string is something you pretty much never need. I only support it in Psalm for completeness (hence why there's no documentation on it).

[ptomulik]

Hi,

phpunit 11.2 introduced CoversTrait attribute, and it uses the trait-string. But it seems that trait-string is still kind of broken. So running psalm on projects using phpunit 11.2 yields tons of InvalidArgument errors

InvalidArgument: Argument 1 of PHPUnit\Framework\Attributes\CoversTrait::__construct expects trait-string, but FooTrait::class provided (see https://psalm.dev/004)

Can we do something about it?