src/Composer/DependencyResolver/Solver.php
private function revert($level)
    {
        while (!$this->decisions->isEmpty()) {
            $literal = $this->decisions->lastLiteral();

            if ($this->decisions->undecided($literal)) {
                break;
            }

            $decisionLevel = $this->decisions->decisionLevel($literal);

            if ($decisionLevel <= $level) {
                break;
            }

            $this->decisions->revertLast();
            $this->propagateIndex = count($this->decisions);
        }

        while (!empty($this->branches) && $this->branches[count($this->branches) - 1][self::BRANCH_LEVEL] >= $level) {
            array_pop($this->branches);
        }
    }
private function revert($level)
    {
        while (!$this->decisions->isEmpty()) {
            $literal = $this->decisions->lastLiteral();

            if ($this->decisions->undecided($literal)) {
                break;
            }

            $decisionLevel = $this->decisions->decisionLevel($literal);

            if ($decisionLevel <= $level) {
                break;
            }

            $this->decisions->revertLast();
            $this->propagateIndex = count($this->decisions);
        }

        while (!empty($this->branches) && $this->branches[count($this->branches) - 1][self::BRANCH_LEVEL] >= $level) {
            array_pop($this->branches);
        }
    }
Reverts a decision at the given level.

@param int $level