A PHP 7 to 8 migration tool for WordPress sites: what it should do

What “migration” means for a WordPress site

On a WordPress site you don’t migrate code by hand, file by file. Your host changes the PHP version, and every plugin and theme must cope with it. The migration is: find what won’t, fix it (update, replace or change the code), then switch. The tool you need is the one that does the finding well.

PHP 7.4 has had no security fixes since 28 November 2022 (php.net), so most sites still on it are moving now, often straight to 8.3 or later.

Check every step, not just 8.0

Your host switches 7.4 directly to the version you choose. But the changes of every version in between still apply: code that stops on 8.0 also stops on 8.5. PHP 8.0 has by far the longest list (php.net): removed functions such as create_function() and each(), curly-brace offsets, old-style constructors. The later versions add a few more breaks and many notices. The full map is in moving from PHP 7.4 to PHP 8.

What the tool should tell you, per plugin

• Will it break, or only show notices? Fix the first group before switching; plan the second.
• Is an update available? Often the developer has already fixed it.
• Is it your own code? Custom code gets no update: someone has to change it.
• Where exactly, and how to fix it: the file, the line, and an example.

How CompatNav does it

The free CompatNav plugin, on your server:

A real finding, from one of the PHP 8.0 removals:

Code protected by function_exists() or a PHP version check is not reported, so the list stays short. And CompatNav says what it can’t see: problems that depend on values while the site runs, such as count() on something that isn’t a list.

Then switch

Fix what will break, test on a staging copy if you can, switch at a quiet time, and watch the error log for a week.