Chris@13: <?php
Chris@13: 
Chris@13: namespace PhpParser;
Chris@13: 
Chris@13: use PhpParser\Node\Expr;
Chris@13: use PhpParser\Node\Scalar;
Chris@13: 
Chris@13: /**
Chris@13:  * Evaluates constant expressions.
Chris@13:  *
Chris@13:  * This evaluator is able to evaluate all constant expressions (as defined by PHP), which can be
Chris@13:  * evaluated without further context. If a subexpression is not of this type, a user-provided
Chris@13:  * fallback evaluator is invoked. To support all constant expressions that are also supported by
Chris@13:  * PHP (and not already handled by this class), the fallback evaluator must be able to handle the
Chris@13:  * following node types:
Chris@13:  *
Chris@13:  *  * All Scalar\MagicConst\* nodes.
Chris@13:  *  * Expr\ConstFetch nodes. Only null/false/true are already handled by this class.
Chris@13:  *  * Expr\ClassConstFetch nodes.
Chris@13:  *
Chris@13:  * The fallback evaluator should throw ConstExprEvaluationException for nodes it cannot evaluate.
Chris@13:  *
Chris@13:  * The evaluation is dependent on runtime configuration in two respects: Firstly, floating
Chris@13:  * point to string conversions are affected by the precision ini setting. Secondly, they are also
Chris@13:  * affected by the LC_NUMERIC locale.
Chris@13:  */
Chris@13: class ConstExprEvaluator
Chris@13: {
Chris@13:     private $fallbackEvaluator;
Chris@13: 
Chris@13:     /**
Chris@13:      * Create a constant expression evaluator.
Chris@13:      *
Chris@13:      * The provided fallback evaluator is invoked whenever a subexpression cannot be evaluated. See
Chris@13:      * class doc comment for more information.
Chris@13:      *
Chris@13:      * @param callable|null $fallbackEvaluator To call if subexpression cannot be evaluated
Chris@13:      */
Chris@13:     public function __construct(callable $fallbackEvaluator = null) {
Chris@13:         $this->fallbackEvaluator = $fallbackEvaluator ?? function(Expr $expr) {
Chris@13:             throw new ConstExprEvaluationException(
Chris@13:                 "Expression of type {$expr->getType()} cannot be evaluated"
Chris@13:             );
Chris@13:         };
Chris@13:     }
Chris@13: 
Chris@13:     /**
Chris@13:      * Silently evaluates a constant expression into a PHP value.
Chris@13:      *
Chris@13:      * Thrown Errors, warnings or notices will be converted into a ConstExprEvaluationException.
Chris@13:      * The original source of the exception is available through getPrevious().
Chris@13:      *
Chris@13:      * If some part of the expression cannot be evaluated, the fallback evaluator passed to the
Chris@13:      * constructor will be invoked. By default, if no fallback is provided, an exception of type
Chris@13:      * ConstExprEvaluationException is thrown.
Chris@13:      *
Chris@13:      * See class doc comment for caveats and limitations.
Chris@13:      *
Chris@13:      * @param Expr $expr Constant expression to evaluate
Chris@13:      * @return mixed Result of evaluation
Chris@13:      *
Chris@13:      * @throws ConstExprEvaluationException if the expression cannot be evaluated or an error occurred
Chris@13:      */
Chris@13:     public function evaluateSilently(Expr $expr) {
Chris@13:         set_error_handler(function($num, $str, $file, $line) {
Chris@13:             throw new \ErrorException($str, 0, $num, $file, $line);
Chris@13:         });
Chris@13: 
Chris@13:         try {
Chris@13:             return $this->evaluate($expr);
Chris@13:         } catch (\Throwable $e) {
Chris@13:             if (!$e instanceof ConstExprEvaluationException) {
Chris@13:                 $e = new ConstExprEvaluationException(
Chris@13:                     "An error occurred during constant expression evaluation", 0, $e);
Chris@13:             }
Chris@13:             throw $e;
Chris@13:         } finally {
Chris@13:             restore_error_handler();
Chris@13:         }
Chris@13:     }
Chris@13: 
Chris@13:     /**
Chris@13:      * Directly evaluates a constant expression into a PHP value.
