psalm/src/Psalm/Checker/StatementsChecker.php

<?php
namespace Psalm\Checker;

use PhpParser;
use Psalm\Checker\Statements\Block\ForChecker;
use Psalm\Checker\Statements\Block\ForeachChecker;
use Psalm\Checker\Statements\Block\IfChecker;
use Psalm\Checker\Statements\Block\SwitchChecker;
use Psalm\Checker\Statements\Block\TryChecker;
use Psalm\Checker\Statements\Block\WhileChecker;
use Psalm\Checker\Statements\ExpressionChecker;
use Psalm\Checker\Statements\Expression\AssignmentChecker;
use Psalm\Config;
use Psalm\Context;
use Psalm\Issue\ContinueOutsideLoop;
use Psalm\Issue\InvalidGlobal;
use Psalm\Issue\InvalidNamespace;
use Psalm\Issue\UnrecognizedStatement;
use Psalm\IssueBuffer;
use Psalm\StatementsSource;
use Psalm\Type;

class StatementsChecker
{
    /**
     * @var StatementsSource
     */
    protected $source;

    /**
     * @var array<string, int>
     */
    protected $all_vars = [];

    /**
     * @var string|null
     */
    protected $class_name;

    /**
     * @var string|null
     */
    protected $parent_class;

    /**
     * @var string
     */
    protected $namespace;

    /**
     * @var array<string,string>
     */
    protected $aliased_classes;

    /**
     * @var string
     */
    protected $file_name;

    /**
     * @var string
     */
    protected $checked_file_name;

    /**
     * @var string|null
     */
    protected $include_file_name;

    /**
     * @var bool
     */
    protected $is_static;

    /**
     * @var string
     */
    protected $fq_class_name;

    /**
     * @var TypeChecker
     */
    protected $type_checker;

    /**
     * A list of suppressed issues
     *
     * @var array<string>
     */
    protected $suppressed_issues;

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

    /**
     * @param StatementsSource $source
     */
    public function __construct(StatementsSource $source)
    {
        $this->source = $source;
        $this->file_name = $this->source->getFileName();
        $this->checked_file_name = $this->source->getCheckedFileName();
        $this->aliased_classes = $this->source->getAliasedClasses();
        $this->namespace = $this->source->getNamespace();
        $this->is_static = $this->source->isStatic();
        $this->fq_class_name = $this->source->getFQCLN();
        $this->class_name = $this->source->getClassName();
        $this->parent_class = $this->source->getParentClass();
        $this->suppressed_issues = $this->source->getSuppressedIssues();

        $config = Config::getInstance();

        $this->type_checker = new TypeChecker($source, $this);
    }

    /**
     * Checks an array of statements for validity
     *
     * @param  array<PhpParser\Node>        $stmts
     * @param  Context                      $context
     * @param  Context|null                 $loop_context
     * @param  Context|null                 $global_context
     * @return null|false
     */
    public function check(array $stmts, Context $context, Context $loop_context = null, Context $global_context = null)
    {
        $has_returned = false;

        $function_checkers = [];

        // hoist functions to the top
        foreach ($stmts as $stmt) {
            if ($stmt instanceof PhpParser\Node\Stmt\Function_) {
                $function_checker = new FunctionChecker($stmt, $this->source, $context->file_name);
                $function_checkers[$stmt->name] = $function_checker;
            }
        }

        foreach ($stmts as $stmt) {
            foreach (Config::getInstance()->getPlugins() as $plugin) {
                if ($plugin->checkStatement(
                    $stmt,
                    $context,
                    $this->checked_file_name,
                    $this->getSuppressedIssues()
                ) === false) {
                    return false;
                }
            }

            if ($has_returned && !($stmt instanceof PhpParser\Node\Stmt\Nop) &&
                !($stmt instanceof PhpParser\Node\Stmt\InlineHTML)) {
                echo('Warning: Expressions after return/throw/continue in ' . $this->checked_file_name . ' on line ' .
                    $stmt->getLine() . PHP_EOL);
                break;
            }

