[Bug]: call_user_func() fails when resolving Assert\Choice callback on abstract classes

[philiprabbett]

Version

5.9.2

Description

When using Assert\Choice with a callback parameter on a property in an abstract class, Nelmio API Doc Bundle throws a fatal error during documentation generation.

Error Message:

call_user_func(): Argument #1 ($callback) must be a valid callback, cannot call abstract method App\Entity\AbstractAuthor::getGenres()

Reproduction Steps:

1. Create an abstract entity class with an Assert\Choice constraint using a callback:

namespace App\Entity;

use Symfony\Component\Validator\Constraints as Assert;

abstract class AbstractAuthor
{
    #[Assert\Choice(callback: 'getGenres')]
    protected string $genre;

    public static function getGenres(): array
    {
        return ['fiction', 'non-fiction'];
    }
}

2. Run Nelmio API Doc Bundle's documentation generation (e.g., php bin/console api:openapi:export)
3. The error occurs in the callback resolution logic

Root Cause:

The issue is in the callback resolution code that attempts to invoke call_user_func() on an abstract class:

\call_user_func(\is_array($choice->callback) ? $choice->callback : [$reflection->class, $choice->callback]);

Since $reflection->class is an abstract class, call_user_func() cannot instantiate it to invoke the method.

Expected Behavior:

Nelmio should gracefully handle abstract classes by either:

• Skipping callback resolution for abstract classes
• Attempting to resolve the callback on concrete subclasses
• Falling back to a sensible default or warning

Actual Behavior:

A fatal error is thrown, preventing documentation generation.

Workaround:

Currently, the only workaround is to use hardcoded choices instead of a callback or move the constraint to concrete subclasses:

#[Assert\Choice(choices: ['fiction', 'non-fiction'])]
protected string $genre;

or

abstract class AbstractAuthor
{
    protected string $genre;
}

class ConcreteAuthor extends AbstractAuthor
{
    #[Assert\Choice(callback: 'getGenres')]
    protected string $genre;

    public static function getGenres(): array
    {
        return ['fiction', 'non-fiction'];
    }
}

JSON OpenApi

N/A

Additional context

This issue affects any abstract entity class using Assert\Choice with callbacks, which is a common pattern when sharing validation constraints across multiple concrete subclasses.