psalm/src/Psalm/Checker/Statements/ExpressionChecker.php

<?php
namespace Psalm\Checker\Statements;

use PhpParser;
use Psalm\Checker\ClassChecker;
use Psalm\Checker\ClassLikeChecker;
use Psalm\Checker\ClosureChecker;
use Psalm\Checker\CommentChecker;
use Psalm\Checker\MethodChecker;
use Psalm\Checker\Statements\Expression\AssignmentChecker;
use Psalm\Checker\Statements\Expression\CallChecker;
use Psalm\Checker\Statements\Expression\FetchChecker;
use Psalm\Checker\StatementsChecker;
use Psalm\Checker\TypeChecker;
use Psalm\CodeLocation;
use Psalm\Config;
use Psalm\Context;
use Psalm\Issue\ForbiddenCode;
use Psalm\Issue\InvalidStaticVariable;
use Psalm\Issue\PossiblyUndefinedVariable;
use Psalm\Issue\UndefinedVariable;
use Psalm\Issue\UnrecognizedExpression;
use Psalm\IssueBuffer;
use Psalm\Type;

class ExpressionChecker
{
    /**
     * @var array<string,array<int,string>>
     */
    protected static $reflection_functions = [];

    /**
     * @param   StatementsChecker   $statements_checker
     * @param   PhpParser\Node\Expr $stmt
     * @param   Context             $context
     * @param   bool                $array_assignment
     * @param   Type\Union|null     $assignment_key_type
     * @param   Type\Union|null     $assignment_value_type
     * @param   string|null         $assignment_key_value
     * @return  false|null
     */
    public static function check(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr $stmt,
        Context $context,
        $array_assignment = false,
        Type\Union $assignment_key_type = null,
        Type\Union $assignment_value_type = null,
        $assignment_key_value = null
    ) {
        if ($stmt instanceof PhpParser\Node\Expr\Variable) {
            if (self::checkVariable($statements_checker, $stmt, $context, false, null, $array_assignment) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Assign) {
            $assignment_type = AssignmentChecker::check(
                $statements_checker,
                $stmt->var,
                $stmt->expr,
                null,
                $context,
                (string)$stmt->getDocComment()
            );

            if ($assignment_type === false) {
                return false;
            }

            $stmt->inferredType = $assignment_type;
        } elseif ($stmt instanceof PhpParser\Node\Expr\AssignOp) {
            if (AssignmentChecker::checkAssignmentOperation($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\MethodCall) {
            if (CallChecker::checkMethodCall($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\StaticCall) {
            if (CallChecker::checkStaticCall($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\ConstFetch) {
            if (FetchChecker::checkConstFetch($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Scalar\String_) {
            $stmt->inferredType = Type::getString();
        } elseif ($stmt instanceof PhpParser\Node\Scalar\EncapsedStringPart) {
            // do nothing
        } elseif ($stmt instanceof PhpParser\Node\Scalar\MagicConst) {
            // do nothing
        } elseif ($stmt instanceof PhpParser\Node\Scalar\LNumber) {
            $stmt->inferredType = Type::getInt();
        } elseif ($stmt instanceof PhpParser\Node\Scalar\DNumber) {
            $stmt->inferredType = Type::getFloat();
        } elseif ($stmt instanceof PhpParser\Node\Expr\UnaryMinus) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }
            $stmt->inferredType = $stmt->expr->inferredType;
        } elseif ($stmt instanceof PhpParser\Node\Expr\UnaryPlus) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = isset($stmt->expr->inferredType) ? $stmt->expr->inferredType : null;
        } elseif ($stmt instanceof PhpParser\Node\Expr\Isset_) {
            foreach ($stmt->vars as $isset_var) {
                if ($isset_var instanceof PhpParser\Node\Expr\PropertyFetch &&
                    $isset_var->var instanceof PhpParser\Node\Expr\Variable &&
                    $isset_var->var->name === 'this' &&
                    is_string($isset_var->name)
                ) {
                    $var_id = '$this->' . $isset_var->name;
                    $context->vars_in_scope[$var_id] = Type::getMixed();
                    $context->vars_possibly_in_scope[$var_id] = true;
                }
            }
            $stmt->inferredType = Type::getBool();
        } elseif ($stmt instanceof PhpParser\Node\Expr\ClassConstFetch) {
            if (FetchChecker::checkClassConstFetch($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\PropertyFetch) {
            if (FetchChecker::checkPropertyFetch($statements_checker, $stmt, $context, $array_assignment) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\StaticPropertyFetch) {
            if (FetchChecker::checkStaticPropertyFetch($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\BitwiseNot) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\BinaryOp) {
            if (self::checkBinaryOp($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\PostInc) {
            if (self::check($statements_checker, $stmt->var, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\PostDec) {
            if (self::check($statements_checker, $stmt->var, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\PreInc) {
            if (self::check($statements_checker, $stmt->var, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\PreDec) {
            if (self::check($statements_checker, $stmt->var, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\New_) {
            if (CallChecker::checkNew($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Array_) {
            if (self::checkArray($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Scalar\Encapsed) {
            if (self::checkEncapsulatedString($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\FuncCall) {
            if (CallChecker::checkFunctionCall($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Ternary) {
            if (self::checkTernary($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\BooleanNot) {
            if (self::checkBooleanNot($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Empty_) {
            if (self::checkEmpty($statements_checker, $stmt, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Closure) {
            $closure_checker = new ClosureChecker($stmt, $statements_checker->getSource());

