Make XP compiler the Babel of PHP

[thekid]

Scope of Change

This RFC suggests changing the PHP language support in the XP Compiler to support all future PHP features (at the time of writing, PHP 7). This would mean you could already start writing PHP 7 code, and could transpile it for running on older, PHP 5.5, environments.

Rationale

Ease adoption of new language features, decouple from slowly adopting production platforms and environments.

Functionality

Design principles

• The future, now!
• Valid PHP passes through the compiler untouched (except alternative syntax)
• Output is as close as possible line/offset/whitespace wise

Compilation

Compilation can either be done explicitly by calling xcc or by using the JIT compiler.

$ xcc -E php5.5 -sp src/main/php -o target/ # Translates PHP 5.6, 7.0 
$ xcc -E php5.6 -sp src/main/php -o target/ # Translates PHP 7.0 features only
$ xcc -E php7.0 -sp src/main/php -o target/ # Copy-through, more or less
# ...

Features

The following are easy:

• Primitive type hints
• Return types
• Anonymous classes
• Property types
• Spaceship operator
• Null coalesce
• Unicode escapes
• Group use declarations
• Static class constructor
• Trailing commas (for arrays and maps, function calls and in various other places).

These need more investigation:

• Generator delegation - yield from
• Context sensitive lexer - might be possible via __call...
• Named arguments

These might not work in a fast and reliable way:

• Exceptions in the engine

Experimental support could be added for features currently under discussion:

• Additional splat operator usage
• Named parameters
• Enum - like in Hack language
• Union types
• Nullsafe operator

We could also add Hack language features

• Attributes -> Annotations
• Array types - array<string> and array<string, Object>
• Generics -> Transform to XP generics?
• Hack lambdas
• Constructor argument promotion

We might want to include support for PHP 5.6:

• Exponentiation operator
• Argument unpacking and variadics
• Importing functions

Security considerations

Speed impact

Dependencies

Related documents

Inspired by http://channel9.msdn.com/Events/Build/2015/3-644

[thekid]

<?php namespace test;

use util\cmd\Console;
use peer\http\HttpConnection;

// https://wiki.php.net/rfc/group_use_declarations
use peer\{ConnectException, SocketException};

// https://wiki.php.net/rfc/variadics
function println(... $_) {

  // https://wiki.php.net/rfc/argument_unpacking
  return Console::writeLine(...$_);
}

class Uri {
  // https://docs.hhvm.com/hack/types/annotations#class-properties
  // (https://wiki.php.net/rfc/property_type_hints)
  private HttpConnection $conn= null;

  // https://docs.hhvm.com/hack/other-features/constructor-parameter-promotion
  public function __construct(private string $uri) { }

  // https://github.com/xp-framework/rfc/issues/241
  public function __toString(): string ==> $this->uri;

  // https://docs.hhvm.com/hack/attributes/introduction
  <<deprecated('Use connection() instead')>>
  public function getConnection() ==> $this->connection();

  // https://wiki.php.net/rfc/isset_ternary
  public function connection(): HttpConnection {
    return $this->conn ?? $this->conn= new HttpConnection($this);
  }
}

// https://docs.hhvm.com/hack/operators/lambda
// (https://wiki.php.net/rfc/arrow_functions)
$get= (Uri $uri) ==> $uri->connection()->get();

try {
  $r= $get(new Uri($argv[1] ?? 'http://localhost'));
  println($r);

  $s= $r->header('Content-Length')[0];
  println('read(', $s, ') => ', strlen($r->readData($s)));
} catch (ConnectException | SocketException $e) {

  // https://wiki.php.net/rfc/multiple-catch
  println('Error ', $e->compoundMessage());
} finally {
  println('Done');
}

[thekid]

Developed as library

https://github.com/xp-framework/compiler

[thekid]

Some interesting ECMAScript proposals matching or related to PHP RFCs and HHVM features:

• https://github.com/tc39/proposal-trailing-function-commas
• https://github.com/tc39/proposal-throw-expressions
• https://github.com/tc39/proposal-optional-chaining & https://github.com/gisenberg/proposal-null-coalescing

(via https://github.com/tc39/proposals)

[thekid]

Static imports?

<?php namespace demo;

use function util\cmd\Console::writeLine;

class HelloWorld {

  public static function main(array $args): int {
    writeLine('Hello, World!');
    return 0;
  }
}

http://php.net/manual/en/language.namespaces.importing.php

[thekid]

Library has reached version 0.5.0 in the meantime, looking good!

[thekid]

Library has reached surpassed 1.0.0. by now and is in productive use