            /*
            if (isset($context->vars_in_scope['$value_types'])) {
                var_dump($stmt->getLine() . ' ' . $context->vars_in_scope['$value_types']);
            }
            */

            if ($stmt instanceof PhpParser\Node\Stmt\If_) {
                IfChecker::check($this, $stmt, $context, $loop_context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\TryCatch) {
                TryChecker::check($this, $stmt, $context, $loop_context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\For_) {
                ForChecker::check($this, $stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Foreach_) {
                ForeachChecker::check($this, $stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\While_) {
                WhileChecker::check($this, $stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Do_) {
                $this->checkDo($stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Const_) {
                $this->checkConstAssignment($stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Unset_) {
                foreach ($stmt->vars as $var) {
                    $var_id = ExpressionChecker::getArrayVarId(
                        $var,
                        $this->fq_class_name,
                        $this->namespace,
                        $this->aliased_classes
                    );

                    if ($var_id) {
                        $context->remove($var_id);
                    }
                }
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Return_) {
                $has_returned = true;
                $this->checkReturn($stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Throw_) {
                $has_returned = true;
                $this->checkThrow($stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Switch_) {
                SwitchChecker::check($this, $stmt, $context, $loop_context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Break_) {
                // do nothing
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Continue_) {
                if ($loop_context === null) {
                    if (IssueBuffer::accepts(
                        new ContinueOutsideLoop(
                            'Continue call outside loop context',
                            $this->checked_file_name,
                            $stmt->getLine()
                        ),
                        $this->suppressed_issues
                    )) {
                        return false;
                    }
                }

                $has_returned = true;
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Static_) {
                $this->checkStatic($stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Echo_) {
                foreach ($stmt->exprs as $expr) {
                    ExpressionChecker::check($this, $expr, $context);
                }
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Function_) {
                $function_context = new Context($this->file_name, $context->self);
                $function_checkers[$stmt->name]->check($function_context, $context);
            } elseif ($stmt instanceof PhpParser\Node\Expr) {
                ExpressionChecker::check($this, $stmt, $context);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\InlineHTML) {
                // do nothing
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Use_) {
                foreach ($stmt->uses as $use) {
                    $this->aliased_classes[strtolower($use->alias)] = implode('\\', $use->name->parts);
                }
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Global_) {
                if (!$global_context) {
                    if (IssueBuffer::accepts(
                        new InvalidGlobal(
                            'Cannot use global scope here',
                            $this->checked_file_name,
                            $stmt->getLine()
                        ),
                        $this->suppressed_issues
                    )) {
                        return false;
                    }
                }
                else {
                    foreach ($stmt->vars as $var) {
                        if ($var instanceof PhpParser\Node\Expr\Variable) {
                            if (is_string($var->name)) {
                                $var_id = '$' . $var->name;

                                $context->vars_in_scope[$var_id] = isset($global_context->vars_in_scope[$var_id])
                                    ? clone $global_context->vars_in_scope[$var_id]
                                    : Type::getMixed();

                                $context->vars_possibly_in_scope[$var_id] = true;
                            } else {
                                ExpressionChecker::check($this, $var, $context);
                            }
                        }
                    }
                }
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Property) {
                foreach ($stmt->props as $prop) {
                    if ($prop->default) {
                        ExpressionChecker::check($this, $prop->default, $context);

                        if (isset($prop->default->inferredType)) {
                            if (!$stmt->isStatic()) {
                                if (AssignmentChecker::checkPropertyAssignment(
                                    $this,
                                    $prop,
                                    $prop->name,
                                    $prop->default->inferredType,
                                    $context
                                ) === false) {
                                    return false;
                                }
                            }
                        }
                    }
                }
            } elseif ($stmt instanceof PhpParser\Node\Stmt\ClassConst) {
                foreach ($stmt->consts as $const) {
                    ExpressionChecker::check($this, $const->value, $context);

                    if (isset($const->value->inferredType) && !$const->value->inferredType->isMixed()) {
                        ClassLikeChecker::setConstantType(
                            $this->fq_class_name,
                            $const->name,
                            $const->value->inferredType
                        );
                    }
                }
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Class_) {
                (new ClassChecker($stmt, $this->source, $stmt->name))->check();
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Nop) {
                // do nothing
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Goto_) {
                // do nothing
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Label) {
                // do nothing
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Namespace_) {
                if ($this->namespace) {
                    if (IssueBuffer::accepts(
                        new InvalidNamespace(
                            'Cannot redeclare namespace',
                            $this->checked_file_name,
                            $stmt->getLine()
                        ),
                        $this->suppressed_issues
                    )) {
                        return false;
                    }
                }