            if (self::checkClosureUses($statements_checker, $stmt, $context) === false) {
                return false;
            }

            $use_context = new Context($statements_checker->getFileName(), $context->self);

            if (!$statements_checker->isStatic()) {
                $this_class = ClassLikeChecker::getThisClass();
                $this_class = $this_class &&
                    ClassChecker::classExtends($this_class, $statements_checker->getFQCLN())
                    ? $this_class
                    : $context->self;

                if ($this_class) {
                    $use_context->vars_in_scope['$this'] = new Type\Union([new Type\Atomic($this_class)]);
                }
            }

            foreach ($context->vars_in_scope as $var => $type) {
                if (strpos($var, '$this->') === 0) {
                    $use_context->vars_in_scope[$var] = clone $type;
                }
            }

            foreach ($context->vars_possibly_in_scope as $var => $type) {
                if (strpos($var, '$this->') === 0) {
                    $use_context->vars_possibly_in_scope[$var] = true;
                }
            }

            foreach ($stmt->uses as $use) {
                // insert the ref into the current context if passed by ref, as whatever we're passing
                // the closure to could execute it straight away.
                if (!isset($context->vars_in_scope['$' . $use->var]) && $use->byRef) {
                    $context->vars_in_scope['$' . $use->var] = Type::getMixed();
                }

                $use_context->vars_in_scope['$' . $use->var] = isset($context->vars_in_scope['$' . $use->var])
                    ? clone $context->vars_in_scope['$' . $use->var]
                    : Type::getMixed();

                $use_context->vars_possibly_in_scope['$' . $use->var] = true;
            }

            $closure_checker->check($use_context);

            $stmt->inferredType = Type::getClosure();
        } elseif ($stmt instanceof PhpParser\Node\Expr\ArrayDimFetch) {
            if (FetchChecker::checkArrayAccess(
                $statements_checker,
                $stmt,
                $context,
                $array_assignment,
                $assignment_key_type,
                $assignment_value_type,
                $assignment_key_value
            ) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Int_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getInt();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Double) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getFloat();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Bool_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getBool();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\String_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getString();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Object_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getObject();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Array_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getArray();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Unset_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            $stmt->inferredType = Type::getNull();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Clone_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            if (property_exists($stmt->expr, 'inferredType')) {
                $stmt->inferredType = $stmt->expr->inferredType;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Instanceof_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }

            if ($stmt->class instanceof PhpParser\Node\Name &&
                !in_array($stmt->class->parts[0], ['self', 'static', 'parent'])
            ) {
                if ($context->check_classes) {
                    $fq_class_name = ClassLikeChecker::getFQCLNFromNameObject(
                        $stmt->class,
                        $statements_checker->getNamespace(),
                        $statements_checker->getAliasedClasses()
                    );

                    if (ClassLikeChecker::checkFullyQualifiedClassLikeName(
                        $fq_class_name,
                        new CodeLocation($statements_checker->getSource(), $stmt->class),
                        $statements_checker->getSuppressedIssues()
                    ) === false) {
                        return false;
                    }
                }
            }

            $stmt->inferredType = Type::getBool();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Exit_) {
            // do nothing
        } elseif ($stmt instanceof PhpParser\Node\Expr\Include_) {
            $statements_checker->checkInclude($stmt, $context);
        } elseif ($stmt instanceof PhpParser\Node\Expr\Eval_) {
            $context->check_classes = false;
            $context->check_variables = false;

            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\AssignRef) {
            if ($stmt->var instanceof PhpParser\Node\Expr\Variable) {
                if (is_string($stmt->var->name)) {
                    $context->vars_in_scope['$' . $stmt->var->name] = Type::getMixed();
                    $context->vars_possibly_in_scope['$' . $stmt->var->name] = true;
                    $statements_checker->registerVariable('$' . $stmt->var->name, $stmt->var->getLine());
                } else {
                    if (self::check($statements_checker, $stmt->var->name, $context) === false) {
                        return false;
                    }
                }
            } else {
                if (self::check($statements_checker, $stmt->var, $context) === false) {
                    return false;
                }
            }

