Template covariance

[zjbarg]

No description provided.

[zjbarg]

@prewk can we use @template-covariant?

We are getting errors when running phpstan level 6, like

Method ...someMethod() should return
Prewk\Result<array{report_document_id: string, url: string, compression_algorithm: string|null}, ...some-error-type>
but returns 
Prewk\Result\Ok<array{report_document_id: string, url: string, compression_algorithm: string|null}>.                                               
return.type                                                                             
Template type T on class Prewk\Result is not covariant. Learn more:                      
https://phpstan.org/blog/whats-up-with-template-covariant   

[prewk]

I'm trying to be a supportive but passive maintainer these days. Could you give me an opinion here, @t1sh0o?

[t1sh0o]

@zjbarg I don't think that adding @template-covariant is possible here, because we use the T and E params as input as well. Covariant is fine if we use them only as return types, but when as input params of functions like and, or, etc. it should be contravariant, and as far as I understand variance, you cannot have both co and contra. This is why the errors from psalm.
I also tried to reproduce your case, but it works for me, I guess I ma not doing something like you are. Nevertheless, I would try to use a DTO combined with results, and in most cases, it works.
Here is my simulation. Note that if I hardcode 'compression_algorithm' => null or some string, it errors, but then the error is obvious that both return type and what is returned are not the same, because of them being invariant.

getResult();

/**
 * @return Result<array{report_document_id: string, url: string, compression_algorithm: string|null}, array{status:string}>
 */
function getResult(?string $algo = null): Result
{
    return ok(['report_document_id' => '123', 'url' => 'https://example.com', 'compression_algorithm' => $algo]);
}

[zjbarg]

@t1sh0o thanks for explaining.

The issue that I'm dealing with is probably phpstan related. Here is an example: https://phpstan.org/r/317eb2b4-eed2-4032-a709-421fab6911f3

of a simpler one https://phpstan.org/r/0dd20e3c-358a-4363-87d9-6a5d5acbd303