HHVM 3.24 is released! This release contains new features, bug fixes, performance improvements, and supporting work for future improvements. Packages have been published in the usual places.

Highlights include:

  • In Hack code, reference arguments must now be marked at the call site, e.g. $foo = [3, 1, 2]; sort(&$foo);
  • Support for using blocks - an alternative to destructors
  • Improved type inference and type checking for lambdas
  • Added the XHP attribute spread operator
  • Improved the typing of XHP attributes and children
  • Clearer error messages for constraint errors on generic methods
  • Improved handling of multiple debuggers (e.g. hphpd + xdebug)
  • hh_parse now offers a --full-fidelity-text-json option, which includes node content in the output
  • In partial mode, Hack no longer assumes that any unknown definitions must be defined in PHP

As a release with long-term support, 3.24 is supported through 2018-12-17; it also marks the end of support for HHVM 3.18.

End Of Support For PHP5

3.24 is the final release targeting PHP5; this includes source-level compatibility for PHP5 extensions (ext_zend_compat). We recommend migrating to Hack or PHP7.

As 3.24 is supported though 2018-12-17, this means that support will end at roughly the same time as PHP5 itself is scheduled to become unsupported (2018-12-31).

End Of Support For Debian 7 Wheezy and Ubuntu 17.04 Zesty

The Debian project is scheduled to end support for Wheezy in May 2018, and the Ubuntu project is scheduled to end support for Ubuntu Zesty in January 2018; as such:

  • HHVM 3.24 will be the last release to support Wheezy and Zesty.
  • HHVM support for Wheezy and Zesty will end when the distributions themselves become unsupported; this includes ending support for the 3.21 and 3.24 HHVM releases.

Reference Arguments

In Hack code, by-ref function arguments must now be marked at the callsite, not just at the function declaration. We have extended HHAST to automate migrations; for example:

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$ bin/hhast-migrate --help
Usage: bin/hhast-migrate [OPTIONS] PATH [PATH ...]

Options:
  --implicit-shape-subtypes
    Allow implicit structural subtyping of all shapes
  --optional-shape-fields
    Migrate nullable shape fields to be both nullable and optional
  --hhvm-3.22-to-3.23
    Apply all migrations for moving from 3.22 to 3.23
  --ctpbr
    Add required ampersands at call sites for byref arguments
  --hhvm-3.23-to-3.24
    Apply all migrations for moving from 3.23 to 3.24
  --include-vendor
    Also migrate files in vendor/ subdirectories
  -v, --verbose
    Increase output verbosity
  -h, --help
    display this text and exit
$ bin/hhast-migrate --ctpbr $HOME/code/fbmarkdown/src/
$ cd $HOME/code/fbmarkdown/src/
$ git diff
diff --git a/src/_Private/decode_html_entity.php b/src/_Private/decode_html_entity.php
index 7891b57..a44b441 100644
--- a/src/_Private/decode_html_entity.php
+++ b/src/_Private/decode_html_entity.php
@@ -25,7 +25,7 @@ function decode_html_entity(string $string): ?(string, string, string) {
     \preg_match(
       '/^&(#[0-9]{1,8}|#X[0-9a-f]{1,8}|[a-z][a-z0-9]*);/i',
       $string,
-      $matches,
+      &$matches,
     ) !== 1
   ) {
     return null;
...

This is not required for PHP code.

Using Blocks

“Using” blocks provide a mechanism to limit an object to a particular scope, invoking code on scope exit, without using destructors. This is done by implementing either IDisposable or IAsyncDisposable:

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/**
  * Objects that implement IDisposable must be constructed in using statements
  */
interface IDisposable {
  /**
   * This method is invoked exactly once at the end of the scope of the
   * using statement, unless the program terminates with a fatal error.
   */
  public function __dispose(): void;
}

For example:

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class Handle implements IDisposable {
  public function __dispose(): void {}
  public function foo(): void {}
}

function disposable_example(): void {
  // Block scope
  using ($x = new Handle()) {
    $x->foo();
  } // $x->__dispose() is implicitly called here

  // Function scope
  using new Handle();
  // handle still exists here
} // __dispose() is now called on the anonymous handle

Further details are available in the documentation.

XHP Attribute Spread Operator

Many XHP elements currently implicitly copy attributes to the root XHP element they produce; this silently overrides elements that are declared on the root element, and is hard to reason about in large codebases.

We have added an attribute spread operator to explicitly copy attributes, and will be removing implicit copying from xhp-lib in the near future:

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class :foo-old extends :x:element {
  use XHPHelpers;
  
  attribute string color, int age;
  public function render(): XHPChild {
    return <bar color="red" />;
  }

class :foo-new {
  attribute string color, int age;
  public function render(): XHPCHild {
    return <bar {...$this} color="red" />;
  }
}

class :bar extends :x:element {
  attribute string color, int age;
}

$xhp = <foo-old color="blue" />;
$xhp2 = <foo-new color="blue" />;
// Old: this XHP renders to <bar color="blue" />.
// New: Spread position matters, so the XHP renders to <bar color="red" />

XHP Attribute and Child Improvements

  • @required attributes can no longer be nullable
  • @required attributes can no longer have a default value
  • Stringish now extends XHPChild
  • XHP child expressions are now required to be of type ?XHPChild
  • Attribute literals can now contain colons - e.g. <foo bar:baz="foo">

Unknown Definitions in Partial Hack

In previous releases, Hack has assumed that if a partial file references an unknown definition (e.g. classes, functions, or constants), that it exists in a PHP file. This is no longer the case. We recommend adding HHI files for PHP libraries that are directly used in Hack code. Alternatively, HH_FIXME comments can be used to suppress these errors.

It is currently also possible to enable the old behavior by setting assume_php=true in your project’s .hhconfig file - however this is no longer a supported configuration, may be buggy, and will be removed from a future release (potentially 3.25). It should be considered a temporary migration aid only.

We are doing this change to:

  • detect more errors; for example, when assume_php=true, Hack is unable to raise errors for typos in function, class, or constant names except in strict files
  • increase soundness
  • reduce the number of options available in Hack