            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\ErrorSuppress) {
            // do nothing
        } elseif ($stmt instanceof PhpParser\Node\Expr\ShellExec) {
            if (IssueBuffer::accepts(
                new ForbiddenCode(
                    'Use of shell_exec',
                    new CodeLocation($statements_checker->getSource(), $stmt)
                ),
                $statements_checker->getSuppressedIssues()
            )) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Print_) {
            if (self::check($statements_checker, $stmt->expr, $context) === false) {
                return false;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\Yield_) {
            self::checkYield($statements_checker, $stmt, $context);
        } elseif ($stmt instanceof PhpParser\Node\Expr\YieldFrom) {
            self::checkYieldFrom($statements_checker, $stmt, $context);
        } else {
            if (IssueBuffer::accepts(
                new UnrecognizedExpression(
                    'Psalm does not understand ' . get_class($stmt),
                    new CodeLocation($statements_checker->getSource(), $stmt)
                ),
                $statements_checker->getSuppressedIssues()
            )) {
                return false;
            }
        }

        $plugins = Config::getInstance()->getPlugins();

        if ($plugins) {
            $code_location = new CodeLocation($statements_checker->getSource(), $stmt);
            
            foreach ($plugins as $plugin) {
                if ($plugin->checkExpression(
                    $stmt,
                    $context,
                    $code_location,
                    $statements_checker->getSuppressedIssues()
                ) === false) {
                    return false;
                }
            }
        }

        return null;
    }

    /**
     * @param   StatementsChecker               $statements_checker
     * @param   PhpParser\Node\Expr\Variable    $stmt
     * @param   Context                         $context
     * @param   bool                            $passed_by_reference
     * @param   Type\Union|null                 $by_ref_type
     * @param   bool                            $array_assignment
     * @return  false|null
     */
    public static function checkVariable(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\Variable $stmt,
        Context $context,
        $passed_by_reference = false,
        Type\Union $by_ref_type = null,
        $array_assignment = false
    ) {
        if ($stmt->name === 'this') {
            if ($statements_checker->isStatic()) {
                if (IssueBuffer::accepts(
                    new InvalidStaticVariable(
                        'Invalid reference to $this in a static context',
                        new CodeLocation($statements_checker->getSource(), $stmt)
                    ),
                    $statements_checker->getSuppressedIssues()
                )) {
                    return false;
                }

                return null;
            }

            $stmt->inferredType = clone $context->vars_in_scope['$this'];

            return null;
        }

        if (!$context->check_variables) {
            $stmt->inferredType = Type::getMixed();

            if (is_string($stmt->name) && !isset($context->vars_in_scope['$' . $stmt->name])) {
                $context->vars_in_scope['$' . $stmt->name] = Type::getMixed();
                $context->vars_possibly_in_scope['$' . $stmt->name] = true;
            }

            return null;
        }

        if (in_array($stmt->name, [
            '_SERVER', '_GET', '_POST', '_COOKIE', '_REQUEST', '_FILES', '_ENV', 'GLOBALS', 'argv', 'argc'
        ])) {
            return null;
        }

        if (!is_string($stmt->name)) {
            return self::check($statements_checker, $stmt->name, $context);
        }

        if ($passed_by_reference && $by_ref_type) {
            self::assignByRefParam($statements_checker, $stmt, $by_ref_type, $context);
            return null;
        }

        $var_name = '$' . $stmt->name;

        if (!isset($context->vars_in_scope[$var_name])) {
            if (!isset($context->vars_possibly_in_scope[$var_name]) ||
                !$statements_checker->getFirstAppearance($var_name)
            ) {
                if ($array_assignment) {
                    // if we're in an array assignment, let's assign the variable
                    // because PHP allows it

                    $context->vars_in_scope[$var_name] = Type::getArray();
                    $context->vars_possibly_in_scope[$var_name] = true;
                    $statements_checker->registerVariable($var_name, $stmt->getLine());
                } else {
                    IssueBuffer::add(
                        new UndefinedVariable(
                            'Cannot find referenced variable ' . $var_name,
                            new CodeLocation($statements_checker->getSource(), $stmt)
                        )
                    );

                    return false;
                }
            }

            if ($statements_checker->getFirstAppearance($var_name)) {
                if (IssueBuffer::accepts(
                    new PossiblyUndefinedVariable(
                        'Possibly undefined variable ' . $var_name .', first seen on line ' .
                            $statements_checker->getFirstAppearance($var_name),
                        new CodeLocation($statements_checker->getSource(), $stmt)
                    ),
                    $statements_checker->getSuppressedIssues()
                )) {
                    return false;
                }
            }
        } else {
            $stmt->inferredType = $context->vars_in_scope[$var_name];
        }

