423 lines
15 KiB
Markdown
423 lines
15 KiB
Markdown
Usage of basic components
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=========================
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This document explains how to use the parser, the pretty printer and the node traverser.
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Bootstrapping
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-------------
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The library needs to register a class autoloader. You can either use the `vendor/autoload.php` file generated by
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Composer or by including the bundled `lib/bootstrap.php` file:
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```php
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<?php
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require 'path/to/PHP-Parser/lib/bootstrap.php';
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// Or, if you're using Composer:
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require 'path/to/vendor/autoload.php';
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```
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Additionally you may want to set the `xdebug.max_nesting_level` ini option to a higher value:
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```php
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<?php
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ini_set('xdebug.max_nesting_level', 3000);
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```
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This ensures that there will be no errors when traversing highly nested node trees.
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Parsing
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-------
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In order to parse some source code you first have to create a `PhpParser\Parser` object, which
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needs to be passed a `PhpParser\Lexer` instance:
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```php
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<?php
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$parser = new PhpParser\Parser(new PhpParser\Lexer);
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// or
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$parser = new PhpParser\Parser(new PhpParser\Lexer\Emulative);
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```
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Use of the emulative lexer is required if you want to parse PHP code from newer versions than the one
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you're running on. For example it will allow you to parse PHP 5.6 code while running on PHP 5.3.
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Subsequently you can pass PHP code (including the opening `<?php` tag) to the `parse` method in order to
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create a syntax tree. If a syntax error is encountered, an `PhpParser\Error` exception will be thrown:
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```php
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<?php
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$code = '<?php // some code';
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$parser = new PhpParser\Parser(new PhpParser\Lexer\Emulative);
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try {
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$stmts = $parser->parse($code);
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// $stmts is an array of statement nodes
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} catch (PhpParser\Error $e) {
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echo 'Parse Error: ', $e->getMessage();
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}
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```
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A parser instance can be reused to parse multiple files.
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Node tree
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---------
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If you use the above code with `$code = "<?php echo 'Hi ', hi\\getTarget();"` the parser will
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generate a node tree looking like this:
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```
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array(
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0: Stmt_Echo(
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exprs: array(
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0: Scalar_String(
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value: Hi
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)
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1: Expr_FuncCall(
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name: Name(
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parts: array(
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0: hi
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1: getTarget
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)
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)
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args: array(
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)
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)
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)
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)
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)
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```
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Thus `$stmts` will contain an array with only one node, with this node being an instance of
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`PhpParser\Node\Stmt\Echo_`.
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As PHP is a large language there are approximately 140 different nodes. In order to make work
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with them easier they are grouped into three categories:
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* `PhpParser\Node\Stmt`s are statement nodes, i.e. language constructs that do not return
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a value and can not occur in an expression. For example a class definition is a statement.
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It doesn't return a value and you can't write something like `func(class A {});`.
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* `PhpParser\Node\Expr`s are expression nodes, i.e. language constructs that return a value
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and thus can occur in other expressions. Examples of expressions are `$var`
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(`PhpParser\Node\Expr\Variable`) and `func()` (`PhpParser\Node\Expr\FuncCall`).
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* `PhpParser\Node\Scalar`s are nodes representing scalar values, like `'string'`
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(`PhpParser\Node\Scalar\String_`), `0` (`PhpParser\Node\Scalar\LNumber`) or magic constants
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like `__FILE__` (`PhpParser\Node\Scalar\MagicConst\File`). All `PhpParser\Node\Scalar`s extend
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`PhpParser\Node\Expr`, as scalars are expressions, too.
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* There are some nodes not in either of these groups, for example names (`PhpParser\Node\Name`)
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and call arguments (`PhpParser\Node\Arg`).
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Some node class names have a trailing `_`. This is used whenever the class name would otherwise clash
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with a PHP keyword.
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Every node has a (possibly zero) number of subnodes. You can access subnodes by writing
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`$node->subNodeName`. The `Stmt\Echo_` node has only one subnode `exprs`. So in order to access it
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in the above example you would write `$stmts[0]->exprs`. If you wanted to access the name of the function
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call, you would write `$stmts[0]->exprs[1]->name`.
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All nodes also define a `getType()` method that returns the node type. The type is the class name
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without the `PhpParser\Node\` prefix and `\` replaced with `_`. It also does not contain a trailing
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`_` for reserved-keyword class names.
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It is possible to associate custom metadata with a node using the `setAttribute()` method. This data
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can then be retrieved using `hasAttribute()`, `getAttribute()` and `getAttributes()`.
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By default the lexer adds the `startLine`, `endLine` and `comments` attributes. `comments` is an array
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of `PhpParser\Comment[\Doc]` instances.
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The start line can also be accessed using `getLine()`/`setLine()` (instead of `getAttribute('startLine')`).
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The last doc comment from the `comments` attribute can be obtained using `getDocComment()`.
