In #790 and #7444 the need to reference dynamic values in constraint options was discovered. A simple example:

use Symfony\Component\Validator\Constraints\Range;
use Symfony\Component\Validator\Constraints\Reference;

/**
 * @Range(min = @Reference("min"), max = @Reference("max"))
 */
private $value;

private $min;

private $max

Here, the values of the "min" and "max" option are determined at runtime. References can contain any valid property path.

XML example:

<property name="value">
    <constraint name="Range">
        <option name="min" reference="min" />
        <option name="max" reference="max" />
    </constraint>
</property>

YAML example:

properties:
    value:
        - Range:
            min: @min

Attention: This example would be consistent with the DIC YAML syntax for service references, but it would be incompatible for options where values starting with "@" are valid expected values. Is this a problem?

PHP example:

$metadata->addPropertyConstraint('value', new Range(array(
    'min' => new Reference('min'),
    'max' => new Reference('max'),
)));

Some implementation hints:

Class Reference should be an annotation but not inherit from Constraint (it is no constraint). It probably needs only a constructor. Additionally, we need a ReferenceResolver (and ReferenceResolverInterface, of course) that receives a PropertyAccessorInterface in its constructor. It needs only a method resolveReference(Reference $reference, ExecutionContextInterface $context) that returns the value of a reference based on the current state of the execution context.

All validators that support references then need the ReferenceResolver to resolve any Reference instances when they find them.