Chris@13:      *
Chris@13:      * May generate Error exceptions, warnings or notices. Use evaluateSilently() to convert these
Chris@13:      * into a ConstExprEvaluationException.
Chris@13:      *
Chris@13:      * If some part of the expression cannot be evaluated, the fallback evaluator passed to the
Chris@13:      * constructor will be invoked. By default, if no fallback is provided, an exception of type
Chris@13:      * ConstExprEvaluationException is thrown.
Chris@13:      *
Chris@13:      * See class doc comment for caveats and limitations.
Chris@13:      *
Chris@13:      * @param Expr $expr Constant expression to evaluate
Chris@13:      * @return mixed Result of evaluation
Chris@13:      *
Chris@13:      * @throws ConstExprEvaluationException if the expression cannot be evaluated
Chris@13:      */
Chris@13:     public function evaluateDirectly(Expr $expr) {
Chris@13:         return $this->evaluate($expr);
Chris@13:     }
Chris@13: 
Chris@13:     private function evaluate(Expr $expr) {
Chris@13:         if ($expr instanceof Scalar\LNumber
Chris@13:             || $expr instanceof Scalar\DNumber
Chris@13:             || $expr instanceof Scalar\String_
Chris@13:         ) {
Chris@13:             return $expr->value;
Chris@13:         }
Chris@13: 
Chris@13:         if ($expr instanceof Expr\Array_) {
Chris@13:             return $this->evaluateArray($expr);
Chris@13:         }
Chris@13: 
Chris@13:         // Unary operators
Chris@13:         if ($expr instanceof Expr\UnaryPlus) {
Chris@13:             return +$this->evaluate($expr->expr);
Chris@13:         }
Chris@13:         if ($expr instanceof Expr\UnaryMinus) {
Chris@13:             return -$this->evaluate($expr->expr);
Chris@13:         }
Chris@13:         if ($expr instanceof Expr\BooleanNot) {
Chris@13:             return !$this->evaluate($expr->expr);
Chris@13:         }
Chris@13:         if ($expr instanceof Expr\BitwiseNot) {
Chris@13:             return ~$this->evaluate($expr->expr);
Chris@13:         }
Chris@13: 
Chris@13:         if ($expr instanceof Expr\BinaryOp) {
Chris@13:             return $this->evaluateBinaryOp($expr);
Chris@13:         }
Chris@13: 
Chris@13:         if ($expr instanceof Expr\Ternary) {
Chris@13:             return $this->evaluateTernary($expr);
Chris@13:         }
Chris@13: 
Chris@13:         if ($expr instanceof Expr\ArrayDimFetch && null !== $expr->dim) {
Chris@13:             return $this->evaluate($expr->var)[$this->evaluate($expr->dim)];
Chris@13:         }
Chris@13: 
Chris@13:         if ($expr instanceof Expr\ConstFetch) {
Chris@13:             return $this->evaluateConstFetch($expr);
Chris@13:         }
Chris@13: 
Chris@13:         return ($this->fallbackEvaluator)($expr);
Chris@13:     }
Chris@13: 
Chris@13:     private function evaluateArray(Expr\Array_ $expr) {
Chris@13:         $array = [];
Chris@13:         foreach ($expr->items as $item) {
Chris@13:             if (null !== $item->key) {
Chris@13:                 $array[$this->evaluate($item->key)] = $this->evaluate($item->value);
Chris@13:             } else {
Chris@13:                 $array[] = $this->evaluate($item->value);
Chris@13:             }
Chris@13:         }
Chris@13:         return $array;
Chris@13:     }
Chris@13: 
Chris@13:     private function evaluateTernary(Expr\Ternary $expr) {
Chris@13:         if (null === $expr->if) {
Chris@13:             return $this->evaluate($expr->cond) ?: $this->evaluate($expr->else);
Chris@13:         }
Chris@13: 
Chris@13:         return $this->evaluate($expr->cond)
Chris@13:             ? $this->evaluate($expr->if)
Chris@13:             : $this->evaluate($expr->else);
Chris@13:     }
Chris@13: 