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Pretty printer
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--------------
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The pretty printer component compiles the AST back to PHP code. As the parser does not retain formatting
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information the formatting is done using a specified scheme. Currently there is only one scheme available,
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namely `PhpParser\PrettyPrinter\Standard`.
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```php
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<?php
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$code = "<?php echo 'Hi ', hi\\getTarget();";
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$parser = new PhpParser\Parser(new PhpParser\Lexer);
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$prettyPrinter = new PhpParser\PrettyPrinter\Standard;
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try {
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// parse
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$stmts = $parser->parse($code);
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// change
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$stmts[0] // the echo statement
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->exprs // sub expressions
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[0] // the first of them (the string node)
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->value // it's value, i.e. 'Hi '
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= 'Hello '; // change to 'Hello '
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// pretty print
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$code = $prettyPrinter->prettyPrint($stmts);
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echo $code;
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} catch (PhpParser\Error $e) {
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echo 'Parse Error: ', $e->getMessage();
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}
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```
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The above code will output:
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<?php echo 'Hello ', hi\getTarget();
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As you can see the source code was first parsed using `PhpParser\Parser->parse()`, then changed and then
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again converted to code using `PhpParser\PrettyPrinter\Standard->prettyPrint()`.
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The `prettyPrint()` method pretty prints a statements array. It is also possible to pretty print only a
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single expression using `prettyPrintExpr()`.
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The `prettyPrintFile()` method can be used to print an entire file. This will include the opening `<?php` tag
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and handle inline HTML as the first/last statement more gracefully.
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Node traversation
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-----------------
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The above pretty printing example used the fact that the source code was known and thus it was easy to
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write code that accesses a certain part of a node tree and changes it. Normally this is not the case.
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Usually you want to change / analyze code in a generic way, where you don't know how the node tree is
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going to look like.
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For this purpose the parser provides a component for traversing and visiting the node tree. The basic
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structure of a program using this `PhpParser\NodeTraverser` looks like this:
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```php
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<?php
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$parser = new PhpParser\Parser(new PhpParser\Lexer\Emulative);
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$traverser = new PhpParser\NodeTraverser;
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$prettyPrinter = new PhpParser\PrettyPrinter\Standard;
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// add your visitor
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$traverser->addVisitor(new MyNodeVisitor);
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try {
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$code = file_get_contents($fileName);
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// parse
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$stmts = $parser->parse($code);
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// traverse
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$stmts = $traverser->traverse($stmts);
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// pretty print
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$code = $prettyPrinter->prettyPrintFile($stmts);
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echo $code;
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} catch (PhpParser\Error $e) {
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echo 'Parse Error: ', $e->getMessage();
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}
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```
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The corresponding node visitor might look like this:
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```php
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<?php
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use PhpParser\Node;
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class MyNodeVisitor extends PhpParser\NodeVisitorAbstract
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{
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public function leaveNode(Node $node) {
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if ($node instanceof Node\Scalar\String_) {
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$node->value = 'foo';
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}
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}
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}
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```
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The above node visitor would change all string literals in the program to `'foo'`.
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All visitors must implement the `PhpParser\NodeVisitor` interface, which defines the following four
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methods:
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public function beforeTraverse(array $nodes);
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public function enterNode(PhpParser\Node $node);
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public function leaveNode(PhpParser\Node $node);
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public function afterTraverse(array $nodes);
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The `beforeTraverse()` method is called once before the traversal begins and is passed the nodes the
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traverser was called with. This method can be used for resetting values before traversation or
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preparing the tree for traversal.
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The `afterTraverse()` method is similar to the `beforeTraverse()` method, with the only difference that
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it is called once after the traversal.
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The `enterNode()` and `leaveNode()` methods are called on every node, the former when it is entered,
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i.e. before its subnodes are traversed, the latter when it is left.
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All four methods can either return the changed node or not return at all (i.e. `null`) in which
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case the current node is not changed.
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The `enterNode()` method can additionally return the value `NodeTraverser::DONT_TRAVERSE_CHILDREN`,
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which instructs the traverser to skip all children of the current node.
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The `leaveNode()` method can additionally return the value `NodeTraverser::REMOVE_NODE`, in which
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case the current node will be removed from the parent array. Furthermove it is possible to return
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an array of nodes, which will be merged into the parent array at the offset of the current node.
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I.e. if in `array(A, B, C)` the node `B` should be replaced with `array(X, Y, Z)` the result will
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be `array(A, X, Y, Z, C)`.
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Instead of manually implementing the `NodeVisitor` interface you can also extend the `NodeVisitorAbstract`
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class, which will define empty default implementations for all the above methods.
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The NameResolver node visitor
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-----------------------------
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One visitor is already bundled with the package: `PhpParser\NodeVisitor\NameResolver`. This visitor
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helps you work with namespaced code by trying to resolve most names to fully qualified ones.
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For example, consider the following code:
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use A as B;
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new B\C();
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In order to know that `B\C` really is `A\C` you would need to track aliases and namespaces yourself.
