Chris@13: Pretty printing
Chris@13: ===============
Chris@13: 
Chris@13: Pretty printing is the process of converting a syntax tree back to PHP code. In its basic mode of
Chris@13: operation the pretty printer provided by this library will print the AST using a certain predefined
Chris@13: code style and will discard (nearly) all formatting of the original code. Because programmers tend
Chris@13: to be rather picky about their code formatting, this mode of operation is not very suitable for
Chris@13: refactoring code, but can be used for automatically generated code, which is usually only read for
Chris@13: debugging purposes.
Chris@13: 
Chris@13: Basic usage
Chris@13: -----------
Chris@13: 
Chris@13: ```php
Chris@13: $stmts = $parser->parse($code);
Chris@13: 
Chris@13: // MODIFY $stmts here
Chris@13: 
Chris@13: $prettyPrinter = new PhpParser\PrettyPrinter\Standard;
Chris@13: $newCode = $prettyPrinter->prettyPrintFile($stmts);
Chris@13: ```
Chris@13: 
Chris@13: The pretty printer has three basic printing methods: `prettyPrint()`, `prettyPrintFile()` and
Chris@13: `prettyPrintExpr()`. The one that is most commonly useful is `prettyPrintFile()`, which takes an
Chris@13: array of statements and produces a full PHP file, including opening `<?php`.
Chris@13: 
Chris@13: `prettyPrint()` also takes a statement array, but produces code which is valid inside an already
Chris@13: open `<?php` context. Lastly, `prettyPrintExpr()` takes an `Expr` node and prints only a single
Chris@13: expression.
Chris@13: 
Chris@13: Customizing the formatting
Chris@13: --------------------------
Chris@13: 
Chris@13: Apart from an `shortArraySyntax` option, the default pretty printer does not provide any
Chris@13: functionality to customize the formatting of the generated code. The pretty printer does respect a
Chris@13: number of `kind` attributes used by some notes (e.g., whether an integer should be printed as
Chris@13: decimal, hexadecimal, etc), but there are no options to control brace placement or similar.
Chris@13: 
Chris@13: If you want to make minor changes to the formatting, the easiest way is to extend the pretty printer
Chris@13: and override the methods responsible for the node types you are interested in.
Chris@13: 
Chris@13: If you want to have more fine-grained formatting control, the recommended method is to combine the
Chris@13: default pretty printer with an existing library for code reformatting, such as
Chris@13: [PHP-CS-Fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer).
Chris@13: 
Chris@13: Formatting-preserving pretty printing
Chris@13: -------------------------------------
Chris@13: 
Chris@13: > **Note:** This functionality is **experimental** and not yet complete.
Chris@13: 
Chris@13: For automated code refactoring, migration and similar, you will usually only want to modify a small
Chris@13: portion of the code and leave the remainder alone. The basic pretty printer is not suitable for
Chris@13: this, because it will also reformat parts of the code which have not been modified.
Chris@13: 
Chris@13: Since PHP-Parser 4.0, an experimental formatting-preserving pretty-printing mode is available, which
Chris@13: attempts to preserve the formatting of code (those AST nodes that have not changed) and only reformat
Chris@13: code which has been modified or newly inserted.
Chris@13: 
Chris@13: Use of the formatting-preservation functionality requires some additional preparatory steps:
Chris@13: 
Chris@13: ```php
Chris@13: use PhpParser\{Lexer, NodeTraverser, NodeVisitor, Parser, PrettyPrinter};
Chris@13: 
Chris@13: $lexer = new Lexer\Emulative([
Chris@13:     'usedAttributes' => [
Chris@13:         'comments',
Chris@13:         'startLine', 'endLine',
Chris@13:         'startTokenPos', 'endTokenPos',
Chris@13:     ],
Chris@13: ]);
Chris@13: $parser = new Parser\Php7($lexer);
Chris@13: 
Chris@13: $traverser = new NodeTraverser();
Chris@13: $traverser->addVisitor(new NodeVisitor\CloningVisitor());
Chris@13: 
Chris@13: $printer = new PrettyPrinter\Standard();
Chris@13: 
Chris@13: $oldStmts = $parser->parse($code);
Chris@13: $oldTokens = $lexer->getTokens();
Chris@13: 
Chris@13: $newStmts = $traverser->traverse($oldStmts);
Chris@13: 
Chris@13: // MODIFY $newStmts HERE
Chris@13: 
Chris@13: $newCode = $printer->printFormatPreserving($newStmts, $oldStmts, $oldTokens);
Chris@13: ```
Chris@13: 
Chris@13: If you make use of the name resolution functionality, you will likely want to disable the
Chris@13: `replaceNodes` option. This will add resolved names as attributes, instead of directlying modifying
Chris@13: the AST and causing spurious changes to the pretty printed code. For more information, see the
Chris@13: [name resolution documentation](Name_resolution.markdown).
Chris@13: 
Chris@13: This functionality is experimental and not yet fully implemented. It should not provide incorrect
Chris@13: code, but it may sometimes reformat more code than necessary. Open issues are tracked in
Chris@13: [issue #344](https://github.com/nikic/PHP-Parser/issues/344). If you encounter problems while using
Chris@13: this functionality, please open an issue, so we know what to prioritize.