        return null;
    }

    /**
     * @param  StatementsChecker    $statements_checker
     * @param  PhpParser\Node\Expr  $stmt
     * @param  Type\Union           $by_ref_type
     * @param  Context              $context
     * @return void
     */
    public static function assignByRefParam(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr $stmt,
        Type\Union $by_ref_type,
        Context $context
    ) {
        $var_id = self::getVarId(
            $stmt,
            $statements_checker->getFQCLN(),
            $statements_checker->getNamespace(),
            $statements_checker->getAliasedClasses()
        );

        if ($var_id && !isset($context->vars_in_scope[$var_id])) {
            $context->vars_possibly_in_scope[$var_id] = true;
            $statements_checker->registerVariable($var_id, $stmt->getLine());
        }

        $stmt->inferredType = $by_ref_type;

        $context->vars_in_scope[$var_id] = $by_ref_type;
    }

    /**
     * @param   StatementsChecker           $statements_checker
     * @param   PhpParser\Node\Expr\Array_  $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected static function checkArray(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\Array_ $stmt,
        Context $context
    ) {
        // if the array is empty, this special type allows us to match any other array type against it
        if (empty($stmt->items)) {
            $stmt->inferredType = Type::getEmptyArray();
            return null;
        }

        /** @var Type\Union|null */
        $item_key_type = null;

        /** @var Type\Union|null */
        $item_value_type = null;

        /** @var array<string,Type\Union> */
        $property_types = [];

        foreach ($stmt->items as $item) {
            if ($item->key) {
                if (self::check($statements_checker, $item->key, $context) === false) {
                    return false;
                }

                if (isset($item->key->inferredType)) {
                    if ($item_key_type) {
                        /** @var Type\Union */
                        $item_key_type = Type::combineUnionTypes($item->key->inferredType, $item_key_type);
                    } else {
                        /** @var Type\Union */
                        $item_key_type = $item->key->inferredType;
                    }
                }
            } else {
                $item_key_type = Type::getInt();
            }

            if (self::check($statements_checker, $item->value, $context) === false) {
                return false;
            }

            if (isset($item->value->inferredType)) {
                if ($item->key instanceof PhpParser\Node\Scalar\String_) {
                    $property_types[$item->key->value] = $item->value->inferredType;
                }

                if ($item_value_type) {
                    $item_value_type = Type::combineUnionTypes($item->value->inferredType, $item_value_type);
                } else {
                    $item_value_type = $item->value->inferredType;
                }
            }
        }

        // if this array looks like an object-like array, let's return that instead
        if ($item_value_type && $item_key_type && $item_key_type->hasString() && !$item_key_type->hasInt()) {
            $stmt->inferredType = new Type\Union([new Type\ObjectLike('array', $property_types)]);
            return null;
        }

        $stmt->inferredType = new Type\Union([
            new Type\Generic(
                'array',
                [
                    $item_key_type ?: new Type\Union([new Type\Atomic('int'), new Type\Atomic('string')]),
                    $item_value_type ?: Type::getMixed()
                ]
            )
        ]);

        return null;
    }

    /**
     * @param   StatementsChecker               $statements_checker
     * @param   PhpParser\Node\Expr\BinaryOp    $stmt
     * @param   Context                         $context
     * @param   int                             $nesting
     * @return  false|null
     */
    protected static function checkBinaryOp(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\BinaryOp $stmt,
        Context $context,
        $nesting = 0
    ) {
        if ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Concat && $nesting > 20) {
            // ignore deeply-nested string concatenation
        } elseif ($stmt instanceof PhpParser\Node\Expr\BinaryOp\BooleanAnd) {
            $left_type_assertions = TypeChecker::getReconcilableTypeAssertions(
                $stmt->left,
                $statements_checker->getFQCLN(),
                $statements_checker->getNamespace(),
                $statements_checker->getAliasedClasses()
            );

            if (self::check($statements_checker, $stmt->left, $context) === false) {
                return false;
            }

            // while in an and, we allow scope to boil over to support
            // statements of the form if ($x && $x->foo())
            $op_vars_in_scope = TypeChecker::reconcileKeyedTypes(
                $left_type_assertions,
                $context->vars_in_scope,
                new CodeLocation($statements_checker->getSource(), $stmt),
                $statements_checker->getSuppressedIssues()
            );

            if ($op_vars_in_scope === false) {
                return false;
            }

            $op_context = clone $context;
            $op_context->vars_in_scope = $op_vars_in_scope;

            if (self::check($statements_checker, $stmt->right, $op_context) === false) {
                return false;
            }

            foreach ($op_context->vars_in_scope as $var => $type) {
                if (!isset($context->vars_in_scope[$var])) {
                    $context->vars_in_scope[$var] = $type;
                    continue;
                }
            }