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The `NameResolver` takes care of that and resolves names as far as possible.
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After running it most names will be fully qualified. The only names that will stay unqualified are
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unqualified function and constant names. These are resolved at runtime and thus the visitor can't
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know which function they are referring to. In most cases this is a non-issue as the global functions
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are meant.
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Also the `NameResolver` adds a `namespacedName` subnode to class, function and constant declarations
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that contains the namespaced name instead of only the shortname that is available via `name`.
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Example: Converting namespaced code to pseudo namespaces
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--------------------------------------------------------
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A small example to understand the concept: We want to convert namespaced code to pseudo namespaces
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so it works on 5.2, i.e. names like `A\\B` should be converted to `A_B`. Note that such conversions
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are fairly complicated if you take PHP's dynamic features into account, so our conversion will
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assume that no dynamic features are used.
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We start off with the following base code:
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```php
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<?php
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$inDir = '/some/path';
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$outDir = '/some/other/path';
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$parser = new PhpParser\Parser(new PhpParser\Lexer\Emulative);
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$traverser = new PhpParser\NodeTraverser;
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$prettyPrinter = new PhpParser\PrettyPrinter\Standard;
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$traverser->addVisitor(new PhpParser\NodeVisitor\NameResolver); // we will need resolved names
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$traverser->addVisitor(new NodeVisitor\NamespaceConverter); // our own node visitor
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// iterate over all .php files in the directory
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$files = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($inDir));
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$files = new RegexIterator($files, '/\.php$/');
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foreach ($files as $file) {
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try {
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// read the file that should be converted
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$code = file_get_contents($file);
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// parse
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$stmts = $parser->parse($code);
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// traverse
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$stmts = $traverser->traverse($stmts);
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// pretty print
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$code = $prettyPrinter->prettyPrintFile($stmts);
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// write the converted file to the target directory
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file_put_contents(
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substr_replace($file->getPathname(), $outDir, 0, strlen($inDir)),
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$code
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);
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} catch (PhpParser\Error $e) {
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echo 'Parse Error: ', $e->getMessage();
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}
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}
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```
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Now lets start with the main code, the `NodeVisitor\NamespaceConverter`. One thing it needs to do
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is convert `A\\B` style names to `A_B` style ones.
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```php
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<?php
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use PhpParser\Node;
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class NodeVisitor_NamespaceConverter extends PhpParser\NodeVisitorAbstract
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{
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public function leaveNode(Node $node) {
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if ($node instanceof Node\Name) {
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return new Node\Name($node->toString('_'));
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}
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}
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}
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```
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The above code profits from the fact that the `NameResolver` already resolved all names as far as
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possible, so we don't need to do that. We only need to create a string with the name parts separated
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by underscores instead of backslashes. This is what `$node->toString('_')` does. (If you want to
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create a name with backslashes either write `$node->toString()` or `(string) $node`.) Then we create
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a new name from the string and return it. Returning a new node replaces the old node.
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Another thing we need to do is change the class/function/const declarations. Currently they contain
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only the shortname (i.e. the last part of the name), but they need to contain the complete name inclduing
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the namespace prefix:
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```php
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<?php
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use PhpParser\Node;
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use PhpParser\Node\Stmt;
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class NodeVisitor_NamespaceConverter extends PhpParser\NodeVisitorAbstract
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{
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public function leaveNode(Node $node) {
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if ($node instanceof Node\Name) {
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return new Node\Name($node->toString('_'));
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} elseif ($node instanceof Stmt\Class_
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|| $node instanceof Stmt\Interface_
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|| $node instanceof Stmt\Function_) {
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$node->name = $node->namespacedName->toString('_');
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} elseif ($node instanceof Stmt\Const_) {
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foreach ($node->consts as $const) {
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$const->name = $const->namespacedName->toString('_');
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}
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}
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}
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}
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```
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There is not much more to it than converting the namespaced name to string with `_` as separator.
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The last thing we need to do is remove the `namespace` and `use` statements:
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```php
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<?php
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use PhpParser\Node;
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use PhpParser\Node\Stmt;
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class NodeVisitor_NamespaceConverter extends PhpParser\NodeVisitorAbstract
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{
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public function leaveNode(Node $node) {
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if ($node instanceof Node\Name) {
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return new Node\Name($node->toString('_'));
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} elseif ($node instanceof Stmt\Class_
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|| $node instanceof Stmt\Interface_
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|| $node instanceof Stmt\Function_) {
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$node->name = $node->namespacedName->toString('_');
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} elseif ($node instanceof Stmt\Const_) {
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foreach ($node->consts as $const) {
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$const->name = $const->namespacedName->toString('_');
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}
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} elseif ($node instanceof Stmt\Namespace_) {
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// returning an array merges is into the parent array
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return $node->stmts;
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} elseif ($node instanceof Stmt\Use_) {
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// returning false removed the node altogether
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return false;
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}
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}
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}
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```
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That's all.
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