                $namespace_checker = new NamespaceChecker($stmt, $this->source);
                $namespace_checker->check(true);
            } elseif ($stmt instanceof PhpParser\Node\Stmt\Declare_) {
                // do nothing
            } else {
                if (IssueBuffer::accepts(
                    new UnrecognizedStatement(
                        'Psalm does not understand ' . get_class($stmt),
                        $this->getCheckedFileName(),
                        $stmt->getLine()
                    ),
                    $this->getSuppressedIssues()
                )) {
                    return false;
                }
            }
        }

        return null;
    }

    /**
     * @param   PhpParser\Node\Stmt\Static_ $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected function checkStatic(PhpParser\Node\Stmt\Static_ $stmt, Context $context)
    {
        foreach ($stmt->vars as $var) {
            if ($var->default) {
                if (ExpressionChecker::check($this, $var->default, $context) === false) {
                    return false;
                }
            }

            if ($context->check_variables) {
                $context->vars_in_scope['$' . $var->name] = $var->default && isset($var->default->inferredType)
                    ? $var->default->inferredType
                    : Type::getMixed();

                $context->vars_possibly_in_scope['$' . $var->name] = true;
                $this->registerVariable('$' . $var->name, $var->getLine());
            }
        }

        return null;
    }

    /**
     * @param   PhpParser\Node\Expr $stmt
     * @return  Type\Union|null
     */
    public static function getSimpleType(PhpParser\Node\Expr $stmt)
    {
        if ($stmt instanceof PhpParser\Node\Expr\ConstFetch) {
            // @todo support this
        } elseif ($stmt instanceof PhpParser\Node\Expr\ClassConstFetch) {
            // @todo support this as well
        } elseif ($stmt instanceof PhpParser\Node\Scalar\String_) {
            return Type::getString();
        } elseif ($stmt instanceof PhpParser\Node\Scalar\LNumber) {
            return Type::getInt();
        } elseif ($stmt instanceof PhpParser\Node\Scalar\DNumber) {
            return Type::getFloat();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Array_) {
            return Type::getArray();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Int_) {
            return Type::getInt();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Double) {
            return Type::getFloat();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Bool_) {
            return Type::getBool();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\String_) {
            return Type::getString();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Object_) {
            return Type::getObject();
        } elseif ($stmt instanceof PhpParser\Node\Expr\Cast\Array_) {
            return Type::getArray();
        } elseif ($stmt instanceof PhpParser\Node\Expr\UnaryMinus || $stmt instanceof PhpParser\Node\Expr\UnaryPlus) {
            return self::getSimpleType($stmt->expr);
        }

        return null;
    }

    /**
     * @param   PhpParser\Node\Stmt\Do_ $stmt
     * @param   Context                 $context
     * @return  false|null
     */
    protected function checkDo(PhpParser\Node\Stmt\Do_ $stmt, Context $context)
    {
        // do not clone context for do, because it executes in current scope always
        if ($this->check($stmt->stmts, $context, $context) === false) {
            return false;
        }

        return ExpressionChecker::check($this, $stmt->cond, $context);
    }

    /**
     * @param  string  $method_id
     * @param  Context $context
     * @return void
     */
    public function checkInsideMethod($method_id, Context $context)
    {
        $method_checker = ClassLikeChecker::getMethodChecker($method_id);

        if ($method_checker &&
            $this->source instanceof FunctionLikeChecker &&
            $method_checker->getMethodId() !== $this->source->getMethodId()
        ) {
            $this_context = new Context($this->file_name, (string) $context->vars_in_scope['$this']);

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

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

            $this_context->vars_in_scope['$this'] = $context->vars_in_scope['$this'];

            $method_checker->check($this_context);

            foreach ($this_context->vars_in_scope as $var => $type) {
                $context->vars_possibly_in_scope[$var] = true;
            }

            foreach ($this_context->vars_in_scope as $var => $type) {
                $context->vars_in_scope[$var] = $type;
            }
        }
    }

    /**
     * @param  string                 $call
     * @param  PhpParser\Node\Arg[]   $args
     * @param  string                 $method_id
     * @return string|null
     */
    protected static function getMethodFromCallBlock($call, array $args, $method_id)
    {
        $fq_class_name = explode('::', $method_id)[0];

        $original_call = $call;

        $call = preg_replace('/^\$this(->|::)/', $fq_class_name . '::', $call);

        $call = preg_replace('/\(\)$/', '', $call);

        if (strpos($call, '$') !== false) {
            $method_params = MethodChecker::getMethodParams($method_id);

            foreach ($args as $i => $arg) {
                $method_param = $method_params[$i];
                $preg_var_name = preg_quote('$' . $method_param['name']);

                if (preg_match('/::' . $preg_var_name . '$/', $call)) {
                    if ($arg->value instanceof PhpParser\Node\Scalar\String_) {
                        $call = preg_replace('/' . $preg_var_name . '$/', $arg->value->value, $call);
                        break;
                    }
                }
            }
        }

        return $original_call === $call || strpos($call, '$') !== false ? null : $call;
    }