            $context->updateChecks($op_context);

            $context->vars_possibly_in_scope = array_merge(
                $op_context->vars_possibly_in_scope,
                $context->vars_possibly_in_scope
            );
        } elseif ($stmt instanceof PhpParser\Node\Expr\BinaryOp\BooleanOr) {
            $left_type_assertions = TypeChecker::getNegatableTypeAssertions(
                $stmt->left,
                $statements_checker->getFQCLN(),
                $statements_checker->getNamespace(),
                $statements_checker->getAliasedClasses()
            );

            $negated_type_assertions = TypeChecker::negateTypes($left_type_assertions);

            if (self::check($statements_checker, $stmt->left, $context) === false) {
                return false;
            }

            // while in an or, we allow scope to boil over to support
            // statements of the form if ($x === null || $x->foo())
            $op_vars_in_scope = TypeChecker::reconcileKeyedTypes(
                $negated_type_assertions,
                $context->vars_in_scope,
                new CodeLocation($statements_checker->getSource(), $stmt),
                $statements_checker->getSuppressedIssues()
            );

            if ($op_vars_in_scope === false) {
                return false;
            }

            $op_context = clone $context;
            $op_context->vars_in_scope = $op_vars_in_scope;

            if (self::check($statements_checker, $stmt->right, $op_context) === false) {
                return false;
            }

            $context->updateChecks($op_context);

            $context->vars_possibly_in_scope = array_merge(
                $op_context->vars_possibly_in_scope,
                $context->vars_possibly_in_scope
            );
        } else {
            if ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Concat) {
                $stmt->inferredType = Type::getString();
            }

            if ($stmt->left instanceof PhpParser\Node\Expr\BinaryOp) {
                if (self::checkBinaryOp($statements_checker, $stmt->left, $context, ++$nesting) === false) {
                    return false;
                }
            } else {
                if (self::check($statements_checker, $stmt->left, $context) === false) {
                    return false;
                }
            }

            if ($stmt->right instanceof PhpParser\Node\Expr\BinaryOp) {
                if (self::checkBinaryOp($statements_checker, $stmt->right, $context, ++$nesting) === false) {
                    return false;
                }
            } else {
                if (self::check($statements_checker, $stmt->right, $context) === false) {
                    return false;
                }
            }
        }

        // let's do some fun type assignment
        if (isset($stmt->left->inferredType) && isset($stmt->right->inferredType)) {
            if ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Plus || $stmt instanceof PhpParser\Node\Expr\BinaryOp\Minus) {
                self::checkPlusOp(
                    $stmt->left->inferredType,
                    $stmt->right->inferredType,
                    $result_type
                );

                if ($result_type) {
                    $stmt->inferredType = $result_type;
                }

            } elseif ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Mul) {
                if ($stmt->left->inferredType->isInt() && $stmt->right->inferredType->isInt()) {
                    $stmt->inferredType = Type::getInt();
                } elseif ($stmt->left->inferredType->hasNumericType() &&
                    $stmt->right->inferredType->hasNumericType()
                ) {
                    $stmt->inferredType = Type::getFloat();
                }
            } elseif ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Div
                && $stmt->left->inferredType->hasNumericType()
                && $stmt->right->inferredType->hasNumericType()
            ) {
                $stmt->inferredType = Type::getFloat();
            }
        }

        if ($stmt instanceof PhpParser\Node\Expr\BinaryOp\BooleanAnd
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\BooleanOr
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\Equal
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\NotEqual
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\Identical
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\NotIdentical
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\Greater
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\GreaterOrEqual
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\Smaller
            || $stmt instanceof PhpParser\Node\Expr\BinaryOp\SmallerOrEqual
        ) {
            $stmt->inferredType = Type::getBool();
        }

        if ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Spaceship) {
            $stmt->inferredType = Type::getInt();
        }

        return null;
    }

    /**
     * @param  Type\Union|null   $left_type
     * @param  Type\Union|null   $right_type
     * @param  Type\Union|null   &$result_type
     * @return void
     */
    public static function checkPlusOp(
        Type\Union $left_type = null,
        Type\Union $right_type = null,
        Type\Union &$result_type = null
    ) {
        if ($left_type && !$left_type->isMixed()) {
            if ($left_type->hasNumericType()) {
                if ($right_type) {
                    if ($left_type->isInt() && $right_type->isInt()) {
                        $result_type = Type::getInt();
                        return;
                    }

                    if ($left_type->hasNumericType() && $right_type->hasNumericType()) {
                        $result_type = Type::getFloat();
                        return;
                    }
                }
            } elseif ($left_type->hasArray()) {
                if (!$right_type || $right_type->isMixed()) {
                    // @todo emit issue
                    $result_type = Type::getMixed();
                    return;
                }

                if (!$right_type->hasArray()) {
                    // @todo emit issue

                    return;
                }

                $var_array_type = $left_type->types['array'];
                $expr_array_type = $right_type->types['array'];

