Slim PHP framework gives Return type error

Question

I have been using Slim PHP framework to provide my API service ( https://api.rsywx.com ).

Recently, I updated my PHP to 8.1 and when I visited the site, it gives the following error:

{
    "statusCode": 500,
    "error": {
        "type": "SERVER_ERROR",
        "description": "ERROR: Return type of App\\Application\\Actions\\ActionPayload::jsonSerialize() should either be compatible with JsonSerializable::jsonSerialize(): mixed, or the #[\\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice on line 67 in file \/home\/tr\/www\/api.rsywx.com\/src\/Application\/Actions\/ActionPayload.php."
    }
}

I have not changed anything in my source code, so I guess the problem raises from Slim framework itself.

Any hints to solve this issue?

Answer 1

As of PHP version 8.1.0, there was an update to the Serializable interface.

You could either use the #[\ReturnTypeWillChange attribute temporarily suppress the notice on the specified line then test further and address other occurrences in a similar fashion.

On the other hand, add the mixed type hint to your function as below, then test further in same fashion to fix subsequent occurrences.

public function jsonSerialize(): mixed
{
  // ...
}