With Rector, we can write code with PHP 8.0 features and deploy it to an environment running lower versions, all the way down to PHP 7.0

PHP 8.0 will be released at the end of this year. Is it possible to introduce it immediately into our projects? Or would we be unable to do it because, for instance, it uses a framework or CMS with legacy code?

This concern affects every PHP-based project — whether based on Laravel, Symfony, Drupal, vanilla PHP, or whatnot — but it is particularly pressing for WordPress, and its community is currently attempting to find a solution.

In its upcoming new release this December, WordPress should upgrade its minimum required PHP version from 5.6 to 7.1. However, it’s been decided to temporarily cancel the PHP version bump, because almost 24 percent of installations still run on either PHP 5.6 or 7.0:

September 2020 WordPress usage stats, via wordpress.org/about/stats.

Under these circumstances, it has been proposed to start having a fixed schedule for upgrading the minimum version, offering a compromise between upgrading to new PHP versions while providing security patches for older versions:

Proposed fixed updated schedule.

Whether this fixed schedule is approved or not, the situation looks dire for developers who want to use the latest improvements to PHP. Themes and plugins are not bounded by the PHP requirements by WordPress, so they could already require version 7.1 or higher. However, doing so limits their potential reach.

For instance, only 10.7 percent of installations currently run on PHP 7.4, and we can expect even less will immediately run on PHP 8.0 after being released. These numbers make it very difficult to introduce typed properties or union types into the codebase, among other valuable features.

This comment by a developer conveys some sense of despair:

So effectively this means that we cannot use PHP 8 syntax in themes/plugins if we want to support all WordPress versions until December 2023, three years after it has been released. This is very disappointing.

Is there anything that can be done to improve the situation today? Or do we have to wait three years to be able to use PHP 8 code for our WordPress themes and plugins? (By which time it will have reached its end of life!)

Babel shows the way

A transpiler is “a type of translator that takes the source code of a program written in a programming language as its input and produces an equivalent source code in the same or a different programming language.”

An exemplary model for transpiling is Babel, the toolchain that allows us to convert ECMAScript 2015+ code into a backwards-compatible version of JavaScript. Thanks to Babel, developers can use new JavaScript language features to convert their source code into versions of JavaScript that can be executed on older browsers.

For instance, Babel converts an ES2015 arrow function to its ES5 equivalent:

// Babel Input: ES2015 arrow function
[1, 2, 3].map((n) => n + 1);

// Babel Output: ES5 equivalent
[1, 2, 3].map(function(n) {
  return n + 1;
});

Following the lead of ES2015, PHP 7.4 has also introduced arrow functions as syntactic sugar over anonymous functions, which have been supported since PHP 5.3:

// PHP 7.4: arrow function
$nums = array_map(fn($n) => $n + 1, [1, 2, 3]);

// PHP 5.3: anonymous function
$nums = array_map(
  function ($n) {
    return $n + 1;
  },
  [1, 2, 3]
);

With a transpiling tool for PHP, we could write PHP 7.4 arrow functions and convert them into the equivalent anonymous functions, which can run on any version of PHP starting from 5.3.

This would enable developers to use features from PHP 7.4 for their WordPress themes and plugins while still allowing users running older versions (such as PHP 7.1) to also install their software.

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