Implement a preloader.

[costdev]

This PR implements a preloader for the upgrade process.

• This is set to preload the wp-includes/Requests directory.
• This is set to skip preloading wp-includes/Requests/Autoload.php on WP < 5.9.
• These are in place as examples but should be part of the overall audit.

Source

• Allow preloading files.
• Allow recursively preloading directories.
• Allow skipping files from preloading.
• Identify additional functionality that may be needed. Please identify in a review for discussion.
• Identify additional functionality that may be helpful. Please suggest in a review for discussion.
• Audit additional files needed by the upgrader.
• Add the additional paths to the preloader, skipping individual files where necessary.

Tests

• Add initial tests.
• If necessary, review the sample files implementation for an alternative.
• Add more tests.
• Manual testing.
• Review documentation.

Trac ticket: https://core.trac.wordpress.org/ticket/54589

[peterwilsoncc]

take a look at validate_file(), I suspect you are doubling up a few things here.

[costdev]

Nice @peterwilsoncc, hadn't thought of that at the time. validate_file() should work nicely here.

[costdev]

Oops. This should actually use WP_Error::merge_from().

i.e.

$errors->merge_from( $result );

[costdev]

I'll split this out to first check if dirlist() has returned false. If it has, I can add a WP_Error for dirlist_not_returned, then continue.

[BrianHenryIE]

The tests seem inadequate.

If class-foo.php, e.g.

class Foo extends Bar {} 

is require_once'd before class-bar.php has been, then it will fail.

I'm not familiar with the WordPress build process itself, but how I would approach this is:

Use Composer\Autoload\ClassMapGenerator::createMap() to build a classmap from the autoload key in the library.
Use either regex (or maybe Rector related tool php-parser) to read each PHP file and know which rely on none and which ones subclass/implement/use others.
Build a new "ordered" classmap that can safely be used with require_once.
This new classmap can be used in a regular autoloader too.

I worked on a library for prefixing namespaces for WordPress plugins to avoid conflicts: https://github.com/BrianHenryIE/strauss

(my point was to show how I've thought of this in terms of WordPress already. But it's honest to say: The same code could be used to rename namespaces, i.e. the WpOrg WPorg WordPress Wordpress namespace discussion that was earlier.)

Again, I'm not familiar with the WordPress build process and how it could use Composer libraries, but I do see how Strauss's functionality could be split into another library that helps this issue – ultimately listing all classes in a library and ordering them based on what they require (extend/implement/use) before require_once.

[BrianHenryIE]

I put together a proof of concept here: https://github.com/BrianHenryIE/composer-require-once

It's really just one function in one class, with a test running against Requests.

Requires composer/composer and nikic/php-parser.