InvalidAttribute error for ReturnTypeWillChange on PHP 8.1

[ramsey]

On PHP 8.1, Psalm responds with an InvalidAttribute error when using the ReturnTypeWillChange attribute. However, it should recognize ReturnTypeWillChange as a valid PHP 8 attribute.

1. To reproduce, save the following to Foo.php in an empty directory.

   <?php
   
   declare(strict_types=1);
   
   namespace Acme;
   
   class Foo implements \JsonSerializable
   {
       /**
        * @return mixed
        */
       #[\ReturnTypeWillChange]
       public function jsonSerialize()
       {
           return [];
       }
   }

2. Execute the following shell commands to download Composer and use Docker to run Psalm on PHP 8.1.

   curl -L -O https://getcomposer.org/download/latest-stable/composer.phar
   docker run --rm -it -v "$PWD:/workspace" -w "/workspace" php:8.1.0RC4-cli-alpine php composer.phar require vimeo/psalm
   docker run --rm -it -v "$PWD:/workspace" -w "/workspace" php:8.1.0RC4-cli-alpine php vendor/bin/psalm --init
   docker run --rm -it -v "$PWD:/workspace" -w "/workspace" php:8.1.0RC4-cli-alpine php vendor/bin/psalm

3. You will see the following output:

   Scanning files...
   Analyzing files...
   
   E
   
   ERROR: InvalidAttribute - Foo.php:12:7 - The class ReturnTypeWillChange doesn’t have the Attribute attribute (see https://psalm.dev/242)
       #[\ReturnTypeWillChange]
   
   
   ------------------------------
   1 errors found
   ------------------------------
   
   Checks took 1.60 seconds and used 40.415MB of memory
   Psalm was unable to infer types in the codebase
   

[psalm-github-bot]

Hey @ramsey, can you reproduce the issue on https://psalm.dev ?

[ramsey]

On psalm.dev, the error is different, I suspect because it's not updated to run 8.1 code yet. https://psalm.dev/r/52f0cbb033

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/52f0cbb033

<?php

declare(strict_types=1);

namespace Acme;

class Foo implements \JsonSerializable
{
    /**
     * @return mixed
     */
    #[\ReturnTypeWillChange]
    public function jsonSerialize()
    {
        return [];
    }
}

Psalm output (using commit 9fb9591):

INFO: UndefinedAttributeClass - 12:7 - Attribute class ReturnTypeWillChange does not exist

[ramsey]

For reference, here is the RFC that introduced ReturnTypeWillChange: https://wiki.php.net/rfc/internal_method_return_types

[orklah]

Thanks for the report. I don't use attributes much myself, is it the first core attribute in PHP?

EDIT: and does this one require specific treatment in Psalm?

[ramsey]

This is not the first core attribute in PHP. Others were added in PHP 8.0.

This attribute is required to suppress a deprecation notice for classes that implement JsonSerialize in projects that want to support PHP earlier than 8.1. The return type signature for JsonSerialize has changed in PHP 8.1. If you change it in your code, the code will result in a fatal error in PHP 8.0 and earlier, so the solution (if you want to support PHP 7.x and 8.0, in addition to 8.1) is to use this new attribute.

I don't know if it requires specific treatment in Psalm.

[orklah]

Do you know the names of the other attributes? I'm trying to locate them in Psalm's code

[ramsey]

I thought there were others, but I can't find them, so it's possible this is the first one that affects core behavior. I know others are in discussion on the PHP wiki.

So far, it looks like there's the Attribute class that may be used to declare a class as an attribute, and there's the ReturnTypeWillChange attribute. See here and here.

The PHP manual has a section about how attributes work: https://www.php.net/attributes