    /**
     * @param   PhpParser\Node\Stmt\Const_  $stmt
     * @param   Context                     $context
     * @return  void
     */
    protected function checkConstAssignment(PhpParser\Node\Stmt\Const_ $stmt, Context $context)
    {
        foreach ($stmt->consts as $const) {
            ExpressionChecker::check($this, $const->value, $context);

            $this->setConstType(
                $const->name,
                isset($const->value->inferredType) ? $const->value->inferredType : Type::getMixed()
            );
        }
    }

    /**
     * @param   string  $const_name
     * @return  Type\Union|null
     */
    public function getConstType($const_name)
    {
        return isset(self::$user_constants[$this->file_name][$const_name])
            ? self::$user_constants[$this->file_name][$const_name]
            : null;
    }

    /**
     * @param   string      $const_name
     * @param   Type\Union  $const_type
     * @return  void
     */
    public function setConstType($const_name, Type\Union $const_type)
    {
        self::$user_constants[$this->file_name][$const_name] = $const_type;
    }

    /**
     * @param  PhpParser\Node\Stmt\Return_ $stmt
     * @param  Context                     $context
     * @return false|null
     */
    protected function checkReturn(PhpParser\Node\Stmt\Return_ $stmt, Context $context)
    {
        $type_in_comments = CommentChecker::getTypeFromComment(
            (string) $stmt->getDocComment(),
            $context,
            $this->source
        );

        if ($stmt->expr) {
            if (ExpressionChecker::check($this, $stmt->expr, $context) === false) {
                return false;
            }

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

        if ($this->source instanceof FunctionLikeChecker) {
            $this->source->addReturnTypes($stmt->expr ? (string) $stmt->inferredType : '', $context);
        }

        return null;
    }

    /**
     * @param   PhpParser\Node\Stmt\Throw_  $stmt
     * @param   Context                     $context
     * @return  false|null
     */
    protected function checkThrow(PhpParser\Node\Stmt\Throw_ $stmt, Context $context)
    {
        return ExpressionChecker::check($this, $stmt->expr, $context);
    }

    /**
     * @param  string $var_name
     * @param  int    $line_number
     * @return void
     */
    public function registerVariable($var_name, $line_number)
    {
        if (!isset($this->all_vars[$var_name])) {
            $this->all_vars[$var_name] = $line_number;
        }
    }

    /**
     * @param  PhpParser\Node\Expr $dim
     * @return Type\Union
     */
    protected static function getArrayTypeFromDim(PhpParser\Node\Expr $dim)
    {
        if ($dim) {
            if (isset($dim->inferredType)) {
                return $dim->inferredType;
            } else {
                return new Type\Union([Type::getInt()->types['int'], Type::getString()->types['string']]);
            }
        } else {
            return Type::getInt();
        }
    }

    /**
     * @param  PhpParser\Node\Expr\Include_ $stmt
     * @param  Context                      $context
     * @return false|null
     */
    public function checkInclude(PhpParser\Node\Expr\Include_ $stmt, Context $context)
    {
        if (ExpressionChecker::check($this, $stmt->expr, $context) === false) {
            return false;
        }

        $path_to_file = null;

        if ($stmt->expr instanceof PhpParser\Node\Scalar\String_) {
            $path_to_file = $stmt->expr->value;

            // attempts to resolve using get_include_path dirs
            $include_path = self::resolveIncludePath($path_to_file, dirname($this->checked_file_name));
            $path_to_file = $include_path ? $include_path : $path_to_file;

            if ($path_to_file[0] !== '/') {
                $path_to_file = getcwd() . '/' . $path_to_file;
            }
        } else {
            $path_to_file = self::getPathTo($stmt->expr, $this->include_file_name ?: $this->file_name);
        }

        if ($path_to_file) {
            $reduce_pattern = '/\/[^\/]+\/\.\.\//';

            while (preg_match($reduce_pattern, $path_to_file)) {
                $path_to_file = preg_replace($reduce_pattern, '/', $path_to_file);
            }

            // if the file is already included, we can't check much more
            if (in_array($path_to_file, get_included_files())) {
                return null;
            }

            /*
            if (in_array($path_to_file, FileChecker::getIncludesToIgnore())) {
                $context->check_classes = false;
                $context->check_variables = false;

                return null;
            }
             */

            if (file_exists($path_to_file)) {
                $include_stmts = FileChecker::getStatementsForFile($path_to_file);
                $old_include_file_name = $this->include_file_name;
                $this->include_file_name = Config::getInstance()->shortenFileName($path_to_file);
                $this->source->setIncludeFileName($this->include_file_name);
                $this->check($include_stmts, $context);
                $this->include_file_name = $old_include_file_name;
                $this->source->setIncludeFileName($old_include_file_name);
                return null;
            }
        }