Chris@13:     private function evaluateBinaryOp(Expr\BinaryOp $expr) {
Chris@13:         if ($expr instanceof Expr\BinaryOp\Coalesce
Chris@13:             && $expr->left instanceof Expr\ArrayDimFetch
Chris@13:         ) {
Chris@13:             // This needs to be special cased to respect BP_VAR_IS fetch semantics
Chris@13:             return $this->evaluate($expr->left->var)[$this->evaluate($expr->left->dim)]
Chris@13:                 ?? $this->evaluate($expr->right);
Chris@13:         }
Chris@13: 
Chris@13:         // The evaluate() calls are repeated in each branch, because some of the operators are
Chris@13:         // short-circuiting and evaluating the RHS in advance may be illegal in that case
Chris@13:         $l = $expr->left;
Chris@13:         $r = $expr->right;
Chris@13:         switch ($expr->getOperatorSigil()) {
Chris@13:             case '&':   return $this->evaluate($l) &   $this->evaluate($r);
Chris@13:             case '|':   return $this->evaluate($l) |   $this->evaluate($r);
Chris@13:             case '^':   return $this->evaluate($l) ^   $this->evaluate($r);
Chris@13:             case '&&':  return $this->evaluate($l) &&  $this->evaluate($r);
Chris@13:             case '||':  return $this->evaluate($l) ||  $this->evaluate($r);
Chris@13:             case '??':  return $this->evaluate($l) ??  $this->evaluate($r);
Chris@13:             case '.':   return $this->evaluate($l) .   $this->evaluate($r);
Chris@13:             case '/':   return $this->evaluate($l) /   $this->evaluate($r);
Chris@13:             case '==':  return $this->evaluate($l) ==  $this->evaluate($r);
Chris@13:             case '>':   return $this->evaluate($l) >   $this->evaluate($r);
Chris@13:             case '>=':  return $this->evaluate($l) >=  $this->evaluate($r);
Chris@13:             case '===': return $this->evaluate($l) === $this->evaluate($r);
Chris@13:             case 'and': return $this->evaluate($l) and $this->evaluate($r);
Chris@13:             case 'or':  return $this->evaluate($l) or  $this->evaluate($r);
Chris@13:             case 'xor': return $this->evaluate($l) xor $this->evaluate($r);
Chris@13:             case '-':   return $this->evaluate($l) -   $this->evaluate($r);
Chris@13:             case '%':   return $this->evaluate($l) %   $this->evaluate($r);
Chris@13:             case '*':   return $this->evaluate($l) *   $this->evaluate($r);
Chris@13:             case '!=':  return $this->evaluate($l) !=  $this->evaluate($r);
Chris@13:             case '!==': return $this->evaluate($l) !== $this->evaluate($r);
Chris@13:             case '+':   return $this->evaluate($l) +   $this->evaluate($r);
Chris@13:             case '**':  return $this->evaluate($l) **  $this->evaluate($r);
Chris@13:             case '<<':  return $this->evaluate($l) <<  $this->evaluate($r);
Chris@13:             case '>>':  return $this->evaluate($l) >>  $this->evaluate($r);
Chris@13:             case '<':   return $this->evaluate($l) <   $this->evaluate($r);
Chris@13:             case '<=':  return $this->evaluate($l) <=  $this->evaluate($r);
Chris@13:             case '<=>': return $this->evaluate($l) <=> $this->evaluate($r);
Chris@13:         }
Chris@13: 
Chris@13:         throw new \Exception('Should not happen');
Chris@13:     }
Chris@13: 
Chris@13:     private function evaluateConstFetch(Expr\ConstFetch $expr) {
Chris@13:         $name = $expr->name->toLowerString();
Chris@13:         switch ($name) {
Chris@13:             case 'null': return null;
Chris@13:             case 'false': return false;
Chris@13:             case 'true': return true;
Chris@13:         }
Chris@13: 
Chris@13:         return ($this->fallbackEvaluator)($expr);
Chris@13:     }
Chris@13: }