src/Composer/DependencyResolver/Problem.php
public function addRule(Rule $rule)
    {
        $this->addReason(spl_object_hash($rule), array(
            'rule' => $rule,
            'job' => $rule->getJob(),
        ));
    }
public function addRule(Rule $rule)
    {
        $this->addReason(spl_object_hash($rule), array(
            'rule' => $rule,
            'job' => $rule->getJob(),
        ));
    }
Add a rule as a reason

@param Rule $rule A rule which is a reason for this problem