X-Git-Url: http://aleph1.co.uk/gitweb/?a=blobdiff_plain;ds=inline;f=vendor%2Fnikic%2Fphp-parser%2Fdoc%2Fcomponent%2FLexer.markdown;fp=vendor%2Fnikic%2Fphp-parser%2Fdoc%2Fcomponent%2FLexer.markdown;h=b22942dd1673e96924d6ca20f14e1d8491b494b2;hb=9917807b03b64faf00f6a1f29dcb6eafc454efa5;hp=0000000000000000000000000000000000000000;hpb=aea91e65e895364e460983b890e295aa5d5540a5;p=yaffs-website diff --git a/vendor/nikic/php-parser/doc/component/Lexer.markdown b/vendor/nikic/php-parser/doc/component/Lexer.markdown new file mode 100644 index 000000000..b22942dd1 --- /dev/null +++ b/vendor/nikic/php-parser/doc/component/Lexer.markdown @@ -0,0 +1,152 @@ +Lexer component documentation +============================= + +The lexer is responsible for providing tokens to the parser. The project comes with two lexers: `PhpParser\Lexer` and +`PhpParser\Lexer\Emulative`. The latter is an extension of the former, which adds the ability to emulate tokens of +newer PHP versions and thus allows parsing of new code on older versions. + +This documentation discusses options available for the default lexers and explains how lexers can be extended. + +Lexer options +------------- + +The two default lexers accept an `$options` array in the constructor. Currently only the `'usedAttributes'` option is +supported, which allows you to specify which attributes will be added to the AST nodes. The attributes can then be +accessed using `$node->getAttribute()`, `$node->setAttribute()`, `$node->hasAttribute()` and `$node->getAttributes()` +methods. A sample options array: + +```php +$lexer = new PhpParser\Lexer(array( + 'usedAttributes' => array( + 'comments', 'startLine', 'endLine' + ) +)); +``` + +The attributes used in this example match the default behavior of the lexer. The following attributes are supported: + + * `comments`: Array of `PhpParser\Comment` or `PhpParser\Comment\Doc` instances, representing all comments that occurred + between the previous non-discarded token and the current one. Use of this attribute is required for the + `$node->getDocComment()` method to work. The attribute is also needed if you wish the pretty printer to retain + comments present in the original code. + * `startLine`: Line in which the node starts. This attribute is required for the `$node->getLine()` to work. It is also + required if syntax errors should contain line number information. + * `endLine`: Line in which the node ends. + * `startTokenPos`: Offset into the token array of the first token in the node. + * `endTokenPos`: Offset into the token array of the last token in the node. + * `startFilePos`: Offset into the code string of the first character that is part of the node. + * `endFilePos`: Offset into the code string of the last character that is part of the node. + +### Using token positions + +The token offset information is useful if you wish to examine the exact formatting used for a node. For example the AST +does not distinguish whether a property was declared using `public` or using `var`, but you can retrieve this +information based on the token position: + +```php +function isDeclaredUsingVar(array $tokens, PhpParser\Node\Stmt\Property $prop) { + $i = $prop->getAttribute('startTokenPos'); + return $tokens[$i][0] === T_VAR; +} +``` + +In order to make use of this function, you will have to provide the tokens from the lexer to your node visitor using +code similar to the following: + +```php +class MyNodeVisitor extends PhpParser\NodeVisitorAbstract { + private $tokens; + public function setTokens(array $tokens) { + $this->tokens = $tokens; + } + + public function leaveNode(PhpParser\Node $node) { + if ($node instanceof PhpParser\Node\Stmt\Property) { + var_dump(isDeclaredUsingVar($this->tokens, $node)); + } + } +} + +$lexer = new PhpParser\Lexer(array( + 'usedAttributes' => array( + 'comments', 'startLine', 'endLine', 'startTokenPos', 'endTokenPos' + ) +)); +$parser = (new PhpParser\ParserFactory)->create(PhpParser\ParserFactory::PREFER_PHP7, $lexer); + +$visitor = new MyNodeVisitor(); +$traverser = new PhpParser\NodeTraverser(); +$traverser->addVisitor($visitor); + +try { + $stmts = $parser->parse($code); + $visitor->setTokens($lexer->getTokens()); + $stmts = $traverser->traverse($stmts); +} catch (PhpParser\Error $e) { + echo 'Parse Error: ', $e->getMessage(); +} +``` + +The same approach can also be used to perform specific modifications in the code, without changing the formatting in +other places (which is the case when using the pretty printer). + +Lexer extension +--------------- + +A lexer has to define the following public interface: + + void startLexing(string $code, ErrorHandler $errorHandler = null); + array getTokens(); + string handleHaltCompiler(); + int getNextToken(string &$value = null, array &$startAttributes = null, array &$endAttributes = null); + +The `startLexing()` method is invoked with the source code that is to be lexed (including the opening tag) whenever the +`parse()` method of the parser is called. It can be used to reset state or preprocess the source code or tokens. The +passes `ErrorHandler` should be used to report lexing errors. + +The `getTokens()` method returns the current token array, in the usual `token_get_all()` format. This method is not +used by the parser (which uses `getNextToken()`), but is useful in combination with the token position attributes. + +The `handleHaltCompiler()` method is called whenever a `T_HALT_COMPILER` token is encountered. It has to return the +remaining string after the construct (not including `();`). + +The `getNextToken()` method returns the ID of the next token (as defined by the `Parser::T_*` constants). If no more +tokens are available it must return `0`, which is the ID of the `EOF` token. Furthermore the string content of the +token should be written into the by-reference `$value` parameter (which will then be available as `$n` in the parser). + +### Attribute handling + +The other two by-ref variables `$startAttributes` and `$endAttributes` define which attributes will eventually be +assigned to the generated nodes: The parser will take the `$startAttributes` from the first token which is part of the +node and the `$endAttributes` from the last token that is part of the node. + +E.g. if the tokens `T_FUNCTION T_STRING ... '{' ... '}'` constitute a node, then the `$startAttributes` from the +`T_FUNCTION` token will be taken and the `$endAttributes` from the `'}'` token. + +An application of custom attributes is storing the exact original formatting of literals: While the parser does retain +some information about the formatting of integers (like decimal vs. hexadecimal) or strings (like used quote type), it +does not preserve the exact original formatting (e.g. leading zeros for integers or escape sequences in strings). This +can be remedied by storing the original value in an attribute: + +```php +use PhpParser\Lexer; +use PhpParser\Parser\Tokens; + +class KeepOriginalValueLexer extends Lexer // or Lexer\Emulative +{ + public function getNextToken(&$value = null, &$startAttributes = null, &$endAttributes = null) { + $tokenId = parent::getNextToken($value, $startAttributes, $endAttributes); + + if ($tokenId == Tokens::T_CONSTANT_ENCAPSED_STRING // non-interpolated string + || $tokenId == Tokens::T_ENCAPSED_AND_WHITESPACE // interpolated string + || $tokenId == Tokens::T_LNUMBER // integer + || $tokenId == Tokens::T_DNUMBER // floating point number + ) { + // could also use $startAttributes, doesn't really matter here + $endAttributes['originalValue'] = $value; + } + + return $tokenId; + } +} +```