1 Lexer component documentation
2 =============================
4 The lexer is responsible for providing tokens to the parser. The project comes with two lexers: `PhpParser\Lexer` and
5 `PhpParser\Lexer\Emulative`. The latter is an extension of the former, which adds the ability to emulate tokens of
6 newer PHP versions and thus allows parsing of new code on older versions.
8 This documentation discusses options available for the default lexers and explains how lexers can be extended.
13 The two default lexers accept an `$options` array in the constructor. Currently only the `'usedAttributes'` option is
14 supported, which allows you to specify which attributes will be added to the AST nodes. The attributes can then be
15 accessed using `$node->getAttribute()`, `$node->setAttribute()`, `$node->hasAttribute()` and `$node->getAttributes()`
16 methods. A sample options array:
19 $lexer = new PhpParser\Lexer(array(
20 'usedAttributes' => array(
21 'comments', 'startLine', 'endLine'
26 The attributes used in this example match the default behavior of the lexer. The following attributes are supported:
28 * `comments`: Array of `PhpParser\Comment` or `PhpParser\Comment\Doc` instances, representing all comments that occurred
29 between the previous non-discarded token and the current one. Use of this attribute is required for the
30 `$node->getDocComment()` method to work. The attribute is also needed if you wish the pretty printer to retain
31 comments present in the original code.
32 * `startLine`: Line in which the node starts. This attribute is required for the `$node->getLine()` to work. It is also
33 required if syntax errors should contain line number information.
34 * `endLine`: Line in which the node ends.
35 * `startTokenPos`: Offset into the token array of the first token in the node.
36 * `endTokenPos`: Offset into the token array of the last token in the node.
37 * `startFilePos`: Offset into the code string of the first character that is part of the node.
38 * `endFilePos`: Offset into the code string of the last character that is part of the node.
40 ### Using token positions
42 The token offset information is useful if you wish to examine the exact formatting used for a node. For example the AST
43 does not distinguish whether a property was declared using `public` or using `var`, but you can retrieve this
44 information based on the token position:
47 function isDeclaredUsingVar(array $tokens, PhpParser\Node\Stmt\Property $prop) {
48 $i = $prop->getAttribute('startTokenPos');
49 return $tokens[$i][0] === T_VAR;
53 In order to make use of this function, you will have to provide the tokens from the lexer to your node visitor using
54 code similar to the following:
57 class MyNodeVisitor extends PhpParser\NodeVisitorAbstract {
59 public function setTokens(array $tokens) {
60 $this->tokens = $tokens;
63 public function leaveNode(PhpParser\Node $node) {
64 if ($node instanceof PhpParser\Node\Stmt\Property) {
65 var_dump(isDeclaredUsingVar($this->tokens, $node));
70 $lexer = new PhpParser\Lexer(array(
71 'usedAttributes' => array(
72 'comments', 'startLine', 'endLine', 'startTokenPos', 'endTokenPos'
75 $parser = (new PhpParser\ParserFactory)->create(PhpParser\ParserFactory::PREFER_PHP7, $lexer);
77 $visitor = new MyNodeVisitor();
78 $traverser = new PhpParser\NodeTraverser();
79 $traverser->addVisitor($visitor);
82 $stmts = $parser->parse($code);
83 $visitor->setTokens($lexer->getTokens());
84 $stmts = $traverser->traverse($stmts);
85 } catch (PhpParser\Error $e) {
86 echo 'Parse Error: ', $e->getMessage();
90 The same approach can also be used to perform specific modifications in the code, without changing the formatting in
91 other places (which is the case when using the pretty printer).
96 A lexer has to define the following public interface:
98 void startLexing(string $code, ErrorHandler $errorHandler = null);
100 string handleHaltCompiler();
101 int getNextToken(string &$value = null, array &$startAttributes = null, array &$endAttributes = null);
103 The `startLexing()` method is invoked with the source code that is to be lexed (including the opening tag) whenever the
104 `parse()` method of the parser is called. It can be used to reset state or preprocess the source code or tokens. The
105 passes `ErrorHandler` should be used to report lexing errors.
107 The `getTokens()` method returns the current token array, in the usual `token_get_all()` format. This method is not
108 used by the parser (which uses `getNextToken()`), but is useful in combination with the token position attributes.
110 The `handleHaltCompiler()` method is called whenever a `T_HALT_COMPILER` token is encountered. It has to return the
111 remaining string after the construct (not including `();`).
113 The `getNextToken()` method returns the ID of the next token (as defined by the `Parser::T_*` constants). If no more
114 tokens are available it must return `0`, which is the ID of the `EOF` token. Furthermore the string content of the
115 token should be written into the by-reference `$value` parameter (which will then be available as `$n` in the parser).
117 ### Attribute handling
119 The other two by-ref variables `$startAttributes` and `$endAttributes` define which attributes will eventually be
120 assigned to the generated nodes: The parser will take the `$startAttributes` from the first token which is part of the
121 node and the `$endAttributes` from the last token that is part of the node.
123 E.g. if the tokens `T_FUNCTION T_STRING ... '{' ... '}'` constitute a node, then the `$startAttributes` from the
124 `T_FUNCTION` token will be taken and the `$endAttributes` from the `'}'` token.
126 An application of custom attributes is storing the exact original formatting of literals: While the parser does retain
127 some information about the formatting of integers (like decimal vs. hexadecimal) or strings (like used quote type), it
128 does not preserve the exact original formatting (e.g. leading zeros for integers or escape sequences in strings). This
129 can be remedied by storing the original value in an attribute:
133 use PhpParser\Parser\Tokens;
135 class KeepOriginalValueLexer extends Lexer // or Lexer\Emulative
137 public function getNextToken(&$value = null, &$startAttributes = null, &$endAttributes = null) {
138 $tokenId = parent::getNextToken($value, $startAttributes, $endAttributes);
140 if ($tokenId == Tokens::T_CONSTANT_ENCAPSED_STRING // non-interpolated string
141 || $tokenId == Tokens::T_ENCAPSED_AND_WHITESPACE // interpolated string
142 || $tokenId == Tokens::T_LNUMBER // integer
143 || $tokenId == Tokens::T_DNUMBER // floating point number
145 // could also use $startAttributes, doesn't really matter here
146 $endAttributes['originalValue'] = $value;