Error_handling.markdown

Error handling

Errors during parsing or analysis are represented using the PhpParser\Error exception class. In addition to an error message, an error can also store additional information about the location the error occurred at.

How much location information is available depends on the origin of the error and how many lexer attributes have been enabled. At a minimum the start line of the error is usually available.

Column information

In order to receive information about not only the line, but also the column span an error occurred at, the file position attributes in the lexer need to be enabled:

$lexerOptions = array(
    'usedAttributes' => array('comments', 'startLine', 'endLine', 'startFilePos', 'endFilePos'),
);
$parser = (new PhpParser\ParserFactory())->createForHostVersion($lexerOptions);

try {
    $stmts = $parser->parse($code);
    // ...
} catch (PhpParser\Error $e) {
    // ...
}

Before using column information, its availability needs to be checked with $e->hasColumnInfo(), as the precise location of an error cannot always be determined. The methods for retrieving column information also have to be passed the source code of the parsed file. An example for printing an error:

if ($e->hasColumnInfo()) {
    echo $e->getRawMessage() . ' from ' . $e->getStartLine() . ':' . $e->getStartColumn($code)
        . ' to ' . $e->getEndLine() . ':' . $e->getEndColumn($code);
    // or:
    echo $e->getMessageWithColumnInfo($code);
} else {
    echo $e->getMessage();
}

Both line numbers and column numbers are 1-based. EOF errors will be located at the position one past the end of the file.

Error recovery

The error behavior of the parser (and other components) is controlled by an ErrorHandler. Whenever an error is encountered, ErrorHandler::handleError() is invoked. The default error handling strategy is ErrorHandler\Throwing, which will immediately throw when an error is encountered.

To instead collect all encountered errors into an array, while trying to continue parsing the rest of the source code, an instance of ErrorHandler\Collecting can be passed to the Parser::parse() method. A usage example:

$parser = (new PhpParser\ParserFactory())->createForHostVersion();
$errorHandler = new PhpParser\ErrorHandler\Collecting;

$stmts = $parser->parse($code, $errorHandler);

if ($errorHandler->hasErrors()) {
    foreach ($errorHandler->getErrors() as $error) {
        // $error is an ordinary PhpParser\Error
    }
}

if (null !== $stmts) {
    // $stmts is a best-effort partial AST
}

The partial AST may contain Expr\Error nodes that indicate that an error occurred while parsing an expression.

The NameResolver visitor also accepts an ErrorHandler as a constructor argument.