        $context->check_classes = false;
        $context->check_variables = false;
        $context->check_functions = false;
        return null;
    }

    /**
     * @param  string  $method_id
     * @param  int     $argument_offset
     * @return boolean
     */
    protected function isPassedByReference($method_id, array $args, $argument_offset)
    {
        $function_params = FunctionLikeChecker::getParamsById($method_id, $args, $this->file_name);

        return $argument_offset < count($function_params) && $function_params[$argument_offset]->by_ref;
    }

    /**
     * @param  PhpParser\Node\Expr $stmt
     * @param  string              $file_name
     * @return string|null
     */
    protected static function getPathTo(PhpParser\Node\Expr $stmt, $file_name)
    {
        if ($file_name[0] !== '/') {
            $file_name = getcwd() . '/' . $file_name;
        }

        if ($stmt instanceof PhpParser\Node\Scalar\String_) {
            return $stmt->value;
        } elseif ($stmt instanceof PhpParser\Node\Expr\BinaryOp\Concat) {
            $left_string = self::getPathTo($stmt->left, $file_name);
            $right_string = self::getPathTo($stmt->right, $file_name);

            if ($left_string && $right_string) {
                return $left_string . $right_string;
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\FuncCall &&
            $stmt->name instanceof PhpParser\Node\Name &&
            $stmt->name->parts === ['dirname']
        ) {
            if ($stmt->args) {
                $evaled_path = self::getPathTo($stmt->args[0]->value, $file_name);

                if (!$evaled_path) {
                    return null;
                }

                return dirname($evaled_path);
            }
        } elseif ($stmt instanceof PhpParser\Node\Expr\ConstFetch && $stmt->name instanceof PhpParser\Node\Name) {
            $const_name = implode('', $stmt->name->parts);

            if (defined($const_name)) {
                $constant_value = constant($const_name);

                if (is_string($constant_value)) {
                    return $constant_value;
                }
            }
        } elseif ($stmt instanceof PhpParser\Node\Scalar\MagicConst\Dir) {
            return dirname($file_name);
        } elseif ($stmt instanceof PhpParser\Node\Scalar\MagicConst\File) {
            return $file_name;
        }

        return null;
    }

    /**
     * @return string|null
     */

    /**
     * @param   string  $file_name
     * @param   string  $current_directory
     * @return  string|null
     */
    protected static function resolveIncludePath($file_name, $current_directory)
    {
        $paths = PATH_SEPARATOR == ':'
            ? preg_split('#(?<!phar):#', get_include_path())
            : explode(PATH_SEPARATOR, get_include_path());

        foreach ($paths as $prefix) {
            $ds = substr($prefix, -1) == DIRECTORY_SEPARATOR ? '' : DIRECTORY_SEPARATOR;

            if ($prefix === '.') {
                $prefix = $current_directory;
            }

            $file = $prefix . $ds . $file_name;

            if (file_exists($file)) {
                return $file;
            }
        }

        return null;
    }

    /**
     * @return array<string>
     */
    public function getAliasedClasses()
    {
        return $this->aliased_classes;
    }

    /**
     * @return array<string>
     */
    public function getSuppressedIssues()
    {
        return $this->suppressed_issues;
    }

    /**
     * @return string
     */
    public function getCheckedFileName()
    {
        return $this->checked_file_name;
    }

    /**
     * @return string
     */
    public function getFileName()
    {
        return $this->file_name;
    }

    /**
     * @return string|null
     */
    public function getParentClass()
    {
        return $this->parent_class;
    }

    /**
     * @return string|null
     */
    public function getClassName()
    {
        return $this->class_name;
    }

    /**
     * @return string
     */
    public function getFQCLN()
    {
        return $this->fq_class_name;
    }

    /**
     * @return string
     */
    public function getNamespace()
    {
        return $this->namespace;
    }

    /**
     * @return bool
     */
    public function isStatic()
    {
        return $this->is_static;
    }

    /**
     * @return StatementsSource
     */
    public function getSource()
    {
        return $this->source;
    }

    /**
     * The first appearance of the variable in this set of statements being evaluated
     *
     * @param  string  $var_name
     * @return int|null
     */
    public function getFirstAppearance($var_name)
    {
        return isset($this->all_vars[$var_name]) ? $this->all_vars[$var_name] : null;
    }

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

        ExpressionChecker::clearCache();
    }
}