Tools: Hackificator

While you should always start new projects with Hack (<?hh), we realize that there is a whole vast PHP codebase out there that cannot be thrown away or rewritten from scratch.

The Hackificator is the first tool to use to begin converting your PHP codebase to Hack.

hackificator [options] <directory or file path>

If you want to see all the options available to the Hackificator, you can see the help via hackificator --help.

Hackifying PHP Code

First, put a .hhconfig file in the top root of your codebase. This is required.

Then, when running the Hackificator, it scans your project/codebase for PHP files and does two steps:

  1. Converts your file from <?php to <?hh. At this point you are officially a Hack file.
  2. It makes some super simple changes to your code to help stop Hack typechecker errors. For example, if you gave a type-hinted parameter a null default value, it will normally be prepended with nullable ?.

Here is an example of a conversion:


class A {}

function foo(A $a = null) {
  return true;



class A {}

function foo(?A $a = null) {
  return true;

Note we did not add any type annotations for the return type of foo. This will come later with hh_server --convert.

Also, it is important to note that if you already have any Hack files in the project that you are trying to hackify, they must be typechecker clean. i.e., running hh_client must produce No errors!.

Upgrading Hack Typechecker Modes

You can also use the hackificator to upgrade current Hack files (not PHP files) to the strictest mode possible. So, for example, you can use it to go from partial to strict mode, assuming a conversion to strict mode won't cause any typechecker errors.

hackificator --upgrade <directory or file path>