                $result_type = Type::combineTypes([$var_array_type, $expr_array_type]);
            }
        }
    }

    /**
     * @param  PhpParser\Node\Expr $stmt
     * @param  string              $this_class_name
     * @param  string              $namespace
     * @param  array               $aliased_classes
     * @param  int|null            &$nesting
     * @return string|null
     */
    public static function getVarId(
        PhpParser\Node\Expr $stmt,
        $this_class_name,
        $namespace,
        array $aliased_classes,
        &$nesting = null
    ) {
        if ($stmt instanceof PhpParser\Node\Expr\Variable && is_string($stmt->name)) {
            return '$' . $stmt->name;
        }

        if ($stmt instanceof PhpParser\Node\Expr\StaticPropertyFetch
            && is_string($stmt->name)
            && $stmt->class instanceof PhpParser\Node\Name
        ) {
            if (count($stmt->class->parts) === 1 && in_array($stmt->class->parts[0], ['self', 'static', 'parent'])) {
                $fq_class_name = $this_class_name;
            } else {
                $fq_class_name = ClassLikeChecker::getFQCLNFromNameObject(
                    $stmt->class,
                    $namespace,
                    $aliased_classes
                );
            }

            return $fq_class_name . '::$' . $stmt->name;
        }

        if ($stmt instanceof PhpParser\Node\Expr\PropertyFetch && is_string($stmt->name)) {
            $object_id = self::getVarId($stmt->var, $this_class_name, $namespace, $aliased_classes);

            if (!$object_id) {
                return null;
            }

            return $object_id . '->' . $stmt->name;
        }

        if ($stmt instanceof PhpParser\Node\Expr\ArrayDimFetch && $nesting !== null) {
            $nesting++;
            return self::getVarId($stmt->var, $this_class_name, $namespace, $aliased_classes, $nesting);
        }

        return null;
    }

    /**
     * @param  PhpParser\Node\Expr $stmt
     * @param  string              $this_class_name
     * @param  string              $namespace
     * @param  array               $aliased_classes
     * @return string|null
     */
    public static function getArrayVarId(
        PhpParser\Node\Expr $stmt,
        $this_class_name,
        $namespace,
        array $aliased_classes
    ) {
        if ($stmt instanceof PhpParser\Node\Expr\ArrayDimFetch &&
            $stmt->dim instanceof PhpParser\Node\Scalar\String_
        ) {
            $root_var_id = self::getArrayVarId($stmt->var, $this_class_name, $namespace, $aliased_classes);
            return $root_var_id ? $root_var_id . '[\'' . $stmt->dim->value . '\']' : null;
        }

        return self::getVarId($stmt, $this_class_name, $namespace, $aliased_classes);
    }

    /**
     * @param  Type\Union                   $return_type
     * @param  array<PhpParser\Node\Arg>    $args
     * @param  string|null                  $calling_class
     * @param  string|null                  $method_id
     * @return Type\Union
     */
    public static function fleshOutTypes(Type\Union $return_type, array $args, $calling_class = null, $method_id = null)
    {
        $return_type = clone $return_type;

        $new_return_type_parts = [];

        foreach ($return_type->types as $key => $return_type_part) {
            $new_return_type_parts[] = self::fleshOutAtomicType($return_type_part, $args, $calling_class, $method_id);
        }

        return new Type\Union($new_return_type_parts);
    }

    /**
     * @param  Type\Atomic                  &$return_type
     * @param  array<PhpParser\Node\Arg>    $args
     * @param  string|null                  $calling_class
     * @param  string|null                  $method_id
     * @return Type\Atomic
     */
    protected static function fleshOutAtomicType(Type\Atomic $return_type, array $args, $calling_class, $method_id)
    {
        if ($return_type->value === '$this' || $return_type->value === 'static' || $return_type->value === 'self') {
            if (!$calling_class) {
                throw new \InvalidArgumentException(
                    'Cannot handle ' . $return_type->value . ' when $calling_class is empty',
                    null
                );
            }

            $return_type->value = $calling_class;
        } elseif ($return_type->value[0] === '$' && $method_id) {
            $method_params = MethodChecker::getMethodParams($method_id);

            if (!$method_params) {
                throw new \InvalidArgumentException(
                    'Cannot get method params of ' . $method_id,
                    null
                );
            }

            foreach ($args as $i => $arg) {
                $method_param = $method_params[$i];

                if ($return_type->value === '$' . $method_param->name) {
                    $arg_value = $arg->value;
                    if ($arg_value instanceof PhpParser\Node\Scalar\String_) {
                        $return_type->value = preg_replace('/^\\\/', '', $arg_value->value);
                    }
                }
            }

            if ($return_type->value[0] === '$') {
                $return_type = new Type\Atomic('mixed');
            }
        }

        if ($return_type instanceof Type\Generic) {
            foreach ($return_type->type_params as &$type_param) {
                $type_param = self::fleshOutTypes($type_param, $args, $calling_class, $method_id);
            }
        }

        return $return_type;
    }

    /**
     * @param   StatementsChecker           $statements_checker
     * @param   PhpParser\Node\Expr\Closure $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected static function checkClosureUses(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\Closure $stmt,
        Context $context
    ) {
        foreach ($stmt->uses as $use) {
            if (!isset($context->vars_in_scope['$' . $use->var])) {
                if ($use->byRef) {
                    $context->vars_in_scope['$' . $use->var] = Type::getMixed();
                    $context->vars_possibly_in_scope['$' . $use->var] = true;
                    $statements_checker->registerVariable('$' . $use->var, $use->getLine());
                    return;
                }

                if (!isset($context->vars_possibly_in_scope['$' . $use->var])) {
                    if ($context->check_variables) {
                        IssueBuffer::add(
                            new UndefinedVariable(
                                'Cannot find referenced variable $' . $use->var,
                                new CodeLocation($statements_checker->getSource(), $use)
                            )
                        );

                        return false;
                    }
                }

                if ($statements_checker->getFirstAppearance('$' . $use->var)) {
                    if (IssueBuffer::accepts(
                        new PossiblyUndefinedVariable(
                            'Possibly undefined variable $' . $use->var . ', first seen on line ' .
                                $statements_checker->getFirstAppearance('$' . $use->var),
                            new CodeLocation($statements_checker->getSource(), $use)
                        ),
                        $statements_checker->getSuppressedIssues()
                    )) {
                        return false;
                    }

                    return null;
                }

                if ($context->check_variables) {
                    IssueBuffer::add(
                        new UndefinedVariable(
                            'Cannot find referenced variable $' . $use->var,
                            new CodeLocation($statements_checker->getSource(), $use)
                        )
                    );

                    return false;
                }
            }
        }

        return null;
    }

    /**
     * @param   StatementsChecker           $statements_checker
     * @param   PhpParser\Node\Expr\Yield_  $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected static function checkYield(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\Yield_ $stmt,
        Context $context
    ) {
        $type_in_comments = CommentChecker::getTypeFromComment(
            (string) $stmt->getDocComment(),
            $context,
            $statements_checker->getSource()
        );

        if ($stmt->key) {
            if (self::check($statements_checker, $stmt->key, $context) === false) {
                return false;
            }
        }

        if ($stmt->value) {
            if (self::check($statements_checker, $stmt->value, $context) === false) {
                return false;
            }

            if ($type_in_comments) {
                $stmt->inferredType = $type_in_comments;
            } elseif (isset($stmt->value->inferredType)) {
                $stmt->inferredType = $stmt->value->inferredType;
            } else {
                $stmt->inferredType = Type::getMixed();
            }
        } else {
            $stmt->inferredType = Type::getNull();
        }

        return null;
    }

    /**
     * @param   StatementsChecker               $statements_checker
     * @param   PhpParser\Node\Expr\YieldFrom   $stmt
     * @param   Context                         $context
     * @return  false|null
     */
    protected static function checkYieldFrom(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\YieldFrom $stmt,
        Context $context
    ) {
        if (self::check($statements_checker, $stmt->expr, $context) === false) {
            return false;
        }

        if (isset($stmt->expr->inferredType)) {
            $stmt->inferredType = $stmt->expr->inferredType;
        }

        return null;
    }

    /**
     * @param   StatementsChecker           $statements_checker
     * @param   PhpParser\Node\Expr\Ternary $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected static function checkTernary(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\Ternary $stmt,
        Context $context
    ) {
        if (self::check($statements_checker, $stmt->cond, $context) === false) {
            return false;
        }

        $t_if_context = clone $context;

        if ($stmt->cond instanceof PhpParser\Node\Expr\BinaryOp) {
            $reconcilable_if_types = TypeChecker::getReconcilableTypeAssertions(
                $stmt->cond,
                $statements_checker->getFQCLN(),
                $statements_checker->getNamespace(),
                $statements_checker->getAliasedClasses()
            );

            $negatable_if_types = TypeChecker::getNegatableTypeAssertions(
                $stmt->cond,
                $statements_checker->getFQCLN(),
                $statements_checker->getNamespace(),
                $statements_checker->getAliasedClasses()
            );
        } else {
            $reconcilable_if_types = $negatable_if_types = TypeChecker::getTypeAssertions(
                $stmt->cond,
                $statements_checker->getFQCLN(),
                $statements_checker->getNamespace(),
                $statements_checker->getAliasedClasses()
            );
        }

        $if_return_type = null;

        $t_if_vars_in_scope_reconciled = TypeChecker::reconcileKeyedTypes(
            $reconcilable_if_types,
            $t_if_context->vars_in_scope,
            new CodeLocation($statements_checker->getSource(), $stmt),
            $statements_checker->getSuppressedIssues()
        );

        if ($t_if_vars_in_scope_reconciled === false) {
            return false;
        }

        $t_if_context->vars_in_scope = $t_if_vars_in_scope_reconciled;

        if ($stmt->if) {
            if (self::check($statements_checker, $stmt->if, $t_if_context) === false) {
                return false;
            }
        }

        $t_else_context = clone $context;

        if ($negatable_if_types) {
            $negated_if_types = TypeChecker::negateTypes($negatable_if_types);

            $t_else_vars_in_scope_reconciled = TypeChecker::reconcileKeyedTypes(
                $negated_if_types,
                $t_else_context->vars_in_scope,
                new CodeLocation($statements_checker->getSource(), $stmt),
                $statements_checker->getSuppressedIssues()
            );

            if ($t_else_vars_in_scope_reconciled === false) {
                return false;
            }

            $t_else_context->vars_in_scope = $t_else_vars_in_scope_reconciled;
        }

        if (self::check($statements_checker, $stmt->else, $t_else_context) === false) {
            return false;
        }

        $lhs_type = null;

        if ($stmt->if) {
            if (isset($stmt->if->inferredType)) {
                $lhs_type = $stmt->if->inferredType;
            }
        } elseif ($stmt->cond) {
            if (isset($stmt->cond->inferredType)) {
                $if_return_type_reconciled = TypeChecker::reconcileTypes(
                    '!empty',
                    $stmt->cond->inferredType,
                    '',
                    new CodeLocation($statements_checker->getSource(), $stmt),
                    $statements_checker->getSuppressedIssues()
                );

                if ($if_return_type_reconciled === false) {
                    return false;
                }

                $lhs_type = $if_return_type_reconciled;
            }
        }

        if (!$lhs_type || !isset($stmt->else->inferredType)) {
            $stmt->inferredType = Type::getMixed();
        } else {
            $stmt->inferredType = Type::combineUnionTypes($lhs_type, $stmt->else->inferredType);
        }

        return null;
    }

    /**
     * @param   StatementsChecker               $statements_checker
     * @param   PhpParser\Node\Expr\BooleanNot  $stmt
     * @param   Context                         $context
     * @return  false|null
     */
    protected static function checkBooleanNot(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\BooleanNot $stmt,
        Context $context
    ) {
        $stmt->inferredType = Type::getBool();
        return self::check($statements_checker, $stmt->expr, $context);
    }

    /**
     * @param   StatementsChecker           $statements_checker
     * @param   PhpParser\Node\Expr\Empty_  $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected static function checkEmpty(
        StatementsChecker $statements_checker,
        PhpParser\Node\Expr\Empty_ $stmt,
        Context $context
    ) {
        return self::check($statements_checker, $stmt->expr, $context);
    }

    /**
     * @param   StatementsChecker               $statements_checker
     * @param   PhpParser\Node\Scalar\Encapsed  $stmt
     * @param   Context                         $context
     * @return  false|null
     */
    protected static function checkEncapsulatedString(
        StatementsChecker $statements_checker,
        PhpParser\Node\Scalar\Encapsed $stmt,
        Context $context
    ) {
        /** @var PhpParser\Node\Expr $part */
        foreach ($stmt->parts as $part) {
            if (self::check($statements_checker, $part, $context) === false) {
                return false;
            }
        }

        $stmt->inferredType = Type::getString();
        return null;
    }

    /**
     * @param  string  $fq_class_name
     * @return boolean
     */
    public static function isMock($fq_class_name)
    {
        return in_array($fq_class_name, Config::getInstance()->getMockClasses());
    }

    /**
     * @return void
     */
    public static function clearCache()
    {
        self::$reflection_functions